Electron-impact ionization of the chlorine molecule

Abstract

Relative partial ionization cross sections for the formation of Cl 2 ϩ , Cl ϩ and Cl 2ϩ from molecular chlorine have been recorded as a function of the ionizing electron energy. In these measurements particular attention has been paid to the efficient collection of fragment ions with high translational energies and the minimization of any mass-dependent discrimination effects. The cross sections show that at electron energies above the double ionization threshold the yield of fragment ions can be comparable with the ion yield of nondissociative ionization. Further analysis shows that at electron energies above 50 eV the yield of fragment ions from multiple ionization is comparable with the yield of fragment ions from single ionization: dissociative multiple ionization contributes 14% of the ion yield at 50 eV electron energy and 26% at 100 eV. The decay of Cl 2 2ϩ by heterolytic cleavage to form Cl 2ϩ is a result of approximately 5% of the dissociative double ionization events. This heterolytic process has a threshold of 41.8Ϯ1.5 eV. Electron-impact induced triple ionization to form long-lived Cl 2 3ϩ ions has been detected for the first time. This nondissociative triple ionization process makes up approximately 2% of the triple ionization events and triple ionization is responsible for approximately 2% of the ion yield above 100 eV. The threshold for dissociative triple ionization is determined to be 65.3Ϯ1.5 eV, a value in good agreement with a trication precursor state energy derived from the kinetic energy release for the fragmentation of Cl 2 3ϩ to Cl 2ϩ and Cl ϩ , which provides the first experimental estimate of the triple ionization energy of molecular chlorine.

The formation of boron containing fragment ions from the ionization of BCl3

“…The ionic collection efficiency for energetic ions from multiple ionization can in fact be determined from the coincidence data. Hence, even for very highly energetic ions from high levels of ionization, we can in fact assess and allow for any ion losses [14][15][16]18]. Recent data recorded on our apparatus for the ionization of N 2 O [22] is in excellent agreement with the latest reported PICSs [23] for formation of all the fragment ions that are formed.…”

“…The resulting ion flight times from the TDC are then transferred to a memory module which, when full, is rapidly dumped to a PC. As discussed in previous publications [14,18], it has been confirmed experimentally that there are no mass discrimination effects occurring in this apparatus, ensuring that quantitative data can be extracted from the mass spectra [19,20].…”

“…1 and has been discussed previously in the literature [14,16], so only a brief synopsis is given here. The experiment couples pulsed electron-impact ionization with a time-of-flight mass spectrometer (TOFMS).…”

“…The apparatus is designed to detect any ions with a translational energy component of less than 11 eV perpendicular to the axis of the mass spectrometer [14]. Curtis and Eland [21] determined the total kinetic energy release (KER) from a dicationic dissociation to commonly be less than 9 eV, so even the most energetic fragment ions formed via dissociative double ionization should reach the detector in our current configuration.…”

“…This experimental technique enables the arrival of single product ions, pairs of product ions and, in principle, three product ions at the detector to be identified and quantified. Recent studies using this technique of the ionization of Cl 2 and HCl show the experiment yields accurate relative PICSs over the current ionizing energy range [14,15]. The experiment also allows the contribution to the ion yields from various levels of ionization to be differentiated.…”