An analysis of the F(O u+) ion-pair state of I 2 by optical-optical double resonance

Abstract

An optical-optical double resonance (OODR) technique has been applied to study the spectroscopic details of the F(0 u +) ion-pair state of I 2 which correlates with I −( 1S) + I +( 3P 0) at the dissociation limit. In the excitation scheme, F(0 u +)- B 3Π(0 u +)- X 1Σ g +, the OODR excitation spectra show the vibrational progressions consisting of O, Q, and S branches in accordance with the selection rule (Δ J = 0, ±2) of the F(0 u +)- B 3Π(0 u +) two-photon transition. The F(0 u +)- X 1Σ g + fluorescence is resolved to establish the absolute vibrational numbering of the F(0 u +) state. Dunham parameters of the F(0 u +) state, based on a global least-squares fit analysis of 1184 transitions ( v′ = 0–48, J′ = 6–107), are reported. The main parameters, T e = 47 217.350 cm −1, ω e = 96.313 cm −1, and r e = 3.596 A ̊ , are consistent with the results derived from the vibrational analyses of the F(0 u +)- X 1Σ g + emission in the discharge. Our detailed analysis indicates some evidence that the lower vibrational levels of the F(0 u +) state are perturbed by an ion-pair state.