Collision-induced electronic energy transfer in ion-pair excited bromine: Collisions with He, Ar, Xe and CF4

PHYS 392

Nathan T. La Porte, J. Matthew Hutchison, Justin T. Massey, Robin R. O'Hern, Yury V. Suleimanov, Alexei A. Buchachenko, and Thomas A. Stephenson, Department of Chemistry and Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA 19081
We have examined the electronic energy transfer pathways that occur when diatomic bromine, prepared in the E ion-pair electronic state, collides with He, Ar, Xe and CF4. As in similar experiments on ion-pair excited iodine, we find selective and efficient electronic energy transfer, with bromine population in the D, D' and β electronic states. The vibronic level structure in the ion-pair states of bromine make it possible to distinguish the importance of energy gap and Franck-Condon effects in determining the vibrational distributions with each electronic state. We find that He collisions lead predominately to vibrational distributions in accord with Franck-Condon factors, while energy gap constraints are much more important for the heavier collision partners. Quantum scattering calculations are in excellent agreement with the experimental data and highlight the relative importance of the repulsive and attractive portions of the intermolecular potential in modulating electronic energy transfer dynamics.