Substitution effects in elastic electron collisions with CH₃X (X=F, Cl, Br, I) molecules

We report absolute elastic differential, integral, and momentum transfer cross sections for electron interactions with the series of molecules CH₃X (X=F, Cl, Br, I). The incident electron energy range is 50–200 eV, while the scattered electron angular range for the differential measurements is 15°–150°. In all cases the absolute scale of the differential cross sections was set using the relative flow method with helium as the reference species. Substitution effects on these cross sections, as we progress along the halomethane series CH₃F, CH₃Cl, CH3Br, and CH₃I, are investigated as a part of this study. In addition, atomic-like behavior in these scattering systems is also considered by comparing these halomethane elastic cross sections to results from other workers for the corresponding noble gases Ne, Ar, Kr, and Xe, respectively. Finally we report results for calculations of elastic differential and integral cross sections for electrons scattering from each of the CH₃X species, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements was found to be quite remarkable in each case.This work was conducted under the support of the Japanese Ministry of Education, Sport, Culture and Technology and also by the Ministerio de Educación Ciencia e Innovación Plan Nacional de Fisica, Project No. FIS2006- 00702, the Consejo de Seguridad Nuclear and the European Science Foundation COST Action No. CM0601. Additional support from the Australian Research Council, through its Centres of Excellence Program, and the Korea Science and Engineering Foundation Grant No. 2009-0052415 is further noted. One of us H.K. also acknowledges the Japan Society for the Promotion of Science JSPS for his fellowships as grants-in-aid for scientific research and, most recently, to facilitate his visit to Flinders University and the ANU