Photodissociation of highly vibrationally excited NH3 in the 5νN–H region: Initial vibrational state dependence of N–H bond dissociation cross section

Abstract

Ultraviolet photolysis of highly vibrationally excited NH3(X̃ 1A1′) in the 5νN–H band has been studied using a crossed laser and molecular beams method. Relative cross sections of N–H bond dissociation via the Ã←X̃ transition have been determined by the measurement of the action spectrum, utilizing a (2+1) resonance enhanced multiphoton ionization scheme of product H atoms. The obtained cross section for the photolysis of the 4ν1+ν3 state (4 quanta in the symmetric stretching and 1 quantum in the antisymmetric stretching) was 1.23±0.06 times as large as that of the 5ν1 state. To interpret the ratio of the obtained cross sections, we have evaluated the Franck–Condon factors for these vibrational states, by utilizing time-dependent wave-packet calculations on the potential energy surfaces constructed by an ab initio molecular orbital procedure.