OSU – June – 2013 - SGK1 STEVE KUKOLICH, ERIK MITCHELL ╬, SPENCER CAREY, MING SUN, AND BRYAN SARGUS, Dept. of Chemistry and Biochemistry, The University.

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STEVE KUKOLICH, ERIK MITCHELL╬ , SPENCER CAREY, MING SUN, AND BRYAN SARGUS, Dept. of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721.

MICROWAVE STRUCTURE FOR THE PROPIOLIC ACID – FORMIC ACID COMPLEX†

╬ Present address: Patrick Air Force Base, 32925, United States † This material is based on work supported by the National Science Foundation under Grant Nos. CHE-0721505, CHE-0809053 and CHE-10557796

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HYDROGEN-BONDED STRUCTURES ARE NOT STATIC ADAM DALY

CONCERTED PROTON TUNNELING

Microwave measurements of proton tunneling and structural parameters for the propiolic acid – formic acid dimer1 (2011)

1. Adam M. Daly, Kevin O. Douglass, Laszlo C. Sarkozy, Justin L. Neill, Matt T. Muckle, Daniel P. Zaleski, Brooks H. Pate and Stephen G. Kukolich, J Chem. Phys., 135(15), 154304/1-154304/12 (2011)

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PROTON TUNNELING

• Observed transitions were split into doublets > concerted proton tuneling • The small splittings of 1 to 1.5 MHz for the a-dipole transitions are due to the

differences in rotational constants for the upper and lower tunneling states. • The b-dipole transitions are combination transitions with change in rotational state

and tunneling state and provide direct information on the tunneling splittings.

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• PREVIOUS RESULTS FOR THE PROPIOLIC ACID – FORMIC ACID DIMER C.O.M. SEPARATION > WELL DETERMINED, BUT, RELATIVE

ORIENTATIONS OF THE MONOMERS, NOT WELL DETERMINED. TUNNELING FREQUENCY FOR HCCCOOD···DOOCH BASED ON FEW

MEASUREMENTS.• HOW TO FIX THIS? MEASURE MORE ISOTOPOLOGUES! (BOB KUCZKOWSKI RECOMMENDATION)

NEW MEASUREMENTS• DCCCOOH···HOOCH and HCCCOOD···DOOCH isotopologues, measured in

the 4.9-15.4 GHz range IMPROVED STRUCTURE and OD···DO TUNNELING FREQUENCY

PROPIOLICACID COM(ORIGIN)

FORMICACID COM

X

Y

CM

CM FA

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• SUMMARY OF RESULTS

• Hydrogen bond lengths are r(O1-H1··O4) of 1.64 Å and r(O3-H2··O2) 1.87 Å. Average of hydrogen bond lengths is rav(exp) = 1.76 Å, in good agreement with rav(theory) = 1.72 Å.

• The experimental structure exhibits a greater asymmetry for the two hydrogen bond lengths than was obtained from the ab initio mp2 calculations

• Tunneling frequency for HCCCOOD···DOOCH is = 3.48 MHz (compared with = 291.4 MHz for OH ···HO)

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Experimental

• A new coaxial-beam FTMW spectrometer with multiple FID data acquisition completed by Ming Sun provided good resolution and sensitivity.

• Propiolic acid-CD (DCCCOOH) was prepared in 32-54% yield by the decarboxylation of acetylenedicarboxylic acid monopotassium salt in D2O, by Spencer Carey

• 7 a-dipole transitions measured for DCCCOOH···HOOCH (lower tunneling state only)• A = 5994., B =890.536, C = 775.780 MHz

• Propiolic acid-OD samples were prepared using both simple hydrogen exchange with methanol(OD) (99.5%), and by making sodium propiolate using NaOH in methanol, and adding D2SO4.

• 45 transitions measured for HCCCOOD···DOOCH (a and b-dipole)

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The Jka,kc = 41,4 → 30,3 b-type doublet of the ProOD-FAOD. The b-dipole ro-vibrational transitions are

weak, 5000 pulses, 10 FID’s each pulse.

11210.43 11210.76 11217.30 11217.60

JKa,Kc = 4 1,4 3 0,3

v0+ v0

-

v0+v0

-

Frequency (MHz)

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Table 2. Spectroscopic Constants for ProOD-FAOD in MHz.a

ProOD-FAOD(+) ProOD-FAOD(-) A 5824.76(7) 5824.85(7) B 922.190(3) 922.190(3) C 796.0357(2) 796.0313(2) DJ

b 0.000024(14) 0.000024(14) DJK

b 0.0015(6) 0.0015(6) DK

b 1.06(38) 1.06(38) ΔE 3.48(7) Fab -56.9(13) rms 0.012 a Errors are 1 in the last quoted decimal places. b Values from the lowest tunneling state are used during fitting.

ProOD-FAOD vs ProOH-FAOH tunneling frequency RATIO in good agreement with recent calculations by J. Bowman and Y. Wang (submitted for pub.)

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Determining the COM separation of the monomers is easy

• The formula is: ICC = ICC(Pro) + ICC(FA) + R2CM.

Complex ICC (amu-Å2) RCM (Å) R(C1-C4) (Å)

HCCCOOH-HOOCH (normal) 628.585 3.8720 3.822

HCCCOOH-HOO13CH 636.247 3.8815 3.822

HCCCOOH-DOOCH 631.130 3.8487 3.818

HCCCOOD-HOOCH 632.380 3.8562 3.830

HCCCOOH-HOOCD 642.955 3.9026 3.817

HCCCOOD-DOOCH 634.872 3.8326 3.822

DCCCOOH-HOOCH 651.543 3.9188 3.819

____________________________________________________________________ rC1-C4 values are in good agreement and do not exhibit a significant shortening of

the H bonds with deuterium substitution. RCM value for the normal isotopologue of

3.8720 Å agrees well with value 3.8645 from the fit using all 7 isotopologues.

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PROPIOLICACID COM(ORIGIN)

FORMICACID COM

X

Y

CM

CM FA

Determining the RELATIVE ORIENTATION of the monomers is not so easy.

1) Fix the monomer structures using best parameters available.2) Assume PLANAR structure (= 1.33 amu Å2 )3) Fix the origin of XCM, YCM coordinate system at COM of PROPIOLIC4) Adjust the location (XCM, YCM) and orientation FA of FORMIC to fit B and C rotational constants

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HCOOH1 and HCCCOOH2 structures fixed at monomer values ISOTOPOLOGUES > HCCCOOH•••HOOCH,

HCCCOOH•••DOOCH, HCCCOOD•••HOOCH, HCCCOOH•••HOO13CH, HCCCOOH•••HOOCD3,

HCCCOOD•••DOOCH, DCCCOOH•••HOOCH (new)

Experimental B and C for 7 isotopologues fit with = 0.7 MHz

The best-fit hydrogen bond lengths are r(O1-H1··O4) = 1.64 Å and r(O3-H2··O2) =1.87 Å.

Average (O-H) is rav(exp) = 1.76 Å, in good agreement with rav(theory) = 1.72 Å. Center of mass separation of monomers is RCM = 3.864 Å.

_______________________________

1. Davis, R. W.; Robiette, A. G.; Gerry, M. C. L.; Bjarnov, E.; Winnewisser, G. J. Mol. Spec. 1980, 81, 93-109.

2. Lister, D. G.; Tyler, J. K. Spectochimica Acta 1972, 28A, 1423-1427.

3. Daly, A. M.; Douglass, K. O.; Sarkozy, L. C.; Neill, J. L.; Muckle, M. T.; Zaleski, D. P.; Pate, B. H.; Kukolich, S. G. J. Chem.Phys. 2011, 135, 154304/1-154304/12

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Most significant difference is ASYMMETRY OF H-BOND LENGTHS

Do the O-H bond lengths change on complex formation?

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Key Structural Parameters:Parameter - (Å) Experimental Calculated *

H1-O4 1.64 1.71

H2-O2 1.87 1.73

O1-O4 2.59 2.70

O2-O3 2.80 2.72

C1-O1-H1 106º 109º

H2-O3-C4 106º 109º

MP2/6-311++G**(Gaussian) basis set COM separation Uncertainty (0.015 Å)

Uncertainty of FA, of 1.1º. Experimental

uncertainty in FA propagated to 0.02 Å

uncertainties in H-bond lengths

Not enough to account for differences between experimental and ab initio calculated results

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Acknowledgements

• N$F - This material is based upon work supported by the National Science Foundation under Grant Nos. CHE-0809053, CHE-0721505 and CHE-10557796. This support from the National Science Foundation is gratefully acknowledged

Adam Daly (UA – JPL); Yimin Wang and Joel Bowman (Emory U.)

•Department of Chemistry, University of Arizona.

•Earlier work > Phil Bunker – NRC, > Kevin Douglas, Brooks Pate – U. Virginia

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ISOTOPOLOGUES > HCCCOOH•••HOOCH, HCCCOOH•••DOOCH, HCCCOOD•••HOOCH,

HCCCOOH•••HOO13CH, HCCCOOH•••HOOCD†, HCCCOOD•••DOOCH, DCCCOOH•••HOOCH (new)

• The best-fit hydrogen bond lengths are r(O1-H1··O4) = 1.64 Å and r(O3-H2··O2) =1.87 Å. Average is rav(exp) = 1.76 Å, in good agreement with rav(theory) = 1.72 Å. Center of mass separation of monomers is RCM = 3.864 Å.

† Daly, A. M.; Douglass, K. O.; Sarkozy, L. C.; Neill, J. L.; Muckle, M. T.; Zaleski, D. P.; Pate, B. H.; Kukolich, S. G. J. Chem.Phys. 2011, 135, 154304/1-154304/12

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