Electronic States of the Ultramarine Chromophore S3 -

Abstract

The potential energy surfaces and the spin–orbit couplings for states correlating with the lowest dissociation asymptote S2(X 3 Σ - g ) + S-(2 P) 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: X 2 B 1, A 2 B 2, B 2 A 1, C 2 A 2, 4 Σ 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 S2(X 3 Σ - g ) + S-(2 P). Along the dissociation path the regions of vibronic and spin–orbit couplings were located. For the R S2 - S larger than about 2.6Å the electron spin-states of the lowest dissociation asymptote are strongly mixed. The properties of the S3 - electronic states are compared with those of O3 -.