Observation of a new high-energy, shallow-bound Rydberg state in I2 by optical triple resonance

A new 0u+ 6s Rydberg state built on an excited ionic core of I2 has been observed by optical triple resonance via the B(0u+) valence and E0g+(3P2) ion-pair states with ionization detection. A vibrational progression, v = 0-27, was observed for selected rotational levels and molecular constants are presented. The Rydberg state is weakly bound and was determined to have an internuclear separation of 4.500 ± 0.003 Å.