Total cross sections for electron scattering on chloromethanes: Formulation of the additivity rule

Total cross sections for electron scattering on CH3Cl, CH2Cl2, and CHCl3 ha ve been measured by an absolute method in the (75-4000)-eV energy range. Th e overall experimental error is below 5%. A formulation of the additivity r ule is proposed. The molecular cross sections are approximated by a Born-li ke two-parameter formula. We show that the low-energy parameter is correlat ed to the molecular polarizability. We show also that the high-energy param eter for a given molecule can be expressed as the sum of the high-energy pa rameters of the constituent atoms. The model has been successfully verified for two groups of halomethanes: the CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 se ries and the CF4, CF3Cl, CF2Cl2, CFCl3, and CCl4 series. The model has been successfully extended to molecules containing Si and S atoms, such as H2S, SF6, SiH4, and SiF4. [S1050-2947(99)10102-1].