NONLINEAR LATTICE RELAXATION MECHANISM FOR PHOTOEXCITED DIMETAL-HALLIDE CHAIN COMPOUNDS

The 31 P n. m. r. spectrum and spin–lattice relaxation time in polycrystalline P 4 S 3 have been measured between 77 and 500 K in the range 7 to 25 MHz. In phase II the 31 P n. m. r. spectra and second moments are dominated by the anisotropic chemical shift interactions. Close to the first-order phase transition at 314 K the spectra are narrowed by reorientation of the molecules about their triad axes. This motion also generates anisotropicshift spin-lattice relaxation notable for its absence of frequency dependence. The activation energy of this motion was found to be 34 kJ mol -1 . Nuclear dipolar interactions play only a minor role. In phase 1 the molecules exhibit rapid quasi-isotropic reorientation and diffusion. The anisotropic broadening interactions are averaged out and an AB 3 high-resolution spectrum of a doublet and quartet are resolved at 420 K, well below the melting point, 446 K. In this phase the spin–rotation interaction relaxation mechanism becomes dominant. Taking advantage of the remarkable motional narrowing in this compound we report the first solid-state n. m. r. J spectrum. This spectrum, recorded at 410 K, allowed the J coupling between apical and basal nuclei in solid P 4 S 3 to be measured accurately, 70.4 ± 0.5 Hz.

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Spin-Gitter-Relaxation im Triplett-Zustand von Chinoxalin in Perdeutero-Naphthalin und zwei ähnlichen Mischkristallen

Zeitschrift für Naturforschung A ◽

10.1515/zna-1975-6-707 ◽

1975 ◽

Vol 30 (6-7) ◽

pp. 754-770 ◽

Cited By ~ 5

Author(s):

U. Konzelmann ◽

D. Kilpper ◽

M. Schwoerer

Keyword(s):

Triplet State ◽

Deep Trap ◽

Lattice Relaxation ◽

Relaxation Mechanism ◽

Mixed Crystals ◽

Spin Lattice Relaxation ◽

Relaxation Processes ◽

Shallow Trap ◽

Field Range ◽

Spin Lattice

Abstract Spin Lattice Relaxation in the Triplet State of Qainoxaline in Perdeuteronaphthalene and of two Similar Mixed Crystals The spin lattice relaxation in the excited triplet state of three mixed crystals was investigated: Quinoxaline in perdeutero-naphthalene, quinoxaline in naphthalene (X-traps) and quinoxaline in durene. They differ by the depth of their traps, which are shallow (90 cm -1), very shallow (60 cm -1) and deep (6600 cm -1), respectively. In order to identify the relaxation processes and the relaxation mechanism, the experiments were performed in the large magnetic field range be-tween 0.2 T and 5.4 T. By use of a non-resonant optical method and by ESR and ODMR it could be shown that at high fields the direct process (emission of resonant phonons) is the only efficient process up to 4.2 K. At low fields Raman-processes are dominant. Thereby the spin lattice relaxation probability per unit time, w, increases with the ninth power of the temperature in the shallow trap systems and with the fifth power in the deep trap system. By the analysis of the very strong anisotropy of w it could be shown that the efficient relaxation mechanism in the shallow trap systems is a guest-host-interaction modulated by phonons.

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Study of NMR spin-lattice relaxation mechanism and mutual viscosity in some substituted alcohols

Journal of Molecular Liquids ◽

10.1016/j.molliq.2004.10.041 ◽

2005 ◽

Vol 121 (2-3) ◽

pp. 110-114 ◽

Cited By ~ 2

Author(s):

Anupam Singh ◽

A.K. Singh ◽

N.K. Mehrotra

Keyword(s):

Lattice Relaxation ◽

Relaxation Mechanism ◽

Spin Lattice Relaxation ◽

Spin Lattice

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1HNMR Study on the Motion of NH4+ in Ferroelectric NH4H(ClH2CCOO)2 and Mixed (NH4)1-xRbxH(ClH2CCOO)2 (x = 0.15)

Zeitschrift für Naturforschung A ◽

10.1515/zna-2002-1107 ◽

2002 ◽

Vol 57 (11) ◽

pp. 883-887 ◽

Cited By ~ 1

Author(s):

M. Zdanowska-Fra̡czek ◽

A. Kozaka ◽

R. Jakubasb ◽

J. Wa̡sickia ◽

R. Utrechta

Keyword(s):

Relaxation Time ◽

Group Dynamics ◽

Nmr Relaxation ◽

Activation Parameters ◽

Lattice Relaxation ◽

Relaxation Mechanism ◽

Lattice Relaxation Time ◽

Spin Lattice Relaxation ◽

Temperature Dependent ◽

Spin Lattice

Temperature-dependent proton NMR relaxation time measurements have been performed at 60 MHz in order to study the NH4+ dynamics in ferroelectric NH4H(ClH2CCOO)2 and mixed Rbx(NH4)1-x(ClH2CCOO)2, where x = 0.15. The data indicate that the dominant relaxation mechanism for the NMR spin-lattice relaxation time T 1 in both crystals involves simultaneous NH4 group reorientation about their C2 and C3 symmetry axis in the paraelectric phase. Details of the NH4+reorientation have been inferred from analysis of temperature dependence of T1 assuming the Watton model. The activation parameters of the motionshave been determined.It has been found that the substitution of Rb does not change the activation parameters of the NH4 group dynamics.

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Chlorine Nuclear Quadrupole Relaxation due to the Motion of Pyridinium Cations in Pyridinium Hexachlorometallates(IV): (pyH)2 MCl6 (M = Sn, Pb, Te)

Zeitschrift für Naturforschung A ◽

10.1515/zna-1990-3-446 ◽

1990 ◽

Vol 45 (3-4) ◽

pp. 477-480 ◽

Cited By ~ 7

Author(s):

Yutaka Tai ◽

Tetsuo Asaji ◽

Daiyu Nakamura

Keyword(s):

Lattice Relaxation ◽

Relaxation Mechanism ◽

Lattice Relaxation Time ◽

Spin Lattice Relaxation ◽

Reorientational Motion ◽

Quadrupole Relaxation ◽

Potential Wells ◽

Spin Lattice ◽

Pyridinium Cations ◽

Nuclear Quadrupole Relaxation

Abstract The temperature dependence of the chlorine quadrupole spin-lattice relaxation time T1Q was observed for one of the three 35Cl NQR lines of (pyH)2 MCl6(M = Sn, Pb, Te). Each T1Q curve can be devided into three temperature regions. In the low-and high-temperature regions, T1Q is dominantly determined by the relaxation mechanism due to the libration and reorientation of [MCl6]2- , respectively. In the intermediate temperature region, T1Q results from the modulation of the electric field gradient by the motion of the neighboring pyridinium cations. This way the reorientational motion of the cation between potential wells with nonequivalent depths is precisely characterized.

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