Knowledge Bank

The infrared spectrum of the weakly-bound Ar-CO van der Waals complex in the $2150cm-1$ region of the CO stretch has been studied using a continuous supersonic slit jet expansion coupled with a tunable laser spectrometer, and also with a cooled (57 K) long-path cell coupled with a Fourier transform spectrometer. Seven new subbands were observed, and numerous previously observed bands were observed in greater detail. Four substates were thus identified for the first time, including the excited van der Waals stretching state, $v3=1$, and the excited bend, $v2=1$, within the ground CO stretching state, $vco=0$. The observed bending bending and stretching frequencies were $v2$ = $12.014cm-1$ and $v3=18.110cm-1$ (for $vco=0$). A comprehensive simultaneous analysis was made of all the existing infrared and microwave data on the complex for levels with , in order to obtain an accurate and self-consistent set of substate origins, rotational parameters, and centrifugal distortion parameters. A strong Coriolis interaction between $K=1$ of the bend and $K=0$ of the stretch was analyzed in detail. The results are in rather good agreement with energy level calculations by G. $Jansena$ which are based on an adjusted ab initio potential surface. These calculations also indicate that there is considerable mixing of bending and stretching in Ar-CO, so that, for example, labeling the $12cm-1$ vibration as the ‘bend’ is only very approximate.