An analysis of the F′(0 u+) ion-pair state of I 2 by optical-optical double resonance

Abstract

An optical-optical double resonance technique utilizing a stepwise three-photon transition has been applied to study the F′(0 u +) ion-pair state of I 2 which correlates with I −( 1S) + I +( 1D) at the dissociation limit. Two pulsed tunable dye lasers are used to excite the molecules to appropriate levels of the B 3Π(0 u +) state, and subsequently into the F′(0 u +) state by a simultaneous two-photon transition. The optical-optical double resonance excitation spectra show 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 absolute vibrational numbering of the F′(0 u +) state is established by the direct observation of the F′(0 u +)- X 1Σ g + fluorescence interpreted using the Franck-Condon factor calculations. Dunham parameters of the F′(0 u +) state, based on a global least-squares fit analysis of 1361 transitions ( v′ = 0–38, J′ = 6–108), are Y 00 = 51706.237(2), Y 10 = 131.00041(83), Y 20 = −0.516270(143) Y 30 = 4.2640(104) X 10 −3, Y 40 = −4.5797(330) X 10 −5, Y 50 = 2.8381(376) X 10 −7 Y 01 = 0.02194899(46), Y 11 = −9.2508(99) X 10 −5, Y 21 = 8.359(79) X 10 −7 Y 31 = −8.550(167) X 10 −9, andY 02 = −2.632(37) X 10 −9 (all in cm −1 with 1 SD in parentheses).