Vibrational study and molecular structure of two S-4 isomers in sulphur vapour

Raman spectra of sulphur vapour for two pressures (0.1 and 0.2 MPa) and var ious temperatures up to 700 degrees C were recorded using several krypton i on and argon ion laser exciting radiation wavelengths. Resonance Raman enha ncement effects in conjunction with S-32/S-34 isotopic effects allow one to distinguish three fundamental vibrational modes (v(s), v(c), delta(s)) of a green absorbing (lambda(max) = 530 nm) chain-like S-4 molecule from the m odes belonging to S-3 and other cyclic S-6, S-7 and S-8 molecules, Moreover , using a 647.1 mm excitation wavelength, several vibrational modes of anot her red absorbing (lambda(max) = 560-660 mm) branched-ring S-4 isomer were characterized. Finally, normal coordinate treatments confirm the trans plan ar C-2h structure of the chain-like S-4 species, whereas a comparison of th e observed and calculated wavenumbers for the red absorbing S-4 isomer is i n agreement with a branched-ring structure. Copyright (C) 1999 John Wiley & Sons, Ltd.