History 50 y rotational tunneling with high resolution

History < 50 y: rotational tunneling with high resolution neutron scattering Werner Press, Uni Kiel principles start of activities what has been achieved ? some people and conferences where do we stand today ? DMA Phys. Lett. 1976 B. Alefeld A. Kollmar Werner Press, Univ. Kiel 50 years neutron backscattering

molecules with large rotational constant B = ħ 2/(2 I) ~ 1 me. V -CH 3, NH 3 CH 4, NH 4+ hydrogen 80 barn deuterium 2. 2 barn

coherent tunneling / quantum rotations incoherent tunneling ~ α - decay

canonical example: solid hydrogen (H 2), almost free rotation E = BJ(J+1) para-ortho E 01= 13. 6 me. V nuclear spin! not exactly backscattering, separate game start of high-resolution neutron scattering: … a matter of definition… H. Kapulla & W. Glaeser TOF 1970; methane (CH 4 II) Karlsruhe

new cold source at Dido in Juelich: and HADAS improved resolution ! 0. 5 e. V and ~ 30 e. V Bert Alefeld † Achim Kollmar † DMA Phys. Lett. 1976 same place, same time (1974/5): 3 axis HADAS -picoline B. Alefeld, A. Kollmar, B. Dasannacharya tunneling in CH 4 II WP & A. Kollmar

and many more, particularly from IN 10 (and IN 5), ILL Grenoble and IRIS, ISIS Michael Prager † isotope effect pressure T-dependence matrix-isolation Jim Morrison †, Toni Heidemann Stan Clough battle against nuclear spins, total wavefunctions spin conversion (sort of alpha decay) cryostats, shutdowns (strikes) etc.

Theory ! hij = <ΦilĤlΦj> Alfred Hueller: 1972 onward, from 1980 – 2005 Erlangen pocket states start about 1967: Tsunebo Yamamoto † et al : „Kyoto group“ free rotor expansions Alfred Tsunebo Yamamoto and his wife Kazuo Maki

Conferences, workshops, reviews: ODIC Orientational disorder in crystals 1976 to 1998 (Gordon Conference) Quantum Tunneling in Molecular Solids Start 1980, ongoing QTMS XVIII (Juergen Eckert!) early review WP „Single particle rotations“ (1981) systems: Michael Prager & Toni Heidemann „Tunneling Atlas“ (1997)

beyond single particle with molecules at symmetry positions • rotation translation coupling P. Schiebel: Ĥ(φ, ū) • disorder δh(120°) M. Prager et al, J. Colmenero • partial deuteration (CH 2 D 2) K. Maki, A. Hicks + J. Larese • intermolecular interaction: γ-picoline M. Neumann, Marie Plazanet, M. Johnson, P. Trommsdorff which author ? ? ?

γ-picoline Start of long story : - B. Alefeld, A. Kollmar, B. Dasannacharya J. Chem. Phys. 1975 ~ free 6 -fold - F. Fillaux, C. Carlile 1985 - 1995 strong chain coupling; quantum sine-Gordon doubts: restart ~ 2000 M. Neumann et al J. Chem. Phys. ( 2004); new data on IN 10 B with off-set • Rotation precession (libration) coupling • CH 3 -CH 3 coupling (strength several me. V)

IN 10 B data and fit with model calculation with clusters of different length

CH 2 D 2 or unknown methane: (1) partial deuteration (XH 2 D 2): Fermion + Boson asymmetric top H H D (2) D/H interaction ~ unchanged dynamical effect: D 2 to deeper wells „orientational energy“ (K. Maki et al. JCP 1981) CH 2 D 2 III spectra not fully understood despite structure determination - 2 different sites D

(3) CH 4 on Mg. O (BASIS at SNS) A. Hicks, John Larese; Chem. Phys. 2013 resolution, dynamical range single site (2 mm) model with 180° overlap

(4) progress report (K. Maki, WP, IK) pocket state analysis of CH 4 data: 120° overlap with easy (75 e. V) and hard (15 e. V) axes scaling to CH 2 D 2: too many lines! H D D H SSSSSSS easy axes asymm. top: should solve Ĥ(ω, ū) - rotation translation coupling Int spectra (from last weeks): only easy axis with/without HD 2 „unbalanced quantum wheel“ expect a hell of a task! E ( e. V)

Situation today ? BASIS again, MP et al only occasional experiments & publications ! few groups (theory in particular) curiosity-driven research, not application-based funding ? though: NH 4 Cl. O 4, aspirin, methane hydrate, etc. many open questions improved backscattering + TOF instruments NB Need for a program library? Neutron intensity calculations

Appendix Neutrons and m. K Charlie‘s insert! ) A. Heidemann et al. CH 4 & 0. 25% O 2 (1983) Charlie Neumaier

early Gordon conf. , 1978 top: Peter Trommsdorff (left) bottom: Alfred Hüller (as experimentalist)

Gordon conf. ODIC 1992 (? )

30 years ago Gordon 1978 California Selection comm. Mike Klein & WP Proceedings? ? ?

The methyl group rotation barrier of dimethyl acetylene in the solid at 4. 5 K B. Alefeld and A. Kollmar Physics Letters A 57 289 -290 (June 1976) The librational ground state splitting of methyl molecules in solid Dimethylacetylene has been measured by high resolution neutron scattering at 4. 5 K. A threefold rotational barrier of 45 +/- 5 me. V has been obtained. Backscattering (polished Si) at pi-spectrometer External neutron laboraratory, DIDO-reactor, KFA Juelich