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Molecules in nonuniform fields
Abstract
In this dissertation we use a perturbation approach to determine the interaction between the induced moments and the field gradients for a molecule in a nonuniform field. These relationships are called the higher order polarizabilities and are distinctly different from the idea of hyperpolarizabilities. These higher order polarizabilities interact with the field gradients, whereas the hyperpolarizabilities interact only with the field. Next we examine the contribution of these higher order polarizabilities, as well as the permanent moments, to the potential energy of the molecule in a nonuniform field. We investigate some specific cases for methane, in which symmetry considerations allow for simplifications in the equations for the potential energy and the induced moments. We also calculate the contribution of the permanent octupole moment versus one of the higher order polarizability terms for methane in a sample cavity. We find that, to a large extent, these two molecular properties determine the potential energy behavior of methane in a nonuniform field, where the relative importance of each property depends upon the field and the field gradients involved. The static moments and the higher order polarizabilities are determined from SCF calculations using the finite field method. Potential energy calculations show excellent agreement between results produced by our model and those produced by the SCF method. The advantage of our model is that it includes the rotational dependence of the potential energy and the induced moment in an analytical function. This makes it more accurate than previous analytical models (such as the Lennard-Jones potential) but it does not require the time needed for an ab initio calculation.
Subject Area
Chemistry
Recommended Citation
Fischer, Joyce Eileen, "Molecules in nonuniform fields" (1992). ETD collection for University of Nebraska-Lincoln. AAI9314399.
https://digitalcommons.unl.edu/dissertations/AAI9314399