THE VACUUM-ULTRAVIOLET PHOTODISSOCIATION OF NH2((X)OVER-TILDE(2)B(1))-]NH(A(3)PI)+H

The photodissociation of NH2-->NH(A (3) Pi)+H was investigated by photolyzing NH2 in a flow system with tunable synchrotron radiation from 200 to 105 nm and other vuv light sources. The NH photofragments were analyzed by their triplet emission at 336 nm. Additionally, ab initio configuration interaction calculations were performed for the electronic states of NH2 involved in the photodissociation process. Vertical excitation energies, bending potentials for the excited states, Franck-Condon factors, and transition moments were calculated in order to interpret the experimental observations. The following picture evolves for the dynamics of the NH2 photodissociation: At about 7.8 eV, NH2 is excited to the 2 (2)A(1)(A') state, which possesses the same bending angle as the (X) over tilde B-2(1) ground state. The upper state correlates with the fragments NH(A (3) Pi)+H. Since the bending angle is not changed, the NH(A) radicals are formed with little rotational excitation. However, the symmetric stretch becomes excited at the beginning of the dissociation leaving the NH(A) fragment with vibrational excitation. Because of symmetry conservation, the formation of the Pi(A') component of NH(A) is preferred. In the region of similar to 9 eV, transitions to the 1 (2)A(2) and/or 3 B-2(1) states (both have A'' symmetry in C-s) occur. The bending potentials of both states have minima for linear configurations. Therefore, the structure of the excitation spectrum is determined by a progression in the bending motion and a preferred population of high rotational NH(A) levels is observed. Vibrational excitation is small suggesting that the unbroken NH bond stays unchanged during the dissociation process. According to symmetry conservation, the Pi(A'') component of NH(A) is preferably formed.