Development of analysis strategies for multidimensional spectroscopic data

Chemical reaction or equilibrium data collected along a single compositional dimension are highly correlated and are of limited utility in resolving individual component responses. The utilization of ultraviolet (UV) resonance-Raman spectroscopy for monitoring the compositional axis in a two-dimensional measurement can provide sufficient information to resolve individual component contributions and determine the reaction mechanism. Elastic scattering from the sample interface and Rayleigh scattering from the bulk solvent are significant sources of background in these experiments. Solutions of aromatic compounds provide cut-off filtering of elastically scattered UV radiation due to the sharp profiles of their optical density curves. Solution filters were designed and characterized for specific UV excitation wavelengths for common pulsed laser sources. Monitoring the kinetics of excited-state molecules and of photochemical intermediates during their formation and subsequent decay can provide important information about the reaction mechanism. A time-resolved, two-laser pump-probe UV-resonance Raman spectrometer was developed and used to probe structural and kinetic and the resultant ketyl radical recombination on a time scale of 10 ns to 100 μs. Self-modeling curve resolution (SMCR), which does not appeal to a physical model describing the reaction mechanism was used on the time-dependent spectral data yielding well-resolved ground state/solvent, benzophenone triplet, and benzophenone ketyl radical spectra. A nonlinear least-squares (NLS) approach was also employed to resolve the data into individual components through the use of a physical model describing the Norrish Type II quenching of triplet benzophenone by triethylamine. Kinetic results describing the formation rate of ketyl radical from triplet benzophenone as well as the subsequent decay of the ketyl- and amine-radical species were also obtained. Fluorescent dyes are used for studies of flow between injection and production wells for management of geothermal reservoirs. An HPLC-laser-induced fluorescence (HPLC-LIF) instrument was constructed, and rank annihilation analysis methods were applied to the two-dimensional chromatographic-spectroscopic data of actual geothermal tracer samples. Quantitative results were obtained for fluorescein concentrations as low as 40 parts per quadrillion (1 ppq = 1 part in 10 15), a nearly three order of magnitude improvement over current filter fluorimetry and spectrofluorimetry techniques.