from femtoseconds to nanoseconds: simulation of ibr− photodissociation dynamics in co2 clusters
DESCRIPTION
This is my thesis defense talk. Be afraid!TRANSCRIPT
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
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
Outline
Motivation
Theory
Near-IR Results
Ground-State Recombination
UV Results
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
Outline
Motivation
Theory
Near-IR Results
Ground-State Recombination
UV Results
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
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
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
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
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
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
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
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
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
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
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
Outline
Motivation
Theory
Near-IR Results
Ground-State Recombination
UV Results
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
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
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
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
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
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
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
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
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
Solute-Solvent InteractionsDistributed Multipole Analysis
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
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
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
Minimum Energy IBr−(CO2)n Structures
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
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
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
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
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
Outline
Motivation
Theory
Near-IR Results
Ground-State Recombination
UV Results
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
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
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
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
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
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
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
Outline
Motivation
Theory
Near-IR Results
Ground-State Recombination
UV Results
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Outline
Motivation
Theory
Near-IR Results
Ground-State Recombination
UV Results
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Thank you for coming.Fin.
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
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
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
Sanov IBr− Fit
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
LCAO-MO Anomalous Charge Flow
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
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
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
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
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
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
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
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
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
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
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
GSR Times for LJ Fit
1
10
100
1000
10000
Abs
orpt
ion
Rec
over
y T
ime
(ps)
5 6 7 8 9 10 11 12 13 14 15 16No. of CO2 Solvent on IBr
−
1
10
100
1000
10000
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
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
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
GSR Results with 770 and 840 nm
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)
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
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
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
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
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
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
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
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
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
GSR Solv. Flow Plot of IBr−(CO2)14
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
IBr−(CO2)6 After UV Exc.
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
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
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
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−