Knowledge Bank

Rotational spectra have been observed for several $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C/18O$ isotopic species of the pseudolinear acetylene-carbon monoxide dimer using the pulsed, Fourier transform Balle/Flygare microwave spectrometer. Our results complement an earlier report by Legon on the $dimer.1$. A quadrature detection system has been incorporated in the data processing system to avoid folding of the spectrum onto itself in taking the Fourier transform. Dipole moments of 0.3112(12) and 3.29(3) D were determined for the parent species and for HCN-HCCN, respectively. Structural properties were derived from the various measurements, including a well depth of $300cm-1$ from Dj, and the results are compared with those reported earlier for HCN-HCCH. A substitution analysis is developed in which the rotational properties of the pseudolinear dimer are treated as a symmetric $top2$. A simple method is described for determining effects of the off-axis bending of the monomers.