Rotational constants and dipole moments of interstellar polyynes: a comparative MP2 and density functional (BP86) study Original Research Article

By means of theoretical calculations the rotational constants and dipole moments of the first members of the polyynes families (cyanopolyynes, methylcyanopolyynes and isocyanopolyynes) have been calculated at the MP26-31G∗ and BP866-31G∗ levels. The calculations of rotational constants given in this paper show that the predicted values using density functional theory are in reasonable agreement with the experimental and the MP2 results. A good evaluation of the dipole moments requires the introduction of the electronic correlation, which can be made using density functional calculations. The results are considerably improved using a least squares fit between the experimental and calculated dipole moments including electronic correlation.