Merging Complementary Techniques in Laboratory Spectroscopy for Remote Sensing Applications

分子光谱学使我们能够在不容易到达的地方识别分子，比如地球大气层的上层、星际云、其他行星、彗星和冷恒星的大气层。光谱线的形状为我们提供了一个“窗口”，使我们能够深入了解控制辐射吸收和发射的机制，并在迄今为止接受的经典图像之外解释它们。除了分子鉴定和定量外，光谱技术还可以提供有关远程环境物理性质的信息。这是广泛用于大气研究的遥感的基础。对线形的极其精确的光谱测量可以帮助我们理解分子动力学的基本过程和遥感数据的解释。从遥感光谱中提取信息需要来自实验室光谱学和理论模型的量子态解析数据（线的位置、强度和形状）。对包括系外行星大气在内的各种天体物理环境中常见的分子线参数的高精度汇编的需求日益增加。这是由越来越高分辨率的望远镜和仪器的可用性所驱动的，包括天基的如赫歇尔，未来的JWST，飞机上的如索菲亚，以及地面上的如ALMA。对于许多感兴趣的分子，线列表需要能够跨越很大的温度范围，因为它们存在于跨越很宽温度范围的不同环境中。我建议研究N2O3，这是一项最具挑战性的工作，因为N2O3的化学不稳定性和各种实验技术和理论建模的组合，包括从头计算，是必需的。该研究的目标是通过首次记录NO和NO2/N2O4的冷却混合物的高分辨率远红外光谱，获得更准确的非对称（可能是对称）n2o3低空红外波段信息。实验室实验中的浓度误差可以通过同时测量来克服，在同一样品上，使用我们实验室重新安置的激光光谱仪在8-10µm左右进行适当的红外吸收，并通过高分辨率傅里叶变换光谱（FTS）同时记录纯旋转光谱来确定实际浓度。因此，项目的顺利完成需要两种实验技术的结合：傅里叶变换红外光谱和二极管激光光谱。这项提议的一部分还包括对低温巨行星和热系外行星的行星大气中的甲烷进行近红外研究。我建议采用理论与高分辨率实验相结合的方法来确定K波段h2展宽甲烷特征的高精度谱线参数。测量将集中在a)在4450 - 4700 cm-1之间较弱的谱线，使用低温（215 - 296 K）下的新光谱用于冷巨行星，b)在4300 - 4450 cm-1之间较强的谱线，使用高温（296 - 350 K）的光谱用于太阳系外行星（如热木星）。测量的h2加宽线宽、压力位移和温度依赖指数系数将能够在广泛的温度范围内进行精确的逐行计算。这项研究将支持利用地面和太空观测（现在和将来）对行星和系外行星大气的分析，并将允许理论家扩展他们的“全球甲烷分析”。

Molecular spectroscopy allows us to identify molecules in locations not easily accessible, such as the upper layers of the Earth’s atmosphere, interstellar clouds, and the atmospheres of other planets, comets and of cool stars. It is the shape of a spectral line that provides a “window” for us to look inside the mechanism governing the absorption and emission of radiation and interpret them beyond the classical pictures accepted so far. In addition to molecular identification and quantitation, spectroscopic techniques can provide information on the physical properties of remote environments. This is the basis of remote sensing which is used extensively in atmospheric studies. Extremely precise spectral measurements of a line shape can help us understand fundamental processes of molecular dynamics and in the interpretation of remote sensing data. Extracting information from remote sensing spectra requires quantum state-resolved data (line positions, intensities, and shapes) from both laboratory spectroscopy and from theoretical models. There is an increasing need for highly accurate compilations of line parameters of molecules that are common in various astrophysical environments including exoplanet atmospheres. This is being driven by the availability of ever increasingly high-resolution telescopes and instruments, including space-based such as Herschel, the future JWST, plane-based such as SOFIA, and ground based such as ALMA. For many of the molecules of interest, the line lists need to be able to span a large temperature range since they exists in different environments that span a wide temperature range. I propose to investigate N2O3, an undertaking that is most challenging because of the chemical instability of N2O3 and the fact that combinations of various experimental techniques and theoretical modelling, including ab initio calculations, are required. The goal of the proposed research is to obtain more accurate information on the low lying infrared bands in asymmetric- and possibly symmetric-N2O3 by recording, for the first time, the high resolution far-infrared spectrum of a cooled mixture of NO and NO2/N2O4. The concentration errors in the laboratory experiments can be overcome by measuring simultaneously, and on the same sample, suitable IR absorptions around 8-10 µm with a laser spectrometer that will be re-located from our lab for the experiments, and to determine the actual concentration by simultaneously recording the pure rotational spectrum by high resolution Fourier Transform Spectroscopy (FTS). Therefore, the successful completion of the project requires two experimental techniques to be combined: Fourier Transform Infrared Spectroscopy and diode laser spectroscopy. Part of this proposal is also a near infrared study of methane for planetary atmospheres of cold giant planets and hot exoplanets. I propose to use a combination of theory and high-resolution experiments to determine highly accurate line parameters of H2-broadened methane features in the K band. The measurements will focus on a) weaker lines between 4450 and 4700 cm-1, using new spectra at cold temperatures (215 – 296 K) for cold giant planets, and b) stronger lines in the 4300 – 4450 cm-1 using spectra at elevated temperatures (296 – 350 K) for extra-solar planets (e.g. hot-Jupiters). The measured H2-broadened linewidths, pressure-shifts, and temperature dependence exponent coefficients will enable accurate line-by-line calculations for a wide range of temperatures. This study will support analyses of planetary and exoplanetary atmospheres using ground-, and space-based observations (present and future) and will allow the theorists to extend their “global analysis of methane”.