1. Determining the Tunneling Path of the Ar-CHF 3 Complex L. Coudert, a W. Caminati, b A. Maris, b P. Ottaviani, b and A. C. Legon c a Laboratoire Interuniversitaire des Systèmes Atmosphériques Créteil, France b Dipartimento de Chimica “G. Ciamician,” Universita de Bologna Bologna, Italy c School of Chemistry, University of Bristol, Bristol, England

2. Overview Previous investigations of Ar  CH 3 F The two large amplitude motions What large amplitude motion takes place in the complex Analysis of the data Results

3. Previous Investigations The microwave spectrum was first investigated by Caminati et al. 1 1 Caminati, Maris, Melandri, Favero, and Ottaviani, 57th Int. Symposium on Molecular Spectroscopy, Paper M109, June 17  21, 2002. No satisfactory global analysis could be carried out. 112 transitions measured in the 60  105 GHz range. Highest J is 20.

4. x z y   The Large Amplitude Coordinates

5. The 3 Equilibrium Configurations 1  e  60,  e  51.6 2  e  180,  e  51.6 3  e  300,  e  51.6

6. Energy level diagram The symmetry group to be used is C 3v. A  8200 MHz 1 B  MHz C  1080 MHz 1 Caminati et al., 57th Int. Symposium on Molecular Spectroscopy, Paper M109, June 17  21, 2002.

7. The Rotation-type Tunneling Motion

8. The Wagging-RotationTunneling Motion

9. Which motion occurs in the complex? The rotational dependence of the splitting depends on the tunneling motion. It will be calculated with an IAM- type approach. 1 1 Hougen, J. Mol. Spec. 114, 395 (1985) and Coudert and Hougen, J. Mol. Spec. 130, 86 (1988).

10. Tunneling splitting rotational dependence

11. Which motion occurs in the complex? Values for the angles  2,  2, and  2 will also be obtained from an analysis of the microwave data.

12. Results lowest Ka-values

13. Results: Ka = 3  2

14. Results: Ka = 5  4

15. Rigid-rotator parameters All H’s also determined 116 transitions fitted, 3 excluded, RMS  1.2 MHz

16. Tunneling parameters