-
Isotope-specific reactions of acetonitrile (CH3CN) with
trapped,translationally cold CCl+
O. A. Krohn,1, 2, a) K. J. Catani,1, 2 J. Greenberg,1, 2 S. P.
Sundar,3 G. da Silva,3 and H. J. Lewandowski1, 21)Department of
Physics, University of Colorado, Boulder, Colorado, USA2)JILA,
National Institute of Standards and Technology and the University
of Colorado, Boulder, Colorado,USA3)Department of Chemical
Engineering, The University of Melbourne, Parkville 3010,
Victoria,Australia
(Dated: 23 November 2020)
The gas-phase reaction of CCl+ with acetonitrile (CH3CN) is
studied using a linear Paul ion trap coupledto a time-of-flight
mass spectrometer. This work builds on a previous study of the
reaction of CCl+ withacetylene1 and further explores the reactivity
of CCl+ with organic neutral molecules. Both of the reactantspecies
are relevant in observations and models of chemistry in the
interstellar medium (ISM). Nitriles, inparticular, are noted for
their relevance in prebiotic chemistry, such as is found in the
atmosphere of Titan, oneof Saturn’s moons. This work represents one
of the first studied reactions of a halogenated carbocation witha
nitrile, and the first exploration of CCl+ with a nitrile. Reactant
isotopologues are used to unambiguouslyassign ionic primary
products from this reaction: HNCCl+ and C2H3
+. Branching ratios are measured andboth primary products are
determined to be equally probable. Quantum chemical and statistical
reaction ratetheory calculations illuminate pertinent information
for interpreting the reaction data, including:
reactionthermodynamics, a potential energy surface for the
reaction, as well as rate constants and branching ratios forthe
observed products. In particular, the reaction products and
potential energy surface stimulate questionsregarding the strength
and role of the nitrile functional group, which can be further
explored with morereactions of this class.
I. INTRODUCTION
Nitriles and nitrogen-containing compounds play aprominent role
in the chemical reactions thought to takeplace in the interstellar
medium (ISM). These moleculespermeate space: from small cyanides
such as HCN andDCN found in the Orion Nebula2,3 to larger
moleculessuch as benzonitrile, whose initial discovery in the
ISMwas relatively recent.4 Nitriles, defined by their
C–––Nfunctional group, are of particular interest as
pre-bioticmolecules and potential precursors of amino acids.
Sev-eral nitriles have been identified in the atmosphere ofTitan
using the Ion Neutral Mass Spectrometer on theCassini spacecraft,
and are believed to be important intholin formation,5 as well as
astrobiology.6
Acetonitrile (CH3CN; the neutral reactant in thisstudy) has been
found abundantly throughout many re-gions of space since its
initial identification in the ISMin 1971.7 It has been observed in
cold dark clouds,8
low-mass protostars,9,10 and is considered an indica-tor of the
presence of hot cores.11,12 CH3CN has alsobeen discovered in dust
from comet Halley,13 Hale-Bopp(C/1995 O1)14 and, more recently, at
the surface ofcomet 67P/Churyumov-Gerasimenko.15 These
cometaryidentifications can yield critical glimpses into the
pastconditions and evolutionary history of the Milky Way.Deuterated
variants CD3CN and CDH2CN have beenidentified in hot cores and
star-formation regions,16 and
a)Electronic mail: [email protected]
the presence of isotopologues of CH3CN are used to studyrelative
populations of hydrogen and deuterium in someregions of the
ISM.17
Halogen-containing compounds have also been iden-tified in the
ISM, but their role and evolution are lesswell understood. In
particular, chlorine-containing com-pounds have been found in the
ISM in several smallmolecules (NaCl, AlCl, KCl, HCl),18 as well as
inCH3Cl
19 and H2Cl+.20,21 The only halogenated carboca-
tion to be observed thus far in the ISM is CF+,18 whereasCCl+
has been predicted to occur, although only in lowabundances.22 CCl+
can be produced from reactions ofC+ + HCl,23 and once formed, has
been assumed to bepredominantly nonreactive. Specifically, CCl+ has
beenshown to not react with HCN (or CO2, CO, O2, H2O,CH4, H2).
However, it has been shown to react with NH3and H2CO.
24 Recent work from our group demonstratedCCl+ reacts with
acetylene (C2H2), producing small fun-damental carbocations after
losing neutral Cl or HCl.1
Despite this, much remains unknown about the role ofhalogenated
carbocations; it is possible that they have ahitherto
underestimated role in astronomical chemistry.
In contrast to CCl+, laboratory reactions of nitrileshave been
much more widely studied. Ion cyclotronresonance (ICR) spectrometry
has been used to mea-sure reactions with HCN and carbocations,25
whileother ion trap experiments have investigated reactionsof CH3CN
with multiple carbocations.
26 Selected-ionflow-tube mass spectrometry (SIFT) experiments
demon-strated reactivity of CH3CN with O
+, H+, D+, HeD+,and HeH+,27 as well as with C2H4
+,28 and C2H2+.29
However, very few measurements have reported reactions
arX
iv:2
011.
1015
2v1
[ph
ysic
s.ch
em-p
h] 1
9 N
ov 2
020
mailto:[email protected]
-
2
of halogenated carbocations with any nitrile. The onlyreported
reaction of this type is the reaction of CF3
+ withCH3CN and benzonitrile, both of which were shown toproduce
only the adduct.30 The reactions of CF3
+ wereexecuted in a higher pressure regime than that of
thecurrent experiment, where reactive intermediates are un-able to
be stabilized through collisions with backgroundgas. The reactivity
of halogenated carbocations with ni-triles is in need of further
exploration, particularly in acold, low-pressure environment. This
work seeks to un-derstand more about this reaction class by
studying thereaction of CCl+ + CH3CN in this regime.
The cold, low-pressure environment provided by us-ing a linear
Paul ion trap (LIT) is excellent for elucidat-ing ion-neutral
chemical reactions.31,32 This experimen-tal setup affords a
significant amount of control, includ-ing the manipulation of
collisional energy,33,34 nuclearspin,35 and the measurement of
isomer,36,37 isotope,38,39
and quantum state40,41 dependencies. Ions of interest
areco-trapped and sympathetically cooled with laser-cooledCa+,
forming a mixed species Coulomb crystal, achiev-ing translationally
cold, trapped ions. Furthermore, theaddition of a time-of-flight
mass spectrometer (TOF-MS)provides detection of ionic reactants and
products withhigh mass resolution – a powerful tool for probing
reac-tion products and kinetics.
The reaction of sympathetically cooled CCl+ withCH3CN is studied
using our LIT TOF-MS. This workseeks to illuminate the role and
reactivity of these novelspecies in the gas phase under
experimental conditionsthat are approximate to that of the ISM and
planetaryatmospheres. The primary products are found to beC2H3
+ and HNCCl+, which are unambiguously assignedthrough the use of
isotope substitutions. Computationalmodeling also supports these
product assignments, sug-gesting a reaction pathway requiring
cleavage of the C–––Nbond of CH3CN in order to form the observed
products.Furthermore, the study of CCl+ + CH3CN signifies aninitial
investigation in reactions of halogenated carboca-tions with
nitriles.
