Rotationally resolved ultraviolet spectroscopy of indole, indazole, and benzimidazole: Inertial axis reorientation in the <i>S</i>1(1<i>L</i> <i>b</i>)←<i>S</i> transitions

Abstract

Rotationally resolved laser induced fluorescence excitation spectra of the S1(1Lb)←S0 origin bands of indole, indazole, and benzimidazole have been measured. From these spectra, the rotational constants in both electronic states have been determined. The spectra of all three molecules exhibit ‘‘anomalous’’ rotational line intensities. These intensity perturbations are a result of the reorientation, upon electronic excitation, of the inertial axes of the molecule. Intensity analysis of the rotational lines yielded information about the inertial axis reorientation, and the direction of the transition moment vector for each molecule.