PURE ROTATIONAL SPECTRUM AND STRUCTURE OF THE BENZENE-CO VAN-DER-WAALS COMPLEX

Pure rotational transitions of four isotopic species of the benzene-CO van der Waals complex have been observed in the microwave region betw een 8-18 GHz. Double resonance experiments on the parent species have been used to confirm the assignment of the spectrum resembling that of a symmetric top. The structure of the complex, with CO above the plan e of benzene, has been determined from the measured moments of inertia for the isotopic species. Only an upper limit for the barrier to inte rnal rotation of CO may be derived in the absence of transitions in ex cited internal rotation states.