THE PREDISSOCIATION DYNAMICS OF AMMONIA - A THEORETICAL-STUDY

A quantum mechanical model of the ammonia predissociation dynamics is presented. The effects of an excited state barrier and well, a deep co nical intersection between the ground and excited states, and strong a ngular dependence of the potential energy surfaces are explored. The p redissociation rate is sensitive to both the vibrational (v(2)') and t he rotational (J',K') level of the initially excited metastable state. The product state distribution following excitation within the v(2)' = 0 band reflects the shape of the ground bend resonance and is broad, extending to the energetic limit. The photofragment angular distribut ions following excitation of magnetic-rovibronic state-selected parent molecules depend sensitively on the photon frequency. Their structure varies markedly with the internal state of the accompanying NH, fragm ent, The results are traced to the complex excitation dynamics, which prepare a frequency-dependent superposition of rotational states, and to the strong forces exerted on the dissociating system in the region of the conical intersection.