Experimental Studies of H~(13)CO~+ Recombining with Electrons at Energies between 2-50 000 meV

摘要

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 ~1Σ~+) + H, 54 ± 10%; CO(a ~3Π) + H, 23 ± 4%; and CO(a′ ~3Σ~+) + 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.