II. METHODS
A. Experimental Methods
Reaction data were collected using a LIT radially cou-pled to a
TOF-MS. Detailed descriptions of the appara-tus have been outlined
previously,1,42 and only a briefsummary focusing on the specific
details relevant to thecurrent experiment will be given here. CCl+
was pro-duced using tetrachloroethylene (TCE, C2Cl4) seededin a
pulsed supersonic expansion of rare atomic gas(1.4% C2Cl4 in ∼1000
Torr He). The skimmed molec-ular beam was overlapped with a focused
beam (216 nm)from a pulsed dye laser (LIOPTEC LiopStar; 10 ns
pulse,100µJ/pulse) in the center of the trap.
Non-resonantmultiphoton ionization of TCE resulted in several
frag-
ments, including C35Cl+, C37Cl+, 35Cl+, 37Cl+, C2+,
and small amounts of C235Cl+ (hereafter, the more
abundant isotope 35Cl will be referred to as simply Cl,while
37Cl will be specified when appropriate). Unwantedions were ejected
from the trap by sweeping over res-onance frequencies of the
specific mass-to-charge ratio(m/z) of undesired ions.43 This
provided a clean sampleof either CCl+ or C37Cl+ with minimal
impurities, asdemonstrated in Fig. 1.
After removing unwanted ionization products from thetrap, Ca+
was loaded by non-resonantly photoionizing aneffusive beam of
calcium using the third harmonic of anNd:YAG (Minilite, 10 Hz, ∼ 7
mJ/pulse). The result-ing Ca+ ions were Doppler laser cooled by two
externalcavity diode lasers, forming a Coulomb crystal
structure,which sympathetically cooled the co-trapped CCl+ ionsvia
the Coulomb interaction. Ca+ ion fluorescence wascollected using a
microscope objective and focused ontoan intensified CCD camera
located above the trap, al-lowing for qualitative visual monitoring
of the experi-ment. The heavier “dark” CCl+ ions arrange
themselvesin outer shells around the Ca+ ions, deforming the
flu-orescing Coulomb crystal as seen in Fig. 1b. A typi-cal
experiment utilized 150-250 CCl+ ions trapped with∼ 1000 Ca+ ions,
all of which were translationally cold(∼ 10 K).
10 15 20 25 30 35 40 45 50 55 60
CCl+
Ca+
a)
b)
mass (U)
FIG. 1. a) TOF traces demonstrating before and b) aftercleaning
using secular excitations. After cleaning, only Ca+
(m/z 40, m/z 42, and m/z 44) and CCl+ (m/z 47) remain
inquantities greater than ∼ 5 ions. Also included on the left isa
false-color CCD image of fluorescing Ca+ ions, the resultingCoulomb
crystal is deformed primarily in the center sectionby the heavier
CCl+ ions. The crystal appears truncatedbecause it expands slightly
beyond the CCD camera frame.
-
3
After CCl+ and Ca+ ions were loaded, neutral CH3CN(9-10% CH3CN
or CD3CN in N2) was leaked into the vac-uum chamber (2× 10−9 Torr
gas pressure at 300 K) for aset duration of time using a pulsed
leak-valve scheme.40,44
The measurements of gas partial pressures in the cham-ber were
recorded using a Bayard-Alpert hot cathode ion-ization gauge. The
opening of the leak valve (LV) definedthe zero-time point; the LV
remained open for 0, 10, 30,60, 90, 120, 150, 180, 210, 240, or 330
s before ejectingthe ions into the TOF-MS. This process was
repeatedabout 10 times for every time step and measured ionnumbers
from each mass were averaged over each timestep. The average number
of reactant and product ionswere then normalized by the initial
CCl+ numbers andplotted against time, forming a reaction curve.
Thesereaction curves were then used to determine the rele-vant rate
constants. Reaction curves were collected inthe same manner for
isotopologues C37Cl+ and CD3CN,such that all four possible
combinations of isotopologueswere used. The chemical formula of
each mass peak wasconfirmed by examining the shift in mass spectra
as aresult of isotopologue substitution (see section III B).
Inaddition, all of the ionic species were tracked via TOF-MS
traces. The total number of ions were compared foreach time point
to ensure that the numbers were con-stant throughout the
experiment; this ruled out system-atic losses of ions from the
trap. Figures illustrating con-servation of charge over each
reaction are given with morecontext in the supplementary
material.
B. Computational Methods
Several theoretical methods were used to explore thepotential
energy surface for the reaction of CCl+ +CH3CN. In a previous
study, the M06-2X/aug-cc-pVTZlevel of theory was found to produce
accurate geometriesand energies for small nitrogen- and
chlorine-containingcompounds,45 and was therefore chosen to
determinepossible stationary points. Scans over bond
lengths,angles, and dihedrals allowed identification of minimaand
saddle points. Transition states were verified byvisually
inspecting the single imaginary frequency andalso by using
intrinsic reaction coordinate (IRC) anal-ysis. The geometries of
the reactants, products, in-termediate states, and transition
states were then usedas starting points for calculations at the
MP2/aug-cc-pVTZ level of theory. Zero point energy (ZPE)
correc-tions from calculated harmonic vibrational
frequencies(MP2/aug-cc-pVTZ) were added to CCSD(T)/CBS sin-gle
point energies [CCSD(T)/CBS//MP2/aug-cc-pVTZnomenclature is used in
the subsequent discussions]. Ad-ditional higher order calculations
were carried out atthe CCSD(T)/CBS//CCSD/aug-cc-pVTZ level of
the-ory for reactants and predicted products to provide ac-curate
energetics for the thermodynamic limits of the re-action within
0.04 eV. Even though 37Cl and D isotopesubstitutions were used
experimentally to determine the
chemical formulas of the products, calculations accom-modating
these substitutions are outside the scope of thiswork. Density
functional theory (DFT) calculations andrelaxed potential energy
surface scans were done usingGaussian 16,46 while the higher order
MP2 and CCSDcomputations were done using Psi4 v1.3.2.47
Statistical reaction rate theory calculations were per-formed to
simulate the kinetics of the CCl+ + CH3CNreaction. These
calculations were carried out using a cus-tom version of the
MultiWell2020 suite of programs,48–50
modified to treat bath-gas collisions using the Langevinmodel.
Simulations followed a general approach that wehave used
extensively to investigate ion reaction dynam-ics in a diverse
range of instruments, including ion trap,51
tandem,52 and ion mobility53 mass spectrometers. Elec-tronic
energies, vibrational frequencies, and momentsof inertia were from
the CCSD(T)/CBS//MP2/aug-cc-pVTZ model chemistry calculations.
Microscopic rateconstants were calculated via
Rice-Ramsperger-Kassel-Marcus (RRKM) theory, on the basis of
rigid-rotorharmonic-oscillator sums and densities of state. For
bar-rierless ion-molecule reactions, association rate coeffi-cients
were set at the ADO theory value, with the re-stricted Gorin
model54 then applied to fit an effectivetransition state structure.
Energy grained master equa-tion simulations were performed in order
to predict theCCl+ + CH3CN reaction products. These
calculationsfeatured energy grains of 10 cm−1 and a single
exponen-tial down collisional energy transfer model, with the
av-erage energy in deactivating collisions set at 200 cm−1.55
Simulations comprised 1010 trajectories, and in each casea
reaction was predicted to be complete within less thanthe time
required for one bath-gas collision (i.e., effec-tively
collisionless). Simulations were performed at apressure of 2×10−9
Torr N2, with temperature varied be-tween 40 and 400 K in order to
examine predicted ratesfrom atmospheric down to astrochemically
relevant con-ditions.
