It will be argued that in the process of chemical adsorption/desorption on a surface, a molecule with several electrons involved in formation of chemical bonds will always pass extended regions of degeneracy with electronically excited molecular configurations. Such degeneracy allows a process similar to Inverse Electronic Relaxation to take place. Conditions at which the above-mentioned phenomenon can appear as a particularly strong nonadiabatic effect will be examined and links drawn to experimental observations made on several systems as well as to theoretical attempts to account for these effects.
In the model proposed, dissipation of the energy from “hot” coordinate(s) of the system is resonantly-enhanced by excited electronic configuration of the molecule; the mechanism leads to preferential dissipation of large energy quanta in form of excitons, rather than to direct generation of electron-hole pairs commonly discussed in the connection to nonadabatic effects within the “friction force” model. It will be argued that experiments
with electronically excited species can provide vital information for understanding of the very nature of the passways of surface chemical reactions and of the corresponding reaction dynamics effects.
The excited potential energy surface topology, which follows from the consideration, strongly suggests an unexplored previously possibility to initiate elementary chemical transformations on interfaces via electronic excitation of gas-phase molecules. The principal differences of the new approach with the photochemistry within gas phase and/or within molecular aggregates/adsorbates will be emphasized.
Finally, experimental results demonstrating the first surface chemical reaction with electronically excited molecules and a new experimental approach, capable of producing macroscopic fluxes of excited reagents, will be presented . We will report a quantum yield close to 1 for dissociative adsorption of electronically excited SO2 molecules on a surface leading to formation of molecular sulphur.
1. J. J. Madhukeswara and V. V. Petrunin, Chem. Phys. Lett. 445, 309-314, 2007.
|Period||20. Sep 2007|
|Event title||The origin of the strong nonadiabatic effects on passways of surface chemical reactions: unexplored possibilities to control chemical transformations on interphases|