The vibrational spectra of molecular ions isolated in solid neon.: XVI.: SO2+, SO2-, and (SO2)2-

When a Ne:SO2 mixture is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes absorptions assigned with the aid of isotopic substitution studies to SO, SO2+, SO2-, (SO2)(2)(-), and, tentatively, SO-. The fundamental and first overtone absorptions of SO lie 0.9 and 1.8 cm(-1), respectively, below the gas-phase band centers. Ab initio calculations at the Hartree-Fock level show an instability in the v(3) vibration of SO2+ which is avoided by higher-level calculations. The nu(3) and nu(1) fundamentals of SO2- isolated in solid neon are identified at 1086.2 and 990.8 cm(-1), respectively. In agreement with an earlier proposal, the 1042 cm(-1) absorption originally assigned to nu(3) of SO2- trapped in solid argon is reassigned to MSO2, with M an alkali metal. Near the photodetachment threshold for SO2- isolated in a neon matrix, electron capture by SO2 nearest-neighbor pairs results in growth of infrared absorptions of (SO2)(2)(-), which has been shown by gas-phase studies to have a significantly higher photodetachment threshold than does SO2-. The isotopic substitution studies require that the two sulfur atoms in (SO2)(2)(-) be nonequivalent, favoring the linking of the two SO2 units by a S ... O bond. (C) 2000 American Institute of Physics. [S0021- 9606(00)00225-7].