Formation of molecular hydrogen from methane ice

Jiao He, Kun Gao, Gianfranco Vidali, Chris J. Bennett, Ralf I. Kaiser

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

To study the formation of molecular hydrogen in the wake of the processing of interstellar ices by energetic cosmic-ray particles, we investigated the interaction of energetic electrons, as formed in the track of galactic cosmic-ray particles, with deuterated methane ices (CD4) at 11 K. The energetic electrons mimic energy-transfer processes that occur in the track of the trajectories of energetic cosmic-ray particles; deuterated methane ice was utilized to discriminate the molecular deuterium (m/z = 4) formed during the radiation exposure from the residual molecular hydrogen gas (m/z = 2) released inside the ultrahigh vacuum scattering chamber from outgassing of the stainless steel material. The ices were characterized online and in situ using Fourier transform infrared spectroscopy, while the evolution of the molecular deuterium (D2) into the gas phase was monitored using a mass spectrometer. A mass spectrometric signal proportional to the number density of the deuterium molecules generated inside the ice and released during the irradiation was analyzed kinetically using a set of coupled rate equations. From the fit to the experimental data, we obtain activation energies for the diffusion of atomic deuterium (E0 = 37 ± 1 meV), and for the desorption of atomic (E1 = 32 ± 1 meV) and molecular deuterium (E2 = 32 ± 1 meV). These energies are placed in context and then transferred to atomic and molecular hydrogen to yield astrophysically relevant data. The experimental yield of molecular deuterium is then used to calculate the formation rate of molecular hydrogen due to cosmic-ray interaction with ice-covered grains in dense clouds.

Original languageEnglish (US)
Pages (from-to)1656-1662
Number of pages7
JournalAstrophysical Journal
Volume721
Issue number2
DOIs
StatePublished - Oct 1 2010

Keywords

  • Astrochemistry
  • Cosmic rays
  • ISM: molecules
  • Infrared: ISM
  • Methods: laboratory
  • Molecular processes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint Dive into the research topics of 'Formation of molecular hydrogen from methane ice'. Together they form a unique fingerprint.

  • Cite this