Low-temperature absorption spectrum of the (0120)-(0000) <sup>13</sup>CH<sub>4</sub> band. Line assignment
The <sup>13</sup>CH<sub>4</sub> absorption spectra in the range between 7400 and 7600 cm<sup>-</sup><sup>1</sup> have been recorded at for temperatures from 296 to 200 K by the Fourier spectrometer IFS-125M at a spectral resolution of 0.03 cm<sup>-</sup><sup>1</sup>. A 220 cm cell was used, which provided a threshold sensitivity to absorption on the order of 10<sup>-</sup><sup>6</sup> cm<sup>-</sup><sup>1</sup>. Line assignment of the n<sub>2</sub> + 2n<sub>3 </sub>band of the <sup>13</sup>CH<sub>4</sub> molecule was performed. Rotational constants of the (0120) state and the integral intensity of the n<sub>2</sub> + 2n<sub>3</sub><sup>13</sup>CH<sub>4</sub> band were determined for the first time.