Redetermination of the depolarisation of light scattering in gases and vapours

6. Summary

It is pointed out that the existing depolarisation data of gases and vapours are gravely defective, and a redetermination of the values has been made with improved experimental technique. The results obtained are strikingly different from those of previous workers, and afford at the same time a natural explanation of many of the existing anomalies. The genuine depolarisation of methane appears to be only of the order of 0·3% which is in all probability to be attributed to the highly depolarised vibration Raman lines. The depolarisation shows a steady increase as one goes to the higher members of the homologous series, but the values in all cases are much smaller than they were hitherto assumed to be. Cyclopropane shows a very small depolarisation in conformity with the known small depolarisation of cyclohexane, while propylene shows a high value as would be expected from the presence of the double bond in it. Methyl chloride is more anisotropic than ethyl chloride, and the depolarisation factor of the former is much higher than that of methane. Carbon tetrachloride shows an extremely small depolarisation of 0·15% which is discussed in detail. It is tentatively concluded that the depolarisation of argon is nil. The depolarisation of H₂S is only 0·3%. An explanation is offered for the low depolarisation of the hydride molecules in general.