Charge stabilization by chloromethane molecules on multilayer Kr films

We have measured the charge trapping cross section for the chloromethane molecules CCl4, CHCl3, and CH2Cl2 physisorbed onto Kr films. Within the 0-10 eV range investigated, charge is stabilized at the surface as atomic anions which are formed by dissociative electron attachment (DEA) to the molecules. Intermediate anion states previously observed in gas phase experiments are apparent. Below approximate to 4 eV electron impact energy, the charge trapping cross section becomes an absolute cross section for DEA because of the absence of a desorbed ion signal. At higher energies, our results provide a lower limit for this same quantity. Comparisons with gas phase cross sections, show substantial and systematic differences that can be understood in terms of the interaction between the intermediate anion states and electronic polarization held they induce on the Kr surface. (C) 1996 American Institute of Physics.