|Abstract:||Vibrational circular dichroism (VCD) spectroscopy is a powerful spectroscopic tool for determination of structural properties of chiral molecules directly in solution, including their absolute configurations and conformations. More recently, the matrix-isolation (MI) technique which allows substantial control over the sample(s)/carrier gas ratio(s) and deposition conditions has been combined with VCD. It can avoid the solute-solvent interactions and have the molecular target largely in its isolated monomeric form. The MI technique generally yields much narrower IR and VCD bandwidths than those obtained in solution, providing the opportunity to investigate possible conformations of the target molecules in considerable details.
In the current study, the conformational landscapes of tetrahydro-2-fuoric acid (THFA) and its binary aggregates in a cold argon matrix have been investigated. MI-IR and MI-VCD spectra have been obtained at three different deposition temperatures of 10, 24, and 30 K. In addition, extensive searches have been carried out to find stable conformers of the THFA monomer and dimer in an argon matrix. The well-resolved experimental MI-IR and MI-VCD features at 10 K allows one to identify the dominating monomeric conformations. Interestingly, the inclusion of argon using the polarizable continuum model improves the agreement between the theoretical and experimental IR and VCD spectra. At the 24 and 30 K deposition temperatures, the experimental IR and VCD spectral features reveal appearance new species, most likely binary aggregates of THFA, although the IR and VCD features differ greatly from those observed in the previous solution study. Further analyses indicate that these new species are due to the much less stable conformers of the THFA dimer, not observed experimentally before. The structures and the formation mechanism of these unusual species will also be discussed.
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