Infrared Spectra of the Chloromethyl and Bromomethyl Cations in Solid Argon

Infrared spectra of chloromethyl and bromomethyl cations isolated in solid argon are reported. Cocondensation of dichloromethane and dibromomethane with high-frequency discharged argon at 4 K produces the dichloromethane and dibromomethane cations, which dissociate upon visible light irradiation to form the chloromethyl and bromomethyl cations. On the basis of isotopic substitutions (C-13 and deuterium) as well as theoretical frequency calculations, photosensitive absorptions are assigned to different vibrational modes of the chloromethyl and bromomethyl cations. Theoretical calculations predict that the halomethyl cations have a planar C-2 upsilon symmetry with a shorter C-X bond and longer C-H bonds relative to those of the halomethyl free radicals.