1. The rotational spectra of helium- pyridine and hydrogen molecule- pyridine clusters Chakree Tanjaroon and Wolfgang Jäger

2. Pyridine molecule  The C 5 H 5 N structure is similar to C 6 H 6.  Large aromatic surfaces = many Van der Waals binding sites.  A strong polarizer. N-C3 = 2.805 Å Surface area  6.2 Å 2 Dipole moment = 2.2 debye

3. M. J. Heather, D. W. H. Swenson, and C. E. Dykstra. J. Phys. Chem. A, 110, 6399-6407 (2006). Predicted (H 2 ) 20 -C 6 H 6 cluster H 2  7 above--6 along the edge--7 below! The axial H 2 are slippery (floppy).

4. The dimers Helium-pyridineHydrogen molecule-pyridine  MP2 calculations show the T-shaped configuration is most stable. B = 59.3 cm -1 I = 1 (oH 2 ) I = 0 (pH 2 ) (D e = 90 cm -1 )(D e = 327 cm -1 )

5. Rotation of H 2 over C 5 H 5 N surface “H-bond” breaking motion (-327 cm -1 )(-290 cm -1 ) 40 cm -1 up hill More repulsive

6. FTMW Experiment For details see: V. N. Markov, Y. Xu, and W. Jager, Rev. Sci. Instrum. 69, 1198, 4061 (1998). He-C 5 H 5 N: 0.05% pyridine at 8.0 - 40.0 atm. helium H 2 -C 5 H 5 N: 0.05% pyridine + 5.0 % H 2 at 40.0 atm helium

7. Experimental Results He N -C 5 H 5 N He 1 -C 5 H 5 NHe 2 -C 5 H 5 N 12 R-branch transitions. 9 a-type and 3 c-type. 39 hyperfine components. 5 R-branch transitions. All a-type. 18 hyperfine components.

8. The 0 00  1 01 transition He 1 -C 5 H 5 N He 2 -C 5 H 5 N The narrow splitting = He atom tunnelling? 1 of 3 hyperfine components

9. ParameterHe 1 -C 5 H 5 N This experiment He 1 -C 5 H 5 N **Fit to experimental ABC He 1 -C 5 H 5 N MP2/augcc- pvdz He 1 -C 6 H 6 LIF Experiment  A(MHz)3875.2093(48)3869.1154062.5833- B(MHz)3753.2514(45)3771.5683933.70933670(640) C(MHz)2978.4366(81)2959.2102906.18602950(190) R(Å) -3.5063.233.17(37)  (°) 7.30.0613.70.0  (fit) 3.9 kHz--- He 1 -C 5 H 5 N: He 1 -C 5 H 5 N: The rotational constants and some structural parameters.  S. M. Beck, M. G. Liverman, D. L. Monts, and R. E. Smalley, J. Chem. Phys., 70(1), 232-237 (1979). ** Z. Kisiel, P. W. Fowler, and A. C. Legon, J. Chem. Phys. 95(4), 2283-2291, (1991).

10. ParameterHe 2 -C 5 H 5 N This experiment* He 2 -C 5 H 5 N Fit (TopToP) A(MHz)3177.27(50)3070.5431 B(MHz)2707.184(50)2824.7893 C(MHz)2980.374(67)2791.7481 R(Å)(X-He 2 )Rcom = 3.48 He 1 -He 2 = 1.30 He 2 -C 5 H 5 N: He 2 -C 5 H 5 N: The rotational constants and some structural parameters.

