Knowledge Bank

Ab initio calculations on the dipole moment derivatives of acetylene have been performed with a (9,5,2/4,2) Gaussian basis set contracted to (4,2,2/2,2). In view of the fact that the internal consistency of the reported experimental intensities, with the exception of the recent work of Kim and $King1$, is rather poor, especially for the $nu$ bending mode, the stepsize-dependency of the bending mode derivative has been studied in order to get some insight in the magnitude of second order contributions to the dipole moment function. The calculated derivative values are compared to the results of Van Duijneveldt-Van de Rijdt and Van Duijneveldt as reported in our previous paper on $acetylene2$ and to the ab initio work of Jalsovszky and $Pulay.3$ The influence of bond midpoint orbitals vs. P and d polarization functions upon the calculated derivative values will be discussed. In addition the CMO’s have been transformed to LMO’s. A complete set of bond charge parameter values for acetylene has been obtained from the LMO moments calculated at several distorted configurations.