Borja Sierra

The electron-impact dissociative ionization of CCl2F2

An investigation of the formation channels and properties of ion fragments following electron-impact dissociative ionization of the CCl2F2 molecule using electron kinetic energies in the 0–100 eV range is reported. Measurements of ion appearance potentials (APs) and nascent translational energy distributions were made on a supersonic expansion of CCl2F2 in a time-of-flight mass spectrometer. A discussion of the correlation between the channel APs, the precursor bond characters as calculated from the population analysis, and the low-resolution photoelectron spectrum of the CCl2F2 molecule is presented.

Absolute electron-impact total ionization cross sections of chlorofluoromethanes.

An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10-85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles--as a function of the electron-impact energy--have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n> or =3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented.