星际冰类似物中HCOOH的红外光谱
Infrared spectroscopy of HCOOH in interstellar ice analogues
摘要：
背景：HCOOH是星际冰中较常见的物质之一，相对于固体H2O的丰度为1-5%。目的：本研究旨在表征HCOOH光谱特征的天体物理相关的冰混合物，以解释天文数据。方法：在高真空条件下生长冰，用傅里叶变换红外光谱仪记录透射光谱。研究了在15 K和145 K下沉积的纯HCOOH冰，以及含有H2O，CO，CO2和CH 3OH的二元和三元混合物。对于HCOOH：H2O，混合物浓度在50：50%至约10：90%之间变化。研究了HCOOH：X二元混合物和HCOOH：H2O：X三元混合物（X = CO、CO2和CH 3OH）的浓度分别为~10：90%和~7：67：26%。结果：纯冰的HCOOH光谱显示宽谱带，在120 K附近分裂，这是由于二聚体转化为链状结构。宽的单组分谱带被发现与H2O的混合物。另外的光谱成分存在于与CO、CO2和CH 3OH的混合物中。由此产生的峰位置、半峰全宽和谱带强度在很大程度上取决于冰结构、温度、基质成分和HCOOH浓度。固体HCOOH 5.9，7.2和8.1微米的功能与天文数据的比较，对低质量源HH 46和高质量源W 33 A表明，光谱的二元混合物不再现观测到的冰的功能。然而，我们的三元混合物，特别是含有CH 3OH的三元混合物，与天文数据非常吻合。因此，星际HCOOH很可能存在于与H2O、CH 3 OH以及可能还有CO或CO2的三级或更复杂的混合物中，从而限制了其形成。
英文摘要：
Context: HCOOH is one of the more common species in interstellar ices with abundances of 1-5% with respect to solid H2O. Aims: This study aims at characterizing the HCOOH spectral features in astrophysically relevant ice mixtures in order to interpret astronomical data. Methods: The ices are grown under high vacuum conditions and spectra are recorded in transmission using a Fourier transform infrared spectrometer. Pure HCOOH ices deposited at 15 K and 145 K are studied, as well as binary and tertiary mixtures containing H2O, CO, CO2 and CH3OH. The mixture concentrations are varied from 50:50% to ~10:90% for HCOOH:H2O. Binary mixtures of HCOOH:X and tertiary mixtures of HCOOH:H2O:X with X = CO, CO2, and CH3OH, are studied for concentrations of ~10:90% and ~7:67:26%, respectively. Results: Pure HCOOH ice spectra show broad bands which split around 120 K due to the conversion of a dimer to a chain-structure. Broad single component bands are found for mixtures with H2O. Additional spectral components are present in mixtures with CO, CO2 and CH3OH. The resulting peak position, full width at half maximum and band strength depend strongly on ice structure, temperature, matrix constituents and the HCOOH concentration. Comparison of the solid HCOOH 5.9, 7.2, and 8.1 micron features with astronomical data toward the low mass source HH 46 and high mass source W 33A shows that spectra of binary mixtures do not reproduce the observed ice features. However, our tertiary mixtures especially with CH3OH match the astronomical data very well. Thus interstellar HCOOH is most likely present in tertiary or more complex mixtures with H2O, CH3OH and potentially also CO or CO2, providing constraints on its formation.
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