Photoinduced charge-transfer reaction at surfaces. Part I. (HCl)_m··Na_n/LiF(001)+hν (640 nm)→(HCl)_m−1Cl⁻Na_n⁺/LiF(001)+H(g)

A sub-monolayer of atomic sodium, Na_n, was deposited on LiF(001) at 50 K and characterized by temperature-programmed desorption, X-ray photoelectron spectroscopy, and titration with HCl. The Na_n was dosed with HCl to form (HCl)_m··Na_n/LiF(001), which was then irradiated by 640 nm laser-radiation to induce a charge-transfer (CT) reaction. Reaction-product atomic H(g) was observed leaving the surface, by two-color Rydberg-atom time-of-flight (TOF) spectroscopy. These H-atoms gave evidence of arising from the photoinduced harpooning reaction between the sodium clusters, Na_n, on the substrate, and (HCl)_m adsorbed on the Na_n. The translational energy distribution, its vibrational structure, and the angular distribution of H(g) gave information regarding the harpooning event. Translationally and vibrationally excited HCl(g) was shown, by resonance-enhanced multiphoton ionization (REMPI), to be formed as an alternate product; by way of (HCl)_m··Na_n/LiF(001)+602 nm→(HCl)_m−1Na_n/LiF(001)+HCl(g)(0).