Field induced ion-pair formation from ICl studied by optical triple resonance

Multiphoton pathways to the ion-pair states of ICl, at energies close to di ssociation, are presented. These very high vibrational levels (upsilon grea ter than or equal to 10(4)) are detected in the I+ and Cl- channels by puls ed field ionisation. Using a variable time delay before field ionisation, i on-pair states up to 50 cm(-1) below the dissociation limit are shown to su rvive for at least 2 mu s, indicating a stabilisation process analogous to that operating in high Rydberg electronic states. The atomic ion production signal is highly structured both above and below the free ion threshold, i ndicating the role of doorway states which are coupled to the dense ion-pai r manifold near dissociation. This initial coupling appears to be very effi cient and competes successfully with radiative decay and further up-pumping .