11. Parameter (MHz) He 1 -C 5 H 5 NHe 2 -C 5 H 5 NAr-C 5 H 5 N  DJDJ 0.12408(55)0.2259(53)0.00358(5) D JK 0.1200(43)-0.397(14)0.0196(1) DKDK -0.2451(25)--0.023(15) d1d1 0.00427(27)-- d2d2 -0.00016(10)-- HJHJ 0.003053(35)-- H JK -0.006588(473)-- HKHK 0.004114(587)-- 1.5(  cc ) 5.0122(64)5.104(40)- 0.25(  bb -  aa ) 1.5589(19)1.5735(97)- The distortion constants for He 1 -C 5 H 5 N and He 2 - C 5 H 5 N.  T.D. Klots, T. Emilsson, R. S. Ruoff, and H. S. Gutowsky. J. Phys. Chem. 93, 1266 (1989)

12. Experimental Results (H 2 )-C 5 H 5 N o(H 2 )-C 5 H 5 Np(H 2 )-C 5 H 5 N (V 0 )(V 1 ) [ j H2 = 1 ] [ j H2 = 0 ] Ground stateExcited state

13. The 0 00  1 01 transition, (V 0 )  o(H 2 )-C 5 H 5 N: 11 a-type transitions, 52 hyperfine components fitted. o(H 2 )-C 5 H 5 Np(H 2 )-C 5 H 5 N 100 shots, S/N = 2000200 shots, S/N =200  p(H 2 )-C 5 H 5 N: 4 a-type transitions fitted.

14. Hyperfine structures: o(H 2 )  C 5 H 5 N Fig. above illustrates the hyperfine splittings for 0 00  1 01 transition. The larger quadrupole splittings  1.5-2.0 MHz. The smaller spin-rotation splittings are  0.05 MHz. (MHz) F =1  F=1 F =1  F=2 F =1  F=0 0 00  1 01

15. J = 1  J = 2,  K = 0 |K a | = 1 1 11  2 12 1 01  2 02 1 10  2 11 The observed 1 11  2 12 and 1 10  2 11 lines are displaced 1514 MHz from the band center due entirely to the asymmetry splitting. Highest transition is J=3  J=4.

16. The rotational and distortion constants for o(H 2 )-C 5 H 5 N and p(H 2 )-C 5 H 5 N. Parameter (MHz) o(H 2 )-C 5 H 5 N This experiment p(H 2 )-C 5 H 5 N This experiment* (H 2 )-C 5 H 5 N MP2/augcc-pvdz (T-shaped) A4673.016(11)4945.8035(22)4812.9623 B4476.9953(22)4627.9071(8)4639.6078 C2962.6876(33)2964.4795(8)2908.0300 DJDJ 0.03596(94)0.04292(9)- D JK -0.0858(32)-- DKDK 0.0602(24)-- d1d1 0.01724(53)-- d2d2 -0.00458(13)-- C 5 H 5 N: A = 6039.2516(6), B = 5804.9116(6), C = 2959.2117(6) MHz.

17. The quadrupole and spin-rotation coupling constants, and the bond distance R for oH 2 -C 5 H 5 N. Parameter (MHz) o(H 2 )-C 5 H 5 N This experiment C5H5NC5H5N Free  H 2 eQq aa -4.884(7)-4.908(3)- eQq bb 1.451(7)1.434(3)- eQq cc 3.433(10)3.474(3)- M aa 0.0124(45)-- M bb 0.0208(22)- 0.1139 (M  ) M cc 0.0205(12)-- R(parallel)3.76(3) Å-- R(perpendicular)3.58(3) Å--  G. O. Sørensen. J. Molecular Spectroscopy, 22, 325(1967).  N. F. Ramsey. Phys. Rev. 85, 60 (1952).

18. Conclusion He 1 -C 5 H 5 N  T-shaped complex. (H) 2 -C 5 H 5 N  T-shaped complex. (He) 2 -C 5 H 5 N  nearly T-shaped. Helium atoms lie on the same ring side.

19. Acknowledgements Natural Sciences and Engineering Research Council of Canada and Alberta Ingenuity Fund for the financial supports. Qing Wen and Jen Landry for help with the FTMW spectrometer. Thank you for your attention!  More He/H 2 clusters MW talks by our group: TE02: Jen N. Landry TE03: Julie M. Michaud RI01: Wolfgang Jäger