Laser-induced dispersive fluorescence spectrum and the detection of NO_2

摘要

Laser-induced dispersive fluorescence ( LIDF ) spectrum of NO_2 molecule in the spectral region of 508.3-708.3nm is obtained with the 508.0nm excitation wavelength. It is found that at low sample pressure the spectrum is composed of a banded structure superimposed on a continuous one. While the spectrum show itself as a continuous envelope centered at 630.0nm when the pressure with a higher value. NO_2 molecules are excited to the first excited state A~2B_2 by absorbing laser photons. Owing to the strong interaction between X~2A_1～A~2B_2 and A~2B_2 ～ B~2B_1 states, some excited molecules redistribute to X~2A_1 and B~2B_1 states by the process of internal energy conversion or quenching. This induces the fluorescence come from different excited states. Based on the experimental data, the vibration frequencies of the ground electronic state of NO_2 molecule are obtained. They are ω_1=(1319±12)cm~(-1), CO_2=(759.8±0.7)cm~(-1),and ω_3=(1635±29)cm~(-1). The optimum-receiving wavelength for detecting NO_2 gas with the technique of LIDF is proposed.