Coherent tunneling of proton in the intramolecular hydrogen bond of crystalline bromo-hydroxyphenalenone at low temperature

Infrared absorption spectra of 5-bromo-9-hydroxyphenalenone were measured and analyzed in detail as a function of temperature. An intense and broad peak at 83 cm21 occurring in the protonated crystal, but not in the deuterated analog, arises from the coherent tunneling motion of the hydrogen in the intramolecular hydrogen bond. Strong temperature dependence of the frequency and width of the tunneling peak determined by fitting the Gaussian or Lorentzian peak shape function is reproduced well by three-parameter functions representing the thermal population of the excited state of the tunneling proton. q 2004 Elsevier B.V. All rights reserved