Electronic Absorption Spectroscopy of H2X (X=O, Te, Po): Theoretical Treatment of Spin-Orbit Effects

The electronic spectroscopy of H2X (X=O, Te, Po) was investigated by means of spin-orbit configuration interaction (EPCISO) and restricted active space state interaction (SO-RASSI) The transition energies to the low-lying singlet and triplet states of H2O, in which the SO interaction is zero, compare rather well with the experimental data as well as to other theoretical values. The theoretical electronic absorption spectrum is characterized by three allowed transitions A(1)B(1) (2p(x)(O)->sigma(g)*/3s(O)), B(1)A(1) (sigma(g)->sigma(g)*/3s(O)) and A(1)B(2)(sigma(g)->sigma(u)*) calculated at 7.68, 9.94, and 11.72 eV, respectively. The theoretical absorption spectra of H2X (X=Te, Po) are shifted to the red with the A(1)B(1) (np(x)(X)->sigma(g)*) states calculated at 5.06 eV (H2Te) and 4.40 eV (H2Po) and the A(1)B(2) (sigma(g)->sigma(u)*) states calculated at 7.89 eV (H2Te) and 7.77 eV (H2Po). The largest SO splitting amounts to 0.34 eV and is found for the lowest alpha(3)A(1) of H2Po. In H2Te the SO effects are still negligible with a maximum splitting of 0.04 eV for the lowest alpha B-3(2). The two methods lead to comparable results but the EPCISO approach depends strongly on the reference wavefunction.