SPECTROSCOPY AND MULTICHANNEL QUANTUM-DEFECT THEORY ANALYSIS OF THE NP RYDBERG SERIES OF H3

The lowest np Rydberg series of triatomic hydrogen has been studied using optical-optical double-resonance excitation from the metastable 2p2 A2" level. Bound states, detected by field ionization as well as autoionizing states of the p series are characterized using rotational multichannel quantum-defect theory. Deviations from the calculations appear when vibrational interactions give rise to predissociation below threshold or autoionizing interlopers above threshold. The np Rydberg manifold of H-3 provides an almost complete panorama of channel interactions in a polyatomic molecule: rotational and vibrational interactions and autoionization with rich Fano profile structure as well as predissociation.