The high-resolution fluorescence excitation spectrum was measured in the region of 500—532nm at room temperature.Though the spectrum was rather congested,we could determine the molecular constants such as band origins and rotational and spin-rotation constants for 25 vibronic bands in the two most intense absorption regions 505—510nm and 513—520nm.Among the vibronic bands assigned there were 5 new bands observed and reported in this work.All rotational structures analyzed were of the parallel type.It was shown from the experiment that the high lying vibration levels of ground state X～2Ａ1 had heavily perturbed the electronic excited state A～2Ｂ2.