Photo-double ionization of water studied by threshold photoelectrons coincidence spectroscopy

Photo-double ionization of gaseous water has been investigated in the 30-53 eV energy range using synchrotron radiation and the threshold photoelectrons coincidence (TPEsCO) method. The TPEsCO spectrum of H2O, encompassing the formation of the (X) over tilde B-3(1), 1 (1)A(1), (b) over tilde B-1(1) and 2 (1)A(1) states of H2O2+, was recorded. The TPEsCO spectrum is very broad with no discernable vibrational structure. In addition, the TPE spectrum of H2O for the formation of H2O+ was recorded simultaneously. Indirect double ionization of H2O by dissociative autoionization of H2O+ is found to play a major role in the TPEsCO spectrum well below the lowest vertical double IP. (C) 2009 Elsevier B. V. All rights reserved.