Rotationally resolved spectra of the 61 and 6111 band of benzene in a moderately cold molecular beam: Spectral and dynamical analysis

Abstract

Rotationally resolved spectra of the 610 and 610110 band of benzene, C6H6, in a supersonic molecular beam at rotational temperatures between 8 and 50 K are reported. The spectra consist of lines of 85 MHz linewidth. An unexpectedly low saturation intensity of ≊104 W/cm2 is found for the observed one-photon transitions, and it is shown that the saturation intensity differs for different rotational lines within one vibronic band. The rovibronic line spectra are analyzed within the framework of a rigid symmetric top model and highly precise values of the rotational constants are determined. In addition, the rotationless transition frequencies ν00 are obtained with high precision. The spectrum of the 610 band shows no signs of rotational perturbations, while the 610110 band at higher vibrational excess energy shows indications of perturbations for lines with K′ above 10. The decay times of single rotational states within the 6111 vibronic state are reported and no rotational dependence of the decay time is found in agreement with the statistical limit character of the interstate nonradiative process.