Energy Partitioning in Collisions of Slow Polyatomic Ions with Surfaces: Ethanol Molecular Ions on Surfaces Covered by Self-Assembled Monolayers (CF-SAM, CH-SAM, COOH-SAM)

Abstract

Energy transfer in ion−surface interactions between ethanol molecular ion and self-assembled monolayers formed by perfluoro-hydrocarbon (CF-SAM), hydrocarbon (CH-SAM), and hydrocarbon with terminal −COOH group (COOH-SAM) C11 or C12 chains were investigated over the incident energy range of 11−32 eV for several incident angles. Mass spectra and translational and angular distributions of product ions were used to determine distributions characterizing the partitioning of incident energy of the projectile ion into the internal excitation of the projectile, product ion translational energy, and energy absorbed by the surface. For the CF-SAM, the fraction of energy transformed into internal energy of the projectile had a maximum at about 17% of the projectile ion incident energy and did not depend on the incident angle between 40° and 80° (with respect to the surface normal); the fraction of energy in product translation was for the incident angle of 60° (measured at the product ion angular maximum) about 37%. For the CH-SAM and COOH-SAM and incident angle of 60°, the respective fractions were (peak values) 5−6% into internal excitation of the projectile, 27−30% into product translational energy, and about 64−68% absorbed by the surface, very similar as those for collisions with a hydrocarbon-covered stainless steel surface, investigated earlier.