Rovibrational structures of the pseudorotating lithium trimer ~(21)Li_3:Rotationally resolved spectroscopy and ab initio calculations of the A~2E''-X~2E'system

摘要

Based on resonant two-photon ionization of 21Li3 with cw lasers and mass-selective detection of 21Li~ ions by a quadrupole mass spectrometer, isotope-selective rotationally resolved spectra of vibronic bands in the electronic A 2E’?—X 2E’ system have been recorded. The complex but completely resolved spectra could be analyzed using optical—optical double resonance techniques in combination with accurate ab initio calculations which provide potential energy surfaces and rovibronic term values for both electronic states. A detailed comparison between experimental and theoretical results for the (v~ =0, v~=0, v~0>—(v’=0, v~=0, v~=0) band demonstrates excellent agreement. The coupling between pseudorotation and rotational motion is shown to produce complex level patterns which, however, can be accurately represented by an effective pseudo/rotation Hamiltonian in terms of rotational and coupling constants that directly provide structural information. For both electronic states the nuclear dynamics is adequately described as a motion on a single adiabatic potential surface with a geometric phase in for closed loops around the conical intersection at D3h geometries.