Preliminary assignments of 2ν3-ν4 hot band of 12CH4 in the 2 μm transparency window from long-path FTS spectra

► The 2ν3-ν4 band of 12CH4 at 2.1 μm was assigned for the first time. ► From assignments, 2ν3(F2) upper state energies were obtained with better accuracy. ► Assignments were based on FTS (Reims) and Kitt peak (Arizona) spectra. ► A new line list of 196 observed and assigned transitions was constructed.