Pilling S, Rocha W R M, Freitas F M, da Silva P A
Laboratório de Astroquímica e Astrobiologia (LASA), Universidade do Vale do Paraíba (UNIVAP) Av. Shishima Hifumi, 2911 São José dos Campos SP Brazil
Departamento de Física, Instituto Tecnólogico de Aeronáutica, ITA - DCTA Vila das Acácias São José dos Campos 12228-900 SP Brazil.
RSC Adv. 2019 Sep 13;9(49):28823-28840. doi: 10.1039/c9ra04585f. eCollection 2019 Sep 9.
Soft X-rays are an important agent for chemical processing in the Solar System and in the interstellar medium. The photolysis and photodesorption processes of HO-rich ices triggered by soft X-rays was, experimentally, addressed in this paper. The experiments were performed at the Brazilian synchrotron facility LNLS/CNPEN employing broadband radiation (from 6 to 2000 eV; mainly soft X-rays and a small fraction of VUV) in solid samples at temperatures of 20 and 80 K. The icy samples were monitored by infrared spectroscopy. We determined the effective destruction cross section (in the order 10 cm) as well as the formation cross section for the new species produced after the irradiation. Among them, we list OCN, CO, CO, CHOH, HO, HCOO, NH , HCONH and CHHCO, mostly formed in the experiment at 80 K. The chemical equilibrium stage was characterized and molecular abundances were quantified. In addition, we discuss a methodology to estimate the amount of unknown species in the ice produced by photolysis. The samples reach chemical equilibrium at fluences around 2-3 × 10 cm. Timescales for reaching chemical equilibrium in space environments illuminated by X-rays were given, as well as the desorption yields induced by X-rays. The astrophysical implication on the surface chemistry and desorption processes at the moon Enceladus are provided.
软X射线是太阳系和星际介质中化学加工的重要媒介。本文通过实验研究了由软X射线引发的富含HO的冰的光解和光脱附过程。实验在巴西同步加速器设施LNLS/CNPEN进行，使用宽带辐射（6至2000电子伏特；主要是软X射线和一小部分真空紫外光）照射处于20K和80K温度的固体样品。通过红外光谱对冰样进行监测。我们确定了有效破坏截面（约为10平方厘米）以及辐照后产生的新物种的形成截面。其中，我们列出了OCN、CO、CO、CHOH、HO、HCOO、NH、HCONH和CHHCO，这些大多是在80K的实验中形成的。对化学平衡阶段进行了表征，并对分子丰度进行了量化。此外，我们讨论了一种估算光解产生的冰中未知物种数量的方法。样品在通量约为2 - 3×10平方厘米时达到化学平衡。给出了在X射线照射的空间环境中达到化学平衡的时间尺度，以及X射线诱导的脱附产率。还提供了对土卫二表面化学和脱附过程的天体物理学意义。
