Study Of High Resolution Spectra Of Some Isotopologues Of The Atmospheric Molecules

The molecular spectroscopy has long been an important field and achieved great progress owing to the rapid development of scientific instruments in recent years. It helps to understand the structures and properties of molecules and plays an important role in photochemistry, astrophysical and environmental applications. In particular, the studies on the atmospheric molecules is essential for a better understanding of the details of the green house effect, the influences to the ozonosphere from atmospheric photochemistry, and also the mechanism of the air pollution. The present thesis is de-voted to the studies of several atmospheric molecules including their isotopologues. The results can be applied to improve the present spectroscopy database of these im-portant molecules, and also to improve the effective Hamiltonian model.In chapter 1 the fundamentals of the ro-vibrational spectroscopy will be intro-duced. The basic ideas of the effective operator method toward the global fitting of the molecular spectra will be also presented.In chapter 2 the principle of Fourier-transform (FT) spectrometer which was ap-plied in our lab will be presented. The idea and configuration of the continues-wave (cw) cavity ring down spectroscopy (CRDS) is given. To test the performance of the cw-CRDS built in our lab, the spectroscopy of trace acetylene gas was measured. The results shows that a sensitivity of 10-10/cm, has been achieved accompanied with a spectral resolution of 10-4cm-1. The quantitative measurement and trace detection capabilities are also demonstrated. At the present working frequency of 0.8μm, the detection limit of C2H2 was determined to 0.2ppmv.In chapter 3 we focused on several isotopologues of the atmospheric molecule N2O. The FT spectra of 15N14N16O-enriched nitrous oxide has been recorded at the Doppler limited resolution in the 3500-9000cm-1 region. More than 15000 tran-sitions of 15N14N16O have been observed and assigned based on the global effective Hamiltonian mode. The band-by-band analysis led to the determination of the ro-vibrational parameters of totally 133 bands, in which more than 100 bands were ob-served for the first time. Then the CRDS spectra of 14N15N16O(456),15N14N16O(546) and 15N216O(556) near the 6v3 band have been recorded. In total 213,86 and 191 transi- tions were observed for the three isotopologues respectively. For N2O-456 and 556, the v2+6v3←v2 hot band was also observed. The ro-vibrational spectroscopic parame-ters of the upper states are determined from least squares fitting of the transitions. The absolute line intensities of the 6v3 cold bands have been also retrieved by a multi-line fitting procedure from the spectra with an estimated accuracy of 4%for majority of the unblened lines. The vibrational transition dipole moment values and the empirical Herman-Wallis coefficients are also presented. Except the v2+6v3 band of N2O-556, other four bands studied in this work are found to be perturbed. The comparison of the observed line positions to those predicted using effective Hamiltonian models indicates that the effective Hamiltonian model can be further improved with taking into account of the present results.In chapter 4, it will be presented the study of the spectra of CO2 (with natu-ral abundance)in the 7123-7917cm-1 region using a cw-CRDS spectrometer. The achieved sensitivity (noise equivalent absorption) in the order ofαmin～2×10-10cm-1) has allowed to assign 2478 transitions to the 12C16O2,16O12C17O and 16O12C18O iso-topologues, with intensities ranging from 1.22×10-29 to 4.11×10-25cm/molecule. An average uncertainty for the intensities was estimated to be 3%. It represents an impor-tant improvement as in the considered region, the most extensive set of experimental data was the early measurements from Venus spectra by Mandin which only includes 384 transitions. The majority of these lines were measured for the first time. The ef-fective dipole moment parameters of the△P=10 series of transitions in 16O12C18O were also retrieved from the fitting. The previous set of effective dipole moment pa-rameters of the△P=11 series of transitions in the principle isotopologue was refined leading to important differences for the parameters describing the vibrational and rota-tional dependencies. The obtained results will be used to improve the CDSD databank. We also compared our results to the current version of CDSD, the deviation which be-yond the experimental uncertainties illustrated that the obtained results will be valuable to improve different EH models used to generate the CDSD. The CRDS spectrum of 12C16O2 in the region of 12543-12784cm-1 has also been studied.4 overtone bands were observed, including 2 hot bands. The spectral parameters and transition dipole moments were also retrieved. The comparison with CDSD and Campargue's line posi-tion data shows that our data was in good agreement with Campargue's data, but with larger deviation from the data of CDSD. This can be a result from that the present model used in the CDSD database has not include the spectral data over> 9650cm-1. It indicates that the present data will be of particular importance to improve the quality of the CDSD database.