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.

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We describe a new experimental setup for studying the fragmentation dynamics of molecules induced by the impact of keV electrons using the well-known technique of recoil ion momentum spectroscopy. The apparatus consists of mainly a time- and position-sensitive multi-hit particle detector for ion analysis and a channel electron multiplier detector for detecting the ejected electrons. Different components of the setup and the relevant electronics for data acquisition are described in detail with their working principles. In order to verify the reliable performance of the setup, we have recorded the collision-induced ionic spectra of the CO2 molecule by the impact of keV electrons. Information about the ion pairs of CO+:O+, C+:O+ and O+:O+ resulting from dissociative ionizing collisions of 20 and 26 keV electrons with a dilute gaseous target of CO2 molecules has been obtained. Under conditions of the present experiment, the momentum resolutions of the spectrometer for the combined momenta of CO+ and O+ ions in the direction of the time-of-flight axis and perpendicular to the direction of an electron beam are found to be 10.0 ± 0.2 and 15.0 ± 0.3 au, respectively.

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.

The relative partial ionization cross sections for the fragment ions produced in direct and dissociative ionization of a N 2 O molecule are measured for impact of 10-25-keV electrons by using an electron-ion-coincidence technique with a linear time-of-flight spectrometer. The six ionic fragments of N 2 O (N 2 O + , NO + , N 2 + , O + , N + , and N 2+ + O 2+ ) are observed and identified. The impact energy dependence of the partial ionization cross sections for these ions is expressed relative to the cross section of N 2 O + and is found to be nearly invariant. The relative ionic fractions for the produced ions of N 2 O are also obtained and compared with the earlier reported data available at lower energies of electron impact. It is found that the relative ionic fractions for singly charged fragments are almost energy independent. However, for the doubly charged fragment ions (N 2+ + O 2+ ), the present data are found to be higher by almost a factor of four compared to the relative ionic fraction reported earlier at a very low impact energy.

The kinematics and dissociation dynamics of a H2O molecule induced by 10 keV electrons are studied using a time-of-flight mass spectrometer in conjunction with a position-sensitive detector in multi-hit coincidence mode. Five dissociative channels arising from the complete as well as the incomplete Coulomb explosions of H2Oq+ (q = 2, 3) ions are observed and identified. The dissociation mechanisms (concerted and/or sequential) for these channels are examined. Further, the angular correlation of different fragment ions and the geometrical structure of the precursor ion are studied. The kinetic energy release distributions for the observed channels are also determined. It is found that the pure Coulomb explosion model is insufficient to explain the observed kinetic release distributions. The mean kinetic energy release for these channels is compared with the available data reported by earlier workers who have employed different charged projectiles and sources of photons.

The ionic fragmentation of a multiply charged CO molecule is studied under impact of 10-keV electrons using recoil-ion momentum spectroscopy. The kinetic-energy-release distributions for the various fragmentation channels arising from the dissociation of CO q+ (q = 2-4) are measured and discussed in light of theoretical calculations available in the literature. It is observed that the present kinetic-energy-release values are much smaller than those predicted by the Coulomb explosion model. The kinetic-energy-release distribution for the C + + O + channel is suggested to arise from the tunneling process. It is seen that the peak of kinetic-energy-release distribution is larger for that dissociation channel that arises from the same molecular ion which has higher charge on the oxygen atom. Further, the relative ionic fractions for seven ion species originating from ionization and subsequent dissociation of the CO molecule are obtained and compared with the existing data reported at low energy of the electron impact. The precursor-specific relative partial ionization cross sections are also obtained and shown to be about 66.4% from single ionization, 29.9% from double ionization, 3.3% from triple ionization, and about 0.4% from quadruple ionization of the precursor CO molecule contributing to the total fragment ion yield.