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 dissociation, are presented. These very high vibrational levels (upsilon greater than or equal to 10(4)) are detected in the I+ and Cl- channels by pulsed field ionisation. Using a variable time delay before field ionisation, ion-pair states up to 50 cm(-1) below the dissociation limit are shown to survive 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, indicating the role of doorway states which are coupled to the dense ion-pair manifold near dissociation. This initial coupling appears to be very efficient and competes successfully with radiative decay and further up-pumping.