Linking experiment and theory in two-photon spectroscopy: I. Quantitation with two-photon spectroscopy. II. Spectroscopy of metal-metal bonded compounds
Abstract
Molecular electronic states forbidden by the selection rules of conventional single-photon spectroscopy are often accessible by two-photon absorption. Fluorescence detection of two-photon absorption allows the observation of this weakly absorbing phenomenon. Two-photon excited fluorescence investigations of the electronic structure of metal-metal bonded compounds could be employed to temper theoretical computations and, thereby, enhance the current understanding of metal-metal bonding. In order to compare experiment and theory, a basis for the comparison must be selected. State symmetry is an excellent parameter on which to base the comparison of experiment and theory. The state symmetry is experimentally accessible and predicted accurately by X$\alpha$ calculations. Conventional techniques for ascertaining transition symmetries have been reviewed and compared with recent approaches. Decision trees for these assignments have been devised. Trends in the assignments have been delineated in order to assist off-the-cuff predictions concerning the distinction of transition symmetries within a given molecular point group. Comparing experiment and theory for the purpose of tempering theoretical computations will be disastrous if experimental artifacts are not excluded from the data. A chemical reference has been developed to eliminate the source dependencies of the two-photon technique from the experimental data. The utility of this scheme has been demonstrated over a large wavelength range (537 nm to 694 nm). An exhaustive study of the spectroscopy of the chemical reference, bis-MSB, was undertaken to identify potential interferences within the referencing scheme. Several spectroscopic anomalies were discovered. Their repercussions for the referencing scheme are discussed. The applicability of the two-photon technique to metal-metal bonded compounds has been demonstrated with (Pd$\sb2$(MeNC)$\sb6$) $\cdot$2(PF$\sb6$). Compounds of the type Mo$\sb2$X$\sb2$(bridge)$\sb2$(PR$\sb3$)$\sb2$ (where X $\equiv$ Cl, Br; bridge $\equiv$ mhp, dmhp; R $\equiv$ Me, Et, Ph) have been investigated by single-photon spectroscopy in preparation for two-photon studies, and their utility as molecular probes of viscosity has been addressed. Two-photon excited fluorescence data has been collected for K$\sb4$Pt$\sb2$(H$\sb2$P$\sb2$O$\sb5$)$\sb4$.
Degree
Ph.D.
Advisors
Lytle, Purdue University.
Subject Area
Analytical chemistry
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