Perturbation-facilitated optical-optical double-resonance spectroscopy of the 1(u)(D-1) and 2(u)(D-1) ion-pair states of I-2 through the parity mixing intermediate state

We have analyzed the 1(u)(D-1) and 2(u)(D-1) ion-pair states of I-2 by pert urbation-facilitated optical-optical double resonance using the B(3)Pi (0(u )(+)) similar to c1g mixing state as an intermediate. The double-resonance spectra exhibited the strong vibrational progression to the lu(ID) state in accord with the Delta Omega = 0 propensity rule for the valence to ion-pai r state transitions. With the state selection in the intermediate state, ea ch progression shows a simple rotational structure consisting of P and R do ublets, while the extra lines were found in some vibrational states. We int erpreted the occurrence of the extra lines as the interaction with the 2(u) (D-1) state lying closely and extended our observation to its lower vibrati onal states. Finally we identified the 1(u)(D-1) state in the 0 less than o r equal to v < 31 range and the 2(u)(D-1) state in the 0 less than or equal to v less than or equal to 9 range, and analyzed their energy levels inclu ding the heterogenous interaction. The 1(u)(D-1)-2(u)(D-1) interaction was found to be described in the pure precession approximation and the precious molecular constants were reported for the 1(u)(D-1) and 2(u)(D-1) ion-pair states. (C) 2001 Academic Press.