Infrared Absorption Bands in Hydrogen Sulphide

Absorption spectrum of ${\mathrm{H}}_{2}$S in the region from 1.0\ensuremath{\mu} to 10.0\ensuremath{\mu}.---The absorption spectrum of hydrogen sulphide in the infrared has been investigated with a prism spectrometer from 1.0\ensuremath{\mu} to 10.0\ensuremath{\mu}. Two regions of absorption, one at 2.6\ensuremath{\mu} and another 3.7\ensuremath{\mu} were located, both of which revealed fine structure when examined under high dispersion.Structure of the 2.6\ensuremath{\mu} absorption band of ${\mathrm{H}}_{2}$S.---The band at 2.6\ensuremath{\mu} was found to consist of $P$, $Q$, and $R$ branches, the $P$ and $R$ branches being made up of somewhat irregularly spaced lines and the $Q$ branch broadened unsymmetrically, sloping off more steeply toward lower frequencies. The separation between the most prominent lines in the $P$ and $R$ branches was found to be about 10 ${\mathrm{cm}}^{\ensuremath{-}1}$. A slight convergence was observed toward higher frequencies.Structure of the 3.7\ensuremath{\mu} absorption band of ${\mathrm{H}}_{2}$S.---The 3.7\ensuremath{\mu} band was found to consist of but one branch, made up of several prominent lines with weaker satellites on either side. The average spacing between these is about 9.0 ${\mathrm{cm}}^{\ensuremath{-}1}$, and no convergence was discernable.Qualitative quantum mechanical discussion of structure of absorption bands of ${\mathrm{H}}_{2}$S.---Only a qualitative discussion of the structure of the observed bands is given, based on the classical quantum mechanical solution of an asymmetric rotator due to Witmer. The band at 2.6\ensuremath{\mu} is accounted for by a vibration of the electric moment along the least axis of inertia while the band at 3.7\ensuremath{\mu} is shown to arise from a vibration along the intermediate axis. It is pointed out that the rigorous quantum mechanical solutions of asymmetric rotators confirm the conclusions drawn herein and in addition satisfactorily explain the broadening of the $Q$ branch.