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 3B1, 1 1A1, b 1B1 and 2 1A1 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.