On the theoretical description of nuclear quadrupole coupling in Π states of small molecules

Axial ( eQq 0 ) and perpendicular ( eQq 2 ) nuclear quadrupole coupling constants were evaluated from the electric field gradient at the quadrupolar nuclei ( 7 Li, 14 N, 17 O, 33 S, 35 Cl) in diatomic (LiO, CN, NH +, NH, N 2 +, NO, OH, HCl +, CCl, OCl, NS) and polyatomic (C 2 N, C 4 N, NCO, N 3 ) Π states. For diatomics the nuclear quadrupole coupling constants (NQCCs) were determined as a function of the vibrational quantum number. The calculations were performed using the internally contracted multireference configuration interaction and single-configuration coupled-cluster approaches with large correlation-consistent basis sets. The overall quality of the wave functions was tested by comparing the calculated electric dipole moments and diatomic spectroscopic constants with external data. The calculated NQCCs were discussed and compared with previous experimental and theoretical studies.