Multichannel quantum defect analysis of the double resonance photoionization series of $H2O$

A new analysis is presented of the recent photoionization spectrum of $H2O,$ excited by double resonance via several rotational sublevels of the (100) vibrational level of the $C̃(1B1)$ state. Evidence for a previously unsuspected strong f series indicates significant d orbital contamination of the nominal p orbital in the intermediate state. This is the first report of an f series in the Rydberg state of any asymmetric top. Previous d series analyses of single-photon photoionization spectra terminating on the (100) level of $H2O+$ are also corrected and extended to a wider range of excited rotational electronic states. The d series appears to contain absent lines, indicative of predissociation. Some lines remain unassigned, but there is no systematic evidence of either s or p series.