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

In contrast to the electronically excited propynal at 193 nm undergoing aldehyde C–H and C–C bond ruptures, on pulsed TEA-CO2 laser irradiation, multiphoton vibrationally excited propynal undergoes concerted dissociation generating CO and acetylene. Vibrational excitation in the CO product is detected immediately following the CO2 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)×107 s−1, vis-a-vis RRKM calculations, gives an average IR multiphoton excitation level of propynal as 75±4 kcal mol−1.