Total cross section of electron scattering by fluorocarbon molecules

Abstract

A compact linear electron transmission apparatus was used for the measurement of the total electron scattering cross section at 4-500 eV. Total cross sections of chlorofluorocarbon (CCl 2 F 2 ), hydrochlorofluorocarbon (CHClF 2 ), perfluoropropane (C 3 F 8 ), perfluoro-n-pentane (C 5 F 12 ), perfluoro-n-hexane (C 6 F 14 ) and perfluoro-n-octane (C 8 F 18 ) were obtained experimentally and compared with the values obtained from a theoretical calculation and semi-empirical model calculation.

Cross sections for elastic scattering of electrons by CF3Cl, CF2Cl2, and CFCl3

“…4(c)). If we now add the Born rotational and vibrational ICS, and the BEB ionization 63 ICS, to our elastic ICS we find typically very good agreement between the present "experimental" total cross sections and independent measured TCS from Jones, 22 Zecca et al, 23 and Yamada et al 56 (as appropriate for each target molecule). This is clearly visible in Figs.…”

“…Note that the data for CF 4 and CCl 4 were reported previously by our group 1,6 and are included here simply for comparison with the present results. For 18,19 Also included in these figures are the available experimental and theoretical total cross sections, [22][23][24][25][55][56][57] elastic ICSs using the SMC approach, 20 and experimental [58][59][60][61][62]64 and BEB theoretical 63 …”

“…This was undertaken in order to compare the present results to independent measurements and calculations of the total cross section for each species. [22][23][24][55][56][57] In addition, the results from the present IAM-SCAR calculations for the elastic ICS, total cross sections and sum over all inelastic ICS (except vibrational excitations) are also plotted. Note that independent ionization cross sections [58][59][60][61][62][63][64] are also shown for each species, where applicable, to illustrate the efficacy of the BEB model approach.…”

Low-Energy Electron Attachment to the Dichlorodifluoromethane (CCl2F2) Molecule

“…Electron collisions with CCl 2 F 2 at low energies are strongly influenced by four negative ion resonances, 8,10,16 in which the added electron resides in orbitals labeled as 10 16 ). These resonances show up in total scattering, 11,16,[26][27][28][29] vibrational excitation (VE), 30 electronic excitation, 16 and attachment cross sections. 8,16,[31][32][33][34][35][36][37][38][39] Studies of VE revealed a strong mode selectivity of the resonances; 30 energy loss spectra, taken at incident energies of 1.0 eV ( 2 A 1 (C-Cl σ*) resonance) and 4.0 eV ( 2 A 1 (C-F σ*) resonance), for instance, showed preferential excitation of the ν 3 (a 1 ) mode (CCl 2 symmetric stretch, 30 quantum 56.7 meV 40,41 ) and of the ν 1 (a 1 ) mode (CF 2 symmetric stretch, quantum 136.5 meV 41 ).…”

“…Electron collisions with CCl 2 F 2 at low energies are strongly influenced by four negative ion resonances, ,, in which the added electron resides in orbitals labeled as a 1 (C−Cl σ*) (VAE = 0.97 eV), b 2 (C−Cl σ*) (VAE = 2.36 eV), a 1 (C−F σ*) (VAE = 3.86 eV), and b 1 (C−F σ*) (VAE = 6.2 eV). These resonances show up in total scattering, ,,− vibrational excitation (VE), electronic excitation, and attachment cross sections. ,,− Studies of VE revealed a strong mode selectivity of the resonances; energy loss spectra, taken at incident energies of 1.0 eV ( 2 A 1 (C−Cl σ*) resonance) and 4.0 eV ( 2 A 1 (C−F σ*) resonance), for instance, showed preferential excitation of the ν 3 (a 1 ) mode (CCl 2 symmetric stretch, quantum 56.7 meV , ) and of the ν 1 (a 1 ) mode (CF 2 symmetric stretch, quantum 136.5 meV). The low-lying 2 A 1 resonance also dominates DEA at low energies, yielding Cl − anions according to the reaction e − + CCl 2 F 2 → CCl 2 F 2 − * ( 2 A 1 ) → CClF 2 + Cl − + Q with an exothermicity of Q (298 K) = 0.15(11) eV.…”