Molecular Rydberg transitions. XX. Vibronic doubling in alkyl bromides

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Abstract
A doubling of absorption bands occurs in certain transitions associated with first s- and p-Ryderg excitations in C2H5Br and C3H7Br. No such doubling occurs in the first d-Rydberg or second s-Rydberg excitation of C2H5Br. Furthermore, doubling is not evident in any Rydberg transition of CH3Br, CD3Br, or C2D5Br. The interpretation of this doubling phenomenon invokes vibronic coupling between Rydberg states of the same configuration. The active vibration is a C–H stretching mode ??3000 cm−1 and the presence of doubling is determined by coincidence (or near coincidence) of the intraconfigurational splitting and the frequency of the active vibrational mode.