PSEUDOROTATION IN TETRAHYDROFURAN: SUPPLEMENTARY DATA FROM THE FREE JET ROTATIONAL SPECTRUM OF THE $d_{8}$ SPECIES

{R. Meyer, J. C. Lopez, J. L. Alonso, S. Melandri, W. Caminati, and P. G. Favero, J. Chem. Phys. 1999, 111, 7871.{D. G. Melnik, S. Gopalakrishnan, T. A. Miller, F. C. D. Lucia, J. Chem. Phys. 2003, 118, 3589.Author Institution: Dipartimento di Chimica "G. Ciamician" dell'Universita, Via Selmi 2, I-40126 Bologna, Italy; Departamento de Quimica-Fisica y Quimica-Inorganica, Facultad de Ciencias,; Universidad de Valladolid, E-47005 Valladolid, Spain; Sonnenbergstrasse 18, Zufikon, CH-5621, SwitzerlandTetrahydrofuran (THF) is a model molecule for the investigation of the hindered pseudorotation in saturated five-membered rings. Two recent papers, based on millimeter-wave investigations, reported the vibrational spacings among the four lowest pseudorotation states of normal THF, and obtained contrastant results on the potential energy function: four equivalent minima}, or 2 sets of two equivalent minima}. In order to have more information on this problem, we planned to investigate the millimeter wave spectrum of the $d_{8}$ species. We obtained a vibrational spacing of $ca$ 15 GHz between the two lowest pseudorotation states: a result which is not in agreement with both the above mentioned potential energy functions