High-precision laser spectroscopy of H2S for simultaneous probing of multiple-sulfur isotopes

The simultaneous monitoring of the triple stable S-isotopes (32S, 33S and 34S) of hydrogen sulfide has been conducted with a VCOF-CRDS set-up (a V-shaped cavity for optical feedback coupled to a cavity ring down spectrometer). The spectroscopic investigation of H2S was performed for the first time in the near-infrared region (≈1.6 μm) with a stabilized laser of linewidth < 1 kHz and an optical pathlength of 90 km, providing unparalleled sensitivity and precision. Pressure dependencies of the system were explored to as low as 0.1 mbar revealing the Lamb dip feature of the isotopologue transitions. A model was developed to fit experimental spectra with accuracy better by one order of magnitude than what the literature provides. The S-isotope composition δ34S and S-isotope anomaly Δ33S are determined with an uncertainty of 5 × 10−6 within 10 seconds, limited by H2S reactivity inside the measurement cell. Such high precision represents a new benchmark for laser spectroscopy of H2S and optical determination of isotopic measurements and makes VCOF-CRDS a promising tool for a plethora of future applications.