Fingerprints of damped quantum rotation observed in solid-state proton NMR spectra.

(1)H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical.

[1]  T. Ratajczyk,et al.  Theory of damped quantum rotation in NMR spectra. I. Fundamental aspects. , 2005, The Journal of chemical physics.

[2]  J. Jaźwiński,et al.  Carr-Purcell echo spectra in the studies of lineshape effects. Nonclassical hindered rotation of methyl groups in 1,2,3,4-tetrachloro-9,10-dimethyltriptycene. , 2004, Journal of magnetic resonance.

[3]  U. Haeberlen,et al.  The low-temperature 13C and 2H spectra and relaxation rates of methyl groups depend on the azimuth of B0 in the molecular frame. Those of 1H do not. Why? , 2004, Solid state nuclear magnetic resonance.

[4]  H. Zimmermann,et al.  The shape and information content of high-field solid-state proton NMR spectra of methyl groups. , 2004, Solid state nuclear magnetic resonance.

[5]  J. Jaźwiński,et al.  Nonclassical effects in liquid-phase nuclear magnetic resonance spectra of 9-methyltriptycene derivatives , 2003 .

[6]  P. Bernatowicz,et al.  Wave properties of a methyl group under ambient conditions. , 2002, Physical review letters.

[7]  U. Haeberlen,et al.  Iterative lineshape analysis of quadrupolar echo spectra of a damped CD(3) quantum rotor: preliminary evidence of a novel mechanism of stochastic spin exchange. , 2001, Journal of magnetic resonance.

[8]  S. Szymanski.  NUCLEAR MAGNETIC RESONANCE LINE SHAPES OF METHYL-LIKE QUANTUM ROTORS IN LOW-TEMPERATURE SOLIDS , 1999 .

[9]  H. Zimmermann,et al.  13C NMR of tunnelling methyl groups , 1999 .

[10]  S. Szymanski.  Erratum: Theory of thermal effects in nuclear magnetic resonance spectra of metal hydrides undergoing quantum mechanical exchange [J. Chem. Phys. 104, 8216 (1996)] , 1997 .

[11]  S. Szymanski.  Theory of thermal effects in nuclear magnetic resonance spectra of metal hydrides undergoing quantum mechanical exchange , 1996 .

[12]  R. R. Ernst,et al.  Transitions induced in a double minimum system by interaction with a quantum mechanical heat bath , 1990 .

[13]  A. Würger,et al.  Rotational tunnelling in (CH3)2SnCl2: a neutron scattering study , 1990 .

[14]  A. Heuer,et al.  A new method for suppressing baseline distortions in FT NMR , 1989 .

[15]  A. Wurger.  LETTER TO THE EDITOR: The temperature dependence of inelastic rotational tunnelling transitions , 1989 .

[16]  M. Prager,et al.  Inelastic incoherent neutron scattering study of the methyl rotation in various methyl halides , 1987 .

[17]  M. Punkkinen,et al.  Proton spin-lattice relaxation and ammonium tunnelling in (NH4)2ZnCl4 , 1985 .

[18]  A. Hewson.  The temperature dependence of inelastic neutron scattering in rotational tunnelling systems. II. Calculation of the time-dependent correlation functions , 1982 .

[19]  A. Hewson.  The temperature dependence of inelastic neutron scattering in rotational tunnelling systems. I. Formulation and perturbation theory , 1982 .

[20]  G. Binsch,et al.  General theory of exchange-broadened nmr line shapes II. Exploitation of invariance properties , 1970 .

[21]  J. Derissen.  Crystal structure and conformation of methylmalonic acid , 1970 .

[22]  S. Clough,et al.  Nuclear magnetic resonance line shapes of methyl groups undergoing tunnelling rotation , 1968 .

[23]  S. Alexander.  Exchange of Interacting Nuclear Spins in Nuclear Magnetic Resonance. I. Intramolecular Exchange , 1962 .