Spectral Analysis Of Valance Electronic States And Rydberg States Of SO₂ Molecular

The ground electronic state, the low-lying valance excited states and the Rydberg states of the air pollutant SO₂ molecule have been studied with the techniques of various high sensitivity laser spectroscopy. In which the quadruple-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 ps former are used as excitation sources.The laser induced dispersive fluorescence(LIDF) spectra technique has been used to study the vibration structure of the ground electronic state of SO₂ molecule. The SO₂ molecules were excited from ground state X¹A₁ to the high vibrational levels of A¹A₂ and B¹B₁ coupling electronic states by absorbing one photon (266nm). The LIDF spectra show itself as diffuse band accompany with regularly vibrational band structure in the range of 270⁴70nm. It is analyzed that the excited SO₂ molecules can redistribute in many vibrative levels through the progress of collision and internal conversion within its lifetime, and the diffuse band was produced by the fluorescence emission from many different vibrational-rotational levels of the coupled A+B states. The vibronic progressions in the range of 380⁴70nm of the LIDF spectra was ascribed to the transitions from the first excited electronic state a³B₁ to the vibration levels of the ground electronic state X¹A₁. The harmonic frequencies of the symmetry stretch vibration and the bend vibration of X¹A₁ state were calculated from the ascription. They are ω₁=1144cm^-1 and ω₂=534cm^-1 respectively. An apparatus for photo-acoustic detection is devised to tentatively survey the concentration of SO2 in the air base on the analysis of quenching mechanism of the excited SO2 molecules with the equipment of photoacoustic (PA) and laser radiation of 266nm as excitation source. The detection limit can reach 9.1ppm under the condition of atmospheric pressure. The resonance enhanced multiphoton ionization (REMPI) spectrum of SO₂ in the region of 420⁵40nm is obtained with an Optical Parameter Generator and Optical Parameter Amplifier pumped by a picosecond Nd:YAG laser as radiation source. It is definite that ionized signal is due to SO₂ molecule is ionized though (4+1) or (4+2) process and via Rydberg resonant states. The adiabatic ionization potential and the corresponding quantum defect of SO₂ is obtained through a least-square fit depend on Rydberg formula, which is 99586 cm^-1 and 1.86 respectively.