STATE-SPECIFIC REACTIONS OF BA(S-1(0)) AND BA((1)D(2)) WITH WATER AND METHANOL

The reactions of Ba(6s2 1S0) and Ba(6s5d 1D2) with water and methanol were studied under single collision conditions using crossed molecular beams. Reaction of ground state Ba(1S) +H2O led to dominant formation of BaO+H-2 at all collision energies studied (12-30 kcal/mol). Although the reaction Ba(1S)+H2O-->BaOH+H could also be observed at collision energies above the endoergicity of the reaction (13 kcal/mol), it remained a minor channel even at the highest collision energy. Electronic excitation of the Ba atom reactant to the metastable 1 D2 state led to a large enhancement in reactivity, but the products were BaOH+H rather than BaO+H-2. The dominance of BaO+H-2 from ground state Ba(1S) even at collision energies nearly equal to the Ba(1D) excitation energy of 11 395 cm-1 (approximately 32 kcal/mol) indicates that the observed reaction state specificity results from participation of different potential energy surfaces for reactions of ground and excited state atoms. Collisions of Ba(1S) and Ba(1D) with methanol led only to formation of BaOCH3+H. We observed no BaOH+CH3 or BaO+CH4, despite the fact that they are the more thermodynamically favorable channels. Although reactivity with methanol was strongly enhanced by electronic excitation of the incident Ba atom, no reaction was observed from Ba(1S) or Ba(1D)+dimethyl ether (CH3OCH3). These observations strongly suggest that the reactions leading to radical formation involve H-atom migration.