Chemiluminescent reactions of excited calcium atoms with HCl and HBr: Selective charge-transfer "harpooning" and synchronized intermediate complex rearrangement

A "harpooning" mechanism is investigated for the chemiluminescent reactions of Ca*(D-1(2)) atoms with HCl (leading to CaCl* in the A state) and with H Br (leading to CaBr* in both the A and B states). A model of the interactio ns in the entrance channels, which involves an electron jump and leads to a charge-transfer intermediate complex, accounts for the selective dependenc e of reactivity on the relative orientation between the molecule and the ou ter electronic orbital of the atom. The dynamical treatment incorporates in the Landau-Zener approach the synchronization between times for nonadiabat ic transitions and for triggering the rearrangement of the intermediate col lision complex. The treatment accounts for the observed features of the tra nslational energy dependence of the cross sections: The steep initial incre ase with a pronounced maximum, the sharp decline and also fine details, suc h as a stairlike behavior. (C) 2000 American Institute of Physics. [S0021-9 606(00)01802-X].