Hot precursor reactions during the collisions of gas-phase oxygen atoms with deuterium chemisorbed on Pt(100).
We utilized direct rate measurements and temperature programmed desorption to investigate reactions that occur during the collisions of gaseous oxygen atoms with deuterium-covered Pt(100). We find that both D2O and D2 desorb promptly when an oxygen atom beam impinges upon D-covered Pt(100) held at surface temperatures ranging from 90 to 150 K, and estimate effective cross sections of 12 and 1.8 A2, respectively, for the production of gaseous D2O and D2 at 90 K. The yields of D2O and D2 that desorb at 90 K are about 13% and 2%, respectively, of the initial D atom coverage, though most of the D2O product molecules (approximately 80%) thermalize to the surface rather than desorb at the surface temperatures studied. Increasing the surface temperature from 90 to 150 K causes the D2O desorption rate to decay more quickly during O atom exposures to the surface and results in lower yields of gaseous D2O. We attribute the production of D2O and D2 in these experiments to reactions involving intermediates that are not thermally accommodated to the surface, so-called hot precursors. The results are consistent with the production of hot D2O involving first the generation of hot OD groups from the reaction O*+D(a)-->OD*, where the asterisk denotes a hot precursor, followed by the parallel pathways OD*+D(a)-->D2O* and OD*+OD(a)-->D2O*+O(a). The final reaction contributes significantly to hot D2O production only later in the reaction period when thermalized OD groups have accumulated on the surface, and it becomes less important at higher temperature due to depletion of the OD(a) concentration by thermally activated D2O production.
Kan
Heywood H
HH
Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA.
Shumbera
R Bradley
RB
Weaver
Jason F
JF