ON THE ($\nu_{3} + \nu_{4}$) COMBINATION BAND OF METHANE $^{12}CH_{4}$

Abstract

Two ``tetrahedral” branches, In terms of the quantum number $R^{\prime}$, appear in the ($\nu_{3} + \nu_{4}$) band of methane. We assign them as the P and R branches of the transitions which reach the excited states ($R^{\prime}$ = $J^{\prime} - 2$) and ($R^{\prime}$ = $J^{\prime} + 2$), respectively. The symmetries of the lines are defined owing to a remarkable property of the 3-j symbols of type $F^{(3 {jj}^{\prime})}{A}_{2} {p p}$. The lines of the corresponding Q and R, or Q and P branches are obtained simply from differences between known ground-state levels. About 150 transitions have been assigned (see J. Physique, March 1975). A similar method is now applied to the transitions on the ($R^{\prime}$ = $j^{\prime}$, $j^{\prime}$ $\pm$ 1) excited states. The preliminary results are quite encouraging.