Vibrational tuning of the Hydrogen transfer in malonaldehyde - a combined FTIR and Raman jet study

Tunnelling splittings in vibrationally excited malonaldehyde are derived from complementary FTIR and Raman spectra utilising jet cooling and matrix isolation. Values from 0 to 69 cm(-1) (i.e. from complete quenching of the proton tunnelling to an acceleration by a factor of 3) are firmly assigned, underscoring a strong coupling between hydrogen transfer and vibrational excitation. More tentative assignments involve even larger effects for the OO breathing vibration. The results are discussed with respect to the corresponding normal modes and compared to previous theoretical predictions.