Spectroscopy Of Asymmetric Top Free Radicals: Experiments And Theories

Among the family of free radicals, asymmetric top molecules constitute a large proportion and many free radicals of special interests are of asymmetric rotor. Indeed, asymmetric top free radicals play important roles in atmospheric chemistry, biomedicine, and material science. So it is of great significance to pursue the spectroscopy of asymmetric top free radicals. This paper focuses on both experimental and theoretical aspects of the spectra of asymmetric top free radicals.Nitrogen dioxide is a free radical of very importance. Laser Magnetic Resonance (LMR) is a powerful technique in the study of hyperfine and Zeeman characteristics of free radicals. Employing a homemade CO LMR spectrometer, five new sets of hyperfine resolved spectra of the v₃ band of ¹⁴N¹⁶O₂ have been obtained. This measurement leads to a large increase in the number of LMR spectral lines of the v₃ band of ¹⁴N¹⁶O₂, from 24 lines previously to over 300 lines at present, and greatly enriches the experimental data eligible for studying the hyperfine and Zeeman characteristics of the v₃ band of ¹⁴N¹⁶O₂. The background, apparatus, methodology, conditions, and obtained results are detailed here.The theoretical study of the spectra of asymmetric top free radicals aims to analyze the LMR spectra of NO₂. Introducing the high order centrifugal distortion terms, Coriolis interaction, and Zeeman effect into the effective Hamiltonian, an efficient program used for detailed analysis of vib-rotational / rotational spectra of asymmetric top free radicals has been successfully developed. Using the program, a global analysis of spectra of the PO₂ radicals in the ground electronic state yields molecular parameters for this specie the most precise and extensive so far. A detailed analysis of the spectra of NO₂ indicates that the high order centrifugal distortion may effect substantially the high-lying rotational levels. The most precise and extensive molecular parameters for NO₂ have been derived from a global analysis of the spectra of NO₂ in its ground vibronic state. Upon the success of global analysis, some lines near 311 μm, which had been observed previously by far-infrared LMR but not assigned, are assigned as the Q(39) lines of the K=2-1 sub-band. An investigation on the Coriolis coupling between the v₃ and v₁, 2v₂ vibrational states has also been made. These progresses remove substantially hindrance holding up the assignment of the obtained LMR spectra of NO₂.