Rydberg state dynamics of rotating, vibrating H3 and the Jahn–Teller effect

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Abstract
We extend a recently developed multichannel quantum defect theory (MQDT) of electron half-collisions with a triatomic ion. The calculations reproduce much of the observed photoabsorption spectrum of H3 near its lowest ionization thresholds. The method utilizes a rovibronic frame transformation that accounts simultaneously for vibrationally and rotationally inelastic collisions (preionization) and for l-uncoupling effects. Jahn–Teller interactions among degenerate Rydberg states play a crucial role in the formulation. Although H3 is a weak Jahn–Teller molecule, this interaction is responsible for major resonance features seen in the experimental photoabsorption spectra. Calculations over an extended photon energy range for photoabsorption from the H3 (1s23s 2A1′, vi=0, Ni=1, Ki=0) initial state into final states with total angular momentum Nf=0,1,2 are given for parallel and perpendicular (Mi=0, ‖Mf‖=0,1) polarization schemes for the excitation. In spectral regions where experiments have been carried out, semiquantitative agreement with experiment is obtained. The limitations of the present theory are briefly discussed.