Theoretical Study of the Structure and Properties of Polyynes and Monocyano- and Dicyanopolyynes: Predictions for Long Chain Compounds

Abstract

Geometrical parameters and harmonic vibration frequencies of polyynes HC 2 n H ( n = 1−8), cyanopolyynes HC 2 n - 1 N ( n = 1−7), and dicyanopolyynes NC 2 n N ( n = 1−8) have been calculated with various density functionals using the Dunning triple-ζ basis set. For selected data, we propose extrapolation formulas for longer molecules of the series. Bond lengths and electron localization function analysis indicate that a marked bond alternation persists in molecules as long as HC 30 H. The evolution along the series of some vibration frequencies and their accuracy for the identification of long molecules in extraterrestrial systems are also discussed.