Laboratory studies of the infrared spectral properties of CO in astrophysical ices.
Laboratory studies of the infrared spectral properties of CO in astrophysical ices.
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天体物理冰中二氧化碳的红外光谱特性的实验室研究。
DOI：
10.1086/166395
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
G. Valero
中科院分区：
文献类型：
--
作者：
S. A. Sandford;L. Allamandola;A. Tielens;G. Valero
对许多类似天体物理冰的实验室光谱分析表明，在2137厘米-1(4.679微米)附近的固态CO基准带的准确位置、宽度和轮廓可以提供有关在冰增积阶段以及在任何随后的热过程和辐射暴露期间存在的物理条件的重要信息。在所研究的冰中，CO峰的位置从2134到2144厘米-1(4.686到4.664微米)，带宽从2.1到20厘米-1以上，这取决于冰的组成。在以H2O为主的冰基质中，CO峰落在2136.7 cm-1处，半峰宽约为9 cm-1，在2152 cm-1处有一个明显的边带。这种边带和叠加在主带上的次要结构是由捕获在不同基质位置的CO引起的。这些特征提供了有关冰的热和辐射历史的信息。星际光谱中的固体CO谱带通常由宽(12厘米-1)和窄(5厘米-1)组分组成。我们确定了CO的广泛组分，其中CO紧密混合在以极性分子为主的基质中，其中H2O可能是主要组分。对星际和实验室波段分布的检查表明，这些冰中非杨树杂质的丰度必须小于10%，或者这些冰已经过热退火或经紫外线辐射处理。狭窄的成分很可能来自由二氧化碳等非极性分子主导的谷壳。这些成分反映了视线上云层区域的物理和化学条件的差异。实验室对富含H2O的冰中CO基团的吸收强度的测定表明，过去使用的值大约太低了60%，而且以前确定的大多数固态CO柱密度被系统性地高估了。实验室研究中观测到的CO波段丰富的光谱行为清楚地表明，未来在2200-2100厘米-1范围内的高质量天文光谱可以产生丰富的新信息，并为天体物理冰的性质提供更深入的见解。
Analysis of laboratory spectra of numerous astrophysical ice analogs demonstrates that the exact band position, width, and profile of the solid state CO fundamental near 2137 cm-1 (4.679 microns) can provide important information on the physical conditions present during the ice accretion phase as well as during any subsequent thermal processes and radiation exposure. In the ices studied, the CO peak position varies from 2134 to 2144 cm-1 (4.686 to 4.664 microns) and the band width from 2.1 to over 20 cm-1 depending on the composition of the ice. In an ice matrix dominated by H2O, the CO peak falls at 2136.7 cm-1, has a full width at half-maximum of about 9 cm-1, and shows a prominent sideband at 2152 cm-1. This sideband and minor structure superposed on the main band arise from CO trapped in different matrix sites. These features provide information concerning the thermal and radiation history of the ice. The solid CO band in interstellar spectra often has contributions from broad (12 cm-1) and narrow (5 cm-1) components. We identify the broad component with CO intimately mixed in matrices dominated by polar molecules, of which H2O is likely to be the major component. Examination of the interstellar and laboratory band profiles shows that either the abundance of nonpoplar impurities in these ices must be less than 10% or the ices have been thermally annealed or processed by ultraviolet radiation. The narrow component is likely to originate from grain mantles dominated by nonpolar molecules such as CO2. These components reflect differences in the physical and chemical conditions in regions of the cloud along the line of sight. Laboratory determination of the absorption strength of the CO fundamental in H2O-rich ices showed that the value used in the past was approximately 60% too low and that most previously determined solid-state CO column densities have been systematically overestimated. The rich spectral behavior of the CO band observed in the laboratory studies clearly indicates that future high-quality astronomical spectra in the 2200-2100 cm-1 range can produce a wealth of new information and provide deeper insights into the nature of astrophysical ices.