Electronic states of the ultramarine chromophore S-3(-)
Résumé
The potential energy surfaces and the spin-orbit couplings for states correlating with the lowest dissociation asymptote S,,(X-3 Sigma(-)(g)) + S- (P-2) of the radical anion of thiozone have been calculated by full valence complete active space self-consistent field (CASSCF), internally contracted multi-reference configuration interaction (IC-MRCI) and for some of the states also by restricted coupled cluster with perturbative triples (RCCSD(T)) ab initio methods. For six electronic states lying below the electron detachment threshold: (XB1)-B-2, A(2)B(2), B(2)A(1), C(2)A(2), (4)Sigma(-)(g), and the second (2)A(1), equilibrium geometries and harmonic wavenumbers are reported. For the ground state also anharmonic vibrational levels have been evaluated. Due to the intensity borrowing via vibronic coupling with the B(2)A(1) state also the dipole forbidden A-X transition becomes allowed in the Franck-Condon region of the UV spectrum. The C(2)A(2) state responsible for the blue color of ultramarine correlates adiabatically with the first dissociation asymptote S-2(X-3 Sigma(-)(g))+S-(P-2). Along the dissociation path the regions of vibronic and spin-orbit couplings were located. For the Rs2-s larger than about 2.6 angstrom the electron spin-states of the lowest dissociation asymptote are strongly mixed. The properties of the S-3(-) electronic states are compared with those of O-3(-).