Line strength and collisional broadening studies of hydrogen sulphide in the 1.58 μm region using diode laser spectroscopy

Abstract

High resolution diode laser spectroscopy has been applied to the detection of hydrogen sulphide at ppm levels utilizing different transitions within the region of the ν1 + ν2 + ν3 and 2ν1 + ν2 combination bands around 1.58 µm. Suitable lines in this spectral region have been identified, and absolute absorption cross sections have been determined through single-pass absorption spectroscopy and confirmed in the Doppler linewidth regime using cav- ity enhanced absorption spectroscopy (CEAS). The desire for a sensitive system potentially applicable to H2S sens- ing at atmospheric pressure has led to an investigation on suitable transitions using wavelength modulation spec- troscopy (WMS). The set-up sensitivity has been calculated as 1.73 × 10 −8 cm −1 s 1/2 , and probing the strongest line at 1576.29 nm a minimum detectable concentration of 700 ppb under atmospheric conditions has been achieved. Further- more, pressure broadening coefficients for a variety of buffer gasses have been measured and correlated to the intermolec- ular potentials governing the collision process; the H2S-H2S dimer well depth is estimated to be 7.06 ± 0.09 kJ mol −1 .