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arXiv 1312.4571astro-ph.GA
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CO：N2二元冰的间接紫外光脱附--一个有效的颗粒-气体过程

Indirect ultraviolet photodesorption from CO:N2 binary ices - an efficient grain-gas process

Mathieu Bertin, Edith C. Fayolle, Claire Romanzin, Hugo A. M. Poderoso, Xavier Michaut, Laurent Philippe, Pascal Jeseck, Karin I. Öberg, Harold Linnartz, Jean-Hugues Fillion

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21 pages 5 figures
发表信息：
The Astrophysical Journal, 779 (2013), 120
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摘要：

紫外线冰光解吸是一个重要的非热解吸途径，在许多星际环境中，已被调用来解释在磁盘，云和云核中的冷分子的观测。系统的实验室研究的光脱附率，在7和14 eV之间，从CO：N2二元冰，已进行了同步加速器设施SOLEIL的CONORS真空紫外光束线。光脱附光谱分析表明，光脱附过程是间接的，即脱附是由亚表面分子层中的光子吸收引起的，而实际上只有表面分子脱附。因此，二元冰中的CO和N2的光解吸光谱取决于次表层冰层中的主要物种的吸收光谱，这意味着混合和层状冰的光解吸效率和能量依赖性与纯冰相比是显着不同的。特别是，一个薄的（1-2 ML）的N2冰层上的CO将有效地淬灭CO的光脱附，而增强N2的光脱附的几个因素（相比于纯冰）时，冰暴露于一个典型的暗云UV场，这可能有助于解释不同的CO和N2 H+的分子云核心的分布。这种间接的光解吸机制也可以解释在寒冷的星际环境中观察到少量复杂有机物的现象。

英文摘要：

UV ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks, clouds and cloud cores. Systematic laboratory studies of the photodesorption rates, between 7 and 14 eV, from CO:N2 binary ices, have been performed at the DESIRS vacuum UV beamline of the synchrotron facility SOLEIL. The photodesorption spectral analysis demonstrates that the photodesorption process is indirect, i.e. the desorption is induced by a photon absorption in sub-surface molecular layers, while only surface molecules are actually desorbing. The photodesorption spectra of CO and N2 in binary ices therefore depend on the absorption spectra of the dominant species in the subsurface ice layer, which implies that the photodesorption efficiency and energy dependence are dramatically different for mixed and layered ices compared to pure ices. In particular, a thin (1-2 ML) N2 ice layer on top of CO will effectively quench CO photodesorption, while enhancing N2 photodesorption by a factors of a few (compared to the pure ices) when the ice is exposed to a typical dark cloud UV field, which may help to explain the different distributions of CO and N2H+ in molecular cloud cores. This indirect photodesorption mechanism may also explain observations of small amounts of complex organics in cold interstellar environments.

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