The ν12 band of ethylene-1-13C (13C12CH4) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν12 fundamental band of ethylene-1-13C (or 13C12CH4) was recorded with an unapodized resolution of 0.0063 cm−1 in the wavenumber region of 1360-1520 cm−1. Rovibrational constants for the upper state (ν12 = 1) up to five quartic and two sextic centrifugal distortion terms were derived for the first time by assigning and fitting a total of 879 infrared transitions using a Watson's A-reduced Hamiltonian in the Ir representation. The root-mean-square deviation of the fit was 0.00066 cm−1. The ground state rovibrational constants were also determined by a fit of 523 combination-differences from the present infrared measurements, with a rms deviation of 0.00090 cm−1. The A-type ν12 band which is centred at 1439.34607 ± 0.00004 cm−1 was found to be relatively free from local frequency perturbations. From the ν12 = 1 rovibrational constants obtained, the inertial defect Δ12 was found to be 0.242826 ± 0.000002 μÅ2.