Theoretical study of the dipole moment function of OH(X 2Π)

Abstract

We present a theoretical study of the sensitivity of the dipole moment function (DMF) of the X 2Π ground state of OH to basis set saturation and to refinements in the correlation treatment. Emphasis is placed on determining the slope of the DMF at re and the r value at which the maximum occurs. We consider the effect of oxygen polarization functions up through h type, expansion of the active orbital space to include the O 3dδ orbital, the effect of higher excitations using the averaged coupled-pair functional method, and the effect of evaluating the dipole moment as an energy derivative rather than as an expectation value. Our theoretical DMFs, which should be the most accurate to date, differ markedly from an empirical DMF of Turnbull and Lowe that is based on experimentally derived intensity ratios. The theoretical DMFs agree better with a recently published DMF of Nelson et al., but suggest that this empirical DMF is also inaccurate for r>2.3 a0.