Double-resonance spectroscopy of quasi-linear Rydberg states of water

We have studied quasi-linear autoionizing Rydberg states of the water molecule with three quanta of bending vibration using double-resonance excitation through the quasi-linear (Ã)3pb2 state. The use of double resonance resulted in vibrational and rotational selectivity which led to simple, easily understood spectra. We have identified and performed an analysis on one ns series and two nd series ~s and p!, yielding quantum defects for the series and an improved value of the energy of the ionic state which is the convergence limit for these Rydberg states. At low n, the 4dp state showed vibronic splitting consistent with the S–D splitting in the ion core. This splitting vanished at high n as the Rydberg electron uncoupled from the ion core. Comparison of the spectra of bent and linear states in the same energy region displayed the effects of linear-bent interactions on the Rydberg spectrum. © 2002 American Institute of Physics. @DOI: 10.1063/1.1516794#