A Spectroscopic Study of the <i>D</i>() Ion‐Pair State of I₂ by Optical–Optical Double Resonance

Abstract

The D ( ) ion‐pair state of I 2 has been analyzed by the optical–optical double resonance (OODR) technique. In a stepwise three‐photon excitation scheme, D ( )– B 3 Π( )– X 1 , the D ( ) state appeared in the OODR spectrum as the vibrational progressions consisting of O , Q and S branches in accord with the rotational selection rule of Δ J = 0 and ±2 for the coherent two‐photon transition from the B 3 Π( ) state. The D ( )– X 1 fluorescence was resolved to determine the absolute vibrational numbering of the D ( ) state. We derived Dunham parameters effective for ν = 0 through ν = 124 which were used to construct a Rydberg–Klein–Rees (RKR) potential curve.