On Abnormal Rotation of Molecules

Abstract

Hypothetical statements, explaining the abnormal rotation of molecules observed in band spectra, are tested by the investigation of the OH bands. It is known that the OH radicals are excited in the electric discharge through water vapor by simultaneous dissociation of ${\mathrm{H}}_{2}$O and excitation of OH. As expected, strongly abnormal rotation is observed in the emission spectrum. On the other hand, the absorption spectrum of OH in the electric discharge showing normal rotation, confirms the assumption just mentioned regarding the excitation process. By addition of helium the rotation observed in emission is reduced to its normal value; no appreciable persistence of rotation in collisions is evident. In order to judge whether in a given source the temperature can be derived from the rotational structure of the band spectrum, tentative rules are deduced from a review of the known processes by which abnormal rotation may be produced or destroyed. The intensity distribution of the vibrational structure of a band spectrum indicates the temperature of the gas only in special cases.