4. IBr− Simulations
Solvation Dynamics
Why Clusters?
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Solvation in bulk liquids: size O(1023 ) Theory
Model Hamiltonian
Minimal Structures
Large size often means averaging is necessary Simulated Spectrum
Nonadiabatic MD
Clusters allow us to study solvation while avoiding Near-IR Results
the averaging effects Branching Ratios
Ground-State
Recombination
Lineberger group pioneered the use of charged Excited-State Trapping
Long-time Simulations
clusters: use of MS to select clusters
UV Results
Allows study of solvation effects from a single Branching Ratios
Spin-Orbit Quenching
solvent molecule to those from tens of solvent Summary
molecules Future Directions
Focus on the IX− (CO2 )n work—but many more have
been successfully studied
5. IBr− Simulations
How To Do IX− (CO2 )n Photodissociation
Lineberger Group
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
Nonadiabatic MD
Cluster anions generated in expansion
Near-IR Results
Ions size-selected via TOF mass spectrometer Branching Ratios
Ground-State
Laser pulse dissociates cluster Recombination
Excited-State Trapping
Product ratios detected by mass spectrometry Long-time Simulations
UV Results
Ground-state recombination studied via Branching Ratios
Spin-Orbit Quenching
pump-probe
Summary
Future Directions
6. IBr− Simulations
Previous I− (CO2 )n Work
2
Lineberger and Parson Groups
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
2 Systems
Why IBr− (CO2 )n ?
2 +
B Σ g,1/2 Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
− Nonadiabatic MD
1 I* + I
2 Near-IR Results
a' Πu,1/2
Energy (eV)
Branching Ratios
2
a Πu,3/2 Ground-State
2 Recombination
A' Πg,1/2 Excited-State Trapping
−
I+I Long-time Simulations
0
2
A Πg,3/2 UV Results
Branching Ratios
Spin-Orbit Quenching
Summary
2 +
X Σ u,1/2 Future Directions
-1
2 3 4 5 6 7 8
R (Ang)
Good agreement in ratios, sims predicted mech. of
efficient SO quenching in UV
7. IBr− Simulations
Previous ICl− (CO2 )n Work
Lineberger and Parson Groups
100 Motivation
2 Solvation Dynamics
2 + 80 Experiment
B Σ Previous IX− (CO2 )n
1/2
60 − Theory Systems
40
I Why IBr− (CO2 )n ?
Theory
20
Model Hamiltonian
2
a' Π1/2 −
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 Minimal Structures
1 I* + Cl 100 Simulated Spectrum
2 −
a Π3/2
Nonadiabatic MD
Energy (eV)
I + Cl* 80
Near-IR Results
−
60 −
2
A' Π1/2 I + Cl 40
Cl Branching Ratios
Ground-State
20 Recombination
−
I + Cl 0 Excited-State Trapping
0 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13
A Π3/2 100
Long-time Simulations
80
UV Results
Branching Ratios
60 − Spin-Orbit Quenching
2 + 40
ICl
X Σ 1/2
Summary
20
-1 Future Directions
2 3 4 5 6 7 8 0
0 1 2 3 4 5 6 7 8 9 10 11 12 13
R (Ang) No. of CO2
Diff. at large sizes due to formation of ES-trapped ICl−
species; low abs. cross section makes time-resolved
expts hard
8. IBr− Simulations
IBr− (CO2 )n
A “Gentler” System?
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
ICl− (CO2 )n showed interesting dynamics possible Simulated Spectrum
Nonadiabatic MD
with a heteronuclear solute but had expt. and sim.
Near-IR Results
challenges Branching Ratios
Ground-State
IBr− (CO2 )n : Better system to study a heteronuclear Recombination
Excited-State Trapping
solvent? Long-time Simulations
UV Results
Electronegativity diff. btw. I/Br smaller than I/Cl Branching Ratios
Intuition suggests abs. cross section btw. I− and ICl−
2
Spin-Orbit Quenching
Well-known Br-CO2 E − V interaction: could we see Summary
this? Future Directions
24. IBr− Simulations
Expt. Evidence of Trapping in IBr− (CO2 )8
Sanford, et al, JCP, 2005
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
0.8 Systems
Why IBr− (CO2 )n ?
Theory
Normalized two-photon
Model Hamiltonian
Minimal Structures
0.6 Simulated Spectrum
Nonadiabatic MD
Near-IR Results
Branching Ratios
counts
0.4 Ground-State
Recombination
Excited-State Trapping
Long-time Simulations
0.2 UV Results
Branching Ratios
Spin-Orbit Quenching
Summary
0.0 Future Directions
0 200 5000 8000
Pump-probe delay (ps)
GSR recovery time slower than the 10-20 ps seen in
I− (CO2 )n clusters
2
25. IBr− Simulations
IBr− (CO2 )8 PE Surface
Possible Way to Visualize Trapping
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
2.5 Theory
Generated as a quot;pullquot; Model Hamiltonian
Minimal Structures
2 surface from an Simulated Spectrum
IBr− (CO2 )8 minimal
Nonadiabatic MD
1.5 Near-IR Results
energy structure Branching Ratios
Energy (eV)
Ground-State
1 Surface shows a well Recombination
0.5
generated due to Excited-State Trapping
Long-time Simulations
solvent effects on A UV Results
0 state Branching Ratios
Spin-Orbit Quenching
-0.5
Increase in excitation Summary
energy (730 nm) does Future Directions
2 3 4 5 6 7 8
R (Ang) increase 50-ps IBr− GS
yield
26. IBr− Simulations
IBr− (CO2 )8 PE Surface
Problems
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
2.5
Model Hamiltonian
PES is good only for a Minimal Structures
Simulated Spectrum
2 single solute and solvent Nonadiabatic MD
configuration Near-IR Results
1.5 Branching Ratios
Provides no information
Energy (eV)
Ground-State
1 on how the solute and Recombination
Excited-State Trapping
0.5
solvent move in concert Long-time Simulations
UV Results
Can we define a solvent Branching Ratios
0
coordinate and plot that Spin-Orbit Quenching
Summary
-0.5
against solute Future Directions
geometry?
2 3 4 5 6 7 8
R (Ang)
27. IBr− Simulations
Solvent Coordinate,
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Change in energy when Theory
charge of −e is moved Model Hamiltonian
Minimal Structures
from one solute atom to Simulated Spectrum
Nonadiabatic MD
another
Near-IR Results
For a fixed nuclear Branching Ratios
Ground-State
configuration, provides Recombination
measure of the solvent Excited-State Trapping
Long-time Simulations
asymmetry UV Results
Branching Ratios
Plots of R v. provide Spin-Orbit Quenching
a picture of concerted Summary
solvent and solute Future Directions
movement in a
trajectory
28. IBr− Simulations
Excited-State Trapping of IBr− (CO2 )8
50-ps Trajectories
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
89% of trajectories Theory
Model Hamiltonian
trapped in A state after Minimal Structures
Simulated Spectrum
50 ps Nonadiabatic MD
Near-IR Results
Only 5% relax to Branching Ratios
ground-state Ground-State
Recombination
Expt. agrees that Excited-State Trapping
Long-time Simulations
long-time trapping is UV Results
happening Branching Ratios
Spin-Orbit Quenching
Summary
Future Directions
29. IBr− Simulations
Excited-State Trapping of IBr− (CO2 )8
50-ps Trajectories
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
89% of trajectories Theory
Model Hamiltonian
trapped in A state after Minimal Structures
Simulated Spectrum
50 ps Nonadiabatic MD
Near-IR Results
Only 5% relax to Branching Ratios
ground-state Ground-State
Recombination
Expt. agrees that Excited-State Trapping
Long-time Simulations
long-time trapping is UV Results
happening Branching Ratios
Spin-Orbit Quenching
Summary
Future Directions
30. IBr− Simulations
790-nm ns-Simulations of IBr− (CO2 )8
100 2-ns traj., 75 relaxed
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
Nonadiabatic MD
Near-IR Results
Branching Ratios
Ground-State
Recombination
Excited-State Trapping
Long-time Simulations
UV Results
Branching Ratios
Spin-Orbit Quenching
Summary
Future Directions
Cluster needs to achieve more symmetric configuration
to allow transition to ground state
31. IBr− Simulations
Ground-State Recovery Dynamics of
IBr− (CO2 )n Motivation
Solvation Dynamics
10000 Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
Absorption Recovery Time (ps)
1000 Nonadiabatic MD
Near-IR Results
Branching Ratios
Ground-State
Recombination
Excited-State Trapping
100 Long-time Simulations
UV Results
Branching Ratios
Spin-Orbit Quenching
Summary
10 Future Directions
Experimental
Theory
1
5 6 7 8 9 10 11 12 13 14 15 16
−
No. of CO2 Solvent on IBr
35. IBr− Simulations
50-ps UV (355-nm) Simulations
100 Traj. per Ensemble, 50-ps Run-time
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
100 Systems
80 Worse agreement with Why IBr− (CO2 )n ?
Theory
60 experiment cf. IR
−
Model Hamiltonian
%I
40 simulations, but pattern Minimal Structures
Simulated Spectrum
20
is there Nonadiabatic MD
0 Near-IR Results
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Higher KER with UV Branching Ratios
80 excitation Ground-State
Recombination
60
Too small Br· · · CO2
−
Excited-State Trapping
% Br
Long-time Simulations
40
attraction leads to UV Results
20
0
excess Br− product? Branching Ratios
Spin-Orbit Quenching
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
100 GS recombination in Summary
80 Experiment sims: SO quenching Future Directions
Theory
difference?
−
60
% IBr
40
20
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
No. of CO2
36. IBr− Simulations
SO Quenching Mechanism
Delaney, Faeder, Parson, JCP, 1999
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
SO quenching in sims Why IBr− (CO2 )n ?
Theory
via charge transfer Model Hamiltonian
Minimal Structures
Large solvent Simulated Spectrum
asymmetry allows Nonadiabatic MD
Near-IR Results
cluster to compensate Branching Ratios
for SO splitting Ground-State
Recombination
What if there were a Excited-State Trapping
Long-time Simulations
competing process that UV Results
could quench w/o CT? Branching Ratios
Spin-Orbit Quenching
W/o CT, solvent transfer Summary
could be prevented and Future Directions
GSR product inhibited
37. IBr− Simulations
SO Quenching Mechanism
Delaney, Faeder, Parson, JCP, 1999
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
SO quenching in sims Why IBr− (CO2 )n ?
Theory
via charge transfer Model Hamiltonian
Minimal Structures
Large solvent Simulated Spectrum
asymmetry allows Nonadiabatic MD
Near-IR Results
cluster to compensate Branching Ratios
for SO splitting Ground-State
Recombination
What if there were a Excited-State Trapping
Long-time Simulations
competing process that UV Results
could quench w/o CT? Branching Ratios
Spin-Orbit Quenching
W/o CT, solvent transfer Summary
could be prevented and Future Directions
GSR product inhibited
38. IBr− Simulations
Spin-Orbit Quenching in UV Simulations
Difference btw Expt and Sims?
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
Nonadiabatic MD
Near-IR Results
Branching Ratios
Ground-State
Recombination
Excited-State Trapping
Long-time Simulations
UV Results
Branching Ratios
Spin-Orbit Quenching
Summary
Future Directions
SO quenching leading to GSR occurs at +
→ solvated I− and Br∗ quenching
39. IBr− Simulations
Br(2 P1/ 2 ) Quenching
Collisional Quenching via E − V Transfer
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
E−V
Br(2 P1/ 2 ) + CO2 (000 0) → Br(2 P3/ 2 ) + CO2 (100 1) Nonadiabatic MD
Near-IR Results
Branching Ratios
Ground-State
Recombination
Br SO splitting: 3685 cm−1 Excited-State Trapping
Long-time Simulations
CO2 : ν1 + ν3 = (100 1) = 3714.78 cm−1 UV Results
Branching Ratios
kE−V = 1.5 · 10−11 cm3 /molecule/s
Spin-Orbit Quenching
Summary
Branching Ratio: ϕ = 0.87 ± 0.15 Future Directions
Used as the pumping step in some CO2 lasers
40. IBr− Simulations
Summary
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
We have constructed an accurate potential energy Minimal Structures
surface for IBr− with associated properties. Simulated Spectrum
Nonadiabatic MD
Simulations of near-IR photodissociation show good Near-IR Results
Branching Ratios
agreement with experimental product trends. Ground-State
Recombination
Long-time near-IR sims provide confirmation and Excited-State Trapping
explanation for long expt. GS recombination time Long-time Simulations
UV Results
UV simulation agreement generally there, but Branching Ratios
Spin-Orbit Quenching
shows discrepancies possibly due to competing SO Summary
quenching processes Future Directions
41. IBr− Simulations
Future Directions
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Photoelectron imaging of IBr− (CO2 )n Minimal Structures
Simulated Spectrum
Simulate photoelectron signal as prev. done for Nonadiabatic MD
I− (Ar)n
2
Near-IR Results
Branching Ratios
Provide another measure of absorption recovery Ground-State
Possible probe into UV differences: Br v. Br∗ neutral Recombination
Excited-State Trapping
Incorporation of CO2 vibrations? Long-time Simulations
UV Results
Revisiting ICl− (CO2 )n dynamics with our IBr− (CO2 )n Branching Ratios
Spin-Orbit Quenching
knowledge Summary
Future Directions
42. IBr− Simulations
Acknowledgments
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Todd Sanford, Jack Barbera, and Joshua Martin Simulated Spectrum
Nonadiabatic MD
Vladimir, Joshua D., Jeff, many other postdocs Near-IR Results
Branching Ratios
Elisa Miller, Ryan Calvi, and the other PES folks Ground-State
Recombination
Prof. Lineberger Excited-State Trapping
Long-time Simulations
Drs Nicole Delaney, Jim Faeder, Paul Maslen UV Results
Branching Ratios
Spin-Orbit Quenching
Prof. Parson Summary
Future Directions
43. IBr− Simulations
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Theory
Model Hamiltonian
Minimal Structures
Simulated Spectrum
Nonadiabatic MD
Thank you for coming. Near-IR Results
Fin. Branching Ratios
Ground-State
Recombination
Excited-State Trapping
Long-time Simulations
UV Results
Branching Ratios
Spin-Orbit Quenching
Summary
Future Directions
44. IBr− Simulations
Nonadiabatic Molecular Dynamics
Details of Trajectory Methods
Motivation
Solvation Dynamics
Previous IX− (CO2 )n
Systems
Why IBr− (CO2 )n ?
Begin with minimum energy IBr− (CO2 )n cluster Theory
Warm for 40 ps at 60 K followed by 100-ps run to Model Hamiltonian
Minimal Structures
test energy stability Simulated Spectrum
Nonadiabatic MD
Ensemble Construction: Near-IR Results
Branching Ratios
Sample a 2-fs time-step trajectory every 5 ps until
Ground-State
needed number of configurations are constructed Recombination
Long sampling run ensures sufficiently random Excited-State Trapping
Long-time Simulations
geometries UV Results
Branching Ratios
I-Br bond length adjusted to match photon energy Spin-Orbit Quenching
Trajectories run with 1.0-fs time step considered Summary
complete: Future Directions
I-Br bond length exceeds 40 0 → dissociated
20+ crossings of ground-state well → recombined
Simulation duration elapsed → depends...