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Reinvestigation of the Microwave Spectrum of 2-Methylmalonaldehyde



Vadim V. Ilyushin, E A. Alekseev, Y C. Chou, Y-C Hsu, Jon T. Hougen, Francis J. Lovas, L B. Picaux


The molecule 2-methylmalonaldehyde (2-MMA) exists in the gas phase as a six-membered hydrogen-bonded ring [HO-CH=C(CH3)-CH=O] and exhibits two large-amplitude motions, an intramolecular hydrogen transfer and a methyl torsion. The former motion is interesting because transfer of the hydrogen atom from the hydroxyl to the carbonyl group induces a tautomerization in the ring, which then triggers a 60? internal rotation of the methyl group attached to the ring. We present a new experimental study of the microwave spectra of 2-MMA-d0 [HO-CH=C(CH3)-CH=O] and 2-MMA-d1 [DO-CH=C(CH3)-CH=O] isotopologs of the molecule. The new measurements were carried out by Fourier-transform microwave (FTMW) spectroscopy in the 8 GHz to 26 GHz frequency range and by conventional absorption spectroscopy in the 49 GHz to 149 GHz range. In the present work, we use a tunneling-rotational Hamiltonian based on a G12m extended-group theoretical formalism to carry out global fits of 2578 2-MMA-d0 transitions and 2552 2-MMA-d1 transitions to measurement uncertainty, obtaining root-mean-square deviation of 0.015 MHz for both isotopologs. This represents a significant improvement in fitting accuracy over past attempts.Some problems associated with calculating barrier heights from the observed tunneling splittings and assumed tunneling paths are also considered.
Journal of Molecular Spectroscopy


hydrogen transfer, internal rotation, large-amplitude motion, least squares fit, microwave spectrum, tunneling Hamiltonian


Ilyushin, V. , Alekseev, E. , Chou, Y. , Hsu, Y. , Hougen, J. , Lovas, F. and Picaux, L. (2008), Reinvestigation of the Microwave Spectrum of 2-Methylmalonaldehyde, Journal of Molecular Spectroscopy, [online], (Accessed June 20, 2024)


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Created January 10, 2008, Updated October 12, 2021