Diagnostics and modeling of cold plasmas with high hydrogen content; applications to molecular astrophysics

Abstract

Cold plasmas of molecular precursors produced in low pressure glow discharges involve intricate mechanisms of great interest in many scientific and technological fields, such as thin film growth, surface conditioning and so on. In particular, hydrogen containing cold plasmas are currently used in microelectronic devices production, can simulate the border conditions of plasmas generated in fusion reactors, and are efficient sources of very reactive radicals and ions, whose study contributes to clarify the appearance of complex compounds in different regions of interstellar molecular clouds or in Jovian planet ionospheres.

In this work, low pressure glow discharges of mixtures of hydrogen with simple molecules and atoms are experimentally diagnosed, and the main mechanisms controlling their behavior are elucidated by kinetic modeling. According to theoretical predictions supported by experimental data, the formation of new molecular species takes place mainly at the reactor surfaces and competes with the fast wall recycling of the precursors, which are previously dissociated by electron impact. On the other hand, the ion distributions result mainly from the balance between electron impact ionizations, which depend markedly on electron energies, and ion-molecule reactions in gas phase, for which the proton affinity of the different neutral species plays a key role.

The first detection of the deuterated ammonium ion (NH3D+) in the interstellar medium, and the refined spectroscopic characterization of ArH+, the first noble gas molecule found in space, exemplify the successful interaction between plasma spectroscopy and astronomical observations.