From Femtoseconds to Nanoseconds: Simulation of IBr− Photodissociation Dynamics in CO2 Clusters

IBr− Simulations

MotivationSolvation Dynamics

Previous IX− (CO2 )nSystems

Why IBr− (CO2 )n?

TheoryModel Hamiltonian

Minimal Structures

Simulated Spectrum

Nonadiabatic MD

Near-IR ResultsBranching Ratios

Ground-StateRecombinationExcited-State Trapping

Long-time Simulations

UV ResultsBranching Ratios

Spin-Orbit Quenching

Summary

Future Directions

From Femtoseconds to NanosecondsSimulation of IBr− Photodissociation Dynamics in

CO2 Clusters

Matt Thompson

JILAUniversity of Colorado at Boulder

2007-04-13Doctoral Dissertation Defense

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Outline

Motivation

Theory

Near-IR Results

Ground-State Recombination

UV Results

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Outline

Motivation

Theory

Near-IR Results


UV Results

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Solvation DynamicsWhy Clusters?

É Solvation in bulk liquids: size O(1023)É Large size often means averaging is necessaryÉ Clusters allow us to study solvation while avoidingthe averaging effects

É Lineberger group pioneered the use of chargedclusters: use of MS to select clusters

É Allows study of solvation effects from a singlesolvent molecule to those from tens of solventmolecules

É Focus on the IX−(CO2)n work—but many more havebeen successfully studied

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

How To Do IX−(CO2)n PhotodissociationLineberger Group

É Cluster anions generated in expansionÉ Ions size-selected via TOF mass spectrometerÉ Laser pulse dissociates clusterÉ Product ratios detected by mass spectrometryÉ Ground-state recombination studied viapump-probe

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Previous I−2(CO2)n Work

Lineberger and Parson Groups

2 3 4 5 6 7 8R (Ang)

-1

0

1

2

Ene

rgy

(eV

)

X 2Σ+

u,1/2

B 2Σ+

g,1/2

A 2Πg,3/2

A' 2Πg,1/2

a 2Πu,3/2

a' 2Πu,1/2

I* + I−

I + I−

Good agreement in ratios, sims predicted mech. ofefficient SO quenching in UV

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Previous ICl−(CO2)n WorkLineberger and Parson Groups

2 3 4 5 6 7 8R (Ang)

-1

0

1

2

Ene

rgy

(eV

)

X 2Σ+

1/2

A 2Π3/2

A' 2Π1/2

a 2Π3/2

a' 2Π1/2

B 2Σ+

1/2

I* + Cl−

I− + Cl*

I− + Cl

I + Cl−

0 1 2 3 4 5 6 7 8 9 10 11 12 130

20

40

60

80

100

ExperimentTheory

0 1 2 3 4 5 6 7 8 9 10 11 12 130

20

40

60

80

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13No. of CO2

0

20

40

60

80

100

I−

Cl−

ICl−

Diff. at large sizes due to formation of ES-trapped ICl−species; low abs. cross section makes time-resolved

expts hard

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

IBr−(CO2)nA “Gentler” System?

É ICl−(CO2)n showed interesting dynamics possiblewith a heteronuclear solute but had expt. and sim.challenges

É IBr−(CO2)n: Better system to study a heteronuclearsolvent?É Electronegativity diff. btw. I/Br smaller than I/ClÉ Intuition suggests abs. cross section btw. I−2 and ICl−É Well-known Br-CO2 E− V interaction: could we seethis?

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Outline

Motivation

Theory

Near-IR Results


UV Results

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Model HamiltonianMaslen, Faeder, and Parson

É Solute ab initioÉ Eigenstates of bare anionÉ icMRCISD calculated via MOLPROÉ Spin-orbit coupling, transition DMA, and transitionangular momentum calculated

É Solute-solvent interactionsÉ Distributed multipoles for solute charge densityÉ Solvent polarizes solute wavefunctions

É Dispersion-repulsionÉ Pairwise Lennard-Jones atom-atom potentialsÉ Fit to replicate experimental I− · · ·CO2 interactionand CCSD(T) Br− · · ·CO2 calculations

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Potential Energy Curves

2 3 4 5 6 7 8R (Ang)

-1

-0.5

0

0.5

1

1.5

2

Ene

rgy

(eV

)

I + Br−

I− + Br

I− + Br*

I* + Br−

X 2Σ+

1/2

B 2Σ+

1/2

A 2Π3/2

A' 2Π1/2

a 2Π3/2

a' 2Π1/2

É 6-state icMRCI usingECPnMDF ECPs with CPP

É Augmented basis:(7s7p3d2f)/[5s5p3d2f]