III. RESULTS & DISCUSSION
For the sake of clarity, the reaction thermodynamicswill be
discussed with the concluded chemical formula as-signments in
Section III A, followed by experimental sup-port in Section III B.
Finally, in Section III C the mod-eled potential energy surface,
branching ratios, and rateconstants of the reaction are
discussed.
A. Reaction thermodynamics
Overall, the reaction of CCl+ + CH3CN forms the pri-mary ionic
products C2H3
+ and HNCCl+, which proceedto react with excess CH3CN to form
the secondary prod-uct protonated acetonitrile (CH3CNH
+). This model isillustrated in Fig. 2.
-
4
FIG. 2. Reaction model for CCl++ CH3CN, noting the re-action
order and identity of ions. Each arrow represents areaction with a
neutral CH3CN molecule. Red number belowthe molecule denotes m/z
ratio. The molecular ions are de-picted above, with black
indicating carbon, blue for nitrogen,white for hydrogen, and green
for chlorine.
Neutral CH3CN was introduced into the vacuumchamber as a room
temperature gas (300 K). There-fore, when reacting with
translationally cold CCl+ (∼10 K), the calculated collision energy
for the reactionis ∼ 15 meV (160 K). This provides a narrow
upperlimit to the reaction energetics. The observed productsare all
significantly exothermic and well below the up-per limit provided
by the calculated collision energy, asshown by Equations 1-4
[CCSD(T)/CBS//CCSD/aug-cc-pVTZ; accurate within 0.04 eV].
Primary products:
CCl+ + CH3CN −−→ C2H3+ + NCCl∆E = −1.17 eV
(1)
CCl+ + CH3CN −−→ HNCCl+ + C2H2∆E = −2.09 eV
(2)
Secondary products:
C2H3+ + CH3CN −−→ CH3CNH+ + C2H2
∆E = −1.41 eV(3)
HNCCl+ + CH3CN −−→ CH3CNH+ + NCCl∆E = −0.48 eV
(4)
These calculated limits assume the lowest energy iso-mers. For
example, in Eqns. 2 and 3, the C2H3
+ energyrefers to that of the non-classical “bridge” isomer
(seeFig. 2 or PRD2 in Fig. 4). This non-classical isomer iswhere
the third H hovers between the two carbons, as op-posed to the
“classical” or “Y” structure (H2C2H
+, seePRD3). Other possible isomeric products are discussedin
Section III C.
B. Reaction measurements
Curves that are produced from the reaction of CCl+ +CH3CN are
shown in Fig. 3. Here, CCl
+ (m/z 47; blue)reacts to form two primary products: C2H3
+ (m/z 27;green) and HNCCl+ (m/z 62; black). The reduction ofthe
CCl+ population (blue) is concurrent with the growthof C2H3
+ (green) and HNCCl+ (black). Both of the pri-mary product
populations then reduce over time as thesecondary product
CH3CNH
+ (m/z 42; red) populationgrows from reactions with excess
CH3CN. CH3CNH
+ isconfirmed as a second order product because its maxi-mum
slope coincides with the maximum number of pri-mary products.
Experimental reaction rates are deter-mined by fitting the reaction
data to a pseudo-first ordermodel. These curve fits are shown as
lines in Fig. 3.Details of these fits are provided in the
supplementarymaterial.
0 50 100 150 200 250 300time (s)
0
0.2
0.4
0.6
0.8
1
1.2
norm
aliz
ed io
n nu
mbe
rCCl+
C2H
3+
HNCCl+
CH3CNH+
FIG. 3. Rate reaction data (points) and fits (curves)
forpseudo-first order reaction of CCl+ +CH3CN. CCl
+ (blue×)reacts with excess CH3CN resulting in first order
productsC2H3
+ (green◦) and HNCCl+ (black∗). Each of theseprimary products
then reacts with excess CH3CN to formCH3CNH
+ (red2).
The primary product mass assignments, namelyC2H3
+ and HNCCl+, given by the initial reaction ofCCl+ + CH3CN were
verified by using different combina-tions of isotopologues.
Specifically C37Cl+ (m/z 49) andCD3CN (m/z 44) were used to form
four possible combi-nations of reactants. Reaction curves were
measured foreach of the four unique pairs and mass peak shifts
wererecorded for each case. Specifically, when the
reactionproceeded with C37Cl+ + CH3CN, only one of the pri-mary
products shifted, m/z 62→ 64 (HNC37Cl+), iden-tifying it as the
only chlorine-containing product. In thecase of CCl+ + CD3CN, both
primary products shifted:m/z 27 → 30 (C2D3+), and m/z 62 → 63
(DNCCl+).Furthermore, the secondary product shifted, m/z 42 →46
(CD3CND
+). In the final case, C37Cl+ + CD3CN,the mass shifts were
consistent with the aforementioned
-
5
TABLE I. Rate constants for isotopological variations ofCCl+ +
CH3CN primary products. ‘X’ represents a hydro-gen or deuterium
from acetonitrile, and corresponds to theisotopologue used. Rates
are in units of ×10−9 cm3/s, andreported statistical uncertainty is
the calculated 90% confi-dence interval.
Reactants C2X3+ XNCCl+ total
CCl+ + CH3CN 1.6 ± 0.5 2.2 ± 0.5 3.8 ± 0.4C37Cl+ + CH3CN 2.9 ±
0.7 3.0 ± 0.7 5.9 ± 0.3CCl+ + CD3CN 2.4 ± 0.5 3.0 ± 0.5 5.4 ±
0.3C37Cl+ + CD3CN 2.9 ± 0.8 3.4 ± 0.8 6.3 ± 0.3
products. An additional process occurs in reactions in-volving
CD3CN, which produces a small amount of atertiary product m/z 45,
assigned to CD3CNH
+. Thistertiary process occurs possibly by either from H-D
swap-ping or from contributions from a small number of con-taminant
ions remaining from the initial ion loadingscheme (any given
contaminant constitutes ≤ 5% of 150-250 initial CCl+ numbers). The
isotopologue reactioncurves are plotted in the supplementary
material. Ex-trapolated rate constants and branching ratios from
thesereaction curves are provided in Tables I-III.
The measured rate constants for primary products ofCCl+ + CH3CN
are reported in Table I. The Langevincapture model is a natural
starting place for the analysisof experimental reaction rate
constants, as it is the sim-plest and most general approach for
predicting rate con-stants in this regime. Notably
temperature-independent,this theory estimates the likelihood of
collisions betweenan ion and a neutral nonpolar molecule. The
Langevinrate constant was found to be k = 1.11 × 10−9 cm3/s,3-6
times smaller than the total reaction rate constant.This
underestimation is most likely due to the polar na-ture of neutral
CH3CN, which is not accounted for inLangevin theory. Average dipole
orientation (ADO) the-ory expands on Langevin theory to account for
the polar-ity of the neutral reactant and should show closer
agree-ment with the measured total reaction rate constant.56
This is reflected in the fact that CH3CN has a ratherlarge
dipole-locking constant (c) of ∼0.25, leading tokADO,unsub = 3.74 ×
10−9 cm3/s (calculated with thereduced mass of unsubstituted
reactants). Our mea-sured total reaction rate constant for CCl+ +
CH3CN,3.8± 0.7× 10−9 cm3/s (see Table I), reflects good agree-ment
with ADO theory. This agreement testifies to thehigh degree of
efficiency of the CCl+ + CH3CN reaction,where effectively every
ion-molecule collision results inthe formation of new reaction
products, with little refor-mation of the reactants (vide infra).
