基于波长调制-直接吸收光谱的CO分子2.3μm处谱线参数高精度测量

High Precision Measurement of Spectroscopic Parameters of CO at 2.3μm Based on Wavelength Modulation-Direct Absorption Spectroscopy

波长调制-直接吸收光谱(WM-DAS)结合了直接吸收光谱(DAS)可直接测量吸收率和波长调制光谱(WMS)高信噪比的优点,可用于测量气体分子吸收谱线的光谱参数。采用WM-DAS方法结合有效光程约为45 m的Herriott型长光程吸收池,在CO浓度为24.151μmol·L^(-1)、常温常压条件下,测量了CO分子中心频率为4300.700 cm^(-1)谱线的吸收率,用Voigt线型(VP)函数对测量的吸收率进行拟合,结果表明对WM-DAS方法测量结果进行拟合所得的残差标准差比用传统DAS方法减小一半以上,证明WM-DAS方法的抗干扰能力比DAS更强。采用该方法与光程约为50 cm的吸收池结合,对CO分子在4278~4304 cm^(-1)波段的8条弱吸收谱线在不同压力下的吸收率进行测量,实验采用浓度为0.411μmol·L^(-1)的CO标准气体。分别采用VP、Raution线型(RP)和quadratic-speed-dependent-Voigt线型(qSDVP)对测量所得吸收率进行拟合,得到CO分子与空气分子的碰撞展宽系数γ0(T_(0))、Dicke收敛系数β0(T_(0))和速度依赖的碰撞展宽系数γ2(T_(0)),并对测量结果进行不确定度分析。其中由VP拟合所得各谱线的γ0(T_(0))与HITRAN数据库中参考值吻合较好,其相对误差均小于1%;Dicke收敛系数β0(T_(0))和qSDVP中速度依赖的碰撞展宽系数γ2(T_(0))的高精度测量为进一步完善分子光谱数据库及气体参数高精度测量提供了数据基础。

Wavelength modulation-direct absorption spectroscopy(WM-DAS)combines the advantages of DAS and WMS,which can directly measure the absorbance and improve the measurement signal-to-noise ratio(SNR).It can be used to measure the spectroscopic parameters of gas molecular spectral lines.Firstly,the WM-DAS method is used to measure the absorbance of CO molecule 4300.700 cm^(-1)spectral lines under the condition of 24.151μmol·L^(-1)CO concentration,room temperature and pressure,combined with Herriott cell with an effective optical path length of about 45 m.The absorbance is optimally fitted by Voigt profile(VP)and the results show that the standard deviation of the absorbance fitting residual from WM-DAS is reduced by more than half compared with that from the traditional DAS method,which proves that the anti-interference ability of the WM-DAS method is stronger than that of the DAS method.Then,this method combined with an absorption cell with an optical path of about 50 cm was used to measurethe absorbance of 8 weak absorption spectral lines of CO at 4278~4304 cm^(-1)under different pressures.The CO standard gas with a concentration of 0.411μmol·L^(-1)was used in the experiment.The measured absorbance was fitted by VP,Rautionprofile(RP)and quadratic-speed-dependent-Voigt profile(qSDVP)to obtain the collision broadening coefficientγ0(T_(0)),the Dicke narrowing coefficientβ0(T_(0))and the speed-dependent collision broadening coefficientγ2(T_(0))in qSDVP,respectively,and the uncertainty of the measurement results was analyzed.The measuredγ0(T_(0))obtained by Voigt profile fitting agree well with those from the HITRAN database,with a relative error of less than 1%.The measurement results ofβ0(T_(0))andγ2(T_(0))provide an important data for further perfecting molecular spectral database and high-precision measurement of gas parameters.