An ab initio study of the low-lying doublet states of linear and T-shaped Ga center dot N-2

The lowest-lying (2)Pi and (2)Sigma states (linear structure), and (2)A(1), B-2(1), and B-2(2) states (T-shaped structure) of the Ga .N-2 complex were studied by ab initio calculations. The B3LYP, MP2, QCISD, and CCSD(T) meth ods were employed with various all-electron and ECP basis sets to obtain re liable minimum-energy geometries and harmonic vibrational frequencies for t hese electronic states. The ground state was found to be the (X) over tilde (2)Pi state; the other states considered were of ca. 300 cm(-1) higher in energy. The interaction energy (including the full counterpoise correction for basis set superposition error and relativistic correction) of complex f ormation, DeltaE(e)(CP) (Ga .N-2 (X) over tilde (2)Pi), was calculated to b e -1.1 kcal.mol(-1) (-400 cm(-1)) at the RCCSD(T)level with basis sets of b etter than augmented-polarized-valence-quadruple-zeta quality. The best est imates of Do and enthalpy of formation at 298 K for the (X) over tilde (2)P i (1/2,3/2) spin-orbit states are D-0 = 95, 320 cm(-1) and DeltaH(298K) = 0 .07, -0.58 kcal.mole(-1), respectively. Both spin-orbit components of the ( X) over tilde (2)Pi state of Ga .N-2 are weakly bound at 0 K. The complex f ormation of the (X) over tilde (2)Pi (3/2) and (X) over tilde (2)Pi (3/2) s tates are slightly endothermic and exothermic, respectively, at room temper ature.