Centrifugal Distortion Analysis of the Microwave and Millimeter Wave Spectra of Deuterated K e t e n e s 2 Laszlo Nemes 3 and Manfred Winnewisser Physikalisch-Chemisches Institut, Justus Liebig-Universität Giessen (Z. Naturforsch. 31a, 2 7 2 - 2 8 2 [1976] ; received November 18, 1975) Measurements of R and Q branch a-type pure rotational transitions in the frequency range from 8 GHz to 220 GHz are reported for ketene-d! and ketene-d2 . The microwave and millimeter wave transitions were analysed in terms of Watson's reduced Hamiltonian, including the sextic terms HKJ and HJK  The values of the inertial defect and the r defect obtained from the centrifugal distortion analysis are in accord with the planar model for the ketene molecule. I. Introduction The importance of ketene for synthetic work, coupled with the fact that it has a relatively simple and symmetric molecular structure, initiated spec- troscopic investigations comparatively early. It was the subject of some of the earliest microwave studies 1-3 . The analysis of the infrared vibrational spectra 4 and the microwave studies of pure rotational transi- tions 1-3,5 have given us information about the mo- lecular geometry and confirmed the Cov symmetry. Thus, relatively dependable rotational constants have been obtained for the H2 , HD and D2 sub- stituted species 1_4 . It has also been concluded on the basis of the vibrational and rotational spectra that the ketene molecule is planar. This conclusion came mostly from the symmetry properties of ro- tational and rotational-vibrational transitions. There has been only one paper, by Johns, Stone and Win- newisser 6 , in which an inertial defect value for H2 ketene could be derived from the combined analysis of infrared and microwave data. In the present paper we attempt to fill some gaps in the knowledge about the deuterium substituted species. We have measured sufficient millimeter wave transitions to perform the centrifugal distor- tion analysis for both ketene-dj and ketene-d2. These analyses have yielded, in addition to refined 1 This research was supported by funds from the Deutsche Forschungsgemeinschaft. 2 Presented in part at the "Third Colloquium on High Resolution Molecular Spectroscopy", Tours, France, Sep- tember 1 7 - 2 1 , 1973, as Paper J. 6. 3 Present address: Central Research Institute for Chemis- try, Hungarian Academy of Sciences, H-1025 Budapest, Pusztaszeri ut 59 — 67, Hungary. Reprint requests to Dr. M. Winnewisser, Physikalisch- Chemisches Institut, Justus Liebig-Universität, Heinrich- Buff-Ring 58, D-6300 Giessen, Germany. rotational constants, the quartic and sextic centrifu- gal distortion constants, values of the inertial defect and the r defect. Comparison of these inertial defect values with values calculated from a normal co- ordinate analysis supports strongly the planar model for the ketene molecular structure. The frequency predictions of pure rotational tran- sitions together with their calculated standard de- viations provide a basis for a possible search for interstellar deuterated ketene molecules. II. Experimental Procedures Both deuterated ketenes were prepared using a modified Hurd-lamp 7 by pyrolysing hexadeutero- acetone and partially deuterated acetone. In the process of producing ketene-di, following the meth- od reported by Moore and Pimentel 4 , both normal ketene and ketene-d2 are also synthetized. We have not attempted to separate these species since in the vibrational ground state studies their presence has caused no problems. The pyrolysis of acetone gives a number of by-products apart from methane, prin- cipally C0 2 and ethylene. These molecules are, how- ever, nonpolar and therefore their presence in the sample does not lead to disturbing lines in the ro- tational spectrum of the ketenes. However, in order to avoid pressure broadening of the ketene absorp- tion lines a distillation procedure was applied to remove all of the heavy methane and C0 2 , and most of the heavy ethylene. The measurements of centimeter wave lines be- tween 8 and 18 GHz, and between 24 and 36 GHz were carried out using a Hewlet-Packard 8460A Molecular Rotational Resonance spectrometer. A Stark modulation of frequency 33.33 kHz and a two meter X-band Stark cell were employed. The millimeter wave range rotational transitions were measured by means of a spectrometer having Unauthenticated Download Date | 6/24/16 3:57 PM