Coincidence ion pair production (cipp) spectroscopy of diiodine.

Coincidence ion pair production (I + + I - ) (cipp) spectra of I 2 were recorded in a double imaging coincidence experiment in the one-photon excitation region of 71 600-74 000 cm -1 . The I + + I - coincidence signal shows vibrational band head structure corresponding to iodine molecule Rydberg states crossing over to ion-pair (I + I - ) potential curves above the dissociation limit. The band origin ( ν 0 ), vibrational wavenumber ( ω e ) and anharmonicity constants ( ω e x e ) were determined for the identified Rydberg states. The analysis revealed a number of previously unidentified states and a reassignment of others following a discrepancy in previous assignments. Since the ion pair production threshold is well established, the electric field-dependent spectral intensities were used to derive the cutoff energy in the transitions to the rotational levels of the 7pσ(1/2) ( v ' = 3) state.