An optically thingaseous mixture of Rb and low-density Ne is excited by 570～600 nm of the CW dye laser, The excited RbNe molecule isdissociated into the Rb(5P1/2/) or Rb(5P3/2/). The branching ratio isdefined as Ⅰ(D1/)/Ⅰ(D2/) where Ⅰ(D1/) and Ⅰ(D2/) are measuredintensities of the atomic Rb D1/ and D2/ lines. The branching isdetermined in the Ne density range 2 to 8 × 1017/cm-3/. The ratio ofthe dissociation rates and the fine structure changing cross section are obtained. Finestructrue changing cross section has also been measured for resonant excitation of the Rb52PJ state, the results are discussed.