Infrared spectra of two isomers of protonated carbonyl sulfide (HOCS⁺ and HSCO⁺) and t -HOCS in solid para -hydrogen

We report infrared (IR) spectra of HOCS⁺, HSCO⁺, t-HOCS, and other species produced on electron bombardment of a mixture of carbonyl sulfide (OCS) and para-hydrogen (p-H₂) during deposition at 3.2 K. After maintenance of the matrix in darkness for 15 h, the intensities of absorption features of HOCS⁺ at 2945.9 (ν₁), 1875.3 (ν₂), and 1041.9 (ν₃) cm^-1 and those of HSCO⁺ at 2506.9 (ν₁) and 2074.2 (ν₂) cm^-1 decreased through neutralization with trapped electrons. Lines observed at 3563.4, 1394.8, and 1199.0 cm^-1, which decreased slightly in intensity after maintenance in darkness and were nearly depleted after irradiation at 373 nm, are assigned to a t-HOCS radical. The corresponding spectra of their ¹³C- and D-isotopologues were observed. The IR spectra of HSCO⁺ and t-HOCS and those of modes ν₂ and ν₃ of HOCS⁺ are new. The assignments were made according to the expected chemical behavior and a comparison of experimental and calculated wavenumbers and ¹³C- and D-isotopic shifts. The wavenumber of the OH stretching mode (2945.9 cm^-1) of HOCS⁺ in solid p-H₂ is significantly red-shifted from that (3435.16 cm^-1) reported for gaseous HOCS⁺; this shift is attributed to partial sharing of a proton between OCS and H₂. The corresponding p-H₂ induced shift is small in HSCO⁺ because of a much weaker interaction between HSCO⁺ and H₂.