The electron capture dynamics in water dimer (H2O)(2) has been investigated by means of direct ab initio trajectory method. It was found that the solvent reorientation of the water cluster anion occurs spontaneously following the vertical electron capture of the neutral water dimer: namely, the linear form water dimer which is the most stable structure of neutral water dimer, was drastically changed by accepting an excess electron to a dipole orientation form in which the two dipoles of the water molecules coordinate equivalently to the excess electron. The electron was located around the center of two water molecules at the final structure. The water dimer's solvation time was calculated to be about 150-400 fs. The mechanism of the solvent reorientation was discussed on the basis of theoretical results. (C) 2003 Elsevier Science B.V. All lights reserved.