É Spin-orbit effects viaSO-ECP

É Transition DMA, NACME,transition angularmomentum

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Potential Energy CurvesTable of Energetics (in eV)

Calc. Expt. Δ

Spin-Orbit: Br: 0.4237 0.4569 -0.0332I: 0.8932 0.9427 -0.0495

ΔEA: 0.3156 0.3045 0.0111D0: 0.946 0.954 -0.008

Re (Å): 3.05

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions





IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Solute-Solvent InteractionsDistributed Multipole Analysis

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions





IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Minimum Energy IBr−(CO2)n Structures

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Simulated Abs. SpectrumBare Ion

300 400 500 600 700 800 900 1000Wavelength (nm)

0

0.5

1

1.5

Abs

orpt

ion

Cro

ss S

ectio

n (

x10-1

6 cm

2 )

400 600 800 1000 12000

0.01

0.02

0.03

0.04

B 2Σ+

1/2

a' 2Π1/2

A' 2Π1/2

A 2Π3/2a

2Π3/2

Expt. peak740 nm

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Nonadiabatic Molecular DynamicsMaslen, Faeder, and Parson

É Classical path surface-hopping using least switches(Tully, 1990)

É Nuclear deg. of freedom, R(t)É Elec. deg. of freedom quantum, c(t)

É quantum: ιℏc(t) = cE − ιℏ∑

j cjR(t) · dj

É classical: MR(t) = ⟨ϕn|∇RH|ϕn⟩É Hops preserve probabilities |c(t)|2 in an ensembleof trajectories

É Requires only H(R) and its derivatives

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Outline

Motivation

Theory

Near-IR Results


UV Results

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

790-nm Simulations100 Traj. per Ensemble, 50-ps Run-time

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% I− Experiment

Theory

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% B

r−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of CO2

0

20

40

60

80

100

% IB

r−

É I− channel remains openat larger cluster size

É Br− more prevalent insimulation usu. at costof IBr− in mediumclusters

É At n > 8, IBr− productdominates, but...

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

790-nm Simulations - GS Product Only100 Traj. per Ensemble, 50-ps Run-time

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% I− Experiment

Theory

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% B

r−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of CO2

0

20

40

60

80

100

% IB

r−

É IBr− product inmedium-size clustersare primarily trapped onexcited-state

É What is the correctpicture to use forsimulatedphotoproducts?

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

790-nm SimulationsExtrapolation to “Infinite” Time

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% I− Experiment

Theory

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% B

r−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of CO2

0

20

40

60

80

100

% G

roun

d-S

tate

IBr−

É Final product ratiosextrapolated usingresults ofnanosecond-longtrajectories

É What is causing thisexcited-state trappingand can we visualize it?

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Outline

Motivation

Theory

Near-IR Results


UV Results

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Expt. Evidence of Trapping in IBr−(CO2)8Sanford, et al, JCP, 2005

0.0

0.2

0.4

0.6

0.8

0 200 5000 8000Pump-probe delay (ps)

No

rmal

ized

tw

o-p

ho

ton

co

un

ts

GSR recovery time slower than the 10-20 ps seen inI−2 (CO2)n clusters

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

IBr−(CO2)8 PE SurfacePossible Way to Visualize Trapping

2 3 4 5 6 7 8R (Ang)

-0.5

0

0.5

1

1.5

2

2.5

Ene

rgy

(eV

)

É Generated as a "pull"surface from anIBr−(CO2)8 minimalenergy structure

É Surface shows a wellgenerated due tosolvent effects on A′

stateÉ Increase in excitationenergy (730 nm) doesincrease 50-ps IBr− GSyield

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

IBr−(CO2)8 PE SurfaceProblems

2 3 4 5 6 7 8R (Ang)

-0.5

0

0.5

1

1.5

2

2.5

Ene

rgy

(eV

)

É PES is good only for asingle solute and solventconfiguration

É Provides no informationon how the solute andsolvent move in concert

É Can we define a solventcoordinate and plot thatagainst solutegeometry?

