Knowledge Bank

We have studied the spectrum of the water molecule above the ionization limit using resonant excitation through a linear intermediate state. Water vapor in a differentially pumped time-of-flight mass spectrometer was excited to the energy region above the first ionization limit using a stepwise resonant $(1+1\prime )$ REMPI process, in which intense VUV light near 118.5 nm pumped selected rotational levels of the $(A~2A1)3pb21B2$ linear electronic state, followed by further excitation by a scanning dye laser. We observed transitions to Rydberg states which we have tentatively identified as belonging primarily to linear states converging to the $A~2A1$ electronic state of the ion. These electronically autoionizing states perturb the bent Rydberg states which we have studied previously.