Unimolecular dissociation dynamics of vinyl chloride on the ground potential energy surface: The method of excitation and product state distributions of HCl and Cl fragments

Abstract

The unimolecular dissociation dynamics of vinyl chloride on the ground electronic potential energy surface have been investigated. The vibrationally excited vinyl chloride in its ground electronic state is prepared using the isomerization process of alpha -chloroethylidene radical to vinyl chloride via the: hydrogen atom migration, where the chloroethylidene radical is produced by the ultraviolet photolysis of 3-methyl-3-chlorodiazirine. The vinyl chloride molecule formed in this excitation scheme is highly vibrationally excited in its ground electronic state due to the bond formation between two carbon atoms, and undergoes unimolecular reactions of HCl elimination or C-Cl bond fission. The rotational and vibrational state distributions of the HCl fragments and the spin-orbit state branching ratio of the Cl atoms have been measured with a resonantly enhanced multiphoton ionization (REMPI)/time-of-flight mass spectrometry. The overall state distributions of the HCl and Cl fragments are much colder than those in the 193 nm photodissociation. The rotational distributions of the HCl(nu = 0) and HCl(nu = 1) fragments Fit to the Boltzmann distributions at T-rot = 470 and 130 K, respectively. The vibrational branching ratio of HCl(nu = 1)/HCl(nu = 0) and the spin--orbit state branching ratio of Cl*(P-2(1/2))/Cl(2P(3/2)) are measured to be 0.15 +/- 0.03 and 0.15 +/- 0.02, respectively. The differences in the dynamical observations of vinychloride produced by this excitation scheme and the 193 nm photoexcitation are interpreted in terms of the large difference of excitation energies between two excitation schemes.