Friday, June 21, 2013

1306.4857 (S. Bovino et al.)

Modelling CH+ in the ISM: impact of new quantum depletion rates on evolutionary studies    [PDF]

S. Bovino, T. Grassi, M. Tacconi, F. A. Gianturco
We present new, accurate quantum calculations of the reaction rates of methyldyne depleted by hydrogen atoms for temperature ranging from 10 K to 1000 K. Although a wide range of calculations have been presented over the years on the chemistry of CH+, no final assessment for this reaction has been given in the literature. In this study, the negative imaginary potential (NIP) approach, which has been previously shown in other systems to provide accurate results for ionic reactions, was employed to generate quantum reaction cross sections for the depletion path: CH+ + H -> C+ + H2. The relevant rates obtained have been compared with the available experimental data and with various earlier calculations. Our results were found to be in very good agreement with the quantum close-coupling results reported by Warmbier et al. 2011 and also follow the general behaviour found from cold-trap experiment. The new rates have been then included in a sub-network we have chosen from the well-known, extensive UMIST database and their influence on the evolution of the interstellar medium environment was analysed. In particular we report results for the photon dominated regions (PDR) and for the molecular clouds (MC) conditions by varying the extinction coefficient Av. As additional tests on the relevance of our new depletion quantum rates we have run a series of models which include rates proposed by earlier works to the CH+ chemistry. The differences between the UMIST database and our updated sub-network are also discussed in some detail.
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