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We have investigated the dissociative recombination (DR) of the C6D6+ and C6D7+ ions using the CRYRING heavy-ion storage ring at Stockholm University, Sweden. The dissociative recombination branching ratios were determined at minimal collision energy, showing that the DR of both ions was dominated by pathways keeping the carbon atoms together in one product. The absolute reaction cross sections for the titular ions are best fitted by σ(Ecm[eV]) = 1.3 ± 0.4x 10-15 (Ecm[eV])-1.19±0.02 cm² (C6D6+) and σ(Ecm[eV]) = 1.1 ± 0.3x 10-15(Ecm[eV])-1.33±0.02 cm² (C6D7+) in the intervals 3-300 meV and 3-200 meV respectively. The thermal rate constants of the titular reactions are best described by: k(T) = 1.3 ± 0.4 x 10-6(T/300)-0.69±0.02 cm³s-1 for C6D6+ and k(T) = 2.0 ± 0.6 x 10-6 (T/300)-0.83±0.02 cm³s-1 for C6D7+. These expressions correlates well with earlier flowing afterglow studies on the same process. [ABSTRACT FROM AUTHOR]

Dissociative recombination is a corner-stone reaction in the synthesis of interstellar molecules and plays an important role in the ionised layers of the atmospheres of the Earth, other planets, and their satellites. The studies of dissociative recombination reactions was for a long time dominated by afterglow techniques, and these techniques are used in improved versions also today, but the bulk of the relevant data have in recent years been produced at ion storage rings. We review briefly these different experimental techniques. As examples of recent developments in the field, we discuss in particular the dissociative recombination of [image omitted], the role of dissociative recombination in the chemistry of hydrocarbons and sulphur compounds in the interstellar medium and planetary ionospheres, and the synthesis of interstellar methanol. [ABSTRACT FROM AUTHOR]

Measurements of the cross-sections and branching ratios of the dissociative recombination of the ions CH2OH+, CD2OD+ and CD2 [image omitted] have been performed at the CRYRING storage ring located in Stockholm, Sweden. Evaluation of the data yielded reaction rate coefficients of: 7.0 × 10-7(T/300)-0.78 cm3 mol-1 s-1 for CH2OH+; 7.5 × 10-7(T/300)-0.70 cm3 mol-1 s-1 for CD2OD+ and 1.51 × 10-6(T/300)-0.66 cm3 mol-1 s-1 for CD2 [image omitted]. Calculation of the branching ratios for CH2OH+ and its deuterated isotopologue gave the following results for the DR reaction channels involving C-O bond fissure: H2O + CH (2.2%) and CH2 + OH (5.5%) in the reaction of CH2OH+ as well as D2O + CD (5%) and CD2 + OD (18%) for the dissociative recombination of CD2OD+. The remainder of the reaction flux kept the C-O bond intact: 92% for CH2OH+ and 77% for CD2OD+, respectively. Other recent measurements on the CH3 [image omitted] ion indicate dominating bond breaking between the heavy atoms, which is in contrast to this experiment. For CD2 [image omitted] CO-bond breaking was observed for 43% of the reaction flux. [ABSTRACT FROM AUTHOR]

The kinetics of the reactions of vinyl (C2H3) and propargyl (C3H3) radicals with NO2 have been studied in direct measurements at temperatures between 220 and 340 K, using a tubular flow reactor coupled to a photoionization mass spectrometer. The vinyl and propargyl radicals have been homogeneously generated at 193 nm by the pulsed laser photolysis of methyl vinyl ketone (vinyl bromide) and propargyl chloride, respectively. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of NO2 being in large excess over radical concentrations. The bimolecular rate coefficients of both reactions are independent of the bath gas (He or N2) and pressure within the experimental range (1-7 Torr) and are found to depend on temperature as follows: k(C2H3 + NO2) = [(4.19 ± 0.05) × 10-11](T/300 K)-0.60 ± 0.07 cm3 molecule-1 s-1 and k(C3H3 + NO2) = [(2.55 ± 0.05) × 10-11](T/300 K)-1.06 ± 0.10 cm3 molecule-1 s-1, with the uncertainties given as 1 standard deviation. The photolysis of propargyl chloride has also been observed to produce C3H3Cl2 radicals rapidly under the experimental conditions, thus enabling us to measure the bimolecular reaction rate coefficient of the C3H3Cl2 radical with NO2 at room temperature: k(C3H3Cl2 + NO2) = (2.37 ± 0.05) × 10-11 cm3 molecule-1 s-1. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are about ±20%. The only reaction product observed for the vinyl radical reaction with NO2 is NO. The experimental findings have been compared with the results of ab initio calculations, which give insight into possible reaction pathways. [ABSTRACT FROM AUTHOR]

