Photodissociation of pyrrole-ammonia clusters below 218 nm: quenching of statistical decomposition pathways under clustering conditions.

ABSTRACT

The excited state hydrogen transfer (ESHT) reaction in pyrrole-ammonia clusters (PyH·(NH(3))(n), n = 2-5) at excitation wavelengths below 218 nm down to 199 nm, has been studied using a combination of velocity map imaging and non-resonant detection of the NH(4)(NH(3))(n-1) products. Special care has been taken to avoid evaporation of solvent molecules from the excited clusters by controlling the intensity of both the excitation and probing lasers. The high resolution translational energy distributions obtained are analyzed on the base of an impulsive mechanism for the hydrogen transfer, which mimics the direct N-H bond dissociation of the bare pyrrole. In spite of the low dissociation wavelengths attained (~200 nm) no evidence of hydrogen-loss statistical dynamics has been observed. The effects of clustering of pyrrole with ammonia molecules on the possible statistical decomposition channels of the bare pyrrole are discussed.