Methylation effects on the collisional quenching of vibrationally excited benzene derivatives by unexcited parent molecules

The collisional quenching of vibrationally excited methyl substituted benzenes and deuterated isomers, produced From Nd-YAG 266 nm absorption, by unexcited parent molecules was studied by measuring the time-resolved C-H (or C-D) infrared fluorescence at similar to 3.3 mu m (or similar to 4.4 mu m). The collisional quenching efficiency is enhanced almost linearly as the number of methyl groups increases. The deuterium effect of methyl substituted benzene series is not much significant compared to that of azabenzenes and benzene having no methyl group. The results provide a detailed energy transfer mechanism that the vibration-rotation/translation energy transfer channel via low frequency vibrational modes such as methyl internal rotation plays an important role in the quenching process of vibrationally excited methyl substituted benzenes by parent bath molecules. (C) 2000 Published by Elsevier Science B.V. All rights reserved.