The high reactivityof CCl+ toward acetonitrile stands in stark
contrast tomuch of the previous work on the reaction kinetics of
thision with neutral molecules.
The isotope substituted total reaction rate constants(also in
Table I) agree fairly well with the measured rateconstant for CCl+
+ CH3CN, but do trend faster, be-tween 5.4 − 6.4 × 10−9cm3/s,
compared to the unsub-
stituted total reaction rate constant. This trend is
notprecisely captured by ADO theory, which predicts a verysmall (≤
5%) reduction in the rate constant for bothC37Cl+ and CD3CN
substitutions. There is precedencefor the trend of increased rate
constant upon isotope sub-stitution. Indeed, recently, this inverse
kinetic isotopeeffect has been observed using a similar apparatus
andCoulomb crystal environment by monitoring the chargeexchange
reaction between Xe+ and NH3 or ND3. Thiseffect, which was
suggested to be due to intramolecu-lar vibrational redistribution
(IVR) occurring at a fasterrate, and to a higher density of states
in the deuteratedammonia.39 It is possible that we are observing a
simi-lar effect here. It should be emphasized that we use
aBayard-Alpert hot cathode ionization gauge to measurethe partial
pressure of CH3CN gas in the chamber. Whilesensitivity factors for
the gases used in this study havebeen previously measured, they are
not well character-ized at pressures of 10−9 − 10−10 Torr (current
regime).This systematic uncertainty is difficult to quantify, andis
not reflected in our reported uncertainties. For thisreason, we do
not make a definitive assessment as towhether we are observing an
inverse kinetic isotope ef-fect. Instead, more significance is
placed on the determi-nation of branching ratios (see Table II) and
assignmentsof chemical formulas and structures of observed
reactionproducts, rather than to individual rate constant
mea-surements.
TABLE II. Branching ratios for primary products by
isotopo-logical variations of CCl+ + CH3CN reaction. The
calcu-lated branching ratio represents the fraction of
protonatedacetylene rate constant, divided by the total CCl+ decay
rateconstant. ‘X’ represents a hydrogen or deuterium, and
corre-sponds to neutral reactant.
Branching RatioReactants (k(C2X3
+)/ktotal)CCl+ + CH3CN 0.43 ± 0.16C37Cl+ + CH3CN 0.50 ± 0.17CCl+
+ CD3CN 0.44 ± 0.11CCl+ + CD3CN 0.46 ± 0.17
The branching ratios shown in Table II are nearly 50%for each of
the primary products; here reported as therate of the C2H3
+ production over the sum of both pri-mary product rate
constants. If all products branchedfrom the same final step of the
potential energy surface(see Fig. 4), the more exothermic product,
HNCCl+,might be expected to be favored. However, as will
bediscussed in section III C, the potential energy surfaceis much
more complex, with the existence of branchingpathways, as well as
multiple isomers of products. Thisnecessitates an energy grained
master equation approachto obtain quantitative branching ratio
predictions.
Secondary reactions with excess CH3CN are comprisedof a proton
transfer from either C2H3
+ or HNCCl+ form-ing CH3CNH
+. Analysis of the kinetics for these reac-tions is more
straightforward, and the relative proton
-
6
affinities of the neutral molecules guide our expectationsfor
the stability of the products. CH3CN has a largerproton affinity
than either NCCl or C2H2 (see supple-mentary material for
calculated values), and thus bothprimary products transfer a proton
to neutral CH3CNto form the secondary product CH3CNH
+. Reaction dy-namics predicted by relative proton affinities
has prece-dence in ion-neutral gas-phase chemistry, and boundson
proton affinities have been determined by examiningwhich proton
transfers do or do not take place.57 In ad-dition, these reactions
are both energetically favorable,as per the reaction thermodynamics
reported in Eqns.3-4. As for the relative rate constants calculated
for thesecond order reactions, ADO theory predicts a slightlylarger
rate constant for the C2H3
+ + CH3CN reaction(4.3 × 10−9 cm3/s) due to its smaller reduced
mass ascompared to HNCCl+ +CH3CN (3.5×10−9 cm3/s). Thistrend is
consistent with the reported experimental reac-tion rate constants
in Table III. Overall, there is rea-sonable agreement within the
experimental uncertaintybetween the ADO calculated rate constants
and thosemeasured experimentally.
TABLE III. Rate constants for isotope variations of CCl+ +CH3CN
secondary products. ‘X’ represents a hydrogen ordeuterium from
CH3CN, and corresponds to the isotopologueused. Rates are in units
of ×10−9 cm3/s, and reported statis-tical uncertainty is the
calculated 90% confidence interval.
Reactants CX3CNX+
C2H3+ + CH3CN 4.2 ± 1.7
HNCCl+ + CH3CN 4.1 ± 1.2
C2H3+ + CH3CN 6.2 ± 2.0
HNC37Cl+ + CH3CN 3.8 ± 1.1
C2D3+ + CD3CN 6.0 ± 1.5
DNCCl+ + CD3CN 4.4 ± 0.9
C2D3+ + CD3CN 6.2 ± 2.3
DNC37Cl+ + CD3CN 5.9 ± 1.9
C. Modelling the CCl+ + CH3CN reaction
The potential energy surface shown in Fig. 4 representsa few
plausible reaction pathways of the CCl+ + CH3CNreaction. It is a
result of quantum chemical calculationsand is comprised of
equilibrium structures that bridge thereactants and the observed
products. The experimentalconditions are cold and very low
pressure, which thereforemeans that there is no quenching of the
internal energy ofany of the intermediate low energy structures.
Further-more, the stationary points along this reaction pathwayare
all exothermic with respect to the reactants, such thatthe reaction
complex can sample all these intermediarystates until it leaves the
surface irreversibly. It is useful toconsider the potential energy
surface not only because it
is an accessible way to explore the pathways to
eventualexothermic products presented, but also because it
pro-vides a basis for the quantitative master equation-basedkinetic
modeling presented below. For clarity, the non-hydrogen atoms will
be numbered C1, C2, N3, C4, Cl5,as marked on INT1 in Fig. 4.
In the presented potential energy surface, CCl+ andCH3CN
initially form the adduct INT1 as a bond isformed between N3 and
C4. This structure then un-dergoes various changes in its bond
lengths and anglesisomerizing into the lower energy INT2 structure.
INT2can isomerize into INT4, which can dissociate without abarrier
into PRD1 (HNCCl+ + HC2H), PRD2 (C2H3
+ +NCCl; where C2H3
+ is the non-classical bridge struc-ture), or PRD4 (HNCCl+ +
H2C2; where H2C2 is thevinylidene isomer of C2H2). Determining the
exact chem-ical identity of the C2H2 isomer is beyond the scope
ofthis study: while the m/z of ionic products is knownbased on the
mass spectra, neutral products are specula-tive since they cannot
be observed experimentally.
