Semiclassical model for localization and vibrational dynamics in polyatomic molecules Alexander L....
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Transcript of Semiclassical model for localization and vibrational dynamics in polyatomic molecules Alexander L....
Semiclassical model for localization and vibrational dynamics in polyatomic
molecules
Alexander L. Burin
Quantum Coherent Properties of Spins – IIIMany thanks to Enrique del Barco, Stephen Hill
and Philip Stamp for inviting me
Mark Ratner & Alex Burin
Sarah TesarIgor Rubtsov
Semiclassical Model for Vibrational Dynamics in Polyatomic Molecules: Investigation of Internal Vibrational RelaxationAlexander L. Burin, Sarah L. Tesar, Valeriy M. Kasyanenko, Igor V. Rubtsov, and Grigory I. RubtsovJ. Phys. Chem. C, v. 114, pp 20510–20517 (2010)MARK RATNER FESTSCHRIFT
Motivationn-atomic molecule
possesses 3n-6 independent vibrational modes (harmonic approximation)
These modes are coupled by a weak anharmonic interaction
ProblemsEvolution of excited state. Would the molecule remember its
initial excitation?
What is lifetime of excited state?
What are energy relaxation pathways?
OutlineLocalization (Stewart, McDonald)2DIR spectroscopy problems (Rubtsov)Summary of previous theoretical workProblemsSelf-consistent collision integral model Preliminary resultsComparison to experimentsConclusion; future plansAcknowledgement
Theoretical approachesLocal random matrix model (e. g. Bigwood, Gruebele,
Leitner, Wolynes). Replaces anharmonic interaction with random matrix elements . Gives reasonable prediction for localization transition using free parameter for interaction strength
Exact solution of Schrödinger equations on the restricted basis set of global harmonic states (e. g. Dreyer, Moran, Mukamel, 2003). Uses first principles anharmonic force constants, accurate enough in Density Fuctional Theory (Barone, 2005). Restricted to small molecules and low temperature (no more than 10000 states)
This work: Generalizes collision integral approach (Bagratashvili, Kuzmin, Letokhov , Stuchebrukhov, 1985). Determines environment effect self-consistently (Generalized Marcus-Levich-Jortner method)
Hamiltonian and Perturbation
Frequencies and interactions can be determined using first principle DFT method (Gaussian 09). The method works well for infrared absorption spectra (Barone, 05).
Definition of rate constant: preexponential factor
Non-adiabatic or environment controlled adiabatic regimes (Rips, Jortner, 1987)
Relaxation times at room temperature
The calculated relaxation times of the CN and CO stretches are 1.6 ps and 7.0 ps. Consistent with experimentally measured lifetimes in AcPhCN of 1.8 and 3.9 ps.
Energy transport at room temperature, CN stretch is excited at t=0, CO excitation energy is probed
Solvent has been treated in rate equation approximation, =50ps. Maximum shift is reached at t=16ps. Consistent with experimental estimate of 12 ps.
Summary and Future PlansNew self-consistent collision integral approach to
investigate internal vibrational relaxation in polyatomic molecules is proposed
Application of method to the representative AcPhCN molecule shows that this method predicts localization transition temperature, mode decay rates and internal kinetics consistently with the experiment
The modification of the method within the framework of small polaron transport theory and applications to other molecules are in progress