P-R MAXIMA SEPARATIONS IN UNRESOLVED PARALLEL BANDS OF SYMMETRIC- AND SLIGHTLY ASYMMETRIC-TOP $MOLECULES^{*}$

Abstract

“The equations derived by Gerhard and $Dennison^{1}$ for calculating the separation between the P and R-branch maxima, $\Delta \nu_{P - R}$, in unresolved parallel vibration-rotation bands have been tested on a series of symmetric- and slightly asymmetric-top molecules. The molecules were chosen at random from those for which accurate moments of inertia are known or could be calculated from the results of structural determinations. As expected from the assumptions made in deriving the equations, the percentage error in the calculated value of $\Delta \nu_{P - R}$, is highest for molecules with small moments of inertia. The effect of intensity alternations due to nuclear statistics and of slight asymmetry on the measured value of $\Delta \nu_{P - R}$, will be discussed. Generalizations will be made about the structural information that can be reliably deduced from the application of these formulas to the spectra of molecules for which more accurate structural determinations are precluded by experimental difficulties.”