Highly correlated internally contracted multireference configuration interaction wave functions are used to calculate the potential energy and spin-orbit coupling functions for the lowest electronic states of CO2+ dication. Using these functions, the positions and lifetimes of the corresponding vibronic states are evaluated by means of log-phase-amplitude, stabilization, and complex-scaling methods within the framework of a multichannel Schrodinger analysis. For the first time in the literature, the calculated lifetimes are in good agreement with the experiment, thereby proving the reliability of the predicted characteristics and adequacy of the used theory for a theoretical study of other molecular dications.

Large-scale plasma was created in molecular gases (CO, CO2, N2, H2O) and their mixtures by high-power laser-induced dielectric breakdown (LIDB). Compositions of the mixtures used are those suggested for the early earth's atmosphere of neutral and/or mildly reducing character. Time-integrated optical spectra emitted from the laser spark have been measured and analyzed. The spectra of the plasma generated in the CO-containing mixtures are dominated by emission of both C2 and CN radicals. A vibrational temperature of approximately 10(4) K was determined according to an intensity distribution in a vibronic structure of the CN (B2Sigma(+)u-X2Sigma(+)g) violet band. For comparison, the NH3-CH4-H2-H2O mixture has been irradiated as a model of the strongly reducing version of the early earth's atmosphere. In this mixture, excited CN seems to be significantly less abundant than C2. The LIDB experiments were in the molecular gases carried out not only in the static cell but also using a large, double stream pulse jet (gas puff target) placed in the vacuum interaction chamber. The obtained soft X-ray emission spectra indicate the presence of highly charged atomic ions in the hot core of high-power laser sparks.

The potential energy and spin-orbit coupling functions of 11 lowest electronic states of CS(2+) dication have been calculated using internally contracted multireference configuration method. Using these functions, the positions and widths of the corresponding vibronic levels have been evaluated by means of the stabilization and log-phase-amplitude methods. The states governing the second step in the sequential pathway CS2(3+)-->S++CS2+-->S++C++S+ of the overall three-body Coulomb explosion of CS(2)3+ have been determined.

A search has been carried out for the $\mathrm{C}_2^{-}$ ion in diffuse clouds toward HD 23180, HD 24912, HD 24398, HD 46711, and HD 50064 using the HIDES spectrometer on the Okayama 188-cm telescope. An upper limit of $8.3 \times 10^{10}\hbox{--} 1.8\times 10^{12} \,\mathrm{cm}^{-2}$ was obtained for the $\mathrm{C}_2^{-}$ column density. The upper limit value ($3.8 \times 10^{11} \,\mathrm{cm}^{-2}$) toward HD 23180 is two orders of magnitude smaller than that of the $\mathrm{C}_2$ radical. Possible production mechanisms for $\mathrm{C}_2^{-}$ are discussed.

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