INTRAMOLECULAR ENERGY-TRANSFER AND VIBRATIONAL REDISTRIBUTION IN CHIRAL MOLECULES - EXPERIMENT AND THEORY

The quantum vibrational dynamics of the CH-chromophore in a chiral env ironment are studied with the examples CHDTMu, CHDTF and CHFClBr. For the chiral methane isotopomer we use a recently established nine-dimen sional potential hypersurface to extract the three-dimensional short-t ime quantum dynamics and the related CH-overtone spectra. We have carr ied out nb initio (MP2) calculations in the appropriate normal coordin ate subspace for CHDTF, a chiral isotopomer of methylfluoride for whic h we have previously carried out extensive related calculations, and a lso experimental investigations on other isotopomers. For CHFClBr we r eport the first experimental and theoretical study of the CH-chromopho re overtone spectra. The results are systematically analysed in terms of anharmonic coupling constants of the effective hamiltonian as well as the potential hypersurfaces in the appropriate three-dimensional su bspaces. We show that the chiral, symmetry-breaking coupling constant k(sab) is of appreciable absolute magnitude for all three cases (ca. 2 5 cm(-1) for CHFClBr). The resulting fast intramolecular vibrational r edistribution in the highly excited CH-chromophore, on the femtosecond timescale, leads to appreciable population transfer between states of dynamical a' and a '' symmetry for the electronically, 'chemically' c hiral CHFClBr and for CHDTF, which is chiral only by isotope substitut ion. The symmetry-breaking intra-molecular redistribution processes in chiral molecules are briefly discussed in relation to dynamical chira lity, time-dependent optical activity and fundamental symmetry violati ons of parity, and even of charge conjugation, parity and time-reversa l symmetry and their combinations.