The infrared spectrum of the nitrobenzene anion isolated in solid argon is presented. The nitrobenzene anion was prepared by co-deposition of a nitrobenzene/Ar mixture with high-frequency discharged argon at 4 K. Photosensitive absorptions are assigned to different vibrational modes of the nitrobenzene anion on the basis of isotopic substitutions ((15)N and deuterium), as well as theoretical calculations. The anion loses one electron to give the neutral nitrobenzene upon visible light (500 < lambda < 600 nm) irradiation. Theoretical calculations predicated that the anion has a planar C(2v) symmetry with a shorter C-N bond and longer N-O bonds relative to those of neutral nitrobenzene.

Cocondensation of carbon disulfide with high-frequency discharged argon at 4 K produced carbon monosulfide and atomic sulfur, which reacted spontaneously upon annealing to form the carbon trisulfide molecule as identified from the multiplets observed in mixed (12)C, (13)C and (32)S, (34)S isotopic spectra. On the basis of isotopic substitution and theoretical frequency calculations, infrared absorptions at 1263.3 and 570.1 cm(-1) were assigned to predominantly CS stretching and bending vibrations of CS(3) in solid argon. The CS(3) molecule, which was calculated to have a singlet ground state with C(2v) symmetry, dissociated to form the weakly bound SCS-S complex upon visible light irradiation.

UV light irradiation of dimethyl sulfoxide (DMSO) in low temperature solid argon matrix produces sulfenic ester, CH 3SOCH 3, a high energy structural isomer of DMSO. The sulfenic ester molecule further dissociates to the CH 2O-CH 3SH complex under 266 nm laser irradiation. The CH 2S-CH 3OH complex is also formed upon UV light irradiation. The infrared spectra of the aforementioned species are assigned on the basis of isotopic substitutions ( (13)C and deuterium) as well as density functional frequency calculations.

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 ((13)C 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(2v) symmetry with a shorter C-X bond and longer C-H bonds relative to those of the halomethyl free radicals.