The quantum mechanical calculations performed in this work revealed an interesting nature of the stationary states of an excess electron in the guanine-cytosine (G-C) anion. The electron can form either a dipole-bound (DB) state or a covalent state. The coexistence of the two states may enhance the ability of the G-C dimer to capture an excess electron. (C) 2001 Elsevier Science B.V. All rights reserved.