TY - JOUR

T1 - The third and fourth torsional states of acetaldehyde

AU - Kleiner, I.

AU - Hougen, J. T.

AU - Grabow, J. U.

AU - Belov, S. P.

AU - Tretyakov, M. Yu

AU - Cosléou, J.

N1 - Funding Information: The authors are indebted to Drs. R. D. Suenram and F. J. Lovas for making a number of NIST microwave measurements available before publication, and to Drs. A. R. Hight Walker and R. D. Suenram for remeasuring the troublesome ground state J  1 R 0 line at 19 265 MHz. The U.S. portion of this work was supported in part by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S. Department of Energy; the Russian portion was supported in part by the Russian Fund for Fundamental Studies, Grant No. 94-02-05424-a, and the International Science Foundation, Grant R81000; the French portion was supported in part by the G.D.R.P.C.M.G.I. J.-U. G. was supported by a postdoctoral fellowship of the Deutsche Forschungsgemeinshaft. Calculations were carried out at the University of Paris on the IDRIS Computer Center Cray C98 and C94, and at NIST on the Cray YMP.

PY - 1996/9

Y1 - 1996/9

N2 - A least-squares fit is presented of 1105 far-infrared and 2860 microwave transitions in acetaldehyde, which sample rotational levels in all torsional states below the lowest-frequency small-amplitude vibration ν10. Four-fifths of these transitions, involving torsional states below the barrier (υt ≤ 2), were treated in an earlier publication; here the theoretical model is further tested by extending the data set to include the υt = 3 and 4 states above the barrier. The new data set includes (i) 224 υt = 3 ← 2 far-infrared transitions, (ii) Nizhny Novgorod RAD-2 a-type and b-type sub millimeter transitions in υt = 2, which make more precise ΔΚ = ±1 intervals in this last torsional state below the barrier, (iii) RAD-3 a-type submillimeter transitions in υt = 3 and 4, and (iv) microwave and submillimeter measurements or remeasurements from NIST and Lille of transitions with υt ≤ 4. The global fit, which uses an improved version of the computer program previously applied to the υt ≤ 2 data, gave a weighted overall standard deviation of 1.21 with 55 adjusted and 2 fixed parameters. Residuals from the fit were close to experimental uncertainties for the infrared wavenumber measurements and for microwave and submillimeter frequency measurements below the barrier, but some residuals reached several MHz or more for frequency measurements involving levels near ν10. We have attempted to achieve a qualitative understanding of the numerical results by presenting a general overview of internal rotation energy levels above the barrier and a theoretical discussion of torsion-rotation interactions among these levels.

AB - A least-squares fit is presented of 1105 far-infrared and 2860 microwave transitions in acetaldehyde, which sample rotational levels in all torsional states below the lowest-frequency small-amplitude vibration ν10. Four-fifths of these transitions, involving torsional states below the barrier (υt ≤ 2), were treated in an earlier publication; here the theoretical model is further tested by extending the data set to include the υt = 3 and 4 states above the barrier. The new data set includes (i) 224 υt = 3 ← 2 far-infrared transitions, (ii) Nizhny Novgorod RAD-2 a-type and b-type sub millimeter transitions in υt = 2, which make more precise ΔΚ = ±1 intervals in this last torsional state below the barrier, (iii) RAD-3 a-type submillimeter transitions in υt = 3 and 4, and (iv) microwave and submillimeter measurements or remeasurements from NIST and Lille of transitions with υt ≤ 4. The global fit, which uses an improved version of the computer program previously applied to the υt ≤ 2 data, gave a weighted overall standard deviation of 1.21 with 55 adjusted and 2 fixed parameters. Residuals from the fit were close to experimental uncertainties for the infrared wavenumber measurements and for microwave and submillimeter frequency measurements below the barrier, but some residuals reached several MHz or more for frequency measurements involving levels near ν10. We have attempted to achieve a qualitative understanding of the numerical results by presenting a general overview of internal rotation energy levels above the barrier and a theoretical discussion of torsion-rotation interactions among these levels.

UR - http://www.scopus.com/inward/record.url?scp=0002546173&partnerID=8YFLogxK

U2 - 10.1006/jmsp.1996.0182

DO - 10.1006/jmsp.1996.0182

M3 - Article

AN - SCOPUS:0002546173

VL - 179

SP - 41

EP - 60

JO - Journal of molecular spectroscopy

JF - Journal of molecular spectroscopy

SN - 0022-2852

IS - 1

ER -