Feshbach resonances in the water molecule revealed by state-selective spectroscopy
We employ triple-resonance vibrational overtone excitation to access quasibound states of water from several fully characterized bound states of the molecule. Comparison of the measured dissociation spectra allows a rigorous assignment of rotational quantum numbers J, nuclear spin and parity and a tentative vibrational characterization of the observed resonances. Their asymmetrical shapes (Fano profiles) reflect interference of dipole moments for transitions to these resonances with that to the dissociative continuum. The assignments and Fano profile parameters of the resonances stand as a benchmark for the extension of accurate quantum-mechanical calculations to activated complexes of water. The narrow widths of some of these resonances indicate that water molecules may survive for as long as up to 60 ps in states above the dissociation threshold. We consider the possible implication of such long-lived states for the kinetics of water dissociation and the OH+H association reaction.