The 0-1 transition of the out-of-plane bending vibration in trimethylene oxide has been observed at 53.4 em-I. Previously reported bands by Lord and his co-workers [J. Chem. Phys. 33, 294 (1960) ] at 89.8, 105.2, 118.3, 128.9, 139.0, 147.6, 154.9, and 161.8 cm-I have also been confirmed. In addition, six higher members of this series as well as three members of the Av=3 series have been observed. These transitions are readily interpreted in terms of the hot-band series of a slightly perturbed quartic oscillator. A double-minimum potential function of the form az4-bz 2 predicted all the observed transitions to within experimental error (0.5 em-lor better). The central barrier in the potential-energy function, while low, is finite and has a height of 1S.3±0.5 em-I. It had previously been concluded, from ilie variation of the rotational constants with vibrational state obtained from microwave spectroscopy that the potential energy contained a small barrier of the order of zero-point energy at the planar configuration of ilie molecule [J. Chern. Phys. 33, 1643 (1960]. The present far-infrared results are shown to be consistent with the microwave results. Thus an existing discrepancy between the far-infrared and microwave results on the nature of the potential function for this unique out-of-plane bending vibration is finally resolved.

The far-infrared spectra of trimethylene sulfide and cyclobutanone have been investigated. The positions of the trimethylene sulfide bands observed are well fitted by the potential function derived from the microwave studies of Harris et al. However, some of the band shapes cannot be explained in detail although the anomalies are probably due to Coriolis terms in the Hamiltonian. The positions of the lower frequency bands of cyclobutanone can be fit approximately by a quartic—quadratic potential with a small barrier. Although this potential function fits the rotational constants measured by Sharpen et al., it does not predict the positions of the higher frequency bands correctly. Furthermore the band shapes cannot be explained on the basis of the simple potential function, and it is suggested that the low-frequency out-of-plane vibration of cyclobutanone is perturbed by a higher frequency vibration.

The molecular structure and composition of gaseous oxalyl fluoride (OXF) has been investigated by electron diffraction (GED) at nozzle-tip temperatures of -10, 149, and 219 degrees C. The GED data were augmented by molecular orbital calculations, and the analysis was aided by use of rotational constants from microwave (MW) spectroscopy. As in the other oxalyl halides, there are two stable species, of which the more stable is periplanar anti (i.e., trans). However, unlike these other halides in which the second form is gauche, the second form of oxalyl fluoride was known from MW work to be periplanar syn (i.e., cis). Our results are consistent with a mixture of trans and cis forms, and yield values for the structural parameters, the composition of the system at the three temperatures cited, and the thermodynamic quantities deltaG(o), deltaH(o), and deltaS(o) for the reaction trans --> cis. Some trans/cis distances (r(g)/Angstrom) and angles (<(alpha)/deg) at -10 degrees C are r(C=O) = 1.178(2)/1.176(2), r(C-F) = 1.323(2)/1.328(2); r(C-C) = 1.533(3)/1.535(3), <(C-C=O) = 126.4(2)/124.2(2), <(C-C-F) = 109.8(2)/112.2(2), and <(O-C-F) = 123.8(2)/123.6(2). The mixture compositions (percent trans) at -10 degrees C/149 degrees C/219 degrees C are 75(3)/58(7)/52(8), from which deltaH(o) and deltaSO) are found to be 1.14 kcal/mol and 2.12 cal/(mol x deg). The system properties are discussed.

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