The vibrational energy pattern in ethylene (12C2H4)

All known vibrational energies in (C2H4)-C-12((X) over tilde(1)A(g),) are collected. A block-diagonalized vibrational matrix Hamiltonian is set up, combining a Dunham expansion with the 2/10,10, 11/2,12, and the 5,5/9,9, 1,1/11,11, 1,9/5,11 and 1,11/5,9 anharmonic resonances, with the normal modes numbered according to the most usual conventions in the previous literature. A step by step fitting procedure is applied. Vibrational constants are obtained, and vibrational assignments are provided and discussed. A slightly modified ensemble of vibrational constants is also produced by taking care of a more extended set of resonances between the CH-type vibrations. A new constant of the motion N = 3v(1) + 3v(5) + 3v(9) + 3v(11) + 2v(2) + v(10) + v(12) is demonstrated to support the latter vibrational energy pattern.