温度对NH_3气体紫外吸收截面影响研究

Study on Temperature Dependence of Ultraviolet Absorption Cross Sections of Ammonia

为了研究NH3气体在紫外203～220nm内吸收截面随温度的变化规律,采用高分辨率光栅单色仪、氘灯光源、闭式气样室和配气装置,测量NH3气体温度由308K升高至397K的吸收截面。NH3气体吸收截面由离散吸收和连续吸收两部分组成。结果表明,随着温度的升高,基态剩余量子旋转、振动迁移到激发态的概率减少,最终导致离散吸收截面峰值的降低。随着温度由308K升高至397K,在特征波长212.5nm处,离散吸收截面峰值的最大相对减幅为46%。NH3气体在这个波段的吸收截面存在明显的等波长间隔分布特征,约为4nm。随着温度升高,峰值位置未见变化。连续吸收截面整体上随温度升高而减小,且这种减小趋势随波长红移逐渐减弱。由于NH3气体吸收截面随温度的变化呈现较大的变化,实测时应对气体浓度在线测量结果进行温度补偿计算。

The present paper reports the study of the effects of temperature on the absorption cross-sections of ammonia in spec tral region of 200-220 nm. By using a grating monochromator with high resolution, deuterium lamp, closed gas sample cell and gas compounding device, the photoabsorption cross sections of ammonia were measured at temperatures ranging from 308 to 397 K. The absorption spectrum of NH3 consists of discrete bands superimposed on a continuous base. Results indicated that the cross sections at the peaks of the discrete bands decreased with the increase in temperature, which corresponded to the decrease in the population of vibrational and rotational transitions from the base level to higher excitation levels. The absorption cross sec tion peaks decreased when the temperature increased from 308 to 397 K, with a relative drop of 46%. Another distinctive feature of ammonia absorption spectra in the above spectral regions was the quasiperiodic structure of absorption peaks, whose equal wavelength interval was 4 nm. Besides, absorption peak positions were not changed. Continuous absorption cross section decreased with the increase in temperature, and the variation gradient gradually decreased with wavelength red shift. A compensa tion calculation for temperature should be carried out in on-line measurement of concentration because of the greater variation rate of absorption cross sections of ammonia.