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.