An analysis of the ion-pair state of I₂ by a sequential three-photon excitation

Abstract

A three-photon absorption technique that utilizes a visible B'II(o:)-X'Z; transition followed by two-photon absorption was applied to characterize the high-lying vibrational levels of the F'O: ion-pair state of 12, which correlates with I-(IS) + I+('D) at the dissociation limit. The multiphoton spectrum was examined at high resolution using either a single tunable dye laser (3PlC), or two independently tunable pump and probe dye lasers (3P2C), operating in the bluegreen region. The one-color spectrum excited by a single laser shows transitions that have not been assigned by previous workers; these rotational lines are interpreted as being due partly to 3P1C transitions to the F'O: ion-pair state, for which molecular constants are derived to be (for