Resonance Raman spectra of the S3 molecule in sulphur vapour

Sulphur vapour was investigated by Raman spectroscopy using six laser excitation wavelengths located in the electronic absorption band of the S3 molecule (406.7–514.5 nm). With excitation wavelengths close to the S3 λmax (395 nm) the spectra are mainly resonance enhanced. With the excitation located in the S3 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 (ν1) and symmetric bending (ν2) modes. The comparison of spectra of samples with various 34S contents recorded with various excitation wavelengths enable us to determine the ω10 and ω20 harmonic wavenumbers and the anharmonicity constants xx and x, for 32S3 and 34S3. New assignments are proposed for all Raman lines observed. A valence force field treatment with the calculated geometry rss = 1.988 A and α = 117° yields force constants ƒr = 3.91 mdyn A−1 and ƒrr = 0.36 mdyn A−1. These force constants are compared with those of the parent X2 or X3 molecules (X = O, S, Se or Te).