Total cross sections for electron scattering on ${\mathrm{CH}}_3\mathrm{Cl},{\mathrm{CH}}_2{\mathrm{Cl}}_2,$ and ${\mathrm{CHCl}}_3$ have been measured by an absolute method in the (75–4000)-eV energy range. The overall experimental error is below 5%. A formulation of the additivity rule is proposed. The molecular cross sections are approximated by a Born-like two-parameter formula. We show that the low-energy parameter is correlated to the molecular polarizability. We show also that the high-energy parameter for a given molecule can be expressed as the sum of the high-energy parameters of the constituent atoms. The model has been successfully verified for two groups of halomethanes: the ${\mathrm{CH}}_4,{\mathrm{CH}}_3\mathrm{Cl},{\mathrm{CH}}_2{\mathrm{Cl}}_2,{\mathrm{CHCl}}_3,$ and ${\mathrm{CCl}}_4$ series and the ${\mathrm{CF}}_4,{\mathrm{CF}}_3\mathrm{Cl},{\mathrm{CF}}_2{\mathrm{Cl}}_2,{\mathrm{CFCl}}_3,$ and ${\mathrm{CCl}}_4$ series. The model has been successfully extended to molecules containing Si and S atoms, such as ${\mathrm{H}}_2\mathrm{S},{\mathrm{SF}}_6,{\mathrm{SiH}}_4,$ and ${\mathrm{SiF}}_4.$

• Received 24 August 1998

DOI:https://doi.org/10.1103/PhysRevA.59.1341