The high-resolution infrared absorption spectra of eight2H or13C substituted isotopomers of diacetylene have been recorded, and the bands corresponding to the v4 fundamental and v6 combination of the major isotopomer have been analyzed using a Loomis-Wood-type program. Effective ground-state rotational constants have been obtained from ground-state combination differences. A number of r0, rs, rmς, and (rmς)corr structures have been calculated from the available data and are compared to those obtained by ab initio methods. The (rmς)corr structure, which is a reliable near-equilibrium structure of diacetylene, is rC-H=106.131(13) pm;rC-C=137.081(16) pm;rC-C=120.964(14). (rmς)corr structures of the related molecules cyanogen, cyanoacetylene, and cyanodiacetylene have been calculated, and near-equilibrium structures of triacetylene and dicyanoacetylene have been predicted.
- infrared spectroscopy