High-Resolution Fourier Transform Infrared Spectrum of the ν 12 Fundamental Band of Ethylene (C 2H 4)

The infrared spectrum of the ν₁₂ fundamental band of ethylene (C₂H₄) has been measured with an unapodized resolution of 0.004 cm^-1 in the frequency range of 1380-1500 cm^-1 using the Fourier transform technique. By assigning and fitting a total of 1387 infrared transitions using a Watson's A-reduced Hamiltonian in the I^r representation, rovibrational constants for the upper state (v₁₂ = 1) up to five quartic and three sextic centrifugal distortions terms were derived. They represent the most accurate constants for the band so far. The rms deviation of the fit was 0.00033 cm^-1. The A-type ν₁₂ band with a band center at 1442.44299 ± 0.00003 cm^-1 was found to be relatively free from local frequency perturbations. The inertial defect ∆₁₂ was found to be 0.24201 ± 0.00002 u Ų.