title: Electron attachment to POCl3: measurement and theoretical analysis of rate constants and branching ratios as a function of gas pressure and temperature, electron temperature, and electron energy.
abstract: Two experimental techniques, electron swarm and electron beam, have been applied to the problem of electron attachment to POCl3, with results indicating that there is a competition between dissociation of the resonant POCl3-* state and collisional stabilization of the parent anion. In the electron beam experiment at zero electron energy, the fragment ion POCl2- is the dominant ion product of attachment (96%), under single-collision conditions. Small amounts (approximately 2% each) of POCl3- and Cl- were observed. POCl3- and POCl2- ion products were observed only at zero electron energy, but higher-energy resonances were recorded for POCl-, Cl-, and Cl2- ion products. In the electron swarm experiment, which was carried out in 0.4-7 Torr of He buffer gas, the parent anion branching ratio increased significantly with pressure and decreased with temperature. The electron attachment rate constant at 297 K was measured to be (2.5+/-0.6)x10(-7) cm3 s(-1), with ion products POCl2- (71%) and POCl3- (29%) in 1 Torr of He gas. The rate constant decreased as the electron temperature was increased above 1500 K. Theory is developed for (a) the unimolecular dissociation of the nascent POCl3-* and (b) a stepladder collisional stabilization mechanism using the average energy transferred per collision as a parameter. These ideas were then used to model the experimental data. The modeling showed that D0 o(Cl-POCl2-) and EA(POCl3) must be the same within +/-0.03 eV.
authors.affiliation: Department of Chemistry, Holy Cross College, Worcester, Massachusetts 01610-2195, USA.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Van Doren
authors.forename: Jeffery F
authors.initials: JF
authors.lastname: Friedman
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Miller
authors.forename: A A
authors.initials: AA
authors.lastname: Viggiano
authors.forename: S
authors.initials: S
authors.lastname: Denifl
authors.forename: P
authors.initials: P
authors.lastname: Scheier
authors.forename: T D
authors.initials: TD
authors.lastname: Märk
authors.forename: J
authors.initials: J
authors.lastname: Troe