Opened 4 years ago

#266 new enhancement

update Si CX ionization

Reported by: Gary J. Ferland Owned by: nobody
Priority: good to do Milestone:
Component: atomic/molecular data base Version: trunk
Keywords: Cc:

Description

Title:	
Reducing Si population in the ISM by charge exchange collisions with He+: a 
quantum modelling of the process
Authors:	
Satta, M.; Grassi, T.; Gianturco, F. A.; Yakovleva, S. A.; Belyaev, A. K.
Affiliation:	
AA(CNR-ISMN and University of Rome `Sapienza', P. le A. Moro 5, I-00183 Rome, 
Italy; mauro.satta@uniroma1.it), AB(Department of Chemistry and CNISM, University
 of Rome `Sapienza', P.le A. Moro 5, I-00161 Rome, Italy), AC(Department of 
Chemistry and CNISM, University of Rome `Sapienza', P.le A. Moro 5, I-00161 
Rome, Italy), AD(Department of Theoretical Physics and Center for Advanced Study, 
Herzen University, St. Petersburg 191186, Russia), AE(Department of Theoretical 
Physics and Center for Advanced Study, Herzen University, St. Petersburg 191186,
 Russia)

Publication:	
Monthly Notices of the Royal Astronomical Society, Advance Access. 12 pp. (MNRAS Homepage)
Publication Date:	
10/2013
Origin:	
OUP
Astronomy Keywords:	
atomic processes, molecular processes, ISM: evolution
Abstract Copyright:	
2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:	
10.1093/mnras/stt1771
Bibliographic Code:	
2013MNRAS.tmp.2453S
Abstract

The possible losses of silicon atom population during star-forming evolution and in
 the (photon-dominated region) PDR environments of the interstellar medium (ISM)
 can have different origins, one being the charge exchange (CE) encounter with the
 helium cations (Si + He+) one of the most abundant species in those
 environments. This work investigates the different features of the likely interaction
 potentials leading to asymptotic partners like Si, Si+, Si++ and He or He+, in order
 to determine the influence of more accurate cross-sections on the chemical
 evolution of the ISM. We analyse the behaviour of interacting Si and He atoms by
 using ab initio quantum molecular methods. To obtain the corresponding
 transition probabilities, we employ a simple sequential grouping of single-crossing
 Landau-Zener events, and the time-dependent rate coefficients for the CE
 processes involved are obtained over a broad range of the gas temperatures. The
 results are seen to differ substantially from an earlier Langevin-type modelling of
 such process and further suggest a much more complex variety of possible
 molecular evolution mechanisms. We find, in fact, the unexpected presence of
 electron shake-off effects leading to Si++ generation yielding to emission of an
 electron, which has never been considered before and that, although with markedly
 smaller cross-sections, can indeed contribute to Si losses after the primary CE 
event. The consequences of these novel findings are tested on evolutionary model 
calculations and the results discussed in detail.

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