We measure the band strengths in the far-infrared region of interstellar ice analogs of astrophysically relevant species, such as H$_2$O, CO$_2$, CH$_3$OH, and NH$_3$, deposited at low temperature (8-10 $\mathrm{K}$), followed by warm-up, to induce amorphous-crystalline phase transitions when relevant. The spectra of pure H$_2$O, NH$_3$, and CH$_3$OH ices have been measured in the near-, mid- and far-infrared spectroscopic regions using the Interstellar Astrochemistry Chamber (ISAC) ultra-high-vacuum setup. In addition, far-infrared spectra of NH$_3$ and CO$_2$ were measured using a different set-up equipped with a bolometer detector. Band strengths in the far-infrared region were estimated using the corresponding near- and mid-infrared values as a reference. We also performed theoretical calculations of the amorphous and crystalline structures of these molecules using solid state computational programs at density functional theory (DFT) level. Vibrational assignment and mode intensities for these ices were predicted. Infrared band strengths in the 25-500 $μ$m range have been determined for the considered ice samples by direct comparison in the near- and mid-infrared regions. Our values were compared to those we calculated from the literature complex index of refraction. We found differences of a factor of two between the two sets of values. The calculated far-infrared band strengths provide a benchmark for interpreting the observational data from future space telescope missions, allowing the estimation of the ice column densities.
Three-dimensional off-lattice Monte Carlo kinetics simulations of interstellar grain chemistry and ice structure
提出了第一个星际尘埃颗粒表面化学的非格点蒙特卡罗动力学模型。所有表面粒子的位置都是根据相邻原子和分子的成对相互作用产生的局部势最小值明确确定的，而不是通过预定义的晶格结构。该模型能够模拟任何任意的尘埃颗粒形态的化学动力学，由用户定义的每个单独的尘埃颗粒原子的位置。设计了一种简单的方法，用于确定最可能的扩散途径及其相关的表面物种的能垒。该模型适用于一个小的，理想化的尘埃颗粒，采用各种气体密度和使用一个小的化学网络。氢原子和氧原子附着在颗粒上，产生H2O、H2、O2和H2 O2。非格点方法允许冰结构的自由发展，冰地幔孔隙度被发现是依赖于气体密度，控制吸积速率。2 x 10^{4} cm^{-3}的气体密度，适合暗星际云，被发现产生一个相当光滑和无孔的冰地幔。在所有密度下，在颗粒上形成的H2分子聚集在分裂冰结节的裂缝中，以及微孔中（其极端向内的曲率产生强烈的局部势能极小值）。在高密度模型中产生的较大孔隙通常不填充H2。水分子直接沉积在颗粒上表明，以这种方式形成的无定形冰可能比通过表面化学形成的星际冰更加多孔。
Water enhances the formation of refractory sulfur in interstellar ices
Centro de Astrobiología (CAB), INTA-CSIC（西班牙国家航空航天技术研究所-西班牙国家科学研究委员会天体生物学中心）；Departamento de Física de la Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid（马德里康普顿斯大学物理科学学院地球与天体物理学系）；Instituto de Química Física Blas Cabrera (CSIC)（西班牙国家科学研究委员会布拉斯·卡布雷拉物理化学研究所）；Department of Physics, National Central University（中原大学物理系）
Formation of unsaturated hydrocarbons in interstellar ice analogs by cosmic rays
研究了高电荷态高能离子（219 MeV O^{7+}和632 MeV Ni^{24+}）处理纯c-C6 H 12（环己烷）和混合H2O：NH3：c-C6 H 12（1：0.3：0.7）冰时C-C双键和三键的形成。这些实验模拟了星际冰类似物中由中等质量和重离子宇宙射线引起的物理化学。这些测量是在法国卡昂的重离子加速器GANIL（Grand Escheratéur National d 'Ions Lourds）的高真空室内进行的。将气体样品沉积在预先冷却至13 K的抛光CsI衬底上。在不同的离子注量下，通过傅里叶变换红外（FTIR）光谱法进行原位分析。测定了环己烷在天体物理环境中的离解截面和半衰期。轰击冰和年轻恒星源的光谱之间的比较表明，在这些环境中的颗粒的初始成分应该包含H2O，NH3，CO（或CO2），简单的烷烃和CH 3OH的混合物。在放化产物中发现了一些含有双键或三键的化合物，如己烯、环己烯、苯、OCN-、CO、CO2以及一些脂肪族和芳香族烯烃和炔烃。结果表明，另一种方案的生产不饱和烃和可能的芳环（通过脱氢过程）在星际冰引起宇宙射线轰击。
Synthesis of the first nitrogen-heterocycles in interstellar ice analogs containing methylamine (CH$_3$NH$_2$) exposed to UV radiation: Formation of trimethylentriamine (TMT, c-(-CH$_2$-NH)$_3$) and hexamethylentetramine (HMT, (CH$_2$)$_6$N$_4$)
The hunt for formamide in interstellar ices: A toolkit of laboratory infrared spectra in astronomically relevant ice mixtures and comparisons to ISO, Spitzer, and JWST observations
