Laser induced fluorescence of NH2(Ã 2A1) in the supersonic free jet

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Abstract
The fluorescence excitation spectra of the NH2 à 2A1←X̃ 2B1 transition have been measured in the supersonic free jet. The rotational cooling of the ground state NH2 radical results in the observation of only the Π vibronic subbands in the excitation spectra. The fluorescence lifetimes are obtained for single rovibronic levels of the à 2A1 state in the jet. The radiative lifetime is shortened from 10.3 μs for Π(0,8,0) 11,0 to 4.4 μs for Π(0, 14, 0) 11,0 with decreasing the excitation wavelength, which is explained by the cubic transition energy dependence of the Einstein A coefficient. Little difference is observed between the lifetimes of the spin components belonging to the same rotational level and between those of the Fermi resonance pairs. The transition moment of the à 2A1–X̃ 2B1 transition is experimentally determined to be 0.037±0.004e2α20.