Total cross sections for electron scattering on CH 3Cl, CH2Cl2 , and CHCl3 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 twoparameter 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 CH4 ,C H 3Cl, CH2Cl2 , CHCl3 , and CCl4 series and the CF4 ,C F 3Cl, 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# PACS number~s!: 34.80.Bm, 34.80.Gs Chlorine substituted methanes play an important role in atmospheric chemistry @1#; their time in the Earth’s troposphere is several tens of years. Free Cl radicals formed by ultraviolet-induced dissociation act as catalysts in the chain of reactions leading to the destruction of the stratospheric ozone @2#. In particular, chloromethane (CH3Cl), used in refrigerators and organic chemistry, is the most abundant halocarbon present in the atmosphere. CH3Cl is also the most frequently studied halocarbon in electron-scattering experiments.
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