An NMR investigation of the dynamics of a methyl group with tunneling frequency 3.4 MHz

Cleemput, M. Van; Horsewill, A.J.; Gerven, L. Van

doi:10.1016/0921-4526(94)90310-7

Cited by 4 publications

(6 citation statements)

References 4 publications

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“…Usually, − the correlation time of methyl group tunneling is assumed to follow the exponential temperature dependence as The activation energy for the tunneling motion is found to be comparable with the value of E 01 , the energy difference between the ground and the first excited torsional levels of the methyl group. Equation 20 has been assumed by intuition.…”

Section: The Model Of Motionmentioning

confidence: 99%

“…In a number of papers, − the total correlation time ( ) (eq 1), representing the classical motion and rotational tunneling, has been used instead of in eq 60 . In these papers, it is assumed that the spectral density of classical and tunneling jumps contribute to spin−lattice relaxation at high and low temperatures, respectively, and that the classical motion evolves smoothly from the tunneling motion over an intermediate temperature region.…”

Section: Other Models Of the Correlation Function And Spectral Densitymentioning

confidence: 99%

“…The temperature dependence of the spin−lattice relaxation time ( T 1 ) enables a determination of the correlation time ( τ c ) (or correlation times if there are more independent stochastic motions) over a wide temperature range. The fact that the correlation time follows simple Arrhenius behavior with a single activation energy at the high-temperature limit ( E H ) and E 01 activation energy at low temperatures was anticipated by a number of authors. − The authors 11,12 introduced the following phenomenological expression for the temperature dependence of the correlation time ( τ c ): The apparent activation energy ( E L ) has been identified with E 01 = E v 1 − E v 0 , the energy difference between the ground and first excited torsional states of the CH 3 rotator. The activation energy ( E H ) corresponds to the high-temperature classical limit, namely, the barrier height minus the zero point energy.…”

Section: Introductionmentioning

confidence: 99%

“…The fact that the correlation time follows simple Arrhenius behavior with a single activation energy at the high-temperature limit (E H ) and E 01 activation energy at low temperatures was anticipated by a number of authors. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The authors 11,12 introduced the following phenomenological expression for the temperature dependence of the correlation time (τ c ):…”

Section: Introductionmentioning

confidence: 99%

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Proton Spin−Lattice Relaxation of Tunneling Methyl Groups: Calculation of the Time Dependent Correlation Functions

Latanowicz

2004

J. Phys. Chem. A

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A theory of magnetic nuclear relaxation, providing a calculation of the correlation functions of complex motion of methyl groups is presented. The complex motion consists of jumps over the barrier (classical motion) and jumps through the barrier (tunneling). The Schrödinger equation has been applied in the calculation of the rate constant of tunneling jumps through the barrier. The equations for the spectral densities (ω), where ω = (ω I ± ωT), and ω = (m ω I), where m = 1 or 2, ω I is the resonance angular frequency, and ωT is the angular frequency of the tunnel splitting, are derived. These spectral densities concern the motion of spin pairs inside methyl groups (“intra”) and outside methyl groups (“inter”). The calculated spectral densities are applied to analyze the temperature dependencies of the spin−lattice relaxation rate in solids containing methyl groups. A wide regime of temperatures from 0 K up to the melting point is considered. The temperature at which the tunneling process ceases is discussed. The theory proposed explains the different temperature dependencies of T 1 for CH3COOK obtained in the experiments caused by small amounts of CH3COOH or water impurities. The theoretical equations derived in this paper are compared to those known in the literature.

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Section: The Model Of Motionmentioning

confidence: 99%

Section: Other Models Of the Correlation Function And Spectral Densitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Proton Spin−Lattice Relaxation of Tunneling Methyl Groups: Calculation of the Time Dependent Correlation Functions

Latanowicz

2004

J. Phys. Chem. A

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“…By comparing the magnetic field dependence of the low field spectra we learned that the line at 3.35 MHz in this spectrum is a ⌬mϭ0 line, occurring at the tunneling frequency t . This measurement 12 considerably extends the range of low field NMR spectroscopy, the previous upper limit being 1.5 MHz. 8 The spectra in Figs.…”

Section: A Low Field Nmr Spectramentioning

confidence: 63%

Quantum and classical dynamics of a methyl group with tunneling frequency 3.4 MHz studied by low field NMR

Cleemput

Buekenhoudt

Gerven

et al. 1995

The Journal of Chemical Physics

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Nuclear magnetic resonance ͑NMR͒ investigations of methyl tunneling in 2,5-dimethyl-1,3,4-thiadiazole are reported. The tunneling frequency ( t ϭ 3.39 MHz͒ was obtained using low field NMR spectroscopy. By means of rapid field cycling irradiation and relaxation measurements the probabilities of the absorption transitions, responsible for the spectral lines in the low field NMR spectra, can be quantified. The results obtained agree well with the calculated probabilities of rf induced transitions between the eigenstates of a methyl rotor with t ϭ 3.39 MHz. Measurements of the temperature dependence of t , the spin conversion time con and an analysis of the proton spin lattice relaxation time T 1 , the latter two revealing the correlation time c , enabled the study of the methyl group dynamics over a temperature range encompassing both the quantum mechanical and the classical regimes. The dynamical data can be explained well with a threefold hindering barrier of height V 3 /k B ϭ 1175 K and are compared with existing theoretical models.

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Low field NMR investigations of methyl tunnelling

Debenham

Horsewill

Tomsah

et al. 1994

Physica B: Condensed Matter

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An NMR investigation of the dynamics of a methyl group with tunneling frequency 3.4 MHz

Cited by 4 publications

References 4 publications

Proton Spin−Lattice Relaxation of Tunneling Methyl Groups: Calculation of the Time Dependent Correlation Functions

Proton Spin−Lattice Relaxation of Tunneling Methyl Groups: Calculation of the Time Dependent Correlation Functions

Quantum and classical dynamics of a methyl group with tunneling frequency 3.4 MHz studied by low field NMR

Low field NMR investigations of methyl tunnelling

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