Publications by authors named "Thresa A Wells"

Two-dimensional infrared (2DIR) spectroscopy has become an established method for generating vibrational spectra in condensed phase samples composed of mixtures that yield heavily congested infrared and Raman spectra. These condensed phase 2DIR spectrometers can provide very high temporal resolution (<1 ps), but the spectral resolution is generally insufficient for resolving rotational peaks in gas phase spectra. Conventional (1D) rovibrational spectra of gas phase molecules are often plagued by severe spectral congestion, even when the sample is not a mixture.

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High resolution coherent multidimensional spectroscopy has the ability to reduce congestion and automatically sort peaks by species and quantum numbers, even for simple mixtures and molecules that are extensively perturbed. The two-dimensional version is relatively simple to carry out, and the results are easy to interpret, but its ability to deal with severe spectral congestion is limited. Three-dimensional spectroscopy is considerably more complicated and time-consuming than two-dimensional spectroscopy, but it provides the spectral resolution needed for more challenging systems.

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A new method for generating high-resolution coherent 3D (HRC3D) spectra has been developed that is based on the nonparametric four-wave mixing process MENS (multiply enhanced nonparametric spectroscopy). The resulting spectra have rotational patterns that are different from those produced previously using the parametric four-wave mixing process CARS. A change in the rotational pattern facilitates a new approach to scanning where orthogonal 2D slices in 3D space are combined to make a 3D rotational pattern.

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Expansion from coherent 2D spectroscopy to coherent 3D spectroscopy can provide significant advantages when studying molecules that have heavily perturbed energy levels. This paper illustrates such advantages by demonstrating how high resolution coherent 3D (HRC3D) spectroscopy can be used to study a portion of the visible spectrum of nitrogen dioxide. High resolution coherent 2D spectra usually contain rotational and vibrational patterns that are easy to analyze, but severe congestion and complexity preclude its effective use for many parts of the NO2 spectrum.

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High-resolution coherent multidimensional spectroscopy provides an alternative to conventional methods for generating rotationally resolved electronic spectra of gas phase molecules. In addition to revealing information such as the relationships among peaks, it can provide clearly recognizable patterns for spectra that otherwise appear patternless due to rotational congestion. Despite this improvement, high-resolution coherent 2D spectroscopy can still exhibit congestion problems; expansion to the second dimension is often not sufficient to prevent overlapping of peaks from different patterns.

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In the past, high-resolution spectroscopy has been limited to small, simple molecules that yield relatively uncongested spectra. Larger and more complex molecules have a higher density of peaks and are susceptible to complications (e.g.

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