Product branching ratios and thermal rate coefficients for the dissociative recombination of C3D7+ and C4D9+ have been measured in the ion storage ring CRYRING. The results for C3D7+ are believed to be slightly more accurate than those obtained earlier for C3H7+. Only the C–C bond breaking channels could be measured for C4D9+ and were found to be in excellent agreement with earlier data. [ABSTRACT FROM AUTHOR]

CH+3 is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres. However, the rate of one of the major destruction mechanisms of CH+3, dissociative recombination (DR), has long been uncertain, hindering the use of CH+3 as an astrochemical probe. Here, we present the first absolute measurement of the DR of vibrationally cold CH+3, which has been made using the heavy storage ring CRYRING in Stockholm, Sweden. From our collision-energy-dependent cross sections, we infer a thermal rate constant of k(T) = 6.97(± 0.03) × 10–7(T/300)–0.61(± 0.01) cm3 s–1 over the region 10 K ⩽ T ⩽ 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH3 (0.00+0.01– 0.00), CH2 + H (0.35+0.01– 0.01), CH + 2H (0.20+0.02– 0.02), CH + H2 (0.10+0.01– 0.01), and C + H2 + H (0.35+0.01– 0.02), indicating that two or more C-H bonds are broken in 65% of all collisions. We also present vibrational calculations which indicate that the CH+3 ions in the storage ring were relaxed to the vibrational ground state by spontaneous emission during the storage time. Finally, we discuss the implications of these new measurements for the observation of CH+3 in regions of the diffuse interstellar medium where CH+ is abundant. [ABSTRACT FROM AUTHOR]

The dissociative recombination (DR) of N2H+ has been reinvestigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. Thermal rate coefficients for electron temperatures between 10 and 1000 K have been deduced. We show that electron recombination is expected to play an approximately equally important role as CO in the removal of N2H+ in dark interstellar clouds. We note that a deeper knowledge on the influence of the ions' rotational temperature in the DR of N2H+ would be helpful to set further constraints on the relative importance of the different destruction mechanisms for N2H+ in these environments. The branching fractions in the DR of N2H+ have been reinvestigated at ∼0 eV relative kinetic energy, showing a strong dominance of the N2 + H production channel (93+4– 2%) with the rest leading to NH + N. These results are in good agreement with flowing afterglow experiments and in disagreement with an earlier measurement at CRYRING. [ABSTRACT FROM AUTHOR]

Product branching ratios and thermal rate coefficients for the dissociative recombination of CO2+ have been measured in the cryogenic ion source ring ion storage ring. The rate constants were found to be 4.2×10-7(Te/300)-0.75 cm3 s-1. The 300-K result is in agreement with previous flowing afterglow values and is somewhat smaller than a recent determination made at the Aarhas storage ring in Denmark (ASTRID) storage ring. The electron temperature dependence is, however, in good agreement with the ASTRID result of T-0.8. The present results show that only CO plus O are formed, other product branching ratios are zero within experimental error. This is in contradiction to the ASTRID results which show that 9% of the reactivity goes to C+O2. The new results show that the C+O2 channel does not need to be included in the models of the ionospheres of Venus and Mars. [ABSTRACT FROM AUTHOR]