Photodissociation of NH2 in the two-dimensional light-heavy light approximation

Photodissociation dynamics through the 3(2)A'(2(2)A(1)), the 2(2)A ''(2(2)B(1)), and the 3(2)A ''(1(2)A(2)) states of NH2 are studied in the two-dimensional light-heavy-light approximation at the equilibrium angle of the ground state. The NH2 radical is of relevance in the chemistry of interstellar clouds and cometary atmospheres. Photodissociation is the major destruction mechanism of the radical in these environments, Since it is difficult to produce the molecule in the laboratory, little is known about this process from experiments. Total and vibrationally resolved partial cross sections have been calculated. The surfaces of the transition dipole moments are taken into account in all calculations. By far the largest total cross section of photodissociation is found for the 2(2)A ''(2(2)B(1)) state. Through the bound 3(2)A' (2(2)A(1)) state, photodissociation mainly proceeds through resonant levels close to the dissociation limit, corresponding to coupled antisymmetric-symmetric stretching motions. The Fourier transform of the autocorrelation function also contains a number of bound vibrational levels, which are assigned to the antisymmetric and coupled antisymmetric-symmetric stretching vibrational levels. Since the 3(2)A'(2(2)A(1)) state has the same equilibrium bond angle as the X(2)B(1) ground state, the present calculations are expected to give the essential physical properties of the photodissociation dynamics through this state. Direct photodissociation proceeds through the 3(2)A ''(1(2)A(2)) state. By far the largest cross section of photodissociation is found for the 2(2)A ''(2(2)B(1)) state. The results from this work are compared to an experimental fragment fluorescence spectrum from the literature.