1. The pure Inversion-Tunneling Transition of Ammonia in Helium Droplets Rudi Lehnig and Wolfgang Jäger Department of Chemistry, University of Alberta, Edmonton, AB Canada

2. Gas-phase like (that means rotationally resolved) spectra of dopant molecules. Increased moment of inertia (dopant drags normal fluid helium density with it). Line widths range from 75 MHz to several GHz. Microwave spectroscopy may help to understand the line-broadening mechanisms (low-pass filter for droplet excitations). Helium Nanodroplet Spectroscopy

3. pure MW spectroscopy: J = 4 – 3, J = 5 – 4 of HCCCN (10.5 – 14.5 GHz) Reinhard et al., PRL 82, 5036 (1999). Callegari et al., JCP 113, 4636 (2000). J = 1 – 0 of HCN and DCN (58 – 74 GHz) Conjusteau et al., JCP 113, 4840 (2000). MW-IR double resonance: 1 of HCCCN Callegari et al., JCP 113, 4636 (2000). 3 of OCS Grebenev et al., JCP 113, 9060 (2000). Kunze et al., JCP 116, 7473 (2002). Previous Microwave Studies

4. diffusion pump 8000 L / min turbo pump 700 L / min turbo pump 700 L / min turbo pump 700 L / min turbo pump 340 L / min cryostat ca. 14 K skimmer 500 μm doping cell microwave resonator quadrupole mass-spec nozzle 5 μm Helium Nanodroplet Spectrometer ℓHe-cooled bolometer, 1.5 K

5. 2060 cm -1 : 1 photon for 400 helium atoms 8 GHz: 18 photons for 1 helium atom Depletion Spectroscopy

6. Implementation of Microwave Resonator Cavity mirrors Helium droplet beam Use of TWT microwave amplifier; output power: 10 W reflectivity R ~ 0.98; total stored power: ~ 50 * P in

7. Inversion Motion of Ammonia

8. Microwave Inversion Transition of NH 3 @He N 10 -5 depletion

9. diffusion pump 8000 L / min turbo pump 700 L / min turbo pump 700 L / min turbo pump 700 L / min turbo pump 340 L / min cryostat ca. 14 K skimmer 500 μm doping cell microwave resonator quadrupole mass-spec nozzle 5 μm Helium Nanodroplet Spectrometer ℓHe-cooled bolometer, 1.5 K flag

10. Microwave Inversion Transition of NH 3 @He N 10 -5 depletion

11. single ammonia molecule sharp feature is saturated Pick-up Pressure; Saturation Behaviour

12. Microwave Inversion Transition of 15 NH 3 @He N

13. Possible Causes for the Sharp Peak Effect of Bose-Einstein Condensate fraction? Two different relaxation channels? Saturation effect, Lamb Dip? Maser action of ammonia molecule? The overall feature looks like the P-, Q-, R-branches of a vibrational band.

14. Energy level splitting through coupling of ammonia rotation with center- of-mass motion of ammonia in the droplet (particle in a box model). Rotational wavefunction is identical and inversion wavefunction nearly identical  Splitting is similar for both states. Line-Broadening Mechanism K. K. Lehmann, Mol. Phys. 97, 645 (1999). I. Reinhard, C. Callegari, A. Conjusteau, K. K. Lehmann, and G. Scoles, PRL 82, 5036 (1999). K. K. Lehmann, JCP 126, 024108 (2007).

15. 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 Frequency / GHz m’ 13 12 11 10 9 8 6 4 1 13 12 11 10 9 8 6 4 1 m”

16. Frequency / MHz Intensity Simulated Line-Shape

17. E = f 1 m 2 E = h (m+1/2) E = B m(m+1) Results of Simulations

18. $$$ Acknowledgements Chemistry Design and Manufacturing Facility Canada Foundation for Innovation ASRA, ISRIP NSERC University of Alberta