Absorption Spectral Line Parameters of Water and Nitrous Oxide from Cavity Ring-Down Spectroscopy

Author:Liu Gu Liang

Supervisor:hu shui ming liu an zuo


Degree Year:2019





Molecular spectroscopy has been used to studying the interaction between molecules,their surrounding environment,and revealing the internal structure of molecules.Along with the developments of laser techniques,the applications of spectroscopy become more and more extensive.It plays an important role in monitoring global greenhouse gases,tracing the atmospheric pollutants and the astrophysics of interstellar space.These applications strongly depend on accurate and reliable spectral parameters.The cavity ring-down spectroscopy has stood out and gradually become one of the mainstream methods for measuring high-precision spectral parameters owing to the high sensitivity,fast response,and high precision.This dissertation is focusing on the high-precision absorption spectra measurements of small molecules in the atmosphere by cavity ring-down spectroscopy.The proper line profile has been applied to the recorded spectra to determine the spectral parameters of molecular absorption lines,including line positions,intensities,pressure-induced line broadening and shift coefficients,as well as their vibration-rotation assignments.The first chapter briefly introduces the basic theory of spectral line profiles,including the main factors that cause spectral line broadening and the interaction mechanism between these factors.Then the principle and development of different molecular absorption spectroscopy techniques are reviewed.And the basic theory of cavity ring-down spectroscopy has been presented,as well as its development and evolution.The structure of the cavity ring-down spectrometer is introduced in the end.The second chapter is an overview of cavity ring-down spectroscopy setups for measuring the trace constituents of the atmosphere which play an important role in atmospheric chemistry and has a strong influence on air quality,including the greenhouse gases,total reactive nitrogen(NOy),volatile organic compounds,free radicals,other reactive gases and aerosols.The detection wavelength and limitation of the existing works are summarized here.The third chapter introduces cavity ring-down spectroscopy of 170-enriched water vapor between 12 055 and 12 260 cm-1,including the spectrum measurement and analysis work.In total,1344 lines were observed in this region,while more than 1400 absorption transitions were assigned on the basis of previously published experimental energies and the variational calculations based on the results of Partridge and Schwenke.Three hundred and fifty-six ro-vibrational energy levels of H217O water isotopologues were retrieved,one hundred and ten of them are reported for the first time.The fourth chapter introduces the line positions and N2-induced line parameters of the 00°3-00°0 band of 14N2160 by comb-assisted cavity ring-down spectroscopy.Ro-vibrational transitions of the 0003-0000 band around 1.52μm with line intensities in the order of 10-24 to 10-23 cm-1/(molecule·cm-2)have been recorded using a comb-assisted laser-locked cavity ring-down spectrometer with high sensitivity as well as high precision.In total,88 line positions were determined with a sub-MHz uncertainty,better than previous experimental results by 1-2 order of magnitude.N2-induced line shape parameters of 20 isolated transitions were derived by using the Voigt profile and the quadratic Speed-Dependent Voigt profile with relative uncertainties of 1-2%.The fifth chapter is a brief conclusion of the experiments,as well as perspectives for future studies.