SEQUENTIAL 2-PHOTON EXCITATION VIA REPULSIVE INTERMEDIATE STATES

Large bond extensions almost-equal-to 1 angstrom are reported in a two -photon bound-to-bound optical excitation via a repulsive intermediate electronic state. In a one-colour experiment on I2, the ion-pair E st ate is accessed in the sequence E(0g+) (upsilon' almost-equal-to 40-70 ) <-- B(0u+) <-- X with the pump/probe wavelength scanned near the pro minent red extremum of the E-B transition. At this wavelength the cont inuum of the B state is reached in the first step, rather than the bou nd levels conventionally used in OODR spectroscopy. The classical poin t of transition that conserves atomic momentum for the second step the n occurs near R(e) of the ion-pair state.