Rovibronic structure of Rydberg and non-Rydberg states of H2O and D2O

High-resolution vacuum ultraviolet absorption spectra of H 2 O are reported. The rotational structures of the bands below 1200 AA have been resolved for the first time and yield a wealth of new rovibronic information both below and above the first two ionisation potentials. The resolving power of the authors' apparatus is at least equal to the highest resolving power previously achieved at 1240 AA in studies of H 2 O but our experimental method is not limited, as were the earlier ones, to wavelengths longer than 1190 AA. Surprising aspects of rotational structure in the 5s state are commented upon in the light of the group theoretical characterisation of the vacancy. Corresponding observations for D 2 O have also been made.