Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

• Published in: The Journal of chemical physics 2001-09, Vol.115 (9), p.4041-4050
• Main Authors: Torres, I., Martı́nez, R., Sánchez Rayo, M. N., Castaño, F.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1388041

The experimental electron-impact total ionization cross sections (TICSs, ICSs) of CF4, CHF3, CH2F2, and CH3F fluoromethanes reported so far and a new set of data obtained with a linear double focusing time-of-flight mass spectrometer have been compared with the ab initio and (semi)empirical based ICS available methods. TICSs computational methods include: two approximations of the binary-encounter dipole (BED) referred to hereafter as Kim (Kim-BEB) and Khare (Khare-BEB) methods, the Deutsch and Märk (DM) formalism, also requiring atomic and molecular ab initio information, the modified additivity rule (MAR), and the Harland and Vallance (HV) methods, both based on semiempirical or empirical correlations. The molecular ab initio information required by the Kim, Khare, and DM methods has been computed at a variety of quantum chemistry levels, with and without electron correlation and a comprehensive series of basis sets. The general conclusions are summarized as follows: the Kim method yields TICS in excellent agreement with the experimental method; the Khare method provides TICS very close to that of Kim at low electron-impact energies (