INTRAMOLECULAR VIBRATIONAL REDISTRIBUTION IN ALKYLBENZENES .1. NORMAL-MODES AND THEIR ENERGY-DISTRIBUTION

Normal modes for the ground and first excited singlet state are computed for ethylbenzene, pentylbenzene, and hexylbenzene and are assigned in terms of zero-order mode descriptors. The energy distribution, i.e., the partitioning of energy between the ring and chain, is computed for the normal modes and the concept of "system modes," i.e., modes localized on the ring, is examined. Several of the basic assumptions made in traditional interpretations of intramolecular vibrational redistribution in molecules with a "ring + tail" structure are examined in light of the computed normal mode characteristics.