INT2 can also isomerize to INT3, which leads to thebarrierless
dissociation into PRD3, the classical “Y”C2H3
+ structure and NCCl. The isomerization barrierbetween the two
isomers of C2H3
+ has been the sub-ject of rigorous computational and
experimental studies,and was found to be 4.8 meV as calculated at
the CBS-APNO level of theory.58–60 Regardless of which isomer
isproduced in this reaction, both isomers are energeticallyallowed,
with exothermicity larger than the isomeriza-tion barrier.
Therefore, either C2H3
+ isomer may be theexperimentally observed cation.
All of the outlined products are exothermic with re-spect to the
reactants and there are only submerged bar-riers in the potential
energy surface. This indicates thatboth products are likely to
form, which is perhaps re-flected in the experimentally observed
branching ratiosbeing equal. This observation is tested below
throughRRKM theory/master equation kinetic modeling.
To the best of our knowledge, there are no previousmeasurements
for reactions of CCl+ with any nitrileswith which to compare the
current results. It does ap-pear to be significant that the
elucidated potential energysurface requires cleaving of the C–––N
bond of CH3CN.However, this is perhaps unsurprising given that once
abond is formed between the two reactants, more electrondensity
will be pulled toward the more electronegativechlorine group. This
is demonstrated in the first stepof the PES, when INT1 (see Fig. 4)
is formed. TwoC-N bonds are of importance to this discussion: the
C2-N3 bond, which originated from CH3CN, and the C4-N3bond, where
the carbon from CCl+ attaches to the ter-minal nitrogen of CH3CN.
The shift of electron densityfrom the C2-N3 bond to the C4-N3 and
C4-Cl5 bondsoccurs in this first steps of this potential energy
surface.On this surface, the shift of electron density between
sta-tionary points INT1 and TS1 (Fig. 4) suggests the
C–––Nfunctional group pairs with Cl over CH3, stabilizing
thecomplex with respect to the reactants. This is perhaps
-
7
FIG. 4. Potential energy surface for CCl+ + CH3CN, depicting
equilibrium geometries connecting the reactants (REA) tothe
products (PRD1, PRD2, PRD3, and PRD4). In REA, PRD1, PRD2, PRD3,
and PRD4, the bare ‘+’ denotes infinitedistance between the
ion-neutral pair, while the + symbol indicates the ion of the
ion-neutral pair. Geometries were calculatedat MP2/aug-cc-pVTZ
level, with CCSD(T)/CBS//MP2/aug-cc-pVTZ energies. ‘INT’ refers to
intermediate states, while ‘TS’indicates transition states.
Asterisk denotes a step with a very shallow well (depending on the
level of theory), which is discussedin detail in the supplementary
material.
intuitive, as the highly electronegative Cl atom pulls elec-tron
density towards itself, forming a strong bond, fur-ther assisted by
the electron donating methyl group ofCH3CN.
All products that are observed in this study are pos-sibly a
result of this shift and subsequent cleavage. Us-ing the 13CH3
13CN isotopologue as the neutral reactantcould possibly provide
more convincing experimental ev-idence of the C–––N bond cleaving
mechanism, however,the cost of the reagent was prohibitive. While
unsuccess-ful attempts were made to find a reaction pathway thatdid
not cleave this C–––N bond, this did not constitute anexhaustive
search of the PES. Regardless of whether areaction pathway without
cleavage of the C–––N bond ex-ists, this theoretical mechanism is
interesting in its ownright.
To gain further insight into the CCl+ + CH3CN reac-tion, RRKM
theory / master equation simulations wereconducted on the basis of
the potential energy surface re-ported in Fig. 4 (with PRD4
excluded). Predicted rateconstants are plotted in Fig. 5 for the
overall reactionand for formation of the PRD1 - PRD3 products as
afunction of temperature. Here, the overall rate constants
reflect the ADO theory rates less any reverse dissocia-tion of
the ion-molecule complex back to the reactants.Also included in
Fig. 5 is the experimental measurementmade here and the ADO theory
capture rate constants.
Fig. 5 indicates that the total rate constant is in
goodagreement with the experimental value, which in turnis similar
to the ADO capture value. This reflects thehigh efficiency of the
CCl+ + CH3CN reaction, whichleads almost exclusively to new
products. This is in turnattributed to both the low barriers for
CH3CNCCl
+ iso-merization and the availability of dissociation
channelsfor the subsequent isomers at below the reactant
energy.Only at temperatures of around 300 K and above is thereverse
dissociation channel significant, resulting in thepredicted rate
coefficients to fall below the upper limitset by ADO theory.
Branching between the C2H3+ and HNCCl+ product
ions is approximately 50:50, again in accord with
theexperiments. Interestingly, product PRD3 is predictedto be the
dominant pathway to C2H3
+, suggesting thatit is formed in the classical, yet slightly
higher-energy,vinylium form. This result is attributed to
transitionstates TS2 and TS3 throttling the reaction flux from
-
8
FIG. 5. Theoretical (RRKM/ME) rate constants for the CCl+ +
CH3CN reaction as a function of temperature. Values areincluded for
the overall reaction (total) and for the formation of product ions
HNCCl+ (PRD1) and C2H3
+ (PRD2 + PRD3).Included for comparison are the experimental
measurements (at the effective temperature of 160 K) and the ADO
theorycapture rate constants.
INT2 to a similar extent. Once TS2 is overcome, dissoci-ation to
PRD1 outcompetes all other channels (includingPRD2), due to its low
energy and high entropy. Follow-ing TS3, INT3 prefers to dissociate
further to PRD3 thanto isomerize back to INT2, presumably due to
the looseforward dissociation being highly favored in terms of
en-tropy.
IV. CONCLUSION AND OUTLOOK
The gas-phase reaction of CCl+ +CH3CN is presented,with primary
products C2H3
+ and HNCCl+ formed inapproximately equal yields, and both
channels produc-ing a CH3CNH
+ secondary product. The LIT TOF-MSused in this study enables
experimental conditions of lowpressures and collisional energies,
limiting the reactiondynamics to exothermic pathways without
quenching theinternal energy of the reaction complex. In
addition,the high mass resolution afforded by the TOF-MS
yieldsmethodical product identification that is supported byisotope
substitution and quantum chemical calculations.The presented
potential energy surface pathways indicatea series of equilibrium
structures shifting electron densityfrom the original CH3CN C–––N
bond to the new C–––Nbond formed with the carbon of CCl+. The
experimentalrate constants were reported and compared to
Langevinand ADO theory capture rates, as well as to detailedmaster
equation / RRKM theory-based simulations ofthe reaction kinetics on
a multiple-channel multiple-wellpotential energy surface. ADO
theory, which includesthe polarity of the neutral reactant, is in
good agree-ment with the observed experimental primary productrate
constants. The master equation modeling indicates
that reaction is highly efficient, with the total rate con-stant
predicted to approach the capture rate constant.Moreover, these
calculations reproduce the experimen-tally observed branching
fractions between the primaryionic products C2H3
+ and HNCCl+. Although CCl+ hasbeen predicted to not react with
several neutrals, here, wesee this is not the case, which is
consistent with the previ-ously observed reactions with C2H2.
