Measurement of middle infrared spectroscopic parameters of carbon disulfide based on tunable diode laser absorption spectroscopy

Abstract

Carbon disulfide (CS₂) is a toxic volatile sulfur compound with flammability and harmfulness, which can seriously harm the human health and threaten the industrial production safety. Therefore, it is of high importance for monitoring CS₂ concentration in the air. Tunable diode laser absorption spectroscopy is very suitable for the detection of trace gas for it possesses high sensitivity and fast response. And the precise knowledge of spectroscopic parameters is essential for deducing the CS₂ concentration. However, primary database including HITRAN and GEISA lacks spectroscopic parameters of CS₂. Thus, to address this issue, a measurement system of absorption spectrum is built for determining spectroscopic parameters by using a quantum cascade laser with narrow linewidth and high output power operating near 4.6 um as a light source. In this paper, direct absorption spectroscopy is used to measure the CS₂ absorption spectra under different sample pressures and the environment temperature is controlled at 296 K, which is adjusted by an air conditioner. We intensively study the absorption spectra of CS₂ in a range between 2178.99 and 2180.79 cm^–1.According to the relevant reports and the need of actual measurement, four absorption lines are mainly measured in a range of 2180.5−2180.74 cm^–1. Combining with the multiple linear regression algorithm based on the nonlinear least-square method and Beer-Lambert law, the integrated area and Lorentz line width of measured CS₂ absorption spectrum can be determined. Then the spectroscopic parameters including absorption line intensity and air broadening coefficient are precisely obtained by linearly fitting the integrated areas and Lorentz line widths of CS₂ absorption spectra at different pressures. Moreover, nitrous oxide (N₂O) absorption spectrum with high spectral resolution is measured to calibrate the central position of carbon disulfide absorption line according to its known line position extracted from HITRAN database and the results obtained by etalon. The calculated results show that the uncertainty of line intensity and air broadening coefficient are less than 5% and 15%, respectively. It demonstrates that the measured spectroscopic parameters of four absorption lines for this study can be recorded in the database of HITRAN, which is very important for trace gas sensing of CS₂. In the future, we will further improve the system for measuring CS₂ absorption line parameters to fill in the gaps in their spectral parameters in HITRAN and GEISA databases.