Barium atoms, excited, reactions

H. F. Davis, A. G. Suits and Y. T. Lee, Reaction Dynamics of Ground State and Electronically Excited Barium Atoms., in Gas-Phase Metal Reactions, edited by A. Eontijn, pp. 319-347, North-Holland, Amsterdam, 1992. 

Alkaline earth metal atoms have fairly low ionization potentials, as have alkali metal atoms (e.g., 5.21 and 5.14 eV for barium and sodium, respectively [89]). Hence the reactions of alkaline earth metal atoms with oxidizing molecules are also expected to be initiated by an electron transfer and should follow the harpoon mechanism. However, alkali metal atoms are monovalent species, whereas alkaline earth metal atoms have two valence electrons. Hence peculiarities are to be expected in the alkaline earth metal reaction dynamics, especially when doubly charged products such as BaO are to be formed [90]. The second valence electron also opens up the possibility of chemiluminescent reactions, which are largely absent in alkali metal atom reactions [91, 92]. The second electron causes the existence of low-lying excited states in the product. 

A similar correlation diagram can be drawn to interpret the exclusive observation of BaOH chemiluminescence in the reaction of Ba(6s6p P) with water [172]. Here again, the reaction of excited barium can be explained by H-atom migration and formation of the intermediate HBaOH. This mechanism definitely carries some generality since it has been used also by Oberlander and Parson to account for re-... 

One example of this technique is the excited-state spectroscopy of the molecule BaO [10.33]. In the volume that is crossed by an atomic barium beam and a molecular O2 beam, BaO molecules are formed in various vi-bronic levels (u", 7") of their electronic X ground state by the reaction Ba+02 -> BaO + 0 (Fig. 10.13). With a dye laser tuned to the transitions... 

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