Detection of stable carbon isotopes of methane with a 2.4-μm distributed feedback laser

Abstract Direct absorption spectra of methane ( 12 CH 4 and 13 CH 4 ) at room temperature have been recorded using a 2.4-μm distributed feedback laser. Integrated cross-sections of 13 CH 4 were measured and compared with those listed in the HITRAN 2008 and 2012 databases, indicating that there are some discrepancies between our results and both editions of the HITRAN database. The pressure-broadening parameters of those 13 CH 4 lines in synthetic air were also examined experimentally. For the purpose of determining the carbon isotope ratio ( 13 CH 4 / 12 CH 4 ) through the spectral measurements, candidate line pairs of 12 CH 4 and 13 CH 4 within the range 4147–4154 cm −1 were explored. Resultantly, the well-isolated line pair of 12 CH 4 at 4151.843 cm −1 and 13 CH 4 at 4151.966 cm −1 was suggested to be a candidate for determining the carbon isotope ratio of CH 4 in this wavenumber region.