Partial-ionization cross sections of aCO2molecule due to impact of 10–26-keV electrons

Abstract

Experimental data on total-and partial-ionization cross sections of ionic fragments of CO 2 molecule produced by impact of 10-26-keV electrons are obtained on a crossed-beam apparatus in our laboratory. An ejected electron-produced ion-coincidence technique is employed together with a time-of-flight mass spectrometer for analysis of the ions. The six ionic fragments, CO 2 + , CO + , CO 2 2+ , O + , C + , and C 2+ , resulting from dissociative ionization of the CO 2 molecule are observed and identified; their relative ionization cross sections and branching ratios are determined as a function of impact energy. The binary-encounter Bethe model is found to overestimate the experimental data for total-ionization cross sections of the observed ions. No other experimental or theoretical data exist in the investigated energy range to make a direct comparison with the present results.

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

“…The detailed description of the experimental setup is given in our recent publications [28,29]. However, some further modifications in the earlier setup have been made which are given as follows: Firstly, to get rid of the possible oil vapor contamination in the system, the oil diffusion pump is replaced by a 400 liter s −1 turbo molecular pump (Model 8/450, M/s Elettrorava, Italy) which gives the same ultimate vacuum in the system as before; secondly, we have modified our spectrometer by incorporating three new high-transmission (95%) nickel meshes in place of M 1 , R 1 , and M 2 in the spectrometer shown in Fig.…”

“…The singles spectrum represents the conventional TOF spectrum of the ions; doubles and triples spectra correspond to two-and three-ion coincidences, respectively. In all the data analysis described next, the detection efficiency of the spectrometer system D refers to the product of overall transmission efficiency of meshes T and the detection efficiency of MCP; the value of the latter is taken to be the open area ratio of the MCP ion detector (55%) [28]. For our present system, the value of D is estimated to be ∼24%.…”

“…We have experimentally minimized the false coincidences by using the lowest possible values of the gas density n (<10 13 cm −3 ) and the incident beam current I (∼10 pA) as the number of true coincidences is proportional to the product nI , whereas the random coincidences vary as n 2 I 2 . The background subtracted ion counts from singles spectrum N (X n+ = C + , O + , CO + , C 2+ , O 2+ , CO 2 2+ ) are obtained following the same procedure as given in [28]; when these ion counts are divided by the counts of singly ionized parent ion (CO 2 + ), the relative PICSs for the ion X n+ are obtained.…”

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

“…1 and 2, respectively. We subtracted the background from the TOF spectrum following the same procedure as given in [35]. To subtract the random coincidences from the ion-ion coincidence map, we took into account only those counts which follow the law of momentum conservation.…”

Fragmentation ofCO22+in collisions with low-energy electrons

“…The early investigations were mainly devoted to cross section, partial cross section studies, and kinetic energy release (KER, defined by the sum energy of all fragments) mea surements [8,17,21,22,31]. Recently, with the development of two-dimensional ion-ion coincidence techniques, more and more studies focused on the dynamics and mechanism analysis [3,12,18,32], In a simplest case where a diatomic molecule dication breaks into two singly charged atomic ions, the ions are then driven purely by the Coulomb force, i.e., the wellknown Coulomb explosion; the corresponding kinematics is also simple and intuitive and can usually be well reproduced by the simple Coulomb explosion model.…”