1 This study presentsthe first example of this class of
gas-phase reactions tobe studied in a regime more closely
comparable to thatof the ISM (namely low pressure and temperature),
andshould aid in predicting the behavior of halogenated
car-bocations and nitriles in this region.
Future studies could further characterize CH3CN withanalogous
reactions of various halogenated carbocationssuch as the
astrochemically relevant ion CF+. In the-ory, a reaction of CF+
with CH3CN would behave sim-ilarly, and the even more
electronegative fluorine mightbe expected to reproduce chlorine’s
behavior here. Thiswould be particularly relevant to verify, as the
presenceCF+ in the ISM is more firmly established. It wouldalso be
interesting to study the effects of various func-tional groups
(possibly more electron donating or with-drawing) attached to the
C–––N in lieu of the methyl ofCH3CN. For example, benzonitrile
C6H5(CN) with itsattached phenyl group could help stabilize
intermediatesor primary products and thus possibly shift the
observedreaction rates. Studying the reaction of CCl+ with var-ious
substituted nitriles might help elucidate a a trendin nitrile
reactivity in this low pressure and cold regime.Overall, probing
the relative C–––N bond strength acrossnitriles might contribute to
the understanding and pre-dictions of the formation and reactivity
of the nitrilespresent throughout the ISM. Although further
isotope
-
9
tagging is necessary to absolutely verify the experimen-tal
reaction mechanism, the computational results aresuggestive, and
open questions for the role and reactivityof the C–––N bond in
nitriles.
For the LIT-TOFMS apparatus, future directionsalso include the
integration of a traveling wave Starkdecelerator61,62 to expand
control over the internal andexternal energies of polar neutral
molecules. The abilityto slow molecules down into the millikelvin
regime allowsthe elucidation of whether quantum mechanical effects
toplay a greater role ion-neutral chemical dynamics. In thisway, it
presents an opportunity to both understand thisclass of reactions
at a fundamental level, as well as fur-ther our understanding of
ISM chemistry.
SUPPLEMENTARY MATERIAL
See supplementary material for expanded experimen-tal results,
including: plots of averaged total ions overreaction times, details
of reaction curve fits, and re-action data, as well as curves for
isotopologue substi-tuted reactions. See also for computational
results inmore detail: the full potential energy surface,
geometriesfor stationary points at MP2/aug-cc-pVTZ level of
the-ory, and geometries and energies for reaction limits
atCCSD(T)/CBS//CCSD/aug-cc-pVTZ level of theory.
ACKNOWLEDGMENTS
This work was supported by the National ScienceFoundation
(PHY-1734006, CHE-1900294) and the AirForce Office of Scientific
Research (FA9550-16-1-0117).GdS is supported by an Australian
Research Council Fu-ture Fellowship (FT130101340).
DATA AVAILABILITY
The data that support the findings of this study areavailable in
the supplementary material and from the cor-responding author upon
reasonable request.
REFERENCES
1K. J. Catani, J. Greenberg, B. V. Saarel, and H. J.
Lewandowski,J. Chem. Phys. 152, 234310 (2020).
2L. E. Snyder and D. Buhl, Astrophys. J. Lett. 163, L47
(1971).3K. B. Jefferts, A. A. Penzias, and R. W. Wilson, Astrophys.
J.Lett. 179, L57 (1973).
4B. A. McGuire, A. M. Burkhardt, S. Kalenskii, C. N.
Shin-gledecker, A. J. Remijan, E. Herbst, and M. C. McCarthy,
Sci-ence 359, 202 (2018).
5J. H. Waite, D. T. Young, T. E. Cravens, A. J. Coates, F.
J.Crary, B. Magee, and J. Westlake, Science 316, 870 (2007).
6A. Ali, E. C. Sittler, D. Chornay, B. R. Rowe, and C.
Puzzarini,Planet. Space Sci. 109-110, 46 (2015).
7P. M. Solomon, K. B. Jefferts, A. A. Penzias, and R. W.
Wilson,Astrophys. J. 168, L107 (1971).
8H. E. Matthews and T. J. Sears, Astrophys. J. Lett. 267,
L53(1983).
9C. Codella, M. Benedettini, M. T. Beltrán, F. Gueth, S.
Viti,R. Bachiller, M. Tafalla, S. Cabrit, A. Fuente, and B.
Lefloch,Astron. Astrophys. 507, L25 (2009).
10S. E. Bisschop, J. K. Jørgensen, T. L. Bourke, S. Bottinelli,
andE. F. van Dishoeck, Astron. Astrophys. 488, 959 (2008).
11S. Cazaux, A. G. G. M. Tielens, C. Ceccarelli, A. Castets,V.
Wakelam, E. Caux, B. Parise, and D. Teyssier, Astrophys. J.593, L51
(2003).
12S. E. Bisschop, J. K. Jørgensen, E. F. van Dishoeck, and E. B.
M.de Wachter, Astron. Astrophys. 465, 913 (2007).
13J. Kissel and F. R. Krueger, Nature 326, 755 (1987).14N.
Biver, D. Bockelée-Morvan, P. Colom, J. Crovisier, J. K.
Davies, W. R. F. Dent, D. Despois, E. Gérard, E. Lellouch,H.
Rauer, R. Moreno, and G. Paubert, Science 275, 1915 (1997).
15A. D. Morse and Q. H. S. Chan, ACS Earth Space Chem. 3,
1773(2019).
16M. Gerin, F. Combes, G. Wlodarczak, T. Jacq, M. Guelin, P.
En-crenaz, and C. Laurent, Astron. Astrophys. 259, L35 (1992).
17A. Belloche, H. S. P. Müller, R. T. Garrod , and K. M.
Menten,Astron. Astrophys. 587, A91 (2016).
18B. A. McGuire, Astrophys. J., Suppl. Ser. 239, 17
(2018),1809.09132.
19E. C. Fayolle, K. I. Öberg, J. K. Jørgensen, K. Altwegg, H.
Cal-cutt, H. S. P. Müller, M. Rubin, M. H. D. van der Wiel,P.
Bjerkeli, T. L. Bourke, A. Coutens, E. F. van Dishoeck, M.
N.Drozdovskaya, R. T. Garrod, N. F. W. Ligterink, M. V. Pers-son,
S. F. Wampfler, H. Balsiger, J. J. Berthelier, J. De Keyser,B.
Fiethe, S. A. Fuselier, S. Gasc, T. I. Gombosi, T. Sémon, C.
Y.Tzou, and t. R. Team, Nat. Astro. 1, 703 (2017).
20D. C. Lis, J. C. Pearson, D. A. Neufeld, P. Schilke, H. S.
P.Müller, H. Gupta, T. A. Bell, C. Comito, T. G. Phillips, E.
A.Bergin, C. Ceccarelli, P. F. Goldsmith, G. A. Blake, A. Bac-mann,
A. Baudry, M. Benedettini, A. Benz, J. Black, A. Boogert,S.
Bottinelli, S. Cabrit, P. Caselli, A. Castets, E. Caux, J.
Cer-nicharo, C. Codella, A. Coutens, N. Crimier, N. R. Crockett,F.
Daniel, K. Demyk, C. Dominic, M. L. Dubernet, M. Em-prechtinger, P.
Encrenaz, E. Falgarone, A. Fuente, M. Gerin,T. F. Giesen, J. R.
Goicoechea, F. Helmich, P. Hennebelle,T. Henning, E. Herbst, P.
Hily-Blant, A. Hjalmarson, D. Hol-lenbach, T. Jack, C. Joblin, D.
Johnstone, C. Kahane, M. Kama,M. Kaufman, A. Klotz, W. D. Langer,
B. Larsson, J. Le Bourlot,B. Lefloch, F. Le Petit, D. Li, R.
Liseau, S. D. Lord, A. Lorenzani,S. Maret, P. G. Martin, G. J.
Melnick, Menten, K. M., P. Mor-ris, J. A. Murphy, Z. Nagy, B.
Nisini, V. Ossenkopf, S. Pacheco,L. Pagani, B. Parise, M. Pérault,
R. Plume, S.-L. Qin, E. Roueff,M. Salez, A. Sandqvist, P. Saraceno,
S. Schlemmer, K. Schus-ter, R. Snell, J. Stutzki, A. Tielens, N.
Trappe, F. F. S. van derTak, M. H. D. van der Wiel, E. van
Dishoeck, C. Vastel, S. Viti,V. Wakelam, A. Walters, S. Wang, F.
Wyrowski, H. W. Yorke,S. Yu, J. Zmuidzinas, Y. Delorme, J.-P.
Desbat, R. Güsten, J.-M.Krieg, and B. Delforge, Astron. Astrophys.
521, L9 (2010).
21D. A. Neufeld, E. Roueff, R. L. Snell, D. Lis, A. O. Benz, S.
Brud-erer, J. H. Black, M. D. Luca, M. Gerin, P. F. Goldsmith,H.
Gupta, N. Indriolo, J. L. Bourlot, F. L. Petit, B. Larsson,G. J.
Melnick, K. M. Menten, R. Monje, Z. Nagy, T. G. Phillips,A.
Sandqvist, P. Sonnentrucker, F. van der Tak, and M. G.Wolfire,
Astrophys. J. 748, 37 (2012).
22D. A. Neufeld and M. G. Wolfire, Astrophys. J. 706, 1594
(2009).23J. Glosik, D. Smith, P. Španěl, W. Freysinger, and W.
Lindinger,
Int. J. Mass Spectrom. Ion Processes 129, 131 (1993).24G. A.
Blake, V. G. Anicich, and W. T. Huntress, Astrophys. J.300, 415
(1986).
25V. G. Anicich, W. T. Huntress, and M. J. McEwan, J. Phys.Chem.
90, 2446 (1986).
26A. S. Blair and A. G. Harrison, Can. J. Chem. 51, 1645
(1973).
http://dx.doi.org/10.1086/180664http://dx.doi.org/10.1086/181116http://dx.doi.org/10.1086/181116http://dx.doi.org/10.1126/science.aao4890http://dx.doi.org/10.1126/science.aao4890http://dx.doi.org/
10.1016/j.pss.2015.01.015http://dx.doi.org/10.1086/180794http://dx.doi.org/10.1086/184001http://dx.doi.org/10.1086/184001http://dx.doi.org/10.1051/0004-6361/200913340http://dx.doi.org/10.1051/0004-6361:200809673http://dx.doi.org/10.1086/378038http://dx.doi.org/10.1086/378038http://dx.doi.org/10.1051/0004-6361:20065963http://dx.doi.org/10.1038/326755a0http://dx.doi.org/
10.1126/science.275.5308.1915http://dx.doi.org/10.1021/acsearthspacechem.9b00129http://dx.doi.org/10.1021/acsearthspacechem.9b00129http://dx.doi.org/10.1051/0004-6361/201527268http://dx.doi.org/10.3847/1538-4365/aae5d2http://arxiv.org/abs/1809.09132http://dx.doi.org/
10.1038/s41550-017-0237-7http://dx.doi.org/10.1051/0004-6361/201014959http://dx.doi.org/
10.1088/0004-637x/748/1/37http://dx.doi.org/10.1088/0004-637X/706/2/1594http://dx.doi.org/10.1016/0168-1176(93)87037-Shttp://dx.doi.org/10.1086/163815http://dx.doi.org/10.1086/163815http://dx.doi.org/10.1021/j100402a038http://dx.doi.org/10.1021/j100402a038http://dx.doi.org/10.1139/v73-246
-
10
27D. Smith, P. Spanel, and C. A. Mayhew, Int. J. Mass
Spectrom.Ion Processes 117, 457 (1992).
28A. Petrank, M. Iraqi, I. Dotan, and C. Lifshitz, Int. J.
MassSpectrom. Ion Processes 117, 223 (1992).
29M. Iraqi, A. Petrank, M. Peres, and C. Lifshitz, Int. J.
MassSpectrom. Ion Processes 100, 679 (1990).
30M. Tsuji, M. Aizawa, H. Ujita, and Y. Nishimura, Bull.
Chem.Soc. Jpn. 68, 2385 (1995).
31B. R. Heazlewood, Mol. Phys. 117, 1934 (2019).32J. Toscano, H.
J. Lewandowski, and B. R. Heazlewood, Phys.
Chem. Chem. Phys. 22, 9180 (2020).33P. Puri, M. Mills, I.
Simbotin, J. A. Montgomery, R. Côté,
C. Schneider, A. G. Suits, and E. R. Hudson, Nat. Chem. 11,615
(2019).
34K. Okada, Y. Takada, N. Kimura, M. Wada, and H. A.Schuessler,
Rev. Sci. Instr. 88, 083106 (2017).
35A. Kilaj, H. Gao, D. Rösch, U. Rivero, J. Küpper, andS.
Willitsch, Nat. Comm. 9, 1 (2018), arXiv:1804.05925.
36Y.-P. Chang, K. D lugo lȩcki, J. Küpper, D. Rösch, D. Wild,
andS. Willitsch, Science 342, 98 (2013).
37P. C. Schmid, J. Greenberg, T. L. Nguyen, J. H. Thorpe, K.
J.Catani, O. A. Krohn, M. I. Miller, J. F. Stanton, and H.
J.Lewandowski, Phys. Chem. Chem. Phys. 22, 20303 (2020).
38E. Lavert-Ofir, Y. Shagam, A. B. Henson, S. Gersten, J. K
los,P. S. Żuchowski, J. Narevicius, and E. Narevicius, Nat.
Chem.6, 332 (2014).
39L. S. Petralia, A. Tsikritea, J. Loreau, T. P. Softley, and B.
R.Heazlewood, Nat. Comm. 11, 1 (2020).
40P. C. Schmid, M. I. Miller, J. Greenberg, T. L. Nguyen, J.
F.Stanton, and H. J. Lewandowski, Mol. Phys. 0, 1
(2019),https://doi.org/10.1080/00268976.2019.1622811.
41J. Greenberg, P. C. Schmid, M. Miller, J. F. Stanton, and H.
J.Lewandowski, Phys. Rev. A 98, 032702 (2018).
42P. C. Schmid, J. Greenberg, M. I. Miller, K. Loeffler, and H.
J.Lewandowski, Rev. Sci. Instr. 88, 123107 (2017).
43B. Roth, P. Blythe, and S. Schiller, Phys. Rev. A 75,
023402(2007).
