Vibrational study and molecular structure of two S4 isomers in sulphur vapour

Raman spectra of sulphur vapour for two pressures (0.1 and 0.2 MPa) and various temperatures up to 700 °C were recorded using several krypton ion and argon ion laser exciting radiation wavelengths. Resonance Raman enhancement effects in conjunction with 32S/34S isotopic effects allow one to distinguish three fundamental vibrational modes (νs, νc, δs) of a green absorbing (λmax = 530 nm) chain-like S4 molecule from the modes belonging to S3 and other cyclic S6, S7 and S8 molecules. Moreover, using a 647.1 nm excitation wavelength, several vibrational modes of another red absorbing (λmax = 560–660 nm) branched-ring S4 isomer were characterized. Finally, normal coordinate treatments confirm the trans planar C2h structure of the chain-like S4 species, whereas a comparison of the observed and calculated wavenumbers for the red absorbing S4 isomer is in agreement with a branched-ring structure. Copyright © 1999 John Wiley & Sons, Ltd.