Branching ratios in dissociative recombination of formyl and isoformyl cations

The chemistry of protonated species in the martian ionosphere

“…which opens up at relative energies of 0.2-0.5 eV (e.g., Le Padellec et al, 1997;Nordhorn et al, 2011;Larson et al, 2012). The branching ratio of the second channel (RC1b) would not be expected to be large, since significant rearrangement of the bonds of the ion is required for the reaction to produce OH.…”

“…Recently, however, Fonseca dos Santos et al (2014) presented calculated DR coefficients as a function of temperature from $1 K to 5000 K for HCO + that were significantly larger than previous calculations had shown. There is less difference between the theoretical and the experimental values for the temperature dependencies of the cross sections and rate coefficients (e.g., Talbi et al, 1989;Kraemer and Hazi, 1989;Tomashevsky et al, 1998;Larson et al, 2005;Mikhailov et al, 2006;Douguet et al, 2008Douguet et al, , 2009Nordhorn et al, 2011;Pratt and Jungen, 2011;Larson et al, 2012).…”

Role of the direct mechanism in dissociative recombination of HCO+and HOC+

“…Measurements of the branching ratios show that at low collision energies, the HC bond will break [10,20,21]. Using an energy-and position-sensitive surface barrier detector the branching ratios in DR of DCO + have recently been measured as a function of the collision energy in the range 0-25 eV at the TSR ion-storage ring at the Max Planck Institute for Nuclear Physics in Heidelberg [22]. These measurements confirmed * aasal@fysik.su.se that at low collision energies, dissociative recombination of DCO + is dominated by dissociation into D + CO. For collision energies above 2 eV there is a transition into dissociation to DC + O.…”

“…Since then, it has been observed in interstellar environments in both dense [30,31] and diffuse [32] molecular clouds. In measurements on DR using the flowing afterglow technique [17] or a storage ring [22] both isomers HCO + and HOC + are believed to be present. However, so far there is no direct measurement nor theoretical computation of the cross section for DR of HOC + .…”

“…We have previously [22] studied the direct mechanism of DR of HCO + and HOC + using wave-packet propagation on the resonant states including the two radial coordinates and assuming linear geometry. We then focused on the branching ratios and obtained a qualitatively good agreement with the measured branching ratios by assuming a 9% contamination of the HOC + ion in the experiment.…”