Photodissociation of pyrrole-ammonia clusters by velocity map imaging: Mechanism for the H-atom transfer reaction

The photodissociation dynamics of pyrrole-ammonia clusters (PyH·(NH3)n, n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH 4(NH3)n-1 products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (∼0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment. © the Owner Societies 2011.y. L.R.-L. thanks Consejo Superior de Investigaciones Cientı´ficas (CSIC) for a JAE-DOC contract under the Unidad Asociada ‘‘Quı´mica-Fı´sica Molecular’’ between Departamento de Quı´mica Fı´sica I of Universidad Complutense and CSIC. This work has been supported by AECI, Spanish Ministry of Foreign Affairs, project A/7763/07, and by the Spanish Ministry of Science and Innovation through grants CTQ2008-02578/ BQU and Consolider Program SAUUL CSD2007-00013.Peer Reviewe

Photodissociation of pyrrole-ammonia clusters by velocity map imaging: Mechanism for the H-atom transfer reaction

The photodissociation dynamics of pyrrole-ammonia clusters (PyH·(NH3)n, n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH 4(NH3)n-1 products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (∼0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment. © the Owner Societies 2011.Fil: Rubio-Lago, L.. Universidad Complutense de Madrid; EspañaFil: Amaral, G. A.. Universidad Complutense de Madrid; EspañaFil: Oldani, Andres Nicolas. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Rodriguez, J. D.. Universidad Complutense de Madrid; EspañaFil: Gonzalez, M. G.. Universidad Complutense de Madrid; EspañaFil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Complutense de Madrid; EspañaFil: Bañares, L.. Universidad Complutense de Madrid; Españ