Twohyphen;photon laserhyphen;induced fluorescence of theAthinsp;2Sgr;+minus;Xthinsp;2Pgr;isystem of the OH molecule, produced in the burnt gases of a methanehyphen;air flame, has been studied. Over 100 rotational lines in the (0,0) band have been identified and the measured line strengths agree with calculations. The absolute cross section for the (0,0) band is between 2 and 8times;10minus;32cm4/W and the relative intensities for (0,0), (1,1), and (1,0) are 100:25:1. These are compared with theoretical calculations in order to identify the intermediate state(s) responsible for the absorption strength. Good agreement with the absolute magnitude and both ratios is obtained by assuming that nearbyv,thinsp;Jlevels of both theAandXstates serve as the intermediates.
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