44C. Q. Jiao, D. R. A. Ranatunga, W. E. Vaughn, and B.
S.Freiser, J. Am. Soc. Mass Spectrom. 7, 118 (1996).
45F. Castet and B. Champagne, J. Chem. Theory Comput. 8,
2044(2012).
46M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
A.Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Peters-son,
H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino,B. G.
Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian,J. V. Ortiz, A.
F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F.
Lipparini, F. Egidi, J. Goings, B. Peng,A. Petrone, T. Henderson,
D. Ranasinghe, V. G. Zakrzewski,J. Gao, N. Rega, G. Zheng, W.
Liang, M. Hada, M. Ehara,K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J.
A.Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J.
J.Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A.Keith,
R. Kobayashi, J. Normand, K. Raghavachari, A. P. Ren-dell, J. C.
Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M.Millam, M. Klene,
C. Adamo, R. Cammi, J. W. Ochterski, R. L.Martin, K. Morokuma, O.
Farkas, J. B. Foresman, and D. J. Fox,“Gaussian˜16 Revision C.01,”
(2016), gaussian Inc. WallingfordCT.
47R. M. Parrish, L. A. Burns, D. G. A. Smith, A. C. Simmonett,A.
E. DePrince, E. G. Hohenstein, U. Bozkaya, A. Y. Sokolov,R. Di
Remigio, R. M. Richard, J. F. Gonthier, A. M. James, H.
R.McAlexander, A. Kumar, M. Saitow, X. Wang, B. P. Pritchard,P.
Verma, H. F. Schaefer, K. Patkowski, R. A. King, E. F. Valeev,F. A.
Evangelista, J. M. Turney, T. D. Crawford, and C. D. Sher-rill, J.
Chem. Theory Comput. 13, 3185 (2017), pMID: 28489372.
48J. R. Barker, T. L. Nguyen, J. F. Stanton, C. Aieta, M.
Ceotto,F. Gabas, T. J. D. Kumar, C. G. L. Li, L. L. Lohr, A.
Maranzana,N. F. Ortiz, J. M. Preses, J. M. Simmie, J. A. Sonk, and
P. J. Sti-mac, “Multiwell-2020 software suite,”
http://clasp-research.
engin.umich.edu/multiwell/ (2020).49J. R. Barker, Int. J. Chem.
Kinet. 33, 232 (2001).50J. R. Barker, Int. J. Chem. Kinet. 41, 748
(2009).51G. da Silva, B. B. Kirk, C. Lloyd, A. J. Trevitt, and S.
J.
Blanksby, J. Phys. Chem.y Lett. 3, 805 (2012).52K. J. Catani, G.
Muller, G. da Silva, and E. J. Bieske, J. Chem.
Phys. 146, 044307 (2017).53J. N. Bull, M. S. Scholz, E.
Carrascosa, G. da Silva, and E. J.
Bieske, Physical Review Letters 120, 223002 (2018).54G. P. Smith
and D. M. Golden, Int. J. Chem. Kinet. 10, 489
(1978).55A. K. Y. Lam, C. Li, G. Khairallah, B. B. Kirk, S. J.
Blanksby,
A. J. Trevitt, U. Wille, R. A. J. O’Hair, and G. da Silva,
Phys.Chem. Chem. Phys. 14, 2417 (2012).
56T. Su and M. T. Bowers, J. Chem. Phys. 58, 3027 (1973).57J. A.
Burt, J. L. Dunn, M. J. McEwan, M. M. Sutton, A. E.
Roche, and H. I. Schiff, J. Chem. Phys. 52, 6062 (1970).58B. T.
Psciuk, V. A. Benderskii, and H. B. Schlegel, Theor. Chem.
Acc. 118, 75 (2007).59M. W. Crofton, M. Jagod, B. D. Rehfuss,
and T. Oka, J. Chem.
Phys. 91, 5139 (1989).60A. R. Sharma, J. Wu, B. J. Braams, S.
Carter, R. Schneider,
B. Shepler, and J. M. Bowman, J. Chem. Phys. 125,
224306(2006).
61Y. Shyur, N. J. Fitch, J. A. Bossert, T. Brown, and H.
J.Lewandowski, Revi. Sci. Instr. 89, 084705 (2018).
62Y. Shyur, J. A. Bossert, and H. J. Lewandowski, J. Phys.
B:At., Mol. Opt. Phys. 51, 165101 (2018).
http://dx.doi.org/https://doi.org/10.1016/0168-1176(92)80108-Dhttp://dx.doi.org/https://doi.org/10.1016/0168-1176(92)80108-Dhttp://dx.doi.org/
https://doi.org/10.1016/0168-1176(92)80096-Jhttp://dx.doi.org/
https://doi.org/10.1016/0168-1176(92)80096-Jhttp://dx.doi.org/
https://doi.org/10.1016/0168-1176(90)85102-8http://dx.doi.org/
https://doi.org/10.1016/0168-1176(90)85102-8http://dx.doi.org/
10.1246/bcsj.68.2385http://dx.doi.org/
10.1246/bcsj.68.2385http://dx.doi.org/10.1039/D0CP00931Hhttp://dx.doi.org/10.1039/D0CP00931Hhttp://dx.doi.org/
10.1038/s41557-019-0264-3http://dx.doi.org/
10.1038/s41557-019-0264-3http://dx.doi.org/10.1038/s41467-018-04483-3http://arxiv.org/abs/1804.05925http://dx.doi.org/10.1126/science.1242271http://dx.doi.org/
10.1039/D0CP03953Ehttps://doi.org/10.1038/nchem.1857https://doi.org/10.1038/nchem.1857http://dx.doi.org/10.1038/s41467-019-13976-8http://dx.doi.org/
10.1080/00268976.2019.1622811http://arxiv.org/abs/https://doi.org/10.1080/00268976.2019.1622811http://dx.doi.org/10.1103/PhysRevA.98.032702http://dx.doi.org/10.1063/1.4996911http://dx.doi.org/10.1103/PhysRevA.75.023402http://dx.doi.org/10.1103/PhysRevA.75.023402http://dx.doi.org/10.1021/jasms.8b00781http://dx.doi.org/10.1021/ct300174zhttp://dx.doi.org/10.1021/ct300174zhttp://dx.doi.org/10.1021/acs.jctc.7b00174http://clasp-research.engin.umich.edu/multiwell/http://clasp-research.engin.umich.edu/multiwell/http://dx.doi.org/10.1063/1.1679615http://dx.doi.org/
10.1063/1.1672909http://dx.doi.org/10.1007/s00214-006-0242-xhttp://dx.doi.org/10.1007/s00214-006-0242-xhttp://dx.doi.org/10.1063/1.2402169http://dx.doi.org/10.1063/1.2402169http://dx.doi.org/
10.1063/1.5040267http://dx.doi.org/10.1088/1361-6455/aad1b0http://dx.doi.org/10.1088/1361-6455/aad1b0
Isotope-specific reactions of acetonitrile (CH3CN) with trapped,
translationally cold CCl+AbstractI IntroductionII MethodsA
Experimental MethodsB Computational Methods
III Results & DiscussionA Reaction thermodynamicsB Reaction
measurementsC Modelling the CCl+ + CH3CN reaction
IV Conclusion and outlook Supplementary Material Acknowledgments
Data Availability References