Knowledge Bank

The weakly-bound $CO-N2$ complex was $studieda$ in the 4.7 $\mu$m infrared region of the CO stretching vibration using a continuous slit-jet supersonic expansion and a tunable diode laser spectrometer. A total of 152 lines were observed and assigned to four connected subbands with $K=0\leftarrow 1,0\leftarrow 0,1\leftarrow 0$, and 2$\leftarrow $1, and to one unconnected subband with $K=1\leftarrow 1$ Analysis of these bands yielded $K$-state origins, rotational parameters, and centrifugal distortion parameters. The effective intermolecular separation for the complex in its ground state was found to be 4.025 \AA, and predictions of rotational frequencies were made to aid in the search for $CO-N2$ microwave transitions. The spectra observed were surprisingly simple and well-behaved, to the extent that they could virtually be ascribed to a (fictitious) complex of CO with a rare gas atom having a mass of 28 amu. This simplicity may be explained by postulating that the $N2$ undergoes relatively free internal rotation in the complex. All but one of the observed bands involved levels which correlate with the rotationless $J=0$ state of ortho-$N2$. Along with a more limited report of the same $K=1\leftarrow 0$ subband by Kawashima and $Nishizawa,b$ the present work represents the first spectroscopic observation of this rather basic complex. Further infrared, microwave and theoretical studies should be combined in order to learn more about the orientational structure and intermolecular potential of $CO-N2$.