Theoretical and experimental studies of collision-induced electronic energy transfer from v=–3 of the E(g+) ion-pair state of Br2: Collisions with He and Ar

Collisions of Br2, prepared in the E(0g+) ion-pair (IP) electronic state, with He or Ar result in electronic energy transfer to the D, D′, and β IP states. These events have been examined in experimental and theoretical investigations. Experimentally, analysis of the wavelength resolved emission spectra reveals the distribution of population in the vibrational levels of the final electronic states and the relative efficiencies of He and Ar collisions in promoting a specific electronic energy transfer channel. Theoretically, semiempirical rare gas-Br2 potential energy surfaces and diabatic couplings are used in quantum scattering calculations of the state-to-state rate constants for electronic energy transfer and distributions of population in the final electronic state vibrational levels. Agreement between theory and experiment is excellent. Comparison of the results with those obtained for similar processes in the IP excited I2 molecule points to the general importance of Franck–Condon effects in determining vibrational populations, although this effect is more important for He collisions than for Ar collisions.