Fourier transform infrared spectra of formic acid aerosol particles in situ generated in a collisional cooling cell at temperatures ranging between 90 and 210 K are recorded in the mid-infrared and THz/far-infrared regions. Infrared spectroscopic features are used to identify the formic acid dimer above 200 K, the crystalline β₁ phase in the 110–200 K temperature range, and amorphous solid formic acid at ∼90 K. Density functional calculations of discrete clusters and the full periodic β₁ crystalline structure help to assign the low wavenumber intermolecular modes by comparison with experimental far IR and Raman data from the literature. Refractive indices of the formic acid crystal in the mid-IR range are retrieved. These data are essential for radiative transfer modeling of solid formic acid condensed in the terrestrial atmosphere. THz/far IR spectra, in addition to the well documented mid-infrared spectra, may be useful for the identification of solid formic acid in astrophysical environments such as the young stellar object W33A.

中文翻译：

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冷甲酸气溶胶颗粒的太赫兹和中红外光谱

在中红外和太赫兹/远红外区域记录了在碰撞冷却室中在90至210 K之间的温度下原位生成的甲酸气溶胶颗粒的傅里叶变换红外光谱。红外分光特性被用于识别上述200 k中的甲酸二聚物，结晶β ₁相在110-200 K温度范围内，并且无定形固体甲酸在〜90次K.密度离散簇的功能性的计算和全周期β _1个与文献中的实验远红外和拉曼数据相比，晶体结构有助于确定低波数的分子间模式。检索中红外范围内甲酸晶体的折射率。这些数据对于在地面大气中冷凝的固体甲酸的辐射传递建模至关重要。除了充分记录的中红外光谱外，THz /远红外光谱还可用于鉴定天体环境（例如年轻的恒星物体W33A）中的固体甲酸。