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

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Published on October 14, 2008

Author: TheMatt

Source: slideshare.net

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This is my thesis defense talk. Be afraid!

IBr− Simulations Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? From Femtoseconds to Nanoseconds Theory Simulation of IBr− Photodissociation Dynamics in Model Hamiltonian Minimal Structures CO2 Clusters Simulated Spectrum Nonadiabatic MD Near-IR Results Branching Ratios Ground-State Matt Thompson Recombination Excited-State Trapping Long-time Simulations JILA UV Results University of Colorado at Boulder Branching Ratios Spin-Orbit Quenching Summary 2007-04-13 Future Directions Doctoral Dissertation Defense

IBr− Simulations Outline Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Motivation Theory Model Hamiltonian Minimal Structures Simulated Spectrum Theory Nonadiabatic MD Near-IR Results Branching Ratios Near-IR Results Ground-State Recombination Excited-State Trapping Long-time Simulations Ground-State Recombination UV Results Branching Ratios Spin-Orbit Quenching UV Results Summary Future Directions

IBr− Simulations Outline Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Motivation Theory Model Hamiltonian Minimal Structures Simulated Spectrum Theory Nonadiabatic MD Near-IR Results Branching Ratios Near-IR Results Ground-State Recombination Excited-State Trapping Long-time Simulations Ground-State Recombination UV Results Branching Ratios Spin-Orbit Quenching UV Results Summary Future Directions

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

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

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

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

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

IBr− Simulations Outline Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Motivation Theory Model Hamiltonian Minimal Structures Simulated Spectrum Theory Nonadiabatic MD Near-IR Results Branching Ratios Near-IR Results Ground-State Recombination Excited-State Trapping Long-time Simulations Ground-State Recombination UV Results Branching Ratios Spin-Orbit Quenching UV Results Summary Future Directions

IBr− Simulations Model Hamiltonian Maslen, Faeder, and Parson Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Theory Solute ab initio Model Hamiltonian Minimal Structures Eigenstates of bare anion Simulated Spectrum icMRCISD calculated via MOLPRO Nonadiabatic MD Near-IR Results Spin-orbit coupling, transition DMA, and transition Branching Ratios angular momentum calculated Ground-State Recombination Solute-solvent interactions Excited-State Trapping Long-time Simulations Distributed multipoles for solute charge density UV Results Solvent polarizes solute wavefunctions Branching Ratios Spin-Orbit Quenching Dispersion-repulsion Summary Pairwise Lennard-Jones atom-atom potentials Future Directions Fit to replicate experimental I− · · · CO2 interaction and CCSD(T) Br− · · · CO2 calculations

IBr− Simulations Potential Energy Curves Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? 2 Theory 2 + 6-state icMRCI using Model Hamiltonian B Σ 1.5 1/2 ECPnMDF ECPs with CPP Minimal Structures Simulated Spectrum Nonadiabatic MD 2 a' Π1/2 Augmented basis: Near-IR Results − 1 I* + Br (7s7p3d2f)/[5s5p3d2f] Branching Ratios Energy (eV) − Ground-State 0.5 2 I + Br* Spin-orbit effects via Recombination a Π3/2 2 − I + Br SO-ECP Excited-State Trapping Long-time Simulations A' Π1/2 0 2 I + Br − Transition DMA, NACME, UV Results A Π3/2 Branching Ratios transition angular Spin-Orbit Quenching -0.5 momentum Summary 2 + X Σ 1/2 Future Directions -1 2 3 4 5 6 7 8 R (Ang)

IBr− Simulations Potential Energy Curves Table of Energetics (in eV) Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Theory Model Hamiltonian Minimal Structures Simulated Spectrum Nonadiabatic MD Calc. Expt. Near-IR Results Spin-Orbit: Br: 0.4237 0.4569 -0.0332 Branching Ratios Ground-State I: 0.8932 0.9427 -0.0495 Recombination EA: 0.3156 0.3045 0.0111 Excited-State Trapping Long-time Simulations D0 : 0.946 0.954 -0.008 UV Results Branching Ratios Re (Å): 3.05 Spin-Orbit Quenching Summary Future Directions

IBr− Simulations Model Hamiltonian Maslen, Faeder, and Parson Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Theory Solute ab initio Model Hamiltonian Minimal Structures Eigenstates of bare anion Simulated Spectrum icMRCISD calculated via MOLPRO Nonadiabatic MD Near-IR Results Spin-orbit coupling, transition DMA, and transition Branching Ratios angular momentum calculated Ground-State Recombination Solute-solvent interactions Excited-State Trapping Long-time Simulations Distributed multipoles for solute charge density UV Results Solvent polarizes solute wavefunctions Branching Ratios Spin-Orbit Quenching Dispersion-repulsion Summary Pairwise Lennard-Jones atom-atom potentials Future Directions Fit to replicate experimental I− · · · CO2 interaction and CCSD(T) Br− · · · CO2 calculations

IBr− Simulations Solute-Solvent Interactions Distributed Multipole Analysis 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

IBr− Simulations Model Hamiltonian Maslen, Faeder, and Parson Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Theory Solute ab initio Model Hamiltonian Minimal Structures Eigenstates of bare anion Simulated Spectrum icMRCISD calculated via MOLPRO Nonadiabatic MD Near-IR Results Spin-orbit coupling, transition DMA, and transition Branching Ratios angular momentum calculated Ground-State Recombination Solute-solvent interactions Excited-State Trapping Long-time Simulations Distributed multipoles for solute charge density UV Results Solvent polarizes solute wavefunctions Branching Ratios Spin-Orbit Quenching Dispersion-repulsion Summary Pairwise Lennard-Jones atom-atom potentials Future Directions Fit to replicate experimental I− · · · CO2 interaction and CCSD(T) Br− · · · CO2 calculations

IBr− Simulations Minimum Energy IBr− (CO2 )n Structures 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

IBr− Simulations Simulated Abs. Spectrum Bare Ion Motivation Solvation Dynamics Previous IX− (CO2 )n Systems 1.5 Why IBr− (CO2 )n ? Theory 0.04 Model Hamiltonian cm ) 2 + B Σ 2 Minimal Structures 1/2 Simulated Spectrum -16 0.03 Nonadiabatic MD Absorption Cross Section ( x10 1 Near-IR Results Branching Ratios 0.02 Ground-State Recombination 0.01 2 Excited-State Trapping 2 a Π3/2 A Π3/2 Long-time Simulations UV Results 0 0.5 400 600 800 1000 1200 Branching Ratios Spin-Orbit Quenching Summary 2 Future Directions Expt. peak A' Π1/2 2 740 nm a' Π1/2 0 300 400 500 600 700 800 900 1000 Wavelength (nm)

IBr− Simulations Nonadiabatic Molecular Dynamics Maslen, Faeder, and Parson Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Theory Model Hamiltonian Classical path surface-hopping using least switches Minimal Structures Simulated Spectrum (Tully, 1990) Nonadiabatic MD Near-IR Results Nuclear deg. of freedom, R(t) Branching Ratios Elec. deg. of freedom quantum, c (t) Ground-State Recombination quantum: ι c (t) = c E − ι ˙ ˙ j cj R(t) · d j Excited-State Trapping Long-time Simulations classical: MR(t) = 〈ϕn |∇R H|ϕn 〉 ¨ UV Results Branching Ratios Hops preserve probabilities |c (t)|2 in an ensemble Spin-Orbit Quenching of trajectories Summary Future Directions Requires only H(R) and its derivatives

IBr− Simulations Outline Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Motivation Theory Model Hamiltonian Minimal Structures Simulated Spectrum Theory Nonadiabatic MD Near-IR Results Branching Ratios Near-IR Results Ground-State Recombination Excited-State Trapping Long-time Simulations Ground-State Recombination UV Results Branching Ratios Spin-Orbit Quenching UV Results Summary Future Directions

IBr− Simulations 790-nm Simulations 100 Traj. per Ensemble, 50-ps Run-time Motivation Solvation Dynamics Previous IX− (CO2 )n 100 Systems 80 I− channel remains open Why IBr− (CO2 )n ? Theory 60 Experiment at larger cluster size − Model Hamiltonian %I Theory Br− more prevalent in 40 Minimal Structures Simulated Spectrum 20 Nonadiabatic MD 0 simulation usu. at cost Near-IR Results 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 of IBr− in medium Branching Ratios 80 clusters Ground-State Recombination 60 At n > 8, IBr− product − Excited-State Trapping % Br Long-time Simulations 40 dominates, but... UV Results 20 Branching Ratios 0 Spin-Orbit Quenching 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 100 Summary 80 Future Directions − 60 % IBr 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 No. of CO2

IBr− Simulations 790-nm Simulations - GS Product Only 100 Traj. per Ensemble, 50-ps Run-time Motivation Solvation Dynamics Previous IX− (CO2 )n 100 Systems 80 IBr− product in Why IBr− (CO2 )n ? Theory 60 Experiment medium-size clusters − Model Hamiltonian %I Theory 40 are primarily trapped on Minimal Structures Simulated Spectrum 20 excited-state Nonadiabatic MD 0 Near-IR Results 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 100 What is the correct Branching Ratios 80 picture to use for Ground-State Recombination 60 simulated − Excited-State Trapping % Br Long-time Simulations 40 photoproducts? UV Results 20 Branching Ratios 0 Spin-Orbit Quenching 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 100 Summary 80 Future Directions − 60 % IBr 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 No. of CO2

IBr− Simulations 790-nm Simulations Extrapolation to “Infinite” Time Motivation Solvation Dynamics Previous IX− (CO2 )n 100 Systems 80 Final product ratios Why IBr− (CO2 )n ? Theory 60 Experiment extrapolated using − Model Hamiltonian %I Theory 40 results of Minimal Structures Simulated Spectrum 20 nanosecond-long Nonadiabatic MD 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 trajectories Near-IR Results Branching Ratios 100 80 What is causing this Ground-State Recombination 60 excited-state trapping − Excited-State Trapping % Br 40 and can we visualize it? Long-time Simulations UV Results 20 Branching Ratios 0 Spin-Orbit Quenching 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 100 Summary − % Ground-State IBr 80 Future Directions 60 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 No. of CO2

IBr− Simulations Outline Motivation Solvation Dynamics Previous IX− (CO2 )n Systems Why IBr− (CO2 )n ? Motivation Theory Model Hamiltonian Minimal Structures Simulated Spectrum Theory Nonadiabatic MD Near-IR Results Branching Ratios Near-IR Results Ground-State Recombination Excited-State Trapping Long-time Simulations Ground-State Recombination UV Results Branching Ratios Spin-Orbit Quenching UV Results Summary Future Directions

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

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

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)

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

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

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

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

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

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