Publication
Reference
Abdulgalil A. G. M., Marchione D., Thrower J. D., Collings M. P., McCoustra M. R. S., Islam F., Palumbo M. E., Congiu E., Dulieu F. (2013). Laboratory studies of electron and ion irradiation of solid acetonitrile ($CH_3CN$). Phil. Trans. R. Soc. A, 371, 20110586.
Names
  • A. G. M. Abdulgalil
  • D. Marchione
  • J. D. Thrower
  • M. P. Collings
  • M. R. S. McCoustra
  • F. Islam
  • M. E. Palumbo
  • E. Congiu
  • F. Dulieu
Article and keywords
Title
Laboratory studies of electron and ion irradiation of solid acetonitrile ($CH_3CN$)
Abstract
The structure and bonding of solid acetonitrile ($CH_3CN$) films on amorphous silica are studied, and chemical and physical processes under irradiation with 200 keV protons and 250-400 eV electrons are quantified using transmission infrared spectroscopy, reflection-absorption infrared spectroscopy and temperature-programmed desorption, with the assistance of basic computational chemistry and nuclear materials calculations. The thermal desorption profiles are found to depend strongly on the balance between $CH_3CN$-surface and $CH_3CN-CH_3CN$ interactions, passing from a sub-monolayer regime (binding energy: $35-50~kJ.mol^{-1}$) to a multilayer regime (binding energy: $38.2\pm1.0~kJ.mol^{-1}$) via a fractional order desorption regime characteristic of islanding as the coverage increases. Calculations using the SRIM code reveal that the effects of the ion irradiation are dominated by electronic stopping of incident protons, and the subsequent generation of secondary electrons. Therefore, ion irradiation and electron irradiation experiments can be quantitatively compared. During ion irradiation of thicker $CH_3CN$ films, a cross section for secondary electron-promoted chemical destruction of $CH_3CN$ of $4(\pm1)~10^{-18} cm^2$ was measured, while electron-promoted desorption was not detected. A significantly higher cross section for electron-promoted desorption of $0.82-3.2~10^{-15} cm^2$ was measured during electron irradiation of thinner $CH_3CN$ films, while no chemical products were detected. The differences between the experimental results can be rationalized by recognizing that chemical reaction is a bulk effect in the $CH_3CN$ film, whereas desorption is a surface sensitive process. In thicker films, electron-promoted desorption is expected to occur a rate that is independent of the film thickness; i.e. show zeroth-order kinetics with respect to the surface concentration.
Keywords
spectroscopy, absorbance spectra, data analysis, band position, band vibration mode, mid-IR, irradiation process - cosmic rays, irradiation process - electrons, amorphous, crystalline, molecular solid, nitrile, CH3CN, acetonitrile, Titan
Content
spectral data, band list data, phase
Year
2013
Journal
Philosophical Transactions of the Royal Society A
Volume
371
Number
1994
Pages
20110586
Pages number
20
Document type
article
Publication state
published
Doi
10.1098/rsta.2011.0586
Identifiers