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.
, Alekseev, E.
, Chou, Y.
, Hsu, Y.
, Hougen, J.
, Lovas, F.
and Picaux, L.
Reinvestigation of the Microwave Spectrum of 2-Methylmalonaldehyde, Journal of Molecular Spectroscopy, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=841130
(Accessed December 5, 2023)