Knowledge Bank

This paper summarizes the results of a comprehensive study of the infrared spectrum of monodeuteroacetylene, $C2HD$, in the spectral region 6000 - $600cm-1$. About forty bands have been recorded under high resolution and analyzed during a four year period. The observation of all five fundamentals as well as a large number of overtone and combination bands has allowed construction of an extensive vibrational energy level scheme for $C2HD$. The observations include levels of the types $\Sigma +,\Sigma -,\Pi$ and $\Delta$. Several interesting cases of vibrational-rotational interactions were observed and interpreted for this molecule. Consistent sets of vibrational, rotational and interaction parameters have been determined which reproduce the observational data to within experimental uncertainties of 0.005 - $0.010cm-1$. These parameters include new equilibrium inertial and distortion constants. The relationship of these data to those of other acetylene isotopic species will also be discussed.