Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV

By analyzing the data sets of 17.3 pb${}^{-1}$ taken at $\sqrt{s}=3.773$ GeV and 6.5 pb${}^{-1}$ taken at $\sqrt{s}=3.650$ GeV with the BESII detector at the BEPC collider, we have measured the observed cross sections for 12 exclusive light hadron final states produced in $e^{+}{e}^{-}$ annihilation at the two energy points. We have also set the upper limits on the observed cross sections and the branching fractions for $\psi (3770)$ decay to these final states at 90% C.L.