Submillimeter wave spectrum of 12C(H)3^(35)Cl in the (v)6=1 state

A set of 36 new microwave transitions have been measured for o-benzyne, generated by pyrolysis of phthalic anhydride. All 50 known rotational transitions have been fitted to give an improved set of rotational and centrifugal distortion constants. A short waveguide based microwave spectrometer designed specifically for short lived species is described.