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arXiv 1405.7802astro-ph.SRastro-ph.EPcond-mat.mtrl-sciphysics.chem-ph
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星际冰类似物的紫外光谱学。II。非极性冰分子的吸收截面

Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules

G. A. Cruz-Diaz, G. M. Muñoz Caro, Y. -J. Chen, T. -S. Yih

备注：
9 pages, 6 figures, 7 tables
发表信息：
A&A, 562, id.A120 (2014)
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摘要：

在10-20 K温度下，冷的星周区域和暗云内部的尘埃颗粒被冰幔覆盖。一个非热脱附机制被调用来解释在这些环境中的气相分子的存在下，如光致脱附引起的辐射的冰由于二次紫外光子。为了量化冰光处理的影响，需要估计冰幔中的光子吸收。在最近的工作中，我们报道了非极性分子在固相中的真空紫外（VUV）吸收截面。其目的是估计的VUV吸收截面的非极性分子冰成分，包括甲烷，二氧化碳，氮气和氧气。用透射红外光谱法原位测量了8 K下沉积的冰样品的柱密度。冰样品的真空紫外光谱收集在120-160 nm（10.33-7.74 eV）的范围内使用商业微波放电氢流灯。我们发现，正如预期的那样，固体N2具有最低的VUV吸收截面，这比其他物种，如O2，这也是homogeneous低约三个数量级。甲烷（CH 4）冰在Ly-alpha（121.6 nm）附近呈现高吸收，并且在148 nm以下不吸收。冰吸收截面的估计是必不可少的冰photoprocessing模型，并允许估计冰的光解吸率的光解吸分子的数量，每个吸收的光子在冰。

英文摘要：

Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K are covered by ice mantles. A nonthermal desorption mechanism is invoked to explain the presence of gas-phase molecules in these environments, such as the photodesorption induced by irradiation of ice due to secondary ultraviolet photons. To quantify the effects of ice photoprocessing, an estimate of the photon absorption in ice mantles is required. In a recent work, we reported the vacuum-ultraviolet (VUV) absorption cross sections of nonpolar molecules in the solid phase. The aim was to estimate the VUV-absorption cross sections of nonpolar molecular ice components, including CH4, CO2, N2, and O2. The column densities of the ice samples deposited at 8 K were measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. We found that, as expected, solid N2 has the lowest VUV-absorption cross section, which about three orders of magnitude lower than that of other species such as O2, which is also homonuclear. Methane (CH4) ice presents a high absorption near Ly-alpha (121.6 nm) and does not absorb below 148 nm. Estimating the ice absorption cross sections is essential for models of ice photoprocessing and allows estimating the ice photodesorption rates as the number of photodesorbed molecules per absorbed photon in the ice.

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