Formation of He* by ion-ion neutralization reactions of He+ with C6F5X- (X= F, Cl, Br, CF3) in a helium flowing afterglow

The ion-ion neutralization reactions of He+ with C6F5X- (X=F, Cl, Br, CF3) leading to He* have been spectroscopically studied in a helium flowing afte rglow. Although both singlet and triplet He* states were formed when X=F an d Cl, only triplet He* states were produced when X=Br and CF3. More than 99 % of the product He* atoms were formed in the low-lying He(3s, 3p, or 3d) s tates for all the reactions, and their electronic-state distributions were similar. The electronic-state populations decreased rapidly with increasing excitation energy of He*. They were represented by effective electronic te mperatures of 0.070-0.19 eV. The observed electronic-state distributions we re compared with those predicted from a simple statistical theory. (C) 1999 American Institute of Physics. [S0021-9606(99)00706-0].