Degree Name

Master of Science (MS)

Semester of Degree Completion

2000

Thesis Director

Carol A. Deakyne

Abstract

This work is comprised of two separate computational projects, an evaluation of the validity of an assumption made when computing absolute gas phase acidities with a thermochemical cycle and a molecular-orbital study of protonated ammonia-water clusters ions.

Relative gas phase acidities are measured experimentally and then adjusted using Hess' law to align them with an absolute scale. In the Hess' law calculation it is assumed that the electron affinity of A• and the ionization energy of H• are independent of temperature. To test this assumption, absolute enthalpies were computed for the anion (A-) and the radical (A•) at 298 K and 0 K. The difference in these values is our criterion for evaluating the validity of the assumption. For most of the species examined, the temperature effect is smaller than the known experimental uncertainties in the thermochemical data.

Protonated ammonia-water clusters are present in the atmosphere and are representative of a class of matter with properties that are intermediate between those of individual gas phase molecules and liquid phase molecules. These clusters build up solvent shells by sequential addition of solvent molecules to the central ion, and there is some question about whether the first solvent shell is filled before additional shells are started. This work suggests that there may be a mixture of structural isomers present in the equilibrium population of some of these cluster ions.

Basis set superposition error corrections were not a factor in determining the relative stability of the isomeric structures.

Download

Included in

Chemistry Commons

Share

COinS