The reaction gamma d to pi /sup 0/X has been measured with TAPS at MAMI in the energy range E/sub gamma /=140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation functions of integral and differential total cross-sections show no structures of statistical significance gt 2 sigma . Upper limits for the production of narrow isoscalar or isovector dibaryons with masses m lt or=2100 MeV/c/sup 2/ were deduced. They are in the range 2-5 mu b averaged over the 0.8 MeV energy resolution.