DETERMINATION OF THE MOLECULAR-STRUCTURE OF DIACETYLENE FROM HIGH-RESOLUTION FTIR SPECTROSCOPY

The high-resolution infrared absorption spectra of eight H-2 or C-13 substituted isotopomers of diacetylene have been recorded, and the bands corresponding to the v(4) fundamental and 2v(6) 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 r(0), r(5), r(m)(rho), and (r(m)(rho))(corr) structures have been calculated from the available data and are compared to those obtained by ab initio methods. The (r(m)(rho))(corr) structure, which is a reliable near-equilibrium structure of diacetylene, is r(C-H) = 106.131(13) pm; r(C-C) = 137.081(16) pm; r(C=C) = 120.964(14). (r(m)(rho))(corr) structures of the related molecules cyanogen, cyanoacetylene, and cyanodiacetylene have been calculated, and near-equilibrium structures of triacetylene and dicyanoacetylene have been predicted.