Millimeter-wave study of the CO–N 2 van der Waals complex: new measurements of CO– orthoN 2 and assignments of new states of CO– paraN 2

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Rotational transitions of the CO–N 2 van der Waals complex have been measured using the intracavity OROTRON jet spectrometer in the frequency range of 83–133 GHz. For the CO– orthoN 2 spin modification, the observed and assigned 21 rotational transitions belong to the Q- and P-branches of the K=1–0 subband. They complete the previous observation of the corresponding R-branch transitions. In the case of the less abundant form, CO– paraN 2, a new K=1 state, representing simultaneous rotation of both monomers, was detected for the first time. A total of 31 rotational transitions of CO– paraN 2 were assigned to two subbands connecting this new K=1 state with already known lower K=0 and 1 states. The assignments relied in part on energy level differences obtained from precise microwave data. The origin of the newly observed state was determined to be 3.41 cm −1 relative to the K=0 ground state of CO– paraN 2. The analysis yielded rotational parameters, centrifugal distortion parameters and nuclear quadrupole coupling constants due to the presence of two equivalent 14N nuclei for both CO– orthoN 2 and CO– paraN 2.