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

- Direct absorption spectra of 12CH4 and 13CH4 in the 4150 cm−1 region were acquired.
- There are some discrepancies in the integrated cross-sections of 13CH4 between our measurements and the HITRAN database.
- We investigated line pairs of 12CH4 and 13CH4 for their possible application for determining the 13CH4/12CH4 ratio.

Direct absorption spectra of methane (12CH4 and 13CH4) at room temperature have been recorded using a 2.4-μm distributed feedback laser. Integrated cross-sections of 13CH4 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 13CH4 lines in synthetic air were also examined experimentally. For the purpose of determining the carbon isotope ratio (13CH4/12CH4) through the spectral measurements, candidate line pairs of 12CH4 and 13CH4 within the range 4147-4154 cm−1 were explored. Resultantly, the well-isolated line pair of 12CH4 at 4151.843 cm−1 and 13CH4 at 4151.966 cm−1 was suggested to be a candidate for determining the carbon isotope ratio of CH4 in this wavenumber region.