Double-resonance laser excitation and high-resolution energy dispersive photoelectron spectroscopy were used to determine the ionic rotational-state distributions following vibrational autoionization of Rydberg states of water having principal quantum number n = 8-10 and converging to the (X) over tilde B-2(1) (1,0,0) state of H2O+. Where possible, these states were identified by comparison with results of a calculation based on multichannel quantum defect theory. Symmetry and angular momentum constraints link the observed ionic rotational states to particular values of the orbital angular momentum of the Rydberg electron, E, and to the partial-wave composition of the ejected electron. In particular, this connection allows an unambiguous determination of the even or odd character of the partial waves and provides a test of the predicted character of the autoionizing resonances. The effects of l mixing induced by the nonspherical nature of the ionic field are plainly evident in the ion distributions. The present results also allow a tentative assignment of some resonances to the previously unidentified np Rydberg states. (C) 2004 American Institute of Physics.