Ethylene-1-¹³C (¹³C¹²CH₄): First analysis of the ν₂, ν₃ and 2ν₁₀ bands and re–analysis of the ν₁₂ band and of the ground vibrational state

High-resolution FTIR ro-vibrational spectra of the ¹³C¹²CH₄ molecule in the region of 600–1700 cm⁻¹, where the bands ν₃, ν₁₂ and ν₂ are located, were recorded and analyzed with the Hamiltonian model. This model takes resonance interactions between these three bands as well as strong interactions with six neighboring bands, ν₁₀, ν₈, ν₇, ν₄, ν₆, and 2ν₁₀ into account. More than 3800 ro-vibrational transitions belonging to the bands ν₃, ν₁₂, ν₂ and 2ν₁₀ were assigned (for the first time for the ν₂, ν₃ and 2ν₁₀ bands) with the maximum values of quantum numbers J^max./K_a ^max. equal to 22/8, 52/18, 30/11 and 27/12, respectively. On this basis, a set of 62 vibrational, rotational, centrifugal distortion and resonance interaction parameters was obtained from the weighted fit. These parameters reproduce 1562 initial “experimental” ro-vibrational energy levels obtained from unblended lines with the rms error d_rms=2.6×10⁻⁴cm⁻¹. Furthermore, ground state parameters of the ¹³C¹²CH₄ molecule were improved.