Collisions of Slow Polyatomic Ions with Surfaces:Dissociation and Chemical Reactions of C_2H_2~(+ centre dot ),C_2H_3~+,C_2H_4~(+ centre dot),C_2H_5~+,and Their Deuterated Variants C_2D_2~(+ centre dot) and C_2D_4~(+ centre dot) on Room-Temperature a

摘要

Interaction of C_2H_n~+ (n=2-5) hydrocarbon ions and some of their isotopic variants with room-temperature and heated (600 deg C) highly oriented pyrolytic graphite (HOPG) surfaces was investigated over the range of incident energies 11 -46 eV and an incident angle of 60 deg with respect to the surface normal.The work is an extension of our earlier research on surface interactions of CH_n~+ (n=3-5) ions.Mass spectra,translational energy distributions,and angular distributions of product ions were measured.Collisions with the HOPG surface heated to 600 deg C showed only partial or substantial dissociation of the projectile ions;translational energy distributions of the product ions peaked at about 50% of the incident energy.Interactions with the HOPG surface at room temperature showed both surface-induced dissociation of the projectiles and,in the case of radical cation projectiles C_2H_2~(+ centre dot) and C_2H_4~(+ centre dot),chemical reactions with the hydrocarbons on the surface.These reactions were (i) H-atom transfer to the projectile,formation of protonated projectiles,and their subsequent fragmentation and (ii) formation of a carbon chain build-up product in reactions of the projectile ion with a terminal CH_3-group of the surface hydrocarbons and subsequent fragmentation of the product ion to C_3H_3~+.The product ions were formed in inelastic collisions in which the translational energy of the surface-excited projectile peaked at about 32% of the incident energy.Angular distributions of reaction products showed peaking at subspecular angles close to 68 deg (heated surfaces) and 72 deg (room-temperature surfaces).The absolute survival probability at the incident angle of 60 deg was about 0.1 % for C_2H_2~(+ centre dot),close to 1 % for C_2H_4~(+ centre dot) and C_2H_5~+,and about 3-6% for C_2H_3~+.