Dissociative-ionization cross sections for 12-keV-electron impact on CO2

Abstract

The dissociative ionization of a CO 2 molecule is studied at an electron energy of 12 keV using the multiple ion coincidence imaging technique. The absolute partial ionization cross sections and the precursor-specific absolute partial ionization cross sections of resulting fragment ions are obtained and reported. It is found that ∼75% of single ionization, 22% of double ionization, and ∼2% of triple ionization of the parent molecule contribute to the total fragment ion yield; quadruple ionization of CO 2 is found to make a negligibly small contribution. Furthermore, the absolute partial ionization cross sections for ion-pair and ion-triple formation are measured for nine dissociative ionization channels of up to a quadruply ionized CO 2 molecule. In addition, the branching ratios for single-ion, ion-pair, and ion-triple formation are also determined.

Ionic fragmentation of the CO molecule by impact of 10-keV electrons: Kinetic-energy-release distributions

“…The RIFs for CO + , C + , and O + show reasonably good agreement with those at low-energy electron impact because they possibly arise from the dipole allowed transitions, whereas the mismatch in the RIF values for CO 2+ , C 2+ , O 2+ , and C 3+ may arise due to the involvement of the dipole nonallowed transitions. In our earlier experiments, we have also observed the large RIF for doubly charged ions [34,36]. It has been shown [41] that at higher impact energies the multiple ionization is governed mainly by Auger-likeautoionization processes followed by creation of a vacancy in the inner-shell molecular orbital.…”

“…The data was stored in a event by event mode and analyzed off-line by using the Cobold PC software. The ion-detection efficiency (D) of our setup is estimated to be ∼24% [34]. We have taken the same detection efficiency for all ions observed in the present experiment.…”

“…The experimental steup and data analysis procedures are described in detail in our previous publications [33,34]. Briefly, a monoenergetic beam of 10-keV electrons extracted from an electron gun is made to collide with CO molecules (99.99%) effusing from a hypodermic needle (length = 1.2 cm; diameter = 0.01 cm).…”

“…Further, to obtain the precursor specific PICSs, we took the random coincidence corrected data which are also corrected for detection efficiencyD and D 2 for the TOF spectrum and the ion-ion coincidence map, respectively. To get the events arising only from singly ionized molecules, the count considered from the TOF spectrum is corrected by subtracting the contribution of events arising from the doubly, triply, and quadruply ionized CO molecule with consideration of the detection efficiency as given below [34]:…”

“…The RIFs, the precursor specific PICSs, and the involved errors are estimated by using the analysis procedures given in [34,36]. The overall uncertainties in the presented data for each ion single are 2.5%, <4%, 4%, 10%, 6%, 8%, and 15%, for CO + , C + , O + , CO 2+ , C 2+ , O 2+ , and C 3+ , respectively.…”