Effect of Centrifugal Distortion on the Shape of the Hydrogen Sulfide Fundamental Infrared Bands

The fundamental infrared vibration bands of hydrogen sulfide exhibit an interesting intensity anomaly characterized by P branches which are much weaker than the corresponding R branches. This work shows that this anomaly is caused by centrifugal distortion of the nonrigid molecule. A formalism based on a semi-classical approach is used to calculate the vibration—rotational line positions and their intensities. The computed theoretical spectra are in good agreement with the experimental spectra. This formalism also gives a method of determining the relative sign of (∂μ/∂Q) with respect to μ0. The values of (∂μ/∂Q) needed in the calculations were obtained from the experimental integrated band intensities and were found to be (∂μ/∂Q1) = −4.4 esu g−½ and (∂μ/∂Q2) = +8.7 esu g−½.