High-resolution Fourier transform infrared spectroscopy and analysis of the ν12 fundamental band of ethylene-d4

The Fourier transform infrared (IR) spectrum of the ν12 fundamental band of ethylene-d4 (C2D4) has been measured with an unapodized resolution of 0.004 cm−1 in the frequency range of 1030–1130 cm−1. A total of 1340 assigned transitions have been analyzed and fitted using a Watsonʹs A-reduced Hamiltonian in the Ir representation to derive rovibrational constants for the upper state (v12=1) up to five quartic terms with a standard deviation of 0.00042 cm−1. They represent the most accurate constants for the band thus far. The ground state rovibrational constants were also further improved by a fit of combination–differences from the IR measurements. The relatively unperturbed band was found to be basically A-type with a band centre at 1076.98492±0.00003 cm−1.