Coincidence ion pair production (cipp) spectroscopy of diiodine

Abstract

Coincidence ion pair production (I⁺ + I⁻) (cipp) spectra of I₂ 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 (ν⁰), vibrational wavenumber (ω_e) and anharmonicity constants (ω_ex_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.