Product distributions in the reactions of excited noble-gas atoms with hydrogen-containing compounds

Dissociation and ionization of small H-containing molecules following energy transfer from electronically excited (3P0,2) states of Ar, Kr, and Xe have been studied in discharge–flow systems, using the atomic resonance fluorescence and the saturation ion–current techniques. Chemi-ionization is observed in all reactions in which Penning ionization is exothermic, but molecular dissociation is the major channel in all cases. Elimination of H atoms is strongly favored over both loss of H2 and cleavage of central bonds of larger molecules, in contrast to the known vacuum–UV photochemistry of several of the molecules. When strongly exothermic, elimination of two H atoms in a single reactive event is a major and, in some cases, the dominant channel.