Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June.

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1 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Time Domain MW Spectroscopy: Fundamental Physics From Molecular Rotation Jens-Uwe Grabow Gottfried-Wilhelm-Leibniz-Universität Hannover

2 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Microwave spectroscopy Principles of FT-microwave spectroscopy Challenging measurements today Precise FTMW characterization Future High Precision FTMW measurement Rotational Spectroscopy in the Time-Domain: History, Technique & (Future) Capabilities high resolution & sensitivity: Resonator & Jet COBRA instrument Highly Relativistic species with electronic angular momentum: - in-situ generation- Rotational spectrum - Stark effect- Zeeman effect e-EDM sensitive species: lifted degeneracy exploitation of spatial consequences low frequency: exploitation of narrow lineshape precision measurements in the past p-,T-odd effects: electron electric dipole moment e-EDM sensitive atomic & molecular species

3 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Precision Observations by a Microwave Method: An OLD example

4 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Characteristics of rotational spectra : High sensitivity (minimal number density of molecules ~ 10 9 / cm 3 ) Isotopomers in natural abundance molecular structure Microwaves : high spectral purity and wide range tunability frequency range :~ 0.3 - 3000 GHz wavelength range :ca. 100 cm – 0.1 mm cm-wave…submm-wave …far-IR/THz/T-rays Applications : Rotational spectra of polar molecules, molecular complexes and radicals in static gases or jets High resolution ( / ~ 10 7 ) Fine- and hyperfine structure of rotational lines intramolecular dynamics spin-rotation-coupling Microwave Spectroscopy : Introduction

5 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Microwave Spectroscopy: CW vs. FT continuous wave (CW) excitation (t) : slowly varying sample impulse excitation A(t): fast modulation sample S( ) : frequency-domain signal S(t) : time-domain signal t Fourier transformation (FT) ( ) : absorption signal

6 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Microwave Spectroscopy Techniques: Short History continous wavepulsed excitation static gas pulsed supersonic jet expansion + broadband surveys - weakly polar species 2 - linewidth + weakly polar species + linewidth - broadband surveys ++ lower energy levels ++ linewidth ++ weakly polar species,Q ½ -- higher energy states -- broadband surveys MW oscillator MW detector absorption cell use of modulation techniques Σ FT T. J. Balle, W. H. Flygare, Rev. Sci. Instrum. 52, 33 (1981). Σ FT waveguide resonator J. Ekkers, W. H. Flygare, Rev. Sci. Instrum. 47, 448 (1976).

7 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Fourier transform microwave (FTMW) spectroscopy: Principle of Operation Interaction of coherent microwave radiation with the molecular gas sample. Creation of coherent superposition of states by pulsed excitation, and thus macroscopic polarization of the sample. Transient emission signal, oscillating at frequencies of polarized transitions and observed in the time domain. Rotational spectrum obtained by Fourier transformation from time to frequency domain.

8 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 MW local oscillator mixer MW signal oscillator resonator A/D-Conversion and averaging IF frequency pulse generation FT-MW spectroscopy: supersonic jets in resonators Frequency range : ~1 - 140 GHz W. F. Kolbe and B. Leskovar, Rev.Sci.Intrum. 56, 97 (1985). Path length: d · Q 1/2 0.5m · 100000 1/2 = 150m Temperature : < 2K Repetition Rate:20 Hz Waveguide/static-gas vs. Resonator/supersonic-jet spectroscopy: sensitivity (due to population transfer) resolution (due to velocity equilibration) unstable species (due to collision-free expansion) supersonic-jet

9 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Coaxial oriented Beam-Resonator Arrangement (COBRA): molecular excitation t MW pulse 1μs before excitation pulse: dipole moments cancel EbEb EaEa many two-level systems single particle, Schrödinger equation: ensemble properties, von Neumann equation wavefunction density matrix density matrix: (no) coherence: population: J.-U. Grabow, W. Stahl, Z. Naturforsch. 45a, 1043 (1990).

10 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Coaxial oriented Beam-Resonator Arrangement (COBRA): molecular response E t T = 100μs MW signal after excitation pulse:oscillating macroscopic dipole moment density matrix: coherence: population: Fourier Transform Frequency Domain, Spectrum Time Domain, FID U. Andresen, H. Dreizler, J.-U. Grabow, W. Stahl, Rev.Sci.Instrum. 61, 3694 (1990). J.-U. Grabow, W. Stahl, H. Dreizler, Rev.Sci.Instrum. 67, 4072 (1996).

11 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 COBRA chamber

12 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Fabry-Pérot Type Resonator: Spherical Reflectors

13 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Spherical Reflector: Transmit & Receive Antennae supersonic-jet source high-frequency antennae low-frequency antennae

14 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 coaxially oriented beam resonator arrangement (COBRA) FTMW-Spectrometer high-frequency electronics

15 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Supersonic-Jet FTMW spectroscopy: (in-situ) generation/isolation of species laser plasma electric discharge laser photolysis pyrolysis chemical reactions non-volatile species Generation : Motivation : important role of radicals in chemical reactions e.g. in combustion and atmospheric chemistry structure determination (geometry) fine and hyperfine interactions (electronic properties)

16 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Generation of seeded supersonic jet: Coaxial Ablation Twin Source (CATS) volatile compound (1%) in Ne @ ~500 kPa Nd:YAG LASER I Nd:YAG LASER II supersonic expansion rotating/translating rods:elements, alloys, compounds bulk material or compressed powder(s)

17 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 TeSe: Electronic Data From Pure Rotational Spectra 125 Te 77 Se J 4 3 Resolution: 0.0000001 cm -1 Accuracy: 0.00000001 cm -1 r eq = 235.904038(71) pm Deike Banser, Melanie Schnell, Jens-Uwe Grabow, Emilio J. Cocinero, Alberto Lesarri, and Jose L. Alonso, Angew. Chem. Int. Ed. 2005, 44, 6311.

18 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 MSe Multi-Isotopolog Potential Fits: Tracking down tiny effects of different origin,, L. Bizzocchi, B.M. Giuliano, M. Hess, J.-U. Grabow, J. Chem. Phys. 126, 114305(2007). B.M. Giuliano, L. Bizzocchi, S. Cooke, D. Banser, M. Hess, J. Fritzsche, J.-U. Grabow, PCCP 10, 2078(2008). Born-Oppenheimer breakdown correction coefficients: electronic state nuclear volume

19 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 FT-MW Spectroscopy & Supersonic Jet Expansion high resolution rotational spectra of: instable species, intermediates solids, larger, non-volatile species complexes spectroscopic parameters structure, internuclear potential electronic structure, dipole moment chemical bond large amplitude motions barriers, tunneling pathways Very precise information on very different systems! But fundamental physics from molecular rotation spectra?

20 Salamanca, 14.09.2005.ppt Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 YbF - experiment Fundamental Physics: Search for an e-EDM un-paired electrons in large electric fields free electrons: acceleration in electric fields severely limits observation time for precise measurement of tiny effect molecules: no accelaration molecular polarizability can provide large int. @ moderate ext. fields neutral atoms: no accelaration challenging electric fields required Tl - experiment Current limit from atomic spectroscopy: d e =16 x 10 -28 e cm -1 B. C. Regan, E. D. Commins, C. J. Schmidt, D. DeMille, Phys. Rev. Lett. 88 (2002) 071805. Current limit from molecular spectroscopy: d e =10.5 x 10 -28 e cm -1 J. J. Hudson, D. M. Kara, I. J. Smallman, B. E. Sauer, M. A. Tarbutt, E. A. Hinds, Nature 473 (2011) 493.

21 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 The electric dipole moment of the electron (e-EDM) is a property of fundamental importance: It represents direct evidence for new sources of CP violation not covered by the Standard Model of Physics but has never been measured! Super Sym. Std. Mod. Experimental upper limits of an e-EDM

22 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 e-EDM: predictions from various models Current limit: d e =10.5 x 10 -28 e cm -1

23 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Symmetry leads to ±M-degeneracy of any molecule/atom that is not broken by an E-field along quantization axis. The existence of an electron electric dipole moment would break this symmetry. Major Difficulty: A background magnetic field mimics an electron EDM. What Would An electron Electric Dipole Moment (e-EDM) Do? To search for an e-EDM look for U +M –U -M 0 in a strong (internal) E field at alternately parallel/anti-parallel B-fields. A polar heavy atom diatomic in an electric field parallel or anti-parallel to an magnetic field: with a zero eEDM the energy between states that differ only by M F is independent of the relative direction. a nonzero eEDM would cause a small difference in this energy for the parallel and anti-parallel configuration.

24 Salamanca, 14.09.2005.ppt Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Molecules with electronic angular momentum: Heavy-metal fluorides Pb F un-paired p electron: 2 ground state small g-factor hfs due to F (and 207 Pb) spin I = 1/2 large polarizability heavy Pb nucleus: relativistic effects candidate for e-EDM measurements @ reasonabe B-field control \w linear Stark-effect (E int ~30 GV/cm) at moderate ext. fields

25 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Generation of PbF seeded supersonic jet: Coaxial Ablation Twin Source (CATS) SF 6 (1%) / Ne @ ~500 kPa Nd:YAG LASER I Nd:YAG LASER II supersonic expansion rotating/translating rods:elements, alloys, compounds bulk material, compressed powder elementary Pb

26 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Molecules with electronic angular momentum: Zeeman-effect of 208 PbF Splitting/MHz B / gauss Perpendicular Magnetic Field: M = ± 1 Parallel Magnetic Field: M = 0 J, F = 1/2, 0 3/2, 1 J, F = 1/2, 1 3/2, 1

27 Salamanca, 14.09.2005.ppt Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 4.229GHz 8.388 GHz 8.118 GHz 8.201 GHz 8.305 GHz 18.415 GHz 18.460 GHz 3.929GHz 4.189 GHz 3.889GHz 18.499 GHz 22.575 GHz 22.688 GHz 22.398 GHz Molecules with electronic angular momentum: Low-J pure rotational transitions of 208 Pb 19 F

28 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 PbF - Spectroscopic Characterization: Rotational & Hyperfine Constants

29 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Molecules with electronic angular momentum: Concept for a molecular spectroscopy e-EDM experiment accidentally close-lying 207 Pb 19 F states of opposite parity: complete polarizability (yielding ~30GV/cm effective internal fields) at moderate laboratory E fields (200V/cm) 2-spin system: e-, F 3-spin system: e-, F, Pb 208 Pb 19 F 207 Pb 19 F

30 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 PbF: P-odd, T-odd effects Current limit (from Tl atomic spectroscopy): d e =10.5 x 10 -28 e cm -1 J. J. Hudson, D. M. Kara, I. J. Smallman, B. E. Sauer, M. A. Tarbutt, E. A. Hinds, Nature 473 (2011) 493 corresponds to: W P,T κ P,T + W d d e = 17 mHz nuclear anapole moment constants e-EDM V. V. Flambaum, I. B. Khriplovich, O. P. Sushkov, Phys. Lett. B 146 (1984) 367.

31 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Where are we now? accuracy reached with: - standard COBRA-FTMW instrument - <5 d after Pb rod was first inserted measurement linewidth comparable to that in study of YbF: J. Hudson, B. Sauer, M. Tarbutt, E. Hinds, Phys. Rev. Lett. 89 (2002) 23003. from N. Shafer-Ray

32 Salamanca, 14.09.2005.ppt Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Molecules with electronic angular momentum: Tungsten Carbide W C un-paired d electron: 3 ground state small g-factor close Λ-doublets very large polarizability heavy W nucleus: relativistic effects candidate for e-EDM measurements @ reasonabe B-field control \w linear Stark-effect (E int ~60 GV/cm) at moderate ext. fields

33 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Generation of WC seeded supersonic jet: Coaxial Ablation Twin Source (CATS) CH 4 (1%) / Ne @ ~500 kPa Nd:YAG LASER I Nd:YAG LASER II supersonic expansion rotating/translating rods:elements, alloys, compounds bulk material, compressed powder elementary W

34 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Tungsten Carbide WC: 3 Δ electronic ground state Systematically very close-lying Λ-doublets of opposite parity: fields of E ~ 1 V/cm are sufficient for complete polarization (60 GV/cm). from A. Leanhardt Current limit (d e =10.5 x 10 -28 e cm -1 ): would lead to e-EDM effect of 50 mHz E = 0E 0 J = 2 J = 1

35 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Diatomic Rotation: the quest for an Electron electric dipole moment Advanced by Molecular spectroscopy: DREAM – FTMW spectrometer GenerationDeceleratione-EDM experiment

36 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 COBRA FT-MW Spectrometer J.-U. Grabow, W. Stahl, H. Dreizler, Rev. Sci. Instr. 67 (1996) 4072. FWHM: 3 kHz bandwidth: < 1 MHz range: 2-26.5 GHz 10mW…200mW

37 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Diatomic Rotation - The quest for the e-EDM accelarated by Molecular Spectroscopy: DREAM - FTMW

38 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 molecular interaction with radiation short stimulus Density Matrix formalism (no) coherence: thermal population: EbEb EaEa many two-level systems coherence: population equillibration: π/2 pulse

39 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Lifted M-degeneracy: Effect on linearly polarized pulse response U +M –U -M 0U +M –U -M = 0 stationary polarization direction rotating polarization direction +M -M + - + + + - - -

40 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 Acknowledgement Richard J Mawhorter, Pomona College Alexander Baum, Pomona College Benjamin Murphy, Pomona College Neil Shafer-Ray, U. Oklahoma Trevor Sears, Brookhaven Nat. Lab. Aaron Leanhardt, U. Michigan Lukas Alphei Feinmechanikwerkstatt des Instituts für Physikalische Chemie W. Rogge Deutsche Forschungsgemeinschaft (DFG) Deutscher Akademischer Austauschdienst (DAAD) Fonds der Chemischen Industrie (FCI) Land Niedersachsen

41 Institut für Physikalische Chemie & Elektrochemie, Lehrgebiet A Columbus, OH, June 2006.ppt Zentrum für Festkörperchemie & Neue Materialien Columbus, June 2011 molecular interaction with radiation fast passage Density Matrix formalism (no) coherence: thermal population: EbEb EaEa many two-level systems coherence: population equillibration: π/2 pulse