Surface-molecule proton transfer in the scattering of hyperthermal DABCO from H/Pt(111)

Hyperthermal DABCO is scattered from H-covered Pt(111). The ionization by electron and proton transfer is measured as a function of the incident molecular kinetic energy and the angle of incidence. The positive ions produced are energy analyzed showing hyperthermal distributions which are dependent on the incident energy. This means that no equilibration occurs at the surface and therefore protonation at hyperthermal energy is an Eley-Rideal reaction. The protonation yield depends linearly on the incident DABCO flux and the H-coverage on the Pt(111) surface. The ionization yield for both electron and proton transfer depends on the incident energy as k(E_i-E_tr)ⁿ with a similar threshold energy of 1.5 eV. From this we learn that direct protonation occurs by electron transfer and a subsequent binding of an H-atom. Within the error bars we found no difference between H-atom and D-atom transfer. Protonation of other molecules with a high proton affinity such as dimethylaniline at H-covered Pt(111) was measured as well. Analytical applications for both surface analysis and molecular detection are discussed.