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 s ubstituted isotopomers of diacetylene have been recorded, and the band s corresponding to the v(4) fundamental and 2v(6) combination of the m ajor isotopomer have been analyzed using a Loomis-Wood-type program. E ffective ground-state rotational constants have been obtained from gro und-state combination differences. A number of r(0), r(5), r(m)(rho), and (r(m)(rho))(corr) structures have been calculated from the availab le data and are compared to those obtained by ab initio methods. The ( r(m)(rho))(corr) structure, which is a reliable near-equilibrium struc ture 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 cal culated, and near-equilibrium structures of triacetylene and dicyanoac etylene have been predicted.