This article presents a detailed study of the various conical intersections (ci) related to the four lower states of the title system. The approach is based on freezing the positions of the two hydrogens (the distance between them is assumed to be 2.18 a.u. throughout the present study) and allowing the sodium atom to move, undisturbed, to reveal the locations of the ci's as well as the spatial distribution of their nonadiabatic coupling terms (NACTs). We found altogether seven ci's-one between the ground state and the first excited state, thus a (1,2) ci, two between the first excited state and the second excited state thus (2,3) ci's, and the last four are between the second excited state and the third excited state, thus (3,4) ci's. It was established that the (1,2) ci is a C-2v ci located on the symmetry line orthogonal to the HH axis, the (2,3) ci's are C-2v ci's located on the HH axis (at symmetric positions) and, out of the four (3,4) ci's, two are C-2v ci's located on the above-mentioned symmetry line, and the other two are C-s ci's located on both sides of this symmetry line. It was revealed that all seven ci's are of the elliptic type [Chem. Phys. Lett. 354, 243(2002)], namely their NACTs are concentrated along straight lines-five of them are concentrated along lines parallel to the HH axis and two along the symmetry line vertical to the HH axis. Particular attention is given to two-state, three-state, and four-state quantization. From a practical point of view this study revealed the fact that in general, the two lower states of the Na+H-2 system form an isolated group of states, which implies that the two-state system can be diabatized. (C) 2003 American Institute of Physics.