Peláez R J, Maté B, Tanarro I, Molpeceres G, Jiménez-Redondo M, Timón V, Escribano R, Herrero V J
Instituto de Estructura de la Materia (IEM-CSIC), Serrano 121-123, 28006, Madrid, Spain.
Centro de Física da Universidade do Minho, Universidade do Minho, 4710-057, Braga, Portugal.
Plasma Sources Sci Technol. 2018 Mar 14;27:035007. doi: 10.1088/1361-6595/aab185.
Interstellar (IS) dust analogs, based on amorphous hydrogenated carbon (a-C:H) were generated by plasma deposition in RF discharges of CH + He mixtures. The a-C:H samples were characterized by means of secondary electron microscopy (SEM), infrared (IR) spectroscopy and UV-visible reflectivity. DFT calculations of structure and IR spectra were also carried out. From the experimental data, atomic compositions were estimated. Both IR and reflectivity measurements led to similar high proportions (≈ 50%) of H atoms, but there was a significant discrepancy in the sp/sp hybridization ratios of C atoms (sp/sp = 1.5 from IR and 0.25 from reflectivity). Energetic processing of the samples with 5 keV electrons led to a decay of IR aliphatic bands and to a growth of aromatic bands, which is consistent with a dehydrogenation and graphitization of the samples. The decay of the CH aliphatic stretching band at 3.4 µm upon electron irradiation is relatively slow. Estimates based on the absorbed energy and on models of cosmic ray (CR) flux indicate that CR bombardment is not enough to justify the observed disappearance of this band in dense IS clouds.
基于非晶氢化碳（a-C:H）的星际（IS）尘埃类似物是通过在CH + He混合物的射频放电中进行等离子体沉积生成的。通过二次电子显微镜（SEM）、红外（IR）光谱和紫外-可见反射率对a-C:H样品进行了表征。还进行了结构和红外光谱的密度泛函理论（DFT）计算。根据实验数据估算了原子组成。红外和反射率测量都得出了相似的高比例（≈50%）的氢原子，但碳原子的sp/sp杂化比存在显著差异（红外得出的sp/sp = 1.5，反射率得出的sp/sp = 0.25）。用5 keV电子对样品进行高能处理导致红外脂肪族带衰减，芳香族带增长，这与样品的脱氢和石墨化一致。电子辐照下3.4 µm处CH脂肪族伸缩带的衰减相对较慢。基于吸收能量和宇宙射线（CR）通量模型的估算表明，CR轰击不足以解释在致密星际云中观察到的该谱带消失现象。
