Unimolecular Dissociation Dynamics of Vinylchloride on the Ground Electronic Potential Energy Surface: Excitation by Chemical Activation and the Product State Distributions of HCl and Cl Fragments

초록

The dynamics of unimolecular reactions of vinylchloride on the ground electronic potential energy surface have been investigated. The vibrationally excited vinylchloride in its ground electronic state was prepared by using the isomerization of methyl-chlorocarbene radical to vinylchloride via H-atom migration and the carbene radicals were produced by photolysis of 3-methyl-3-chlorodiazirine at 353.6 nm. The vinylchloride molecules formed in this excitation scheme were highly vibrationally excited in its ground electronic state due to the bond formation between two carbon atoms, and were found to undergo unimolecular reactions of HCl elimination and C-Cl bond fission. The rotational and vibrational energy distributions of HCl fragments and the spin-orbit state branching ratio of Cl atoms have been measured with a resonantly enhanced multiphoton ionization (REMPI)/time-of-flight mass spectrometry. The overall energy distributions of HCl and Cl atoms are much colder than those of 193 nm photodissociation[1,2] as expected from the smaller excitation energy. Interestingly, however, the rotational distribution of HCl(v=0) fragments fits to a Boltzmann distribution of a single rotational temperature in contrast to the result of 193 nm photodissociation[1,2], which showed a bi-exponential distribution. The dynamical differences between two excitation schemes will be discussed in terms of the potential energy surfaces involved.