CHARGE STABILIZATION BY CHLOROMETHANE MOLECULES ON MULTILAYER KR FILMS

We have measured the charge trapping cross section for the chlorometha ne molecules CCl4, CHCl3, and CH2Cl2 physisorbed onto Kr films. Within the 0-10 eV range investigated, charge is stabilized at the surface a s atomic anions which are formed by dissociative electron attachment ( DEA) to the molecules. Intermediate anion states previously observed i n gas phase experiments are apparent. Below approximate to 4 eV electr on impact energy, the charge trapping cross section becomes an absolut e cross section for DEA because of the absence of a desorbed ion signa l. 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 int eraction between the intermediate anion states and electronic polariza tion held they induce on the Kr surface. (C) 1996 American Institute o f Physics.