Abstract
Abstract The adsorption and reaction of acetonitrile (CH3CN) on clean and oxygen covered Ag(110) surfaces has been studied using temperature programmed reaction spectroscopy (TPRS), isotope exchange, chemical displacement reactions and high resolution electron energy loss spectroscopy (EELS). On the clean Ag(110) surface, CH3CN was reversibly adsorbed, desorbing with an activation energy of 10 kcal mol-1 at 166 K from a monolayer state and at 158 K from a multilayer state. Vibrational spectra of multilayer, monolayer and sub-monolayer CH3CN were in excellent agreement with that of gas phase CH3CN indicating that CH3CN is only weakly bonded to the clean Ag(110) surface. On the partially oxidized surface CH3CN reacts with atomic oxygen to form adsorbed CH2CN, OH and H2O in addition to forming another molecular adsorption state with a desorption peak at 240 K. This molecular state shows a CN stretching frequency of 1840 cm-1, which is indicative of substantial rehybridization of the CN bond and is associated with side-on coordination via the π system. The CH2CN species is stable up to 430 K, where C-H bond breaking and reformation begins, leading to the formation of CH3CN at 480 K and HCN at 510 K and leaving only carbon on the surface. In the presence of excess oxygen atoms C-H bond breaking and reformation is more facile leading to additional desorption peaks for CH3CN and H2O at 420 K. This destabilizing effect of O(a) on Ch2CN(a) is explained in terms of an anionic (CH2CN-1) species. Comparison of the vibrational spectra from CH2CN(a) and CD2CN(a) supports the following assignment for the modes of adsorbed CH2CN: ν(Ag-C) 215: δ(CCN) 545; ϱt(CH2) 695; ϱw(CH2) 850; ν(C-C) 960; ϱr(CH2) 1060; δ(CH2) 1375; ν(CN) 2075; and ν(CH2) 2940 cm-1. These results serve to further indicate the wide applicability of the acid-base reaction concept for reactions between gas phase Bronsted acids and adsorbed oxygen atoms on solver surfaces.
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