Comparison of UV and high-energy ion irradiation of methanol:ammonia ice

¹ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir, km 4, Torrejón de Ardoz, 28850 Madrid, Spain
e-mail: munozcg@cab.inta-csic.es
² CNRS-INSU, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France
³ Université Paris Sud, Institut d’Astrophysique Spatiale, UMR 8617, bâtiment 121, 91405 Orsay, France
⁴ Centre de Recherche sur les Ions, les Matériaux et la Photonique (CEA/CNRS/ENSICAEN/Université de Caen-Basse Normandie), CIMAP – CIRIL – Ganil, Boulevard Henri Becquerel, BP 5133, 14070 Caen Cedex 5, France

Received: 5 November 2013
Accepted: 30 April 2014

Abstract

Aims. The main goal of this work is to compare the effects induced in ices of astrophysical relevance by high-energy ions, simulating cosmic rays, and by vacuum ultraviolet (UV) photons.

Methods. This comparison relies on in situ infrared spectroscopy of irradiated CH₃OH:NH₃ ice. Swift heavy ions were provided by the GANIL accelerator. The source of UV was a microwave-stimulated hydrogen flow discharge lamp. The deposited energy doses were similar for ion beams and UV photons to allow a direct comparison.

Results. A variety of organic species was detected during irradiation and later during ice warm-up. These products are common to ion and UV irradiation for doses up to a few tens of eV per molecule. Only the relative abundance of the CO product, after ice irradiation, was clearly higher in the ion irradiation experiments.

Conclusions. For some ice mixture compositions, the irradiation products formed depend only weakly on the type of irradiation, swift heavy ions, or UV photons. This simplifies the chemical modeling of energetic ice processing in space.