Infrared laser multiple photon dissociation of thiophene in gas phase

Abstract

Infrared laser multiple photon excitation/dissociation of Thiophene (Th) was studied as a function of Th pressure, laser pulse energy, pulse duration and added buffer gas. While the excitation process was probed via optoacoustic technique, the stable reaction products were analyzed by IR spectroscopy and mass spectrometry. Although C₂H₂ and CH₃C≡CH were the major hydrocarbon products under all experimental conditions, the distribution of these, as well as higher hydrocarbons of lower yield, was found to be very much dependent upon the experimental conditions. The laser induced reaction under dielectric breakdown conditions with either high substrate pressure or laser energy produced significant amount of CS₂ and unidentified polymer as well. We propose a mechanism involving breakage of the C-S bond in Th to form an unstable 1,5-diradical which further decomposed via different channels. However, at higher substrate pressures, radical-Th reactions complicated the overall chemistry of the system. Evidences for collisional energy-pooling and rotational hole-filling were also obtained.