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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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.

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.

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Singly and multiply charged molecular ions are found in diverse environments and hold relevance for a wide range of research areas like combustion chemistry, accelerator physics, atmospheric sciences, plasma physics, astrophysics etc. Molecular dications are of special significance as they can be generated and studied comparatively easily in laboratory experiments. And they have enabled exploration of new and exciting phenomenon such as hydrogen migration, inter-atomic Coulombic decay, plasmonic excitations, orbital tomography etc. The lifetime of a molecular dication is one of its fundamental characteristics, whose measurement contributes to strengthening ab initio calculations and in predicting the concentration of its dissociation products. Most of the already reported lifetimes of molecular dications are in the range of nanoseconds to seconds and metastable states with lifetimes of the order of picoseconds have only been theoretical predicted and an experimental verification is pending. We present a method of measuring subrotational lifetimes of molecular dications formed in three-body sequential breakup of polyatomic molecular precursors. Specifically, we have measured the subrotational lifetime of $$\hbox {SO}^{2+}$$ SO 2 + , which is formed as an intermediate in the three-body sequential fragmentation of $$\hbox {SO}_2^{3+}$$ SO 2 3 + . The lifetime against dissociation is determined to be a fraction of the rotational period of $$\hbox {SO}^{2+}$$ SO 2 + and is of the order of few picoseconds. The method proposed is general and is not restricted to triatomic precursors.

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.

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