Numerical investigation of the (s+p)(X)T1usystem: I. Vibronic eigenstates and absorption spectra

Abstract

The eigenvalue problem of the ideal (s+p)(X)T1u pseudo-Jahn-Teller system is solved by numerical diagonalisation of the energy matrix. Low- and high-energy vibronic eigenstates, absorption lines and spectra at zero temperature are computed for representative values of the electronic 2s-2p spacing in all coupling regimes. In addition the semiclassical absorption lineshape function is calculated: best agreement with the absorption spectra is found for strong coupling. The computational results suggest especially for high energies a factorisation of the vibronic eigenstates for all coupling strengths. A reclassification of the vibronic states is then useful, which provides a link with the adiabatic energy surfaces, enabling a unified description of the absorption spectra. The system exhibits an optical resonance effect, and the calculations show under what conditions this effect can be neglected.