The O Is photoelectron spectrum of water was recorded with the resolution high enough to resolve the vibrational structure of the O 1s(-1) state and the lifetime width and the Franck-Condon (FC) factors were extracted. The experimental spectrum was reproduced well by the molecular ab initio calculations based on the symmetry adapted cluster-configuration interaction (SAC-CI) method. The vibrational structure was attributed mostly to the bending mode of the core-ionized molecule. (C) 2003 Elsevier B.V. All rights reserved.