Lianshui Zhang

Emission spectrum and relaxation kinetics of SO2 induced by 266 nm laser

Laser induced fluorescence (LIF) emission spectrum of SO(2) in the range of 270.0-470.0 nm has been obtained with the quadruple harmonic output (266 nm) of a pulsed Nd:YAG laser as excitation source. The spectrum is composed of a continuous envelope in the short wavelength side, while it shows the character of banded structure superimposed on a continuous one in the long wavelength region. Fluorescence emission from the hybrid states of A(1)A(2)+B(1)B(1) and X(1)A(1)+B(1)B(1) forms the continuous envelope and phosphorescence emission from the triplet state a(3)B(1) forms the banded progression. It is also found that direct emission from laser excited states is very weak. The primary portion of the emission is from the energy levels populated by collision relaxation or collision induced intersystem crossing process. The harmonic frequencies and inharmonic coefficients of the symmetric stretching vibration and the bending vibration of X(1)A(1) state are derived from the ascription of the phosphorescence progression.

Resonance-enhanced multiphoton ionization spectrum of SO2 in the range of 420-540 nm

The resonance enhanced multiphoton ionization (REMPI) spectrum of SO2 in the region of 420~540nm is obtained with a picosecond Nd:YAG laser pumped an Optical Parameter Generator and Optical Parameter Amplifier as radiation source. The ionization pathway is analyzed. SO2 molecule is ionized though (4+1) or (4+2) process and via 4p, 5p and 6p Rydberg resonant states. The near quintic variation of the ionization signal versus laser intensity verified this conclusion further. So the spectral lines can be assigned to np Rydberg series. The adiabatic ionization potential and the quantum defect of SO2 are obtained based on the experimental datum, which is 99586 cm-1 and 1.85 respectively.

Investigation of Rydberg states of nitrogen dioxide with high-power laser

A survey of the Rydberg states of NO2 accessed in optical-optical two-color double-resonant (OODR) manner by the technique of multi-photon ionization (MPI) spectroscopy is presented. The pump laser is the double-frequency output of a Nd:YAG laser. While the probe laser is an optical parameter generator and optical parameter amplifier (OPG/OPA) pumped by the triple-frequency output 355nm of the former. The OODR-MPI spectrum of NO2 is obtained by scanning the probe laser in the range of 465-535nm under the condition that the pump laser is unfocused and the probe laser is focused on the center of the pump laser beam. The ionization peaks could be attributed to E2∑u←A2B2←X2A1(1+2) resonant transitions. This means that NO2 molecule is excited to the appropriate level of the first excited A2B2 state by absorbing one pump laser (ω1) photon. Then from the first excited state it should take three probe photons (ω2) and via final resonant E2∑u state for the ionization. The bending vibration frequency of NO2 E2∑u state obtained from above ionization spectrum is (608.6±2.2)cm-1. It is consistent with the literature.

Two-photon laser-induced fluorescence spectrum of NO

Two-photon laser-induced fluorescence spectrum(TP-LIF) of NO is obtained by using high power laser as excitation source. A few stronger band can be attributed to A2??X2 ? transition. Some molecule constants about NO which in the ground state are deduced by the spectrum. The nature radiation lifetime of NO which is in the excited state A2? is about 180ns by fitting the curve oflifetime verse pressure.