Pyramidal distortions in the ethylene triplet π,π* state

Pyramidal distortions which may stabilize the triplet π,π* state of ethylene are investigated using ab initio molecular orbital calculations. Using a minimal basis set, the calculated stabilization energies are 5.1 kcal mole^?1 for a cis flapped conformation, 3.6 kcal mole^?1 for a trans flapped conformation, and 0.8 kcal mole^?1 for a twisted flapped conformation. With a double zeta basis set the predicted stabilization energies are much smaller: 1.3, 0.7, and 0.0 kcal mole^?1, respectively.