Surface states of pristine silica surfaces: II. UHV studies of the CO 2 adsorption-desorption phenomena

Abstract

UHV and MS have been used in connection with ESR to study the interaction of CO 2 with “fresh” surfaces of silica and other glasses. The fracture (and abrasion) provides an original means to measure isotherms, sticking probabilities and to follow the adsorption kinetics. Emphasis was put also on thermal desorption kinetics in relation with the Eyring's transition state theory. The main results are the following: the adsorption of CO 2 is found to be non-dissociative and non-activated; the adsorption sites are associated with Si atoms; CO 2 has a constant binding energy whatever the coverage, but the isotherm, however, is not of Henry's type: self-reconstruction of the fresh surface is taking place; the activation energy for thermal desorption found by a linear heating program is of the order of 25 kcal/mole and, by a step-function heating program, is 8.55 kcal/mole associated with a pre-exponential factor τ 0 in the Frenkel's formalism of, respectively, 10 −9 sec and 2 × 10 −2 sec.