Density functional theoretical (DFT) study for the prediction of   spectroscopic parameters of ClCCCN
  DFT(B3LYP, B3PW91) level calculations in conjunction with three different of basis sets have been used to investigate the variations in the bond lengths, dipole moment and rotational constants, IR frequencies, IR intensities and rotational invariants of ClCCCN. The nuclear quadrupole constants of chlorine and nitrogen of ClCCCN have been calculated on the experimental r$_{s}$ structure as well as on the B3PW91/6-311++g(d,p) optimized geometry and are found to be within the scale length of the experimental uncertainty. The slopes and intercepts obtained from the regression analysis between the B3LYP/6-311++g(d,p) level calculated and experimental B$_{o}$ values of ClCCCN were used to calculate the reasonable values of rotational constants of all the rare isotopic species of ClCCCN having standard deviation $\pm$0.048 MHz. All the spectroscopic parameters obtained from DFT calculation shows satisfactory agreement with the available experimental data. 
Pradeep Risikrishna Varadwaj