1. The high resolution spectrum of the Ar  C 2 H 2 complex C. Lauzin, a K. Didriche, a M. Herman, a and L. H. Coudert b a Université Libre de Brxuxelles, B-1050, Bruxelles, Belgium b LISA, CNRS/Universités Paris Est et Denis Diderot, Créteil, France

2. Outline Previous experimental investigations The new measurements Preliminary line position analysis Refining the IPES of the ground vibrational state Refining the IPES of the excited vibrational state

3. Previous microwave measurements The 1 10  1 11 is the first measured transition. 1 8 a-type transitions measured by Oshima et al. 2 16 a-type transition with K a  and  measured by Liu and Jäger. 3 1. DeLeon and Muenter, JCP 72 (1980) 6020. 2. Oshima, Iida, and Endo, CPL 161 (1989) 202. 3. Liu and Jäger, JMS 205 (2001) 177.

4. Previous infrared measurements        band region. 72 b-type transitions K' a  and K" a  measured. 1 5 band region. 121 a- and c-type transitions K' a  and K" a  measured. 2   bend         bend band. 21 a-type transitions with K a  measured. 3 1. Hu, Prichard, Sun, Muenter, and Howard, JMS 153 (1992) 486. 2. Oshima, Matsumoto, Takami, and Kuchitsu, JCP 99 (1993) 8385. 3. Bemish, Block, Pedersen, Yang, and Miller, JCP 99 (1993) 8585.

5. Present infrared measurements    band region recorded from 6544 to 6568 cm  using the FANTASIO+ experimental setup. 1-3 207 b-type transitions with K' a and K" a =  measured. The energy of the upper vibrational state is much higher than the binding energy. 1. Lauzin, Didriche, Macko, Demaison, Liévin, and Herman, JPC A. 113 (2009) 2359. 2. Didriche, Lauzin, Foldès, Vaernewijck, and Herman, MP 108 (2010) 2155. 3. Paper TI02 on Tuesday.

6. K a = 1  2 K a  K a = 0  1

7. K a =1  0 K a = 3  2 K a = 2  1

8. Preliminary analysis of the new data Wavenumbers were analyzed calculating the energy with a J  J  expansion: 1 1. Moruzzi, Xu, Lees, Winnewisser, and Winnewisser, JMS 167 (1994) 156. Fit I. K a  a   and  subbands Fit II. K a  K a   0  and 2  subbands

9. A portion of the O  C table Microwave 207 lines fitted. Unitless standard deviation is 2.0 Infraraed Infrared Rotational assignment of the subbands

10. Comparison between Obs. and Cal. spectra Observed Calculated Van der Waals mode ? K a =1  0 K a = 2  1

11. What can we do with the new data? A Watson-type Hamiltonian cannot be used. Ar  C 2 H 2 is a very floppy molecule 1 with a bending frequency of 6 cm . Ab initio calculations show that its IPES is very shallow. 2,3 1. Bemish, Block, Pedersen, Yang, and Miller, JCP 99 (1993) 8585. 2. Munteanu and Fernández, JCP 123 (2005) 014309. 3. Tao, Drucker, and Klemperer, JCP 102 (1995) 7289.

12. The Munteanu and Fernandez IPES Aug-cc-pVQZ-33211 Global Minima M R = 3.99 Å,  at  cm  Local Minima m R = 4.63 Å,  0 at  cm  Saddle point S R = 3.89 Å,  90 at  cm  M M m S Can we refine the IPES of the complex?

13. Refining the IPES of the GS The IPES was expanded using the analytical expression of Bukowski et al. 1 Energies were calculated with the approach developed for the Ar  CO complex. 2 The coefficients of the IPES and B(HCCH) were fitted to GS combination differences. 1. Bukowsky, Sadlej, Jeziorski, Jankowski, Szalewicz, Kucharski, Williams, and Rice, JCP 110 (1999) 3785. 2. Coudert, Pak, and Surin, JCP 121 (2004) 4691.

14. Refining the IPES of the GS The Schrödinger equation for the stretching is solved for each t-value belonging to the DVR grid. 1 1. Bacic and Light, JCP 87 (1997) 4008.

15. Analysis results: GS The difference between the refined IPES and the ab initio one 1 are no larger than 5.3 cm  B(HCCH) = 1.175 32(6) cm     RMS for the 17 microwave transitions is 5.5 MHz. RMS for the 210 IR data is 1.2×10  cm . bend  cm     1. Munteanu and Fernández, JCP 123 (2005) 014309. 2. Herman, MP 105 (2007) 2217. 3. Bemish, Block, Pedersen, Yang, and Miller, JCP 99 (1993) 8585.

16. A portion of the O  C table for the IR data Ground vibrational state under control.

17. Refining the IPES of the excited vibrational state The IPES of the excited vibrational state was refined using the new data. Rotational levels of the excited vibrational states were computed using the results of the previous analysis.

18. Analysis results: excited vibrational state The maximum difference between the refined IPES and the ab initio one 1 is 69 cm  B(HCCH) = 1.160 9(5) cm     RMS for the 29 levels is 6.6×10  cm . 1. Munteanu and Fernández, JCP 123 (2005) 014309. 2. Kou, Guelachvili, Abbouti Temsamani, and Herman, Can. J. Phys. 72 (1994) 1241.

19. The O  C table for the excited vibrational state The IPES of the excited vibrational state is probably quite different from that of the GS. Perturbations due to neighbouring vibrational states of the monomer.