Stereochemical and angular momentum constraints in the photodissociation of ammonia

Abstract

Abstract Time-of-flight spectra of the nascent H atoms, and laser induced fluorescence excitation spectra of the nascent NH2 radicals, are leading to a very complete knowledge of the energy disposal following photodissociation of NH3 through its A1A2 excited state. Both the dissociation rates and the product distributions are sensitive to the values of the vibrational and rotational quantum numbers of the quasi-bound levels of the parent molecule. The most populated fragment states involve the a-axis rotational, and bending vibrational, motions of the NH2 with modest excitation of further rotational degrees of freedom at low internal energy. For most NH2 internal states the accompanying H atoms recoil close to the initial plane of NH3 excitation, but for a specific subset of product states the H atoms recoil perpendicular to this plane. These measurements and their interpretation give a detailed insight into the intramolecular motion of the dissociating NH3 molecule, which is dynamically controlled but yet involves most of the internal degrees of freedom.