Complete basis set,G1,G2,G2MP2,and density functional theory computational studies of the lowest energyy triplet potential energy surface for acetylene-vinylidene rearrangement

摘要

The triplet acetylene-vinylidene potential energy surface was explored with the complete basis set,G1,G2,and G2MP2 ab inito methods,as well as with the hybid,gradient-corrected,and local spin approximation density functional methods to explore the possibility of triplet acetylene transformation in metastable vinylidene.For stationary points (triplet trans-acetylene,triplet cis-acetylene,H and CCH radicals,and triplet vinylidene)in their minima with severaltransition state structures the combine this minima were located on the potential energy surface.It was estimated that a global minima on the potential energy surface is the triplet cis-acetylene.Even if the triplet trans-acetylene is formed by excitation the singlet acetylene,it should be transferred into the more stable triplet cis-acetylene without barrier.Triplet cis-acetylene and triplet vinylidene have almost idetical stabilities,but the activation barrier for the formation of triplet vinylidene from triplet cis-acetylene through the 1,2-hydrogne shift is estimated to be 50.4 kcal/mol.The C-H dissociation-recombination mechanism for the triplet cis-acetylene transformation into triplet vinylindene is even higher,suggesting that direct transformation of acetylene into vinylidene through acetylene excitation and then relaxing the fromed products should not be an energetically preferable path.Detainled analysis of the triplet acetylene-vinylidene potential energy surface with both the ab inition and density functional theory methods were disussed.