^*Department of Applied Physics , Sri Venkateswara College of Engineering, Sriperumbudur-602.102 (india)

Department of Physics,Jaya Engineering College , Thiruninravur, chennai (India)

Department of Physics, Appolo Engineering College

Email-sambathk@svce.ac.in

Quantum mechanical calculation of energies, geometries and vibrational wave numbers of diazopropyne have been carried out by using density functional theory (DFT/B3LYP) method with 6.311++G (d,p) cc-pvdz, Aug-cc-pvdz as basis set. The optimized geometrical parameters obtained by DFT calculations are found to be good agreement with experimental Xray data. The best level of theory in order to reproduce the experimental wave numbers is B3LYP method with the 6.311++G(d,p) basis set. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detail interpretation of the infrared and Raman spectra has also been reported. The entropy of the compound under study is also performed. Application of Redington's method in the solution of eleventh and fourth order problems involved in vibrational analysis of diazopropyne (C₃H₂N₂) molecules. General quadratic valence force field has been used to calculate the force constants and mean amplitudes of vibration are also calculated in the present work. The results are discussed.