THE MICROWAVE SPECTRUM AND STRUCTURE OF MALONALDEHYDE

$^{1}$ W.F. Rowe and E.B. Wilson, Paper P1, 28th Symposium on Molecular Structure and Spectroscopy, Columbus, Ohio (1973). $^{2}$ W.F. Rowe, Ph. D. thesis, Harvard University (1975).Author Institution: Department of Chemistry, Harvard UniversityThe microwave spectrum of malonaldehyde $(C_{3}H_{4}O_{2})$ and a number of its oxygen and deuterium isotopic forms have been investigated. Previously, $^{1,2}$ the normal species had been found to be in a planar hydrogen bonded form and to have a low lying vibrational state (16 $\pm 14 ~cm^{-1}$), indicating a symmetric double minimum potential. A $\mu _{b}$ dipole moment of 2.58 $\pm$ 0.01 D was observed. The spectra for the singly substituted $O^{17}$ and $O^{18}$ species and for the doubly substituted $O^{18}$ species have been observed and yield an apparent $0\ldots 0$ distance of $\sim2.55$ {\AA}. For the singly substituted $O^{18}$ case, a significant $\mu_{a}$ dipole moment is observed. Deviations from a rigid rotor were noted for several isotopic species, suggesting that there may be perturbations arising from the interaction between the low-lying pair of tunnelling states. The implications with respect to the potential function and comparisons with theory will be discussed