We show that a combined technique of Cs^+ reactive ion scattering (Cs^+ RIS) and low-energy secondary ion mass spectrometry (LESIMS) provides a powerful means for probing molecular films and their surface reactions. Simple molecules, including HCI, NH...
We show that a combined technique of Cs^+ reactive ion scattering (Cs^+ RIS) and low-energy secondary ion mass spectrometry (LESIMS) provides a powerful means for probing molecular films and their surface reactions. Simple molecules, including HCI, NH₃, D₂O, and their mixtures, were deposited into a thin film of several monolayer thickness on Ru(001) at low temperature in vacuum, and the surface was characterized by Cs^+ RIS and LESIMS. On pure films, D₂O, HCI, and NH₃ existed in the corresponding molecular states. When HCI and NH₃ were co-deposited, ammonium ion(NH₄^+) was readily formed by proton transfer from HCI to NH₃. In the presence of water molecules, HCI ionized first to hydronium ion(H₃O^+) which subsequently transferred proton to NH₃ to form NH₄^+. The proton transfer, however, did not occur to a completion on ice, in contrast to the complete reaction in aqueous solutions.