Calculation of the Infrared Spectrum of SF4 Using CNDO /2 Techniques

Abstract

Raman spectra of polycrystalline SF₄ at liquid‐nitrogen temperatures are discussed and an alternative to several recent vibrational assignments is suggested. Approximate sets of normal coordinate vectors are established for each of three possible frequency assignments. Relative infrared intensities for gas‐phase SF₄ are then calculated for each vibrational assignment using the approximate normal coordinates and a set of dipole derivatives, ∂P/∂S_j, computed by the CNDO/2 method. Comparisons between the sets of observed and calculated relative intensities for the gas phase indicate that the general intensity trends of the experimental data are reproduced by the semiempirical dipole derivatives. For SF₄, the calculation is moderately sensitive to differences in the vibrational assignment, particularly, for the b₁ and b₂ stretching vibrations. The appealing application of utilizing semiempirical quantum mechanical techniques toward designating vibrational assignments is discussed.