Theoretical study of activation of the C-H bond in C2H4 by the group 5 metal atoms (V, Nb, Ta) in the gas-phase

► Reactants, intermediates and transition states are calculated. ► Many minimum energy crossing points (MECPs) are found. ► The computed SOC matrix elements are strong in these regions for the MECP3. ► Intersystem crossing takes place with a large probability.