Theoretical study of the electronic structure of MCH_2~+(M=Fe,Co,Ni)

摘要

State of the art coupled cluster(CC)methods are applied to accurately characterize the ground state electronic structure and photoelectron spectra of transition metal carbene ions MCH_2~+(M=Fe,Co,and Ni).The geometries and energies of the lowest energy quartet,triplet,and doublet electronic states as well as several low-lying vertical excitation energies of FeCH_2~+,CoCH_2~+,and NiCH_2~+are reported.The excitation energies are computed using the equation-of-motion CC and for states of different symmetries,by the energy differences of single reference ground and excited states(DELTA-CC).The latter employ several reference states;the unrestricted Hartree-Fock,restricted open shell Hartree-Fock,and unrestricted Kohn-Sham.We conclude that the 2A1 electronic ground state of NiCH_2~+is separated by about 30.0 kJ/mol from the next highest state,and the lowest 4B1 and 4B2 states of FeCH_2~+as well as the 3A2 and 3A1 states of CoCH_2~+are nearly degenerate.The presence of metal-pi*_(MCH2)charge transfer states with significant oscillator strengths in the visibleear-UV energy domain of the theoretical spectra of FeCH_2~+and CoCH_2~+are at the origin of the photofragmentation of these compounds observed after irradiation between 310 and 360 ran.