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Solvent Coordinate, Δ

É Change in energy whencharge of −e is movedfrom one solute atom toanother

É For a fixed nuclearconfiguration, providesmeasure of the solventasymmetry

É Plots of R v. Δ providea picture of concertedsolvent and solutemovement in atrajectory

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Excited-State Trapping of IBr−(CO2)850-ps Trajectories

É 89% of trajectoriestrapped in A′ state after50 ps

É Only 5% relax toground-state

É Expt. agrees thatlong-time trapping ishappening

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Excited-State Trapping of IBr−(CO2)850-ps Trajectories

É 89% of trajectoriestrapped in A′ state after50 ps

É Only 5% relax toground-state

É Expt. agrees thatlong-time trapping ishappening

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

790-nm ns-Simulations of IBr−(CO2)8100 2-ns traj., 75 relaxed

Cluster needs to achieve more symmetric configurationto allow transition to ground state

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Ground-State Recovery Dynamics ofIBr−(CO2)n

5 6 7 8 9 10 11 12 13 14 15 16No. of CO2 Solvent on IBr

−

1

10

100

1000

10000

Abs

orpt

ion

Rec

over

y T

ime

(ps)

ExperimentalTheory

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Excited-State Well Statistics

6 7 8 9 10 11 12 13 14 15No. of CO2

-2

-1

0

1

2

∆Φ (

eV)

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Excited-State Well for IBr−(CO2)12

É Both -Δ and +Δ wellsvisible

É Labile GS config leads totwo excitation zones

É Evidence of movementbtw wells shows TSbarrier small → fasterGSR time

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Outline

Motivation

Theory

Near-IR Results


UV Results

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

50-ps UV (355-nm) Simulations100 Traj. per Ensemble, 50-ps Run-time

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% I−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% B

r−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of CO2

0

20

40

60

80

100

% IB

r−

ExperimentTheory

É Worse agreement withexperiment cf. IRsimulations, but patternis there

É Higher KER with UVexcitation

É Too small Br· · ·CO2attraction leads toexcess Br− product?

É GS recombination insims: SO quenchingdifference?

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

SO Quenching MechanismDelaney, Faeder, Parson, JCP, 1999

É SO quenching in simsvia charge transfer

É Large solventasymmetry allowscluster to compensatefor SO splitting

É What if there were acompeting process thatcould quench w/o CT?

É W/o CT, solvent transfercould be prevented andGSR product inhibited

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

SO Quenching MechanismDelaney, Faeder, Parson, JCP, 1999

É SO quenching in simsvia charge transfer

É Large solventasymmetry allowscluster to compensatefor SO splitting

É What if there were acompeting process thatcould quench w/o CT?

É W/o CT, solvent transfercould be prevented andGSR product inhibited

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Spin-Orbit Quenching in UV SimulationsDifference btw Expt and Sims?

SO quenching leading to GSR occurs at +Δ→ solvated I− and Br∗ quenching

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Br(2P1/2) QuenchingCollisional Quenching via E− V Transfer

Br(2P1/2) + CO2(0000)E−V→ Br(2P3/2) + CO2(1001)

É Br SO splitting: 3685 cm−1

É CO2: ν1 + ν3 = (1001) = 3714.78 cm−1

É kE−V = 1.5 · 10−11 cm3/molecule/sÉ Branching Ratio: ϕ = 0.87± 0.15É Used as the pumping step in some CO2 lasers

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Summary

É We have constructed an accurate potential energysurface for IBr− with associated properties.

É Simulations of near-IR photodissociation show goodagreement with experimental product trends.

É Long-time near-IR sims provide confirmation andexplanation for long expt. GS recombination time

É UV simulation agreement generally there, butshows discrepancies possibly due to competing SOquenching processes

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Future Directions

É Photoelectron imaging of IBr−(CO2)nÉ Simulate photoelectron signal as prev. done forI−2 (Ar)n

É Provide another measure of absorption recoveryÉ Possible probe into UV differences: Br v. Br∗ neutral

É Incorporation of CO2 vibrations?É Revisiting ICl−(CO2)n dynamics with our IBr−(CO2)nknowledge

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Acknowledgments

É Todd Sanford, Jack Barbera, and Joshua MartinÉ Vladimir, Joshua D., Jeff, many other postdocsÉ Elisa Miller, Ryan Calvi, and the other PES folksÉ Prof. Lineberger

É Drs Nicole Delaney, Jim Faeder, Paul Maslen

É Prof. Parson

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Thank you for coming.Fin.

