title: Stereodynamics of the photodissociation of nitromethane at 193 nm: unravelling the dissociation mechanism.
abstract: The photodissociation of nitromethane at 193 nm is reviewed in terms of new stereodynamical information provided by the measurement of the first four Dixon's bipolar moments, β0(2)(20), β0(0)(22), β0(2)(02), and β0(2)(22), using slice imaging. The measured speed-dependent β0(2)(20) (directly related with the spatial anisotropy parameter β) indicates that after one-photon absorption to the S3(2 (1)A″) state by an allowed perpendicular transition, two reaction pathways can compete with similar probability, a direct dissociation process yielding ground-state CH3 and NO2(1 (2)A2) radicals and a indirect dissociation through conical intersections in which NO2 radicals are formed in lower-lying electronic states. A particularly important result from our measurements is that the low recoil energy part of the methyl fragment translational energy distribution presents a contribution with parallel character, irrespective of the experimental conditions employed, that we attribute to parent cluster dissociation. Moreover, the positive values found for the β0(0)(22) bipolar moment indicates some propensity for the fragment's recoil velocity and angular momentum vectors to be parallel.
authors.affiliation: Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: J D
authors.initials: JD
authors.lastname: Rodríguez
authors.forename: M G
authors.initials: MG
authors.lastname: González
authors.forename: L
authors.initials: L
authors.lastname: Rubio-Lago
authors.forename: L
authors.initials: L
authors.lastname: Bañares
authors.forename: P C
authors.initials: PC
authors.lastname: Samartzis
authors.forename: T N
authors.initials: TN
authors.lastname: Kitsopoulos