The absorption spectrum of 13CH4 in the region of the 2ν3 band at 1.66 µm: Empirical line lists and temperature dependence

•Spectra of “pure” 13CH4 recorded in the 2ν3 region at 80 K and 296 K.•Empirical list of 7207 and 3717 lines are constructed at 296 and 80 K, respectively.•The 2-Temperature method is applied.•2782 Empirical lower state energy values are determined.

The absorption spectrum of 13CH4 has been recorded at 296 K and 80 K by differential absorption spectroscopy (DAS) in the high energy part of the tetradecad (5853-6201 cm−1) dominated by the 2ν3 band near 5988 cm−1. The achieved noise equivalent absorption of the spectra (αmin≈1×10−7 cm−1) allowed us to double the number of 13CH4 lines previously measured in the region (our lists include about 7200 and 3700 lines at 296 and 80 K, respectively). Empirical values of the lower state energy level, Eemp, were systematically derived from the intensity ratios of the lines measured at 80 K and 296 K. Overall 2782 Eemp values were determined extending significantly the previous set of about 1200 Eemp values available in the literature. The corresponding empirical values of the rotational quantum number, Jemp, show a clear propensity to be close to an integer, illustrating the validity of the method. The line lists at 296 K and 80 K, provided as Supplementary material, are discussed in relation with line lists and rovibrational assignments available in the literature.