Knowledge Bank

There are at least three documented force-field calculations for cyanoacetylene all differing from one another in the magnitude and sign of many off-diagonal $elements.1$ Even the diagonal force-constants are of different magnitude. A critical analysis of the existing results in the light of our own calculations using the frequencies of cyanoacetylene and deuterated cyanoacetylene will be presented. The reproducibility of other experimentally available molecular physical constants (like the centrifugal distortion parameters) will be used as an additional criterion for the choice of a force-field. Our attempts to make a semi-empirical calculation through a consistent force-field $approach2$ to fix the signs of the off-diagonal force-constants will be outlined for this molecule of astrophysical interest.