Merging Complementary Techniques in Laboratory Spectroscopy for Remote Sensing Applications

分子光谱学使我们能够识别不易到达的地方的分子，例如地球大气层的上层、星际云，以及其他行星、彗星和冷星的大气层。它是一条光谱线的形状，为我们提供了一扇“窗口”，让我们深入了解辐射吸收和发射的机制，并超越迄今接受的经典图像来解释它们。除了分子鉴定和定量，光谱技术还可以提供有关偏远环境物理性质的信息。这是在大气研究中广泛使用的遥感的基础。线条形状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在遥感数据的解释中。从遥感光谱中提取信息需要来自实验室光谱和理论模型的量子态分辨数据(线位置、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的线参数的高度精确的汇编的需求越来越大。这是由越来越高分辨率的望远镜和仪器的可用性推动的，包括赫歇尔等天基望远镜，未来的JWST，索非亚等平面望远镜，以及ALMA等陆基望远镜。对于许多感兴趣的分子，线表需要能够跨越很大的温度范围，因为它们存在于跨越很大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，而且需要结合各种实验技术和理论模型，包括从头计算。这项拟议研究的目的是通过首次记录NO和NO2/N2O4冷却混合物的高分辨率远红外光谱，获得关于不对称--可能是对称--N2O中的低红外波段的更准确的信息。为了克服实验室实验中的浓度误差，可以在同一样品上同时测量8-10微米附近的适当红外吸收，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，该项目的成功完成需要两种实验技术的结合：傅立叶变换红外光谱和半导体激光光谱。 这项提议的一部分也是对冷的巨行星和热的系外行星的行星大气中的甲烷进行近红外研究。我建议使用理论和高分辨率实验相结合的方法来确定H_2加宽的甲烷特征在K带中的高精度线参数。测量将集中在a)4450到4700厘米-1之间的较弱的谱线，使用冷温度(215-296K)的新光谱对于冷巨行星，以及b)4300-4450厘米-1的较强的谱线，使用在高温(296-350K)的太阳系外行星(例如热木星)。测量的H2加宽线宽、压力漂移和温度依赖指数系数将使对广泛温度范围的逐行精确计算成为可能。这项研究将支持使用地面和空间观测(现在和未来)对行星和行星外大气的分析，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”.