A novel approach to measure photodesorption rates of interstellar ice analogues - The photodesorption rate of CO ice reinvestigated
A novel approach to measure photodesorption rates of interstellar ice analogues - The photodesorption rate of CO ice reinvestigated
复制标题
测量星际冰类似物光解吸速率的新方法 - 重新研究 CO 冰的光解吸速率
DOI：
--
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
H. Linnartz
中科院分区：
文献类型：
--
作者：
D. Paardekooper;G. Fedoseev;A. Riedo;H. Linnartz
语境。近年来，在专门的实验室实验中已经确定了许多不同星际冰类似物的光解吸速率。这些速率对于模拟非热解吸过程非常重要，例如影响物种的气相丰度并确定原行星盘中光致雪线的位置。然而，不同的小组使用类似的实验发现了显着偏差的光解吸值。目标。这里引入了一种新的测量概念，允许按照不同的实验方法确定光解吸速率。使用纯二氧化碳冰的例子证明了该方法的潜力，这种固体在已发表的结果中给出了最显着的差异。方法。新的实验方法使用激光解吸后电离飞行时间质谱法。它基于这样的概念：通过激光诱导冰解吸获得的羽流的物理和几何特性直接取决于原始冰的厚度。这允许将冰损失确定为真空紫外线（VUV）注量的函数，从而产生光解吸速率。该方法还有一个额外的优点，即它可以记录所有冰种，包括真空紫外线照射产生的光产物。因此，这里介绍的方法也适用于确定混合冰的总体光解吸速率。结果。 20 K 时 CO 冰的光解吸速率已确定为每个入射 VUV 光子 (1.4 ± 0.7) × 10 -3 个分子。该结果与现有的实验和理论值进行了比较，并讨论了天文相关性。
Context. In recent years photodesorption rates have been determined in dedicated laboratory experiments for a number of different interstellar ice analogues. These rates are important in order to model non-thermal desorption processes that, for example, affect gas-phase abundances of species and determine the position of photo-induced snow lines in protoplanetary disks. However, different groups using similar experiments have found significant deviating photodesorption values. Aims. Here a new measurement concept is introduced that allows photodesorption rates to be determined following a different experimental approach. The potential of this method is demonstrated using the example of pure CO ice, the solid that gives the most striking discrepancies in the published results. Methods. The new experimental approach uses laser desorption post-ionisation time-of-flight mass spectrometry. It is based on the concept that the physical and geometrical properties of the plume obtained by laser induced desorption of the ice directly depend on the original ice thickness. This allows the ice loss to be determined as function of vacuum ultraviolet (VUV) fluence, which results in a photodesorption rate. The method has the additional advantage that it records all ice species, including photoproducts generated by the VUV irradiation. As a consequence, the method introduced here is also suited to determine the overall photodesorption rate of mixed ices. Results. The photodesorption rate for CO ice at 20 K has been determined as (1.4 ± 0.7) × 10 -3 molecules per incident VUV photon. This result is compared to existing experimental and theoretical values and the astronomical relevance is discussed.