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

L. RUBIO-LAGO; G. A. AMARAL; A. N. OLDANI; J. D. RODRIGUEZ; M. G. GONZALEZ; G. A. PINO; L. BAÑARES

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2011 vol. 13 p. 1082 - 1091

1463-9076

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 NH4(NH3)n1 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 (B0.15 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.3)n, n = 2?6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH4(NH3)n1 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 (B0.15 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.