# THE THIRD TORSIONAL STATE OF ACETALDEHYDE

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 Title: THE THIRD TORSIONAL STATE OF ACETALDEHYDE Creators: Kleiner, I.; Hougen, Jon T.; Grabow, Jens-Uwe; Belov, S. P.; Tretyakov, M. Yu.; Cosleou, J. Issue Date: 1995 Publisher: Ohio State University Abstract: We have fit to experimental accuracy a data set for acetaldehyde containing (at the present moment) 1105 far-infrared and 2802 microwave transitions. About four-fifths of these transitions, involving only levels below the barrier $(v_{t} \leq 2)$ were treated in an earlier $publication^{1}$. Here we attempt to futher test the theoretical model, developed in a number of papers by E. Herbst and collaborators, by extending our data set to include levels above the barrier. We have thus added to our previous data set some $224 v_{t} = 3 \leftarrow 2$ far-infrared transitions and 518 microwave transitions. The latter consist of: (i) Nizhny Novgorod RAD-2 $($\pm 70 kHz)$a-type and b-type transitions in$v_{t} = 2$which confirm and make more precise$\Delta K = \pm 1$intervals in the last level below the barrier, (ii) RAD-3$(\pm 1 MHz)$a-type transitions in$v_{t} = 3$, together with a few a-type transitions in$v_{t} = 4$, which all lie above the barrier, and (iii) measurements or remeasurements from Lille and other laboratories of transitions with$v_{t}\leq 3$. The global fit, which gave a weighted overall standard deviation of 1.11, uses the same model as for the$v_{t}\leq 2$data, except that the number of adjustable parameters increased somewhat from 48 to 57. In addition to the numerical fit, we have attempted to increase our qualitative understanding of internal rotation phenomena above the barrier by carrying out: (i) a theoretical overview of internal-rotation energy levels above the barrier, (ii) a theoretical discussion of torsion-rotation interactions above the barrier, and (iii) sample intensity calculations for upper$\leftarrow$lower state transitions involving levels characterizable as above$\leftarrow$below and above$\leftarrow$above the barrier. Description:$^{1}\$S. P. Belov, M. Yu. Tretyakov, I. Kleiner and J. T. Hougen, J. Mol. Spectrosc. 160, 61-72 (1993). Author Institution: Université Pierre et Marie Curie et C.N.R.S., Tour 13, 4, Place Jussieu, F-75252 Paris Cedex 05, France; National Institute of Standards and Technology, Gaithersburg, MD 20899; Applied Physics Institute, 46 Ulyanova Street, Nizhny Novgorod, Russia 603024; Université des Sciences et Techniques de Lille, 59655 Villeneuve d'Ascq Cedex, France URI: http://hdl.handle.net/1811/29872 Other Identifiers: 1995-TK-10