Reaction Dynamics of Electronically Excited Barium Atoms With Free Molecules and Molecular Clusters

In this review article we describe some recent results obtained in our laboratory. The successfulcombination of crossed molecular beam techniques and various laser excitation schemes has been used tostudy chemiluminescent reactions of ground and excited electronic states of barium with free moleculesand molecular clusters. Studies include the identification of reaction products in cases where manychemiluminescent reaction channels are opened. The case of Ba ( 6 s p 1 P 1 , 6 s 5 d 1 D 2 , 6 s 5 d 3 D j )reacting withH 2 0, methanol, ethanol, propanol-1, propanol-2, methyl-2, propanol-2, butanol-l, allyl alcohol, dimethylether, diethyl ether and diallyl ether is examined. A reaction mechanism is proposed which accountsfor all these reactions. Studies reported in this review also include the unravelling of reaction dynamicswhere various forms of energy are mixed (electronic and kinetic energy). This is shown in studies ofBa (1 D 2 and 1 P 1 ) + O 2reactions. Finally the role of molecular clusters as reactant is examined. Evidenceis provided that clusters of N 2 0, H 2 0 and CO 2 , in collision with Ba (1 S 0 and 1 P 1 ) + O 2 , do not lead efficiently toboth reactive and non reactive luminescent exit channels.