Detection of the Excited-State NH (Ã A) 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 ÃA state. The dispersed fluorescence spectrum, whose band structure is assigned to the ÃA → X̃B transition, provides evidence of the CH(v=0) + NH(ÃA) 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.