常压N_2O_4合成对基于紫外吸收的NO_2体积分数测量的影响

Effect of NO_2 combination at atmospheric pressure on measurement of its volume fraction by ultraviolet absorption

研究了常压下NO2双合物N2O4的转化率对NO2气体紫外波段（200-220 nm）吸收截面以及NO2体积分数测量的影响.利用高分辨率光栅单色仪,测量了目标气体（NO2＋N2O4）吸收截面随气体总压和自身分压的变化规律.实验结果表明,NO2向N2O4的转化率与气体总压和NO2分压的比值呈线性关系;随着气体总压从低压升高到常压（一个大气压左右）,NO2转化为N2O4的比率显著提高,目标气体有效吸收截面远大于NO2吸收截面.根据气体总压和有效吸收截面,可以得到校正后的NO2体积分数计算公式,能够显著提高NO2体积分数测量的精度.

The effects of monomer-to-dimer conversion of NO2 at atmospheric pressure on the absorption cross-section of gaseous NO2 at 200-220 nm UV absorption band and the measurement precision of NO2 volume fraction were investigated. A high resolution grating monochromator was used to measure the absorption cross-sections of target gas （NO2 ＋ N2O4 ） at various total pressures and partial pressures of the target gas. Experimental results indicated that the conversion rate from NO2 to N2O4 varied linearly with the ratio of total gas pressure to partial pressure of the target gas, As the total gas pressure approached to roughly one atmospheric pressure, the conversion rate from NO2 to N2O4 increased remarkably compared with that at low pressures, and the effective absorption cross-section of the target gas was much larger than that of NO2. A revised calculation formula was proposed combining the effective absorption cross-section and total gas pressure to improve the measurement precision of NO2 volume fraction.