Dynamical Chirality and the Quantum Dynamics of Bending Vibrations of the CH Chromophore in Methane Isotopomers

The time-dependent quantum dynamics of the CH chromophore is investigated by calculations of the wave packet evolution after coherent excitation of the bending modes using realistic potential energy surfaces and electric dipole moment functions for the methane isotopomers CHD 3, CHD 2 T, and CHDT 2 derived previously from ab initio calculations and high-resolution spectroscopic information. Results include discussions on different excitation pathways depending on the bending direction in an internal coordinate frame, the role of quasiclassical and delocalized intramolecular vibrational redistribution on these processes, and a possibility of controlling the dynamics by localization of the wave packet motion in subspaces of the relevant configuration space. Bending excitation is also used to generate dynamical chirality, which is quantified by the enantiomeric excess. The subsequent free evolution of the wave packet after generation of a chiral molecular structure corresponds to a stereomutation reaction on the femtosecond time scale superimposed by a racemization reaction, which is understood as arising from quantum delocalization effects due to intramolecular vibrational redistribution.