Detection of the Excited-State NH 2 (Ã 2 A 1 ) in the Ultraviolet Photodissociation of Methylamine

Ion-imaging and dispersed fluorescence spectroscopy are employed for the photodissociation dynamics study of methylamine in the photolysis wavelength range 205-213 nm. The methyl radical product is found to populate a wide range of ro-vibrational states, among which the CH fragment generated in the v = 0 state shows a bimodal kinetic energy distribution. The internal energy analysis of the NH counterproduct indicates that a lower kinetic energy component, which was observed only with the CH (v=0) fragment, energetically matches the electronically excited à A state. The dispersed fluorescence spectrum, whose band structure is assigned to the à A → X̃ B transition, provides evidence of the CH (v=0) + NH (à A ) pathway. The branching mechanism of the product pathway is discussed in terms of nuclear dynamics in the long-range region, where the conical intersection between the excited- and ground-state potential energy surfaces can play a significant role.