Ab-initio MRD-CI Studies of electric field gradient (efg) and dipole moment of CCN radical at CASSCF optimized geometries for X-2 Pi, a(4)Sigma(-), A(2)Delta, B-2 Sigma(-) and C-2 Sigma(+) electronic states

X(2)Pi, a(4)Sigma(-), A(2)Delta, B(2)Sigma(-) and C(2)Sigma(+) states of CC N radical have been studied using complete active space self-consistent fie ld (CASSCF), multi-reference singles and doubles configuration interaction (MRD-CI) methods. The optimized geometry for electronic states under consid eration seems to be sensitive towards the choice of active orbitals in CASS CF calculations. The equilibrium excitation energies obtained from extrapol ated energies in MRD-CI calculation are in excellent agreement with experim ental results for X(2)Pi-->A(2)Delta and X(2)Pi-->C(2)Sigma(+) systems. The equilibrium excitation energy (T-c), electric field gradient (efg), and di pole moment are sensitive towards the selection of reference configurations , number of roots treated simultaneously, threshold value (T) for configura tion selection and quality of starting one-particle basis molecular orbital s in MRD-CI calculations. Natural orbitals (NO's) obtained from iterative n atural orbital procedure (INO) are very good starting one-particle molecula r orbitals for reliable prediction of one-electron properties in MRD-CI cal culations.