Photoexcitation and predissociation intensities of the c′ 1∑u+ (v=3 and 4), c 1∏u (v=3 and 4), and b′ 1∑u+ (v=10, 12, 13, and 15) states of N2

Abstract

Photofragment spectroscopy is applied to investigate perturbations in the photoexcitation and predissociation of excited singlet states of N2. Discrete rovibrational levels in the Rydberg states c′ 1∑u+ (v=3 and 4) and c 1∏u (v=3 and 4) and in the valence state b′ 1∑u+ (v=10, 12, 13, and 15) are prepared by laser excitation from the metastable a″ 1∑g+ (v=0) state in a fast (3 keV) molecular beam. Fragment atoms produced by predissociation are monitored as a function of exciting laser frequency using a position- and time-sensitive detector to measure the photofragment intensity distribution in the rovibrational bands. The photofragment spectra show extreme departures from normal rovibronic intensity distributions due to strong perturbations in the two highly mixed complexes: c′(3)/c(3)/b′(10) and c′(4)/c(4)/b′(13). The measured photofragment intensities are compared to photoexcitation line strengths calculated using a comprehensive model of the Rydberg-valence state mixing [Stahel, Leoni, and Dressler, J. Chem. Phys. 79, 2541 (1983)]. This theoretical model accurately predicts most of the variations in the photofragment intensities, and reveals the causes of the perturbations. For the states investigated in the present study, the primary factor that determines the photofragment intensity is the degree of b′ character of the state, which favorably affects both photoexcitation and predissociation. Interference effects are found to be important in determining absorption intensities in N2.