Structural studies of linear molecules by microwave spectroscopy

Abstract : Rotational constants were measured for several isotopic forms of fluorine cyanide and fluoro acetylene. Accurate bond-distances were computed for all the halogen cyanides and for fluoro- and chloracetylene, by the method of isotopic substitution at all atoms (except F and I). The CF bonds in these compounds are the shortest yet found. The CN distance is virtually constant at 1.159 A. The nuclear quadrupole coupling constant for nitrogen-14 in fluorine cyanide, -2.67 Mc/s, is the lowest yet measured for a cyanide grouping. The dipole moments of fluorine cyanide and fluoroacetylene, from Stark effects, are 2.17 D and 0.75 D respectively. Rotation spectra of molecules in excited bending vibrational states were analysed for fluorine cyanide, fluoroacetylene and cyanoacetylene.