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Microwave Spectrum of 2-Methylmalonaldehyde: Analysis of the Hydrogen-Transfer and Internal-Rotation Motions

The paper presents a new experimental study of the microwave spectra of 2-MMA-dO [HO-CH=C(CH3)- CH=0] and 2-MMA-dl [DO-CH=C(CH3)-CH=0] isotopologues 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 G,2m extended-group theoretical formalism to carry out global fits of 2578 2-MMA-dO transitions and 2552 2-MMA-dl transitions to measurement uncertainty, obtaining root-mean-square deviation of 0.015 MHz for both isotopologues. This presents a significant improvement in fitting accuracy over past attempts.