A new ionhyphen;pair state of Br2has been observed by an opticalndash;optical double resonance technique utilizing ultraviolet fluorescence detection. The OODR excitations proceed in an onehyphen;photon resonant threehyphen;photon absorption through theB3Pgr;thinsp;(0+u) state. The effects of polarization on their transition strengths are used to determine the symmetry of excited molecular state formed by twohyphen;photon absorption from theBstate. The results indicate that the new state has the 0+usymmetry withTe=53thinsp;899.6(7) cmminus;1, ohgr;e=155.8(2) cmminus;1, andre=3.276(8) Aring; for79Br2. This state is expected to correlate with Br+(3P0)+Brminus;(1S) and named Fthinsp;(0+u) after the wellhyphen;defined I2molecule. The single rovibronic fluorescence spectra of the F(0+u) state show several transitions terminating on lowhyphen;lying valence states.
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