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 becasue it permits intermolecular hydrogen bonding. The molecule has a double minimum potential, and tunneling leads to splitting. Rotational (b-type) transitions were reported in
(1) S. L. Baughcum, 1978, PhD thesis, Harvard University, Cambridge, MA, USA.
Additional transitions were reported by
(2) M. Stolze, D. Hübner, and D. H. Sutter, 1983, J. Mol. Struct. 97, 243,
by
(3) P. Turner, S. L. Baughcum, S. L. Coy, and Z. Smith, 1984, J. Am. Chem. Soc. 106, 2265;
and by
(4) D. W. Firth, K. Beyer, M. A. Dvorak, S. W. Reeve, A. Grushow, and K. R. Leopold, 1991, J. Chem. Phys. 94, 1812.
Rotation-tunneling (a-type) transitions were reported by
(5) T. Baba, T. Tanaka, I. Morino, K. M. T. Yamada, and K. Tanaka, 1999, J. Chem. Phys. 110, 4131.
Some transition frequencies in (1) were reassigned in (3). Even though some sextic distortion parameters appeared to be determined well, their contribution to the reduction of the rms error, as measure of the quality of the fit, was small, and they were omitted from the final fits. This caused a small number of transition frequencies to have large residuals. Therefore, these transition frequencies were omitted from the final fit. The uncertainties of the data from (4) were doubled to 0.8 MHz. Only the microwave transitions from (1) and the data from (2) and (5) were merged.
The predictions should be good enough to search for the molecule in space. Transitions with predicted uncertainties of 0.3 MHz or larger should be viewed with great caution. In addition, transitions with J above 30 and K_a above 10 should be viewed with some 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 by
(6) S. L. Baughcum, R. W. Duerst, W. F. Rowe, Z. Smith, and E. B. Wilson, 1981, J. Am. Chem. Soc. 103, 6296.
The a-dipole moment component was determined in (5) from intensity measurements.