High-Resolution Cavity Ring-down Spectroscopy Of Ro-vibrational Bands Of Some Atmospheric Molecules

Molecular spectroscopy is one of the most important methods to study the internal structure and properties of molecules and it plays an important role in physical, chemi-cal, astrophysical and environmental studies. In particular, the absorption spectroscopy of atmospheric molecules helps us to understand the balance of the atmospheric radi-ation and the atmospheres of planet. Among different spectroscopy techniques, the Cavity Ring-down Spectroscopy(CRDS) has been developed quickly in recent years because of its high sensitivity. The present work is mainly devoted to the study of ro-vibrational spectrum of some atmospheric molecules using CRDS. We obtained a lot of new spectroscopy dada and the results also improved the accuracy of the spectral data of some atmospheric molecules.In chapter1,1will introduce a brief overview of the high-resolution ro-vibrational molecular spectroscopy, high-resolution absorption spectroscopy technologies, some common profile functions of the molecular spectroscopy and the theory of IR ro-vibrational spectroscopy of the linear molecule.In chapter2, a setup which can be cooled down with liquid nitrogen will be pre-sented. It was used in some differential absorption spectroscopy measurements. Spec-trum of CH3D has been recorded at81K around1.58μm (6099-6530cm-1) using differential absorption spectroscopy (αmin≈5×10-8cm-1). In total, more than9000transitions at liquid nitrogen temperature in the6099-6530cm-1and5500transitions at room temperature in the6200-6400cm-1have been obtained. The empirical lower state energies of the transitions were derived from the ratio of the line intensities at different temperatures. The absorption spectrum of CH3D at temperature between81K and294K can be simulated using these data. The results will help to build the model of the CH3D spectrum in the considered region and of great interests for the study of methane-rich atmospheres of planets such as Titan’s.In chapter3,1will present the study of absorption spectrum of13C16O2near806nm using a continuous-wave cavity ring-down spectrometer. Two cold bands of10051-00001and10052-00001, one associated hot band11151-01101have been observed in this region. The line positions, intensities and ro-vibrational spectroscopic parameters of the upper states are determined from fitting of the transitions. The accuracy of these results is one order of magnitude better than that in literatures.In chapter4, the study of absorption spectrum of N2O between6950-7653cm-1using CW-Cavity Ring-down Spectroscopy will be presented. The typical noise equiv-alent absorption, in the order of αmin≈5×10-8cm-1, allowed for the detection of lines with intensity as low as1×10-29cm/molecule. The positions of7203lines of four isotopologues (14N14N16O,14N15N160,15N14N160and14N14N18O) were mea-sured with a typical accuracy of1×10-3cm-1. The transitions were ro-vibrationally assigned on the basis of the global effective Hamiltonian models developed for each isotopologue. More than95bands were obtained, most of them being newly report-ed. The ro-vibrational parameters of the upper states are determined from fits of the transitions.In chapter5, we focus on the high-sensitivity and high-precision cavity ring-down spectroscopy. In order to achieve high-precision, a continuous-wave cavity ring-down spectrometer with sub-MHz absolute frequency accuracy has been built using a thermo-stabilized Fabry-Perot interferometer made of ultra-low-expansion glass. Us-ing low sample pressure, the positions of73H216O lines in the spectral range of784-795nm intensities larger than1×10-25cm-1/(moleculecm-2) have been determined. The relative accuracy of the absolute frequency is estimated to be1x10-9.12C16O2lines of the10051-00001band at room temperature near782nm have also been recorded by the CW cavity ring-down spectrometer. Positions, pressure shift coefficients, intensi-ties and self-broadening coefficients of the55lines have been precisely determined.