Intramolecular energy transfer in highly vibrationally excited methanol. IV. Spectroscopy and dynamics of CH313OH

Abstract

Rotationally resolved spectra in the 5ν1 region of CH313OH reveal strong vibrational splittings, which by analogy to CH312OH, we assign to a resonance between 5ν1 and 4ν1+ν2. Accordingly, the vibrational dynamics on a subpicosecond time scale are similar for the two isotopomers. Comparison of the secondary structure of the first-order states resulting from this strong resonance shows a distinct difference in the two isotopomers. While the CH12 species exhibits sharp secondary structure for the lower energy band resulting from weak coupling to the remaining bath of dark states, the CH13 species shows an equally complex pattern of couplings for both first-order states. The difference between the two isotopic species arises from the relative position of key dark background states. Despite a vibrational density of states of 100 per cm−1, only a small number of states seem to determine the secondary structure, and the difference in the positions of these states relative to the first-order states results in a difference in the vibrational dynamics on a picosecond time scale. What one might consider as statistical intramolecular energy transfer appears to occur on significantly longer time scales.