Far-infrared synchrotron-based spectroscopy of proton tunnelling in malonaldehyde

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University of New Brunswick
Although the internally hydrogen-bonded species malonaldehyde (C3O2H4) is considered an important prototype molecule for intramolecular proton transfer, its far-IR spectrum is not well understood. Using high-resolution spectra obtained from the Canadian Light Source synchrotron in Saskatoon, Saskatchewan, I have made significant progress in understanding its low-energy vibrational structure. A new rotational characterization of the vibrational ground state tunnelling-split pair is presented here, which benefits from these new IR measurements covering a more complete range of rotational parameter space than was reported previously. Full rotational analyses have been performed for three low-energy vibrational states at 241, 390, and 405 cm-1 and these states (as well as states at 273 and 282 cm-1) have been conclusively matched to early microwave measurements [W. F. Rowe, Ph.D. Thesis, Harvard University, 1975]. Progress has been made toward developing a theoretical treatment of malonaldehyde using the Generalized Semi-Rigid Bender Hamiltonian to describe the large-amplitude tunnelling motion.