Date of Completion

5-1-2013

Embargo Period

5-1-2013

Keywords

alkali clusters, van der waals, field control, thermochemistry, quantum chemistry

Major Advisor

Robin Cote

Associate Advisor

John Montgomery Jr

Associate Advisor

H. Harvey Michels

Field of Study

Physics

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The calculation of non-covalent interactions of highly polarizable molecules is an outstanding problem in chemistry and physics. Difficulties arise both in accurate treatments of dispersion interactions between molecules and in the evaluation of surfaces of sufficient size for use in further computations. While ``gold-standard" calculations using coupled cluster theory with singles, doubles and perturbative triples provides a reliable method for evaluating interactions the computational cost involved in calculating more than a few points of an interaction surface becomes prohibitive for even medium sized molecules. Expanding the long range interaction into a van der Waals series reduces the cost of evaluating a surface to the computation of a few parameters. We describe here the implementation of a new computer program for calculating van der Waals coefficients for arbitrary molecules using the sum over states method. The laboratory-frame transformation of the computed van der Waals surface and the inclusion of rotational state dressing on the surface is derived. Analytic approximations for the interactions of two linear molecules in the presence of a small DC electric field are also derived. Recent achievements in the formation and manipulation of ultracold polar molecules have opened the door to exciting new studies in cold chemical reactions. To characterize the energetics and reaction pathways of trimer and tetramer formation and reactions, we have computed the structure and thermochemistry of the model trimer Li$_3$ and every X$_2$Y$_2$ alkali tetramer through Cs. Related interest in the control of molecular ion reactions is also investigated with recent theoretical results for the rubidium hydroxide reaction presented here.

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