Radiation chemistry in ammonia-water ices

Loeffler, M. J.; Raut, U.; Baragiola, R. A.

doi:doi:10.1063/1.3308484

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The single donator-single acceptor hydrogen bonding structure in water probed by Raman spectroscopy

In this work, the Raman spectra of aqueous C12E5 solutions are recorded and utilized to demonstrate the existence of single donator-single acceptor (DA) hydrogen bonding in water. From Raman OH stretching bands of aqueous C12E5 solutions, the relative intensity of 3430 cm−1 subband increases with C12E5 concentrations. For confined water, the DA hydrogen bonding can be expected to be the important hydrogen bonding species. Therefore, the 3430 cm−1 component can be ascribed to OH vibration engage...

Proton disorder and the dielectric constant of type II clathrate hydrates

Computational studies are presented examining the degree of proton disorder in argon and molecular hydrogen sII clathrate hydrates. Results are presented using a variety of model potentials for the dielectric constant, the proton order parameter, and the molecular volume for the clathrate systems. The dielectric constant for the clathrate systems is found to be lower than the dielectric constant of ice in all models. The ratio of the clathrate to ice dielectric constant correlates well with the...

We studied the effects of 100 keV proton irradiation on films of ammonia-water mixtures between 20 and 120 K. Irradiation destroys ammonia, leading to the formation and trapping of H₂, N₂, NO, and N₂O, the formation of cavities containing radiolytic gases, and ejection of molecules by sputtering. Using infrared spectroscopy, we show that at all temperatures the destruction of ammonia is substantial, but at higher temperatures (120 K), it is nearly complete ( ∼ 97% destroyed) after a fluence of 10¹⁶ ions/cm². Using mass spectroscopy and microbalance gravimetry, we measure the sputtering yield of our sample and the main components of the sputtered flux. We find that the sputtering yield depends on fluence. At low temperatures, the yield is very low initially and increases quadratically with fluence, while at 120 K the yield is constant and higher initially. The increase in the sputtering yield with fluence is explained by the formation and trapping of the ammonia decay products, N₂ and H₂, which are seen to be ejected from the ice at all temperatures.

Article Outline

INTRODUCTION
EXPERIMENTAL SETUP
RESULTS
1. IR spectroscopy
2. Sputtering
DISCUSSION
1. Radiochemical pathways
2. DB formation
3. Identification of the 1505 cm⁻¹ band
4. Temperature dependence of IR absorption of H₂ and N₂
5. Quantification of ammonia destruction
6. Sputtering
7. Astrophysical implications: Charon and Enceladus
CONCLUSIONS

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KEYWORDS and PACS

Keywords

ammonia, infrared spectra, mass spectroscopic chemical analysis, microbalances, mixtures, proton effects, radiation chemistry, sputtering, water

PACS

79.20.Rf

Atomic, molecular, and ion beam impact and interactions with surfaces
78.30.Hv

Other nonmetallic inorganics
61.82.-d

Radiation effects on specific materials
61.80.Jh

Ion radiation effects

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3308484

PUBLICATION DATA

ISSN

0021-9606 (print)

1089-7690 (online)

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American Institute of Physics

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