Predictions of the rotational and vibrational spectra of SiF+, PO+, and NS+ by Mo/ller–Plesset perturbation theory

Abstract

In order to predict accurately the spectroscopic constants of SiF+, PO+, and NS+, calculations at the MP4SDQ level have been carried out for the following series of 22 electron diatomics: AlF, SiF+, SiO, PO+, PN, NS+, CS, CCl+, and BCl. Two basis sets, one containing 66 contracted Gaussian‐type orbitals and the other with 93, have been employed for each of the nine molecules to calculate potential energy functions and spectroscopic constants. The a b i n i t i o r e and ω e values for the three ions whose high resolution spectra were not previously observed were corrected by reference to deviations between theory and experiment for the other six species, whose spectra were already well known. The dipole moments and electric field gradients of each species at the equilibrium bond distance were calculated at the CI‐SD level, and their dissociation energies were found to be predicted well by MP2 and very well by MP4SDTQ calculations. In order to understand better the differences between the spectral predictions of the two basis sets,r e and ω e of the well known first row analogs BF, CF+, CO, NO+, and N2 were computed at the MP4SDQ level with a series of five basis sets of increasing flexibility. Using the current prediction for SiF+ we have recently located its rotational spectrum, extensive measurements of which will be published separately.