Identification of a high energy state of I2 by ion dip spectroscopy

A new high energy electronic state of I2 has been characterized by means of ion dip spectroscopy, a two-color multiphoton ionization technique. The method yields rotationally resolved spectra analogous to excited state absorption spectra. The new state is characterized by an extensive 37 cm−1 vibrational progression, an internuclear separation of about 5.3±0.2 Å, and a term energy about 70 000 cm−1, near the ionization limit. Bonding is significantly weaker than in the previously investigated ion-pair states. The new results help to establish the pathway of the multiphoton ionization process in I2.