Abstract
Sulphur vapour was investigated by Raman spectroscopy using six laser excitation wavelengths located in the electronic absorption band of the S~3~ molecule (406.7β514.5 nm). With excitation wavelengths close to the S~3~ Ξ»~max~ (395 nm) the spectra are mainly resonance enhanced. With the excitation located in the S~3~ electronic absorption band edge the observed resonance Raman spectra are mainly due to the vibrationally excited molecules. Most Raman lines involve transitions between overtone or combination levels of the symmetric stretching (Ξ½~1~) and symmetric bending (Ξ½~2~) modes. The comparison of spectra of samples with various ^34^S contents recorded with various excitation wavelengths enable us to determine the Ο~1~^0^ and Ο~2~^0^ harmonic wavenumbers and the anharmonicity constants x x and x, for ^32^S~3~ and ^34^S~3~. New assignments are proposed for all Raman lines observed. A valence force field treatment with the calculated geometry r~ss~ = 1.988 Γ
and Ξ± = 117Β° yields force constants Ζ~r~ = 3.91 mdyn Γ
^β1^ and Ζ~rr~ = 0.36 mdyn Γ
^β1^. These force constants are compared with those of the parent X~2~ or X~3~ molecules (X = O, S, Se or Te).