Electron-nuclear double resonance study of molecular librations of nitroxides in molecular glasses: Quantum effects at low temperatures, comparison with low-frequency Raman scattering

Electron-nuclear double resonance study of molecular librations of nitroxides in molecular glasses: Quantum effects at low temperatures, comparison with low-frequency Raman scattering Full article

Journal

Journal of Chemical Physics
ISSN: 0021-9606

Output data

Year: 2009, Volume: 131, Number: 6, Article number : 064505, Pages count : DOI: 10.1063/1.3206909

Tags

ENDOR; glass; hyperfine interactions; librational states; organic compounds; quantum theory; Raman spectra; vibrational states

Authors

Kulik L.V. ¹ , Rapatsky L.L. ¹ , Pivtsov A.V. ¹ , Surovtsev N.V. ^2,3 , Adichtchev S.V. ² , Grigor'ev I.A. ^3,4 , Dzuba S.A. ^1,3

Affiliations

1	(Данные Web of science) Russian Acad Sci, Inst Chem Kinet & Combust, Novosibirsk 630090, Russia
2	(Данные Web of science) Russian Acad Sci, Inst Automat & Electrometry, Novosibirsk 630090, Russia
3	(Данные Web of science) Novosibirsk State Univ, Novosibirsk 630090, Russia
4	(Данные Web of science) Novosibirsk Organ Chem Inst, Novosibirsk 630090, Russia

Pulsed electron-nuclear double resonance applied to N-15 nitroxide spin probes in molecular glasses is shown to be very sensitive to measurement of the A(XX) principal value of