S Pilling, V S Bonfim
Universidade do Vale do Paraíba - UNIVAP, Laboratório de Astroquímica e Astrobiologia - LASA Av. Shishima Hifumi, 2911, Urbanova São José dos Campos SP Brazil
RSC Adv. 2020 Feb 3;10(9):5328-5338. doi: 10.1039/c9ra10136e. eCollection 2020 Jan 29.
In this theoretical work we evaluate how the chemical environment influences some features presented in the infrared spectrum, such as band intensities and band location of embedded species in icy matrices. The calculations were performed employing the Polarized Continuum Model (PCM) approach with the second-order Møller-Plesset perturbation theory (MP2) level using the Gaussian 09 package. Here, we simulate the effects of molecular vicinity around embedded species in terms of the effects of the dielectric constant () of the icy and solid samples. Gas phase calculation was also performed for comparison purpose. The investigated embedded single molecules were CO, CO, CH, NH, SO HCOOH, CHOH and also HO. The results suggest that for most vibrational modes, the strengths of IR bands show an increase with , which implies they also decrease with respect to porosity. The frequency shifts showed opposite behavior in relation to the band strengths, with few exceptions. A correlation between calculated band intensities with the band strengths (taken from literature) was determined and described by a linear function ∼ 6 × 10 [km mol], with in unity of cm per molecule. In addition, an associative exponential function was adjusted to the studied dataset to characterize the evolution of frequency-shift and intensity-shift and band strength ratio as function of the dielectric constant. Since astrophysical ice mantles over cold dust grains can vastly vary in composition in space (having different dielectric constants) they are a challenge to be well characterized. Therefore, this work can help the astrochemistry community to better understand astrophysical ices and its observations in the infrared.
在这项理论研究中，我们评估了化学环境如何影响红外光谱中呈现的一些特征，例如嵌入冰基质中的物种的谱带强度和谱带位置。计算采用极化连续介质模型（PCM）方法，在二阶Møller-Plesset微扰理论（MP2）水平下，使用高斯09软件包进行。在这里，我们根据冰和固体样品的介电常数（）的影响来模拟嵌入物种周围分子邻近效应。为了进行比较，还进行了气相计算。所研究的嵌入单分子有CO、CO、CH、NH、SO、HCOOH、CHOH以及HO。结果表明，对于大多数振动模式，红外谱带的强度随介电常数增加，这意味着它们也随孔隙率降低。频率位移与谱带强度表现出相反的行为，只有少数例外。计算得到的谱带强度与（取自文献的）谱带强度之间的相关性由线性函数∼6×10[km mol]确定并描述，其中以每分子厘米为单位。此外，对研究数据集拟合了一个关联指数函数，以表征频率位移、强度位移和谱带强度比随介电常数的变化。由于冷尘埃颗粒上的天体物理冰幔在太空中的成分可能有很大差异（具有不同的介电常数），因此对其进行充分表征具有挑战性。因此，这项工作有助于天体化学界更好地理解天体物理冰及其红外观测。
