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Spectra, Structures, and Dynamics of Weakly Bound Clusters from Dimers to Nonamers Wolfgang Jäger Department of Chemistry, University of Alberta.

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Presentation on theme: "Spectra, Structures, and Dynamics of Weakly Bound Clusters from Dimers to Nonamers Wolfgang Jäger Department of Chemistry, University of Alberta."— Presentation transcript:

1 Spectra, Structures, and Dynamics of Weakly Bound Clusters from Dimers to Nonamers Wolfgang Jäger Department of Chemistry, University of Alberta

2 Potential Energy Curves for H-Cl and Kr-Xe

3 Significance of van der Waals Interactions

4 Significance, continued …

5 Fourier Transform Microwave Spectrometer Frequency range: 4 – 26 GHz (ca. 0.1 – 1 cm -1 )

6 microwave cavity nozzle Fourier Transform Microwave Spectrometer

7 Outline for Remainder of Talk large amplitude motions in van der Waals complexes three-body effects in ternary and quaternary clusters successive micro-solvation of molecules with helium atoms

8 Ne-Ethylene in its Principal Inertial Axis System

9 Energy Level Diagram of Ne-trans-C 2 D 2 H 2 (Out-of-Plane Motion)

10 Energy Level Diagram of Ne-trans-C 2 D 2 H 2 (In-Plane Motion)

11 RG N -NH 3 Complexes Ne, Ar, a KrNH 3 Ne, Ar NH 3 Ne, Ar NH 3 15 NH 3 15 NH 3 15 NH 3 ND 3 ND 3 ND 3 ND 2 H ND 2 H ND 2 H NDH 2 NDH 2 NDH 2 a Ar-NH 3, Ar- 15 NH 3 by D. D. Nelson Jr. et al., JCP 85, 512 (1986); E. Zwart et al., JCP 95, 793 (1991); and many others.

12 J=4-3 Transitions of Deuterated Ar 3 -Ammonia

13 Ammonia internal rotation in RG N -NH 3 clusters 14 N nuclear quadrupole coupling constants in MHz 14N nuclear quadrupole coupling constant in free ammonia: P= MHz M. D. Marshall and J. S. Muenter, JMS 85, 322 (1981).

14 Three-Body Interactions

15 Three-body interactions crystal structures of solid rare gases face-centered cubic (observed) hexagonal close-packed (predicted using pairwise additivity)

16 NeAr Ne 2 Ar NeAr 2 Ne 3 Ar Ne 2 Ar 2 NeAr 3 Pure Rare Gas Clusters

17 Survey Scan with Ne/Ar Sample Gas Mixture

18 Transitions J K a K c = of Ne 2 Ar

19 Rotational Energy Level Diagrams Ne 2 ArNeAr 2

20 Comparison with Theoretical Calculations Rotational Constant Experiment pairwise additive pairwise + AT term A (MHz)4724.1(8) B (MHz) (6) C (MHz) (6) References: 1. Ernesti & Hutson, JCP 103, 3386 (1995). 2. Aziz & Slaman, Chem. Phys. 130, 187 (1989). Ne-Ne PES ~ viscosity data & high energy total cross sections 3. Barrow & Aziz, JCP 89, 6189 (1988). Ne-Ar PES ~ low energy total cross section data & low temperature second virial coefficients & room temperature diffusion coefficients & high energy total cross sections modified (scaled r e ) to fit MW data [JCP 102, 1181 (1995)].

21 Helium – Molecule Complexes very weak interactions  high zero point energy  spectra sample significant portion of PES  attractive systems for ab initio calculations relevant wrt spectroscopy of doped helium droplets possibility to measure He n -molecule systems? S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science 279, 2083 (1998).

22 Helium Nanodroplet Isolation Spectroscopy (Background) Grebenev, Toennies, Vilesov, Science 279, 2083 (1998).

23 Helium Nanodroplet Isolation Spectroscopy (more Background) Grebenev, Toennies, Vilesov, Science 279, 2083 (1998).

24 He-OCS in its Principal Inertial Axes System

25 Measured Rotational Transitions of He-OCS

26 He 2 -OCS in its Principal Inertial Axes System

27 J KaKc = Transitions of He 2 -OCS

28 Multidimensional Assignment Procedure a) infrared predictions b) sample conditions (pressure, temperature) c) double resonance experiments d) consistency of isotopic data e) spectral fits

29 Effect of Nozzle Cooling on Cluster Formation He 6 -OCS, J=3-2 at MHz, 0.01% OCS in He at 20.4 atm 100 averaging cycles nozzle at room temperature S/N ~ 2 nozzle at dry ice temperature (-78.5 C) S/N ~ 40

30 Double Resonance Spectrometer

31 Double Resonance Spectrometer (Schematics)

32 Double Resonance Experiments on He 6 -OCS signal: J-3-2, MHz pump: J=2-1, MHz 20 averaging cycles pump power (continuous) off -3 dBm 3 dBm

33 Vibrational Frequency Shifts of He N -OCS Clusters experimental values Tang et al., Science, accepted. values from Whaley and co-workers, JCP 115, (2001).

34 Moment-of-Inertia Shifts of Isotopomers

35 Proposed Structure of He 8 -OCS

36 Spectroscopic Constants of He N -OCS Clusters MoleculeBD Free OCS x10 -5 He-OCS He 2 -OCS He 3 -OCS He 4 -OCS He 5 -OCS He 6 -OCS He 7 -OCS He 8 -OCS OCS in 4 He droplet (N~10,000) (90)11.4(3)

37 Rotational Constants of He N -OCS Clusters

38 Potential Energy Surface of He-N 2 O CCSD(T) level of theory, aug-cc-pVDZ basis set

39 Bound State Calculations

40 Wavefunction of Ground State

41 Wavefunctions of 1 st and 2 nd Excited States

42 J=1-0 Spectrum of He 5 -N 2 O

43 He 6 -N 2 O in its Principal Inertial Axes System

44 Acknowledgements Dr. Yunjie Xu (H31) Dr. Aiko Huckauf Dean Court Dr. Yaqian Liu (H19) Dr. Jennifer van Wijngaarden (H15) Dr. Silas Ngari Kai Brendel (H30) Hans Osthoff Wendy Topic Tobias Klemmer James Song Mike Gerry Bob McKellar PN Roy NSERC ASRA CIPI


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