Production and kinetics of molecular ions of astrophysical interest

AMOC 2015, Anharmonicity in médium-sized molecules and cluster, CSIC, Madrid (Spain), 26-30 April 2015; http://tct1.iem.csic.es/AMOC2015.htmThanks to their spectroscopic fingerprints, more than 200 molecular species have been detected up to date in space. Some of them are quite ¿exotic¿ and unstable under normal terrestrial conditions, such as a good number of protonated ions (H3+, ArH+, N2H+, H3O+¿ and some of their isotopomers). The spectroscopic characterization of these species in laboratories provides very useful data for the astrophysical research. Molecular ions for spectroscopic studies are usually produced in laboratories by cold plasmas generated in low pressure electrical discharges. The investigation of the plasma kinetics is of great interest for the optimization of the desired ion densities and also for the identification of likely pathways of generation and destruction of these ions in space. In this work, the formation of ArH+ and NH4+ in low pressure discharges of Ar + H2 and N2 + H2 mixtures, respectively, is studied both experimentally and theoretically [1,2]. The dependencies of the different ion densities on electron temperature, gas pressure, and relative concentration of the precursors are characterized. The kinetic models developed to explain the present experimental data, which include electron impact ionizations and dissociations, gas phase barrier-less bimolecular reactions and surface processes, are able to reproduce reasonably well the observed results. Electrical discharges similar to those studied here have been used in our laboratory for the measurement of the high resolution IR spectrum of the ¿3 band of NH3D+ [3] and the vibration rotation spectrum of 36ArH+ and 38ArH+ [4], with higher precision and with more measured lines than previously available in the literature. All these ions have been recently discovered in space [5,6]. [1] E. Carrasco, M. Jiménez-Redondo, I. Tanarro, V. J. Herrero, PCCP, 13, 19561 (2011) [2] M. Jiménez-Redondo, M. Cueto, J. L. Doménech et al, RSC Advances, 4, 62030 (2014). [3] J. L. Doménech, M. Cueto, V. J. Herrero, I. Tanarro et al, ApJL, 771, L11 (2013) [4] M. Cueto, J. Cernicharo M. J. Barlow, B. M. Swinyard et al, ApJL, 783, L5 (2014). [5] J. Cernicharo, B. Tercero, A. Fuente, , J. L. Doménech et al, ApJL, 771, L10 (2013) [6] M. J. Barlow, B. M. Swinyard, P. J. Owen et al, Science, 342, 1343 (2013)The authors acknowledge the financial support from the Spanish MINECO through the grants SD2009-00038 (Consolider Astromol), FIS2012-38175 and FIS2013-48087-C2-1-P. Additional funding from the ERC-2013-Syg 610256-NANOCOSMOS project is also aknowledged.Peer Reviewe