The geometry, vibrational frequencies, and total atomization energy of ethylene. A calibration study

The anharmonic part of a recently calculated ab initio quartic force field for ethylene has been combined with geometries and harmonic frequencies at higher levels of theory, including expansion to spdfg basis sets and inclusion of core correlation. Resulting fundamentals and ground-state rotational constants have been compared with experiment. Our best estimate for the re geometry is re(CC) = 1.3307 (3) Å, re(CH) = 1.0809(3) Å, θe(CCH) = 121.44(3)°, whic reproduces the experimental rotational constants to 0.01%. The experimental fundamentals and main resonance partners are calculated with a mean absolute error of 2.3 cm−1. Our best calculated total atomization energy, 531.7(5) kcal/mol, falls within the error bar of the experimental value 531.9(3) kcal/mol.