Infrared multiphoton dissociation of propynal: time resolved observation of CO ( ν≥1) IR emission at 4.7 μm

Abstract

In contrast to the electronically excited propynal at 193 nm undergoing aldehyde C–H and C–C bond ruptures, on pulsed TEA-CO 2 laser irradiation, multiphoton vibrationally excited propynal undergoes concerted dissociation generating CO and acetylene. Vibrational excitation in the CO product is detected immediately following the CO 2 laser pulse by observing infrared (IR) emission at 4.7 μm. The decay of the IR emission was studied as a function of propynal pressure. A vibrational–vibrational relaxation rate constant of CO ( ν≥1) by propynal is found to be 1540±200 Torr −1 s −1. With the collisionless dissociation of propynal, the evaluated unimolecular rate constant of (1.5±0.2)×10 7 s −1, vis-a-vis RRKM calculations, gives an average IR multiphoton excitation level of propynal as 75±4 kcal mol −1.