Experimental Studies of H¹³CO⁺ Recombining with Electrons at Energies between 2–50 000 meV

Abstract

An investigation into the dissociative recombination process for H(13)CO(+) using merged ion-electron beam methods has been performed at the heavy ion storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions of the different product channels at ∼ 0 eV collision energy to be the following: CO + H 87 ± 2%, OH + C 9 ± 2%, and O + CH 4 ± 2%. The formation of electronically excited CO in the dominant reaction channel has also been studied, and we report the following tentative branching fractions for the different CO product electronic states: CO(X (1)Σ(+)) + H, 54 ± 10%; CO(a (3)Π) + H, 23 ± 4%; and CO(a' (3)Σ(+)) + H, 23 ± 4%. The absolute cross section between ∼ 2-50 000 meV was measured and showed resonance structures between 3 and 15 eV. The cross section was fitted in the energy range relevant to astrophysics, i.e., between 1 and 300 meV, and was found to follow the expression σ = 1.3 ± 0.3 × 10(-16) E(-1.29 ± 0.05) cm(2) and the corresponding thermal rate constant was determined to be k(T) = 2.0 ± 0.4 × 10(-7)(T/300)(-0.79 ± 0.05) cm(3) s(-1). Radioastronomical observations with the IRAM 30 m telescope of HCO(+) toward the Red Rectangle yielded an upper column density limit of 4 × 10(11) cm(-2) of HCO(+) at the 1σ level in that object, indicating that previous claims that the dissociative recombination of HCO(+) plays an important role in the production of excited CO molecules emitting the observed Cameron bands in that object are not supported.

Scattering matrix approach to the dissociative recombination of HCO+ and N2H+

“…A comparison with several theoretical and experimental results is given in the figures as well, and discrepancies between the different experimental data also exist in this case. In particular, the cross sections measured in a merged beam experiment by Le Padellec et al 14 and in a recent CRYRING storage ring experiment by Hamberg et al 54 can disagree up to a factor 2-3 in some energy regions. In 6.…”

“…The theoretical DR cross section obtained in this study for pure HCO + (red solid line) and for a mixture (red dashed-dotted line) of the HCO + (90%) and HOC + (10%) isomers. For comparison, we also plotted results of two experiments, merged beam (purple dots) 14 and CRYRING storage ring (blue dots), 54 and previous theoretical calculations (green solid and black dashed lines) 21,22 based on a quantum defect approach. The first vibrational thresholds of each normal mode of HCO + and of the degenerate mode of HOC + are indicated by arrows.…”

“…Error bars correspond to the uncertainty in the CRYRING experiment. 54 Fig . 6, the theoretical DR cross section of HCO + agrees well with the CRYRING experimental data on a wide energy range within 10%-20% for the major part of the energies above 0.02 eV.…”

Simplified model to describe the dissociative recombination of linear polyatomic ions of astrophysical interest

“…Also shown in black solid line, the data of a previous theoretical study by Douguet et al [27]. The experimental data are from a merged beam experiment of Le Padelec et al [36] and the CRYRING storage ring experiment of Hamberg et al [37]. Previous theoretical cross sections are also shown for comparison.…”

On the Energetics of the Reaction and Some Astrochemical Implications

“…Reaction (2), DR of HCO + , has been extensively studied both theoretically and experimentally (for a review see Hamberg et al 2014). Though some issues remain, it is thought to be relatively well understood.…”