High-level ab initio study of LiO (X-2 Pi; A(2)Sigma(+)) and LiO+ (X-3 Sigma(-) ; A(3)Pi): the ionization energy of LiO

RCCSD(T) calculations are performed using basis sets of quadruple- and quin tuple-zeta quality. Potential energy curves are calculated for the lowest t wo neutral states of LiO (X(2)Pi and A(2)Sigma (+)), as well as the lowest two triplet states of LiO+ (X(3)Sigma (-) and A(3)Pi). From these curves sp ectroscopic parameters are calculated, including anharmonic vibrational fre quencies and rotational constants. For the X(2)Pi state, excellent agreemen t with microwave and infrared values is obtained. The I separation is calcu lated to be 2419 cm(-1), and the first adiabatic ionization energy (AIE) co rresponding to the process X(3)Sigma (-) <-- X(2)Pi is calculated to be 8.5 5 +/- 0.05 eV. (C) 2001 Elsevier Science B.V. All rights reserved.