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Nonadiabatic Molecular DynamicsDetails of Trajectory Methods

É Begin with minimum energy IBr−(CO2)n clusterÉ Warm for 40 ps at 60 K followed by 100-ps run totest energy stability

É Ensemble Construction:É Sample a 2-fs time-step trajectory every 5 ps untilneeded number of configurations are constructed

É Long sampling run ensures sufficiently randomgeometries

É I-Br bond length adjusted to match photon energyÉ Trajectories run with 1.0-fs time step consideredcomplete:É I-Br bond length exceeds 40 0 → dissociatedÉ 20+ crossings of ground-state well → recombinedÉ Simulation duration elapsed → depends...

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Sanov IBr− Fit

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

LCAO-MO Anomalous Charge Flow

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

IBr−(CO2)12 Absorption Spectrum

200 300 400 500 600 700 800 900 1000Wavelength (nm)

0

0.2

0.4

0.6

0.8

1

Abs

orpt

ion

Cro

ss S

ectio

n (

x10-1

6 cm

2 )

600 700 8000

0.05

0.1

B 2Σ+

1/2

a' 2Π1/2

A' 2Π1/2

Bare IBr−

n=16

n=11

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Br− · · ·CO2 Interactions

2 3 4 5 6 7 8 9 10RBr-C (Ang)

-300

-200

-100

0

100

200

300

Ene

rgy

(eV

)

T-Shape CCSD(T)Linear CCSD(T)

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Br− · · ·CO2 Fits

2 3 4 5 6 7 8 9 10RBr-C (Ang)

-300

-200

-100

0

100

200

300

400

500

Ene

rgy

(meV

)

NewMD ValuesMDF MRCIMDF CCSD(T)

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Br− · · ·CO2 LJ Interactions

2 3 4 5 6 7 8RBr-C (Ang)

-50

-40

-30

-20

-10

0

10

20

30

40

50

Ene

rgy

(meV

)

TShape LJLinear LJ

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

LJ Fit Branching

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% I−

Experiment

Theory (Inf.)

Theory (CI Fit)

Theory (CC Fit)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% B

r−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of CO2

0

20

40

60

80

100

% IB

r−

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR Times for LJ Fit

1

10

100

1000

10000

Abs

orpt

ion

Rec

over

y T

ime

(ps)


−

1

10

100

1000

10000

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Wavelength Branching

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% I−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

% B

r−

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14No. of CO2

0

20

40

60

80

100

% G

roun

d S

tate

IBr−

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR Results with 770 and 840 nm


−

1

10

100

1000

10000

Abs

orpt

ion

Rec

over

y T

ime

(ps)

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR Dynamics of IBr−(CO2)8100 Trajectory Ensemble, 2000-ps Run-time

0 500 1000 1500 2000Time (ps)

0

20

40

60

80

No.

of R

ecom

b. T

raje

ctor

ies

0 500 1000 1500 20000

0.2

0.4

0.6

0.8

1

Expt. S

ignal (Arb. U

nits)

τMD = 498 ± 23 ps

τexpt = 900 ± 100 ps

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR Dynamics of IBr−(CO2)12223 Trajectory Ensemble, 300-ps Run-time

0 50 100 150 200 250 300Time (ps)

0

50

100

150

200

No.

of R

ecom

b. T

raje

ctor

ies

τ = 61.8 ± 2.1 ps

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

Ground-State Well Statistics

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16No. of CO2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

Initi

al ∆

Φ (

eV)

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR Dynamics of IBr−(CO2)14

0 500 1000 1500 2000Time (ps)

0

20

40

60

80

100

No.

of R

ecom

b. T

raje

ctor

ies

τsing = 68.9 ± 6.0 ps

τfast = 40.9 ± 1.9 psτslow = 1500 ± 440 ps

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR Solv. Flow Plot of IBr−(CO2)14

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

IBr−(CO2)6 After UV Exc.

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

GSR for IBr−(CO2)13 in UV

-2

0 Energy (eV

)

Br

deloc.

I

Charge

-0.02

0

0.02

dPhi

0 200 400 600 800 1000Time (fs)

2

4

6

8

R (A

ng)

IBr− Simulations



Why IBr− (CO2 )n?


Minimal Structures

Simulated Spectrum

Nonadiabatic MD






Summary

Future Directions

IBr− and IBr Curves

2 3 4 5 6 7 8R (Ang)

-1

0

1

2

3

4

5

6

7

E (

eV)

I* + Br*

I + Br

I + Br*

I* + Br

I* + Br−

I− + Br*

I− + Br

I + Br−

From Femtoseconds to Nanoseconds: Simulation of IBr− Photodissociation Dynamics in CO2 Clusters

Education

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