William Miller, Victor Guallar, Victor S. Batista, and
Eduardo A. Coronado, University of California, Berkeley

Research Objectives

This research aims to develop accurate simulation methods to investigate quantum processes and spectroscopy associated with realistic chemical reactions.

Computational Approach

The algorithms are based on efficient semiclassical initial value representation (SC-IVR) strategies that generalize classical molecular dynamics techniques to include quantum interference and even tunneling to some extent within the description. We evaluate a high dimensional integral over initial conditions for semiclassical trajectories that evolve according to classical equations of motion. Trajectories are integrated independently of each other and are computed in parallel.

Accomplishments

Accomplishments achieved during FY 1999 include:
1. The development of adiabatic SC-IVR methods for simulations of the photo-excited double proton transfer reaction in a model DNA base pair.
2. The development of forward-backward SC-IVR methods for simulations of ultrafast pump-probe photoelectron spectroscopy.
3. Simulations of electronic nonadiabatic effects in both the photofragment rotational distributions and the photoabsorption cross section associated with the photodissociation dynamics of ICN in the A continuum.
4. The development of a full dimensional excited state potential energy surface, obtained according to a reaction surface approach, and the simulation of the excited-state intra-molecular proton transfer reaction in 2-(2'-hydroxyphenyl)-oxazole using SC-IVR.
5. The development of an efficient algorithm for time slicing the SC-IVR.

Significance

	The ultrafast excited state double proton transfer in the tautomerization reaction of photo-excited 7-azaindole dimers is visualized in terms of the nuclear wave packet motion on the S1 CIS electronic excited state potential energy surface. Proton transfer usually occurs during the first intermonomer symmetric-stretch vibration, about 100 fs after photo-excitation of the system, and produces an initial 15% population decay of the reactant base-pair, which is significantly reduced by isotopic substitution. The S1 electronic excited state is found to have predominant (HOMO)—>(LUMO) MO excitation, and the largest oscillator strength constant in the FC region.

Incorporating quantum mechanical effects into simulations of chemical reaction dynamics, including modeling of biological systems, could have a major impact on research and technology development.

Publications

V. S. Batista, M. T. Zanni, B. J. Greenblatt, D. M. Neumark, and W. H. Miller, "Femtosecond photoelectron spectroscopy of the I2- anion: A semiclassical molecular dynamics simulation method," J. Chem. Phys. 110, 3736 (1999).

V. Guallar, V. S. Batista, and W. H. Miller, "Semiclassical molecular dynamics simulations of excited state double proton transfer in 7-azaindole dimers," J. Chem. Phys. 110, 9922 (1999).

X. Sun and W. H. Miller, "Forward-backward initial value representation for semiclassical time correlation functions," J. Chem. Phys. 110, 6635 (1999).