Matrix-Isolation Study of the Vacuum-Ultraviolet Photolysis of Methyl Chloride and Methylene Chloride. Infrared and Ultraviolet Spectra of the Free Radicals CCl, H2CCl, and CCl2

Abstract

Infrared and ultraviolet spectroscopic studies have been conducted on the products of the vacuum‐ultraviolet photolysis of normal and isotopically substituted methyl chloride and methylene chloride isolated in argon and nitrogen matrices at 14°K. The cage effect has been found to inhibit halogen detachment processes in these systems. Infrared absorptions attributable to CCl, HCCl, and H₂CCl and the 2800‐Å ultraviolet absorption of CCl appear in the methyl chloride photolysis studies. Observation of a “negative anharmonicity” for the lowest‐frequency infrared absorption of H₂CCl can be explained by postulating that the molecule is planar. The C–Cl stretching force constant of H₂CCl is exceptionally high. The implications of $\mathrm{(p–d)\pi }$ bonding, which may account for the large C–Cl stretching force constant, are explored. An absorption near 2300 Å behaves appropriately for assignment to a second electronic transition of CCl, providing support for the previous tentative assignment of a group of emission bands to such a transition. Photolysis of methylene chloride in a matrix environment leads principally to the stabilization of CCl₂. A revised estimate of the force constants of CCl₂ is given.