The X-2 Sigma(+), A(2) Pi, B-2 Sigma(+) C-2 Sigma(+) states of LiAr and the ground state of LiAr+ are calculated by configuration interaction methods. The existence of a double potential well is found for the C-2 Sigma(+) state. The origin of the double well is surmised to lie in the existence of a nodal plane separating two radial regions of the electron density in the Rydberg atomic orbital. The spectroscopic constants and the transition properties between the calculated states are also reported. (C) 1997 Elsevier Science B.V.