[Effects of temperature on the ultraviolet absorption characteristics of SO2].

Absorption spectrum of SO2 is obtained under the condition of room temperature and atmosphere pressure. The spectrum is composed of banded structure superimposed on a continuum. The continuum structure comes from the transition of SO2 molecule from the ground electronic state to the higher dense rovibronic energy levels, and the banded one comes from the transition of B1B1<--X1A1. The symmetric stretch and bend vibration frequencies are obtained from the banded structure. They are omega1 =(665+/-29) cm-1 and omega2 = (448+/-17) cm-1, respectively. Measuring the absorption spectra of SOz at different temperature, it was also found that the configuration of the spectra is similar. But the absorption cross-section decreases with the increase in temperature. The absorption cross-section corresponding to the absorption peaks varies with temperature in the manner of cube. But the rate coefficients are different. So the effect of temperature on the measurement results must be considered when we use the technique of DOAS for the detection of SO2.

[Theoretical study of 1+2+1 double-resonance multiphoton ionization probability].

The technique of resonance enhanced multiphoton ionization (REMPI) spectroscopy has already become an important method for studying the energy level structure of atoms and molecules. Analytic expression of 1+2+1 double REMPI probability of four-level system has been deduced with the theory of rate equation. Based on the expression, the present paper simulated the variations of ionization probability versus laser intensity, laser pulse duration and collision relaxation rate. It was found that in the 1+2+1 ionization mechanism the ionization probability increases with laser intensity, until saturation phenomenon appears in one and two excitation steps. If laser intensity increases further, the ionization probability will oscillate around the saturation value, and the oscillation amplitude will increase with laser intensity. With regard to the influence of laser pulse duration and collision relaxation rate on the ionization probability, the results show that the ionization probability increases from zero to the saturation value 1 with the increase in laser pulse duration, while it decreases linearly with the increase in collision relaxation rate.