AbstractSulphur vapour was investigated by Raman spectroscopy using six laser excitation wavelengths located in the electronic absorption band of the S3molecule (406.7–514.5 nm). With excitation wavelengths close to the S3λmax(395 nm) the spectra are mainly resonance enhanced. With the excitation located in the S3electronic 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 (ν1) and symmetric bending (ν2) modes. The comparison of spectra of samples with various34S contents recorded with various excitation wavelengths enable us to determine the ω10and ω20harmonic wavenumbers and the anharmonicity constantsx 011x 022andx 012, for32S3and34S3. New assignments are proposed for all Raman lines observed. A valence force field treatment with the calculated geometryrss= 1.988 Å and α = 117° yields force constants ƒr= 3.91 mdyn Å−1and ƒrr= 0.36 mdyn Å−1. These force constants are compared with those of the parent X2or X3molecul