title: Multiphoton dissociation dynamics of BrCl and the BrCl+ cation.
abstract: Ion imaging methods have enabled identification of three mechanisms by which (79)Br(+) and (35)Cl(+) fragment ions are formed following one-color multiphoton excitation of BrCl molecules in the wavelength range 324.6 > lambda > 311.7 nm. Two-photon excitation within this range populates selected vibrational levels (v'= 0-5) of the [X (2)Pi(1/2)]5ssigma Rydberg state. Absorption of a third photon results in branching between (i) photoionization (i.e. removal of the Rydberg electron-a traditional 2 + 1 REMPI process) and (ii)pi*<--pi excitation within the core, resulting in formation of one or more super-excited states with Omega= 1 and configuration [A (2)Pi(1/2)]5ssigma. The fate of the latter states involves a further branching. They can autoionize (yielding BrCl(+)(X (2)Pi) ions in a wider range of v(+) states than formed by direct 2 + 1 REMPI). Further, one-photon absorption by the parent ions resulting from direct ionization or autoionization leads to formation of Br(+) and (energy permitting) Cl(+) fragment ions. Alternatively, the super-excited molecules can fragment to neutral atoms, one of which is in a Rydberg state. Complementary ab initio calculations lead to the conclusion that the observed [Cl**[(3)P(J)]4s + Br/Br*] products result from direct dissociation of the photo-prepared super-excited states, whereas [Br**[(3)P(J)]5p + Cl/Cl*] product formation involves interaction between the [A (2)Pi(1/2)]5ssigma and [X (2)Pi(1/2)]5psigma Rydberg potentials at extended Br-Cl bond lengths. Absorption of one further photon by the resulting Br** and Cl** Rydberg atoms leads to their ionization, and thus their appearance in the Br(+) and Cl(+) fragment ion images.
authors.affiliation: School of Chemistry, University of Bristol, Bristol, UKBS8 1TS.
authors.forename: Olivier P J
authors.initials: OP
authors.lastname: Vieuxmaire
authors.forename: N
authors.initials: N
authors.lastname: Hendrik Nahler
authors.forename: Richard N
authors.initials: RN
authors.lastname: Dixon
authors.forename: Michael N R
authors.initials: MN
authors.lastname: Ashfold
mesh_terms: D000465:Algorithms; D001965:Bromides / Q000737:chemistry*; D002412:Cations; D002712:Chlorides / Q000737:chemistry*; D004735:Energy Transfer / Q000528:radiation effects; D007700:Kinetics; D008956:Models, Chemical; D010782:Photolysis / Q000528:radiation effects*; D017785:Photons; D011839:Radiation, Ionizing; D013057:Spectrum Analysis / Q000379:methods*; D014466:Ultraviolet Rays
chemical_list: D001965:Bromides; D002412:Cations; D002712:Chlorides; C016271:bromine chloride