VIBRATIONAL SPECTRA AND NORMAL COORDINATE ANALYSIS OF METHYL THIONITRITE AND ISOTOPIC ANALOGS

Article abstract of DOI:10.1016/0022-2860(81)85264-7

The observed gas-phase IR frequencies for forty-four fundamentals of methyl thionitrite (CH3SNO) and its d3-, 13C-, and 15N-substituted analogs have been used to calculate a nineteen-parameter symmetry valence force field.The final refinement resulted in an average error of less than 4 cm^-1 (ca. 0.5percent) between the calculated and observed frequencies for the four isotopomers.Contrary to earlier reports, relative intensities, isotopic frequency shifts, as well as the calculated potential-energy distribution, all support the assignment of ν(CS) to a higher frequency than that of ν(SN).For the normal molecule ν(CS) is observed as a weak band at 735 cm^-1; by contrast, ν(SN) absorbs strongly at 646 cm^-1.The NO stretching fundamental occurs at 1535 cm^-1 in the gas-phase spectrum of the unsubstituted molecule but shifts to 1507 cm^-1 when 15N replaces the normal isotope.The five fundamental bands associated with the skeletal vibrations of CH3SNO are compared with the analogous absorptions in the spectra of CF3SNO and CH3ONO.