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

Phys Chem Chem Phys. 2011 Jan 21;13(3):1082-91. doi: 10.1039/c0cp01442g. Epub 2010 Nov 12.

Abstract

The photodissociation dynamics of pyrrole-ammonia clusters (PyH·(NH(3))(n), n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH(4)(NH(3))(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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ammonia / chemistry*
  • Hydrogen / chemistry*
  • Kinetics
  • Photolysis
  • Pyrroles / chemistry*
  • Thermodynamics

Substances

  • Pyrroles
  • Ammonia
  • Hydrogen