Photodissociation of highly vibrationally excited NH[sub 3] in the 5ν[sub N–H] region: Initial vibrational state dependence of N–H bond dissociation cross section.

Ultraviolet photolysis of highly vibrationally excited NH[sub 3](&Xtilde;[sup 1]A[sup ', sub 1]) in the 5 ν[sub N-H] band has been studied using a crossed laser and molecular beams method. Relative cross sections of N-H bond dissociation via the à ← &Xtilde; 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 4 ν[sub 1] + ν[sub 3] 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 5 ν[sub 1] state. To interpret the ratio of the obtained cross sections, we have evaluated the FranckCondon 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. [ABSTRACT FROM AUTHOR]