FAR-INFRARED SYNCHROTRON-BASED SPECTROSCOPY OF PROTON TUNNELLING IN MALONALDEHYDE

Abstract

Malonaldehyde (C$_{3}$O$_{2}$H$_{4}$) is a prototype molecule for the study of intramolecular tunnelling proton transfer. In the case of malonaldehyde, this transfer occurs between the two terminal oxygen atoms in its open-ring structure. Although the ground state tunnelling splitting of 21 wn has been accurately determined from microwave studiesfootnote{T. Baba, T. Tanaka, I. Morinoa, K. M. T. Yamada, K. Tanaka. emph{Detection of the tunneling-rotation transitions of malonaldehyde in the submillimeter-wave region}. J. Chem. Phys., textbf{110}. 4131-4133 (1999)}, the splitting has never been obtained with high resolution in any excited vibrational state. The nub{6} vibrational band was investigated in a diode laser jet experimentfootnote{C. Duan, D. Luckhaus. emph{High resolution IR-diode laser jet spectroscopy of malonaldehyde}. Chem. Phys. Lett., textbf{391}, 129-133 (2004)} in 2004, but the researchers were not able to identify the (-) parity tunnelling component and so could not determine the splitting. We have collected high-resolution far-IR Fourier transform spectra from a number of fundamental vibrational bands of malonaldehyde at the CLS (Canadian Light Source) synchrotron in Saskatoon, Saskatchewan, exploiting the considerable gain in signal-to-noise ratio at the highest resolution available afforded by the intense and well-collimated beam. We will report on our tunnelling-rotation analysis of the anti-symmetric out-of-plane bend near 384 wn and present its tunnelling splitting value. begin{wrapfigure}{r}{0pt} includegraphics[scale=0.13]{MA_2.eps} end{wrapfigure