ChemInform Abstract: VIBRATIONAL FREQUENCIES FROM ANHARMONIC AB INITIO/EMPIRICAL POTENTIAL ENERGY FUNCTIONS. PART V. CYANOGEN. FREQUENCIES AND IR INTENSITIES OF STRETCHING VIBRATIONS

Abstract

Abstract Low-lying stretching vibrational states of five isotopes of cyanogen have been calculated by diagonalisation of an approximate vibrational Hamiltonian which neglects the anharmonic interaction between stretching and bending coordinates. The underlying anharmonic potential energy function was obtained from ab initio SCF calculations and corrected for the most important errors (geometry shift and modification of the harmonic force field). The experimentally known band origins are reproduced with a standard deviation of 2.3 cm−1. The equilibrium geometry, equilibrium rotational constants and centrifugal distortion constants are predicted. Infrared intensities of the stretching fundamentals have been calculated from HF-SCF and SCEP dipole moment functions and the anharmonic vibrational wavefunctions. As previously observed for HCN, the HF-SCF method yields the wrong sign for the first dipole moment derivative with respect to the CN stretching coordinate.