We present a model suggesting high chemical activity of electronically-excited molecules colliding with an isolator
surface. Initial photochemical event is accounted for as the result of molecular evolution on the electronically-excited
potential energy surface (PES), where acceleration and alignment are taking place, guiding all the molecules towards the
intersections with the ground state PES, where transitions to the ground state PES will occur with minimum energy
dissipation. The accumulated kinetic energy may be used to overcome the chemical reaction barrier. While
recombination chemical reactions in a gas phase require participation of a third body, this strong limitation on the
reaction rates is removed upon interaction with a surface.
To observe the predicted phenomenon, we suggested a new experimental approach, Evanescent Wave Photocatalysis1,
based on application of total internal reflection on an insulator surface. Laser photoexcitation is localized in a narrow
boundary gas layer just above the interface; majority of the excited molecules can reach the surface before the relaxation.
The experiments are performed at high gas pressures, so that dense fluxes of the excited reagents can be readily
produced. Products of chemical adsorption and/or chemical reactions induced within adsorbates are aggregated on the
surface and observed by light scattering. We will demonstrate how pressure and spectral dependencies of the chemical
outcomes, polarization of the light and interference of two laser beams inducing the reaction can be used to distinguish
the new process we try to investigate from chemical reactions induced by photoexcitation within adsorbed molecules
and/or gas phase photolysis.