Sorry, I mis-interpreted what the “one shot” turn does — it turns whole models, not the parts of models on the opposite sides of the bond.  You do need “rotation”, e.g.:

rc(“rotation 0 %s %s” % (a1.oslIdent(), a2.oslIdent())  # set up the bond rotation

rc(“rotation 0 %d” % angle)  # actually rotate the bond

—Eric