A series of computations based on multichannel quantum defect theory have been performed in order to produce the cross sections of rotational transitions (excitationsto 10) and of their competitive process, the dissociative recombination, induced by collisions of HD + ions with electrons in the energy range 10 −5 to 0.3 eV. Maxwell anisotropic rate coefficients, obtained from these cross sections in the conditions of the Heidelberg Test Storage Ring (TSR) experiments (k B T t = 2.8 meV and k B T l = 45 μeV), have been reported for those processes in the same electronic energy range. Maxwell isotropic rate coefficients have been presented as well for electronic temperatures up to a few hundred Kelvins. Very good overall agreement is found between our results for rotational transitions and the former theoretical computations as well as with experiment. Furthermore, due to the full rotational computations performed, the accuracy of the resulting dissociative recombination cross sections is improved considerably.

We present a detailed theoretical study of the rotational excitation of CH + due to reactive and nonreactive collisions involving C + ( 2 P), H 2 , CH + , H and free electrons. Specifically, the formation of CH + proceeds through the reaction between C + ( 2 P) and H 2 (ν H 2 = 1, 2), while the collisional (de)excitation and destruction of CH + is due to collisions with hydrogen atoms and free electrons. State-to-state and initial-state-specific rate coefficients are computed in the kinetic temperature range 10-3000 K for the inelastic, exchange, abstraction and dissociative recombination processes using accurate potential energy surfaces and the best scattering methods. Good agreement, within a factor of 2, is found between the experimental and theoretical thermal rate coefficients, except for the reaction of CH + with H atoms at kinetic temperatures below 50 K. The full set of collisional and chemical data are then implemented in a radiative transfer model. Our Non-LTE calculations confirm that the formation pumping due to vibrationally excited H 2 has a substantial effect on the excitation of CH + in photon-dominated regions. In addition, we are able to reproduce, ⋆ alexandre.faure@univ-grenoble-alpes.fr. Europe PMC Funders GroupAuthor Manuscript Mon Not R Astron Soc. Author manuscript; available in PMC 2017 July 06. Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts within error bars, the far-infrared observations of CH + toward the Orion Bar and the planetary nebula NGC 7027. Our results further suggest that the population of ν H 2 = 2 might be significant in the photon-dominated region of NGC 7027.

No abstract

We used the multichannel quantum defect theory to compute cross sections and rate coefficients for the dissociative recombination of CH + initially in its lowest vibrational level v i + = 0 with electrons of incident energy below 0.2 eV. We have focused on the contribution of the 2 2 Π state which is the main dissociative recombination route at low collision energies. The final cross section is obtained by averaging the relevant initial rotational states ( N i + = 0 , ⋯ , 10 ) with a 300 K Boltzmann distribution. The Maxwell isotropic rate coefficients for dissociative recombination are also calculated for different initial rotational states and for electronic temperatures up to a few hundred Kelvins. Our results are compared to storage-ring measurements.

We review the study of dissociative recombination and rovibrational excitation of diatomic and small polyatomic molecular ions initiating complex organic molecules formation. In particular, we show how multichannel quantum defect theory (MQDT) and R-matrix methods are used to compute cross-sections and rate coefficients for cations in well-defined rovibrational levels of the ground electronic state, from sub-meV up to a few eV collision energies. The most recent MQDT results are compared either with other theoretical data or with measured data obtained in storage-ring experiments.