STRUCTURE AND EPR PARAMETERS OF CUC2H2 FROM A DENSITY-FUNCTIONAL APPROACH

The structure, binding energy and harmonic force field of CuC2H2 have been studied using local and gradient-corrected density functionals, All the functionals indicate that the (2)A' electronic state of a C-s vinylic structure corresponds to the absolute energy minimum, whereas the (2)A(2) electronic state of the symmetric C-2v structure corresponds to a low-lying transition state governing the exchange of carbon atoms. The inclusion of gradient corrections and basis set superposition error brings the computed binding energy into reasonable agreement with experiment. The computed hyperfine coupling constants are in good agreement with experiment only for the C-2v structure. Taking into account the low energy difference and the strongly different dipole moments of C-s and C-2v structures, it is possible that matrix trapping alters the relative stabilities of different structures.