Spectral Analysis Of Electronic States And The Optical Detection Of Nitrogen Oxide Compounds

The ground electronic states, the valance excited states and the high-excited electronic states of the air pollutants (NO_x) have been studied with the techniques of various laser spectroscopy, in which the double-frequency outputs of a pulsed Nd:YAG laser and a optical parameter generator and optical parameter amplifier pumped by the third harmonic lines of the former are used as excitation sources.The vibration structure of the A²âˆ‘, X²âˆ electronic states of NO is studied with the technique of two-photon laser induced fluorescence spectroscopy(LIFS). It is found for the first time that the phenomenon of the NO self-absorption makes the distribution of the spectral line intensity departure obviously from that of the Frank-Condon factors. Based on the measurement of the spectral intensity, the variation relationship of the electronic transition moment versus inter-nuclear distance about NO A²âˆ‘(v=0,l)→X²âˆ transition is formulated with the method of least-square fit. The optimum excitation and receiving wavelengths are also determined for detecting NO molecule with the method of resonant fluorescence, which are 429.4nm, 452.4nm and 236.3nm respectively. The vibrational structure of the high-excited electronic states of NO molecule is studied with the method of resonant enhanced multi-photon ionization (REMPI) spectroscopy. It is obtained that the REMPI spectrum via E²âˆ‘ intermediate resonant state, which wasn't reported previously. The different transition selection rules for NO molecule following in multi-photon process are discussed in detail than those of the common diatomic molecules.For studying the spectral characteristic of NO₂ molecule, the vibration structure of X²A₁, A²B₂ and B²B₁ electronic states are probed with the technique of LIFS at first. The results show that there is a strong interaction between A²B₂ state and the high vibration levels of X²A₁ ground electronic state, which induces the radiant lifetime of the excited state to be anomaly long. The excited molecules can realize redistribution among many levels by inner-conversion or collision process and the fluorescence comes from different excited states.It is found that the optimum excitation wavelength for detecting NO molecule with the method of resonant fluorescence is in the 420.0-450.Onm regions, while the best receiving one is 630nm. An apparatus for photo-acoustic detection is devised based on the optical absorption properties of NO2 molecule. The detection limit can reach 6.4ppm under the condition of atmospheric pressure. Finally, the high-excited electronic states of NO2 molecule are studied with the technique of optical-optical double-color and double-resonant multi-photon ionization (OODR-MPI) spectroscopy for the first time. The quantum defect ofp orbit and the converging potential of the np o u Rydberg series are deduced.The results presented in this paper are believed to be of great important to the detection of nitrogen oxide compounds and the study of the molecular physics.