The 0ndash;1 transition of the outhyphen;ofhyphen;plane bending vibration in trimethylene oxide has been observed at 53.4 cmminus;1. Previously reported bands by Lord and his cohyphen;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 cmminus;1have also been confirmed. In addition, six higher members of this series as well as three members of the Dgr;v= 3 series have been observed. These transitions are readily interpreted in terms of the hothyphen;band series of a slightly perturbed quartic oscillator. A doublehyphen;minimum potential function of the formaz4mdash;bz2predicted all the observed transitions to within experimental error (0.5 cmminus;1or better). The central barrier in the potentialhyphen;energy function, while low, is finite and has a height of 15.3plusmn;0.5 cmminus;1. It had previously been concluded, from the variation of the rotational constants with vibrational state obtained from microwave spectroscopy that the potential energy contained a small barrier of the order of zerohyphen;point energy at the planar configuration of the molecule J. Chem. Phys.33,1643 (1960). The present farhyphen;infrared results are shown to be consistent with the microwave results. Thus an existing discrepancy between the farhyphen;infrared and microwave results on the nature of the potential function for this unique outhyphen;ofhyphen;plane bending vibration is finally resolved.
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