Optical–optical double resonance spectroscopy of Br2 through the A 3Π(1u) state: Analyses of the 1u and 0−u(3P1) ion-pair states

Abstract

The technique of optical–optical double resonance is applied to study the ion-pair states of Br2 correlating to Br−(1S)+Br+(3P1). The Br2 molecules in the ground state are pumped to the A3Π(1u) state as an intermediate, and subsequently excited into the ion-pair states by a coherent two-photon transition. The double resonance transition is detected through the dispersed fluorescence terminating on the lower valence states. The 1u(3P1) ion-pair state is observed for the first time and the energy level analyses are made on the v=0 to v=10 levels in detail. The 0−u (3P1) state is also identified through the heterogeneous interaction with the 1u(3P1) state, which is interpreted in terms of the pure precession approximation. The molecular parameters thus obtained in the Dunham expansion are Y00=53 257.605(10), Y10=164.1571(69), Y20=−0.7588(15), Y30=5.650(98)×10−3, Y01=0.040 011 6(40), Y11=−1.7488(42)×10−4, and Y02=−8.40(53)×10−9 for the 1u(3P1) state of 79Br2 isotope species (all in cm−1 with 3σ in parentheses). The main parameters of the 0−u(3P1) state are Y00=53 479.72(25), Y10=148.620(54), and Y01=0.038 021 5(79).