Note: Even though the molecule is better known as malonaldehyde, it is much better described as 3-hydroxypropenal. The enol form of the molecule is greatly favored because it permits intermolecular hydrogen bonding. The molecule has a double minimum potential, and tunneling leads to splitting.
The data set was modified considerably with respect to the first entry of Fen. 2016. Most of the present transition frequencies were determined by
(1) H. S. P. Müller, A. Coutens, J. K. Jørgensen, L. Margulès, R. A. Motiyenko, and J.-C. Guillemin, 2024, Astron. Astrophys. 687, Art. No. A8.
Limited additional microwave transition frequencies were reported in
(2) S. L. Baughcum, R. W. Duerst, W. F. Rowe, Z. Smith, and E. B. Wilson, 1981, J. Am. Chem. Soc. 103, 6296;
and in
(3) M. Stolze, D. Hübner, and D. H. Sutter, 1983, J. Mol. Struct. 97, 243.
The calculation should be accurate enough for radio astronomical searches. Transitions with calculated uncertainties of 0.1 MHz or larger should be viewed with caution.
Spin-statistics matter for the intensities. Ortho and para states are described by K_a + K_c + v_t being odd and even, respectively, and the spin-weight ratio is 3 : 1.
The b-dipole moment component was determined in (2) while the a component was determined from intensity measurements in
(4) T. Baba, T. Tanaka, I. Morino, K. M. T. Yamada, and K. Tanaka, 1999, J. Chem. Phys. 110, 4131.
The partition function refers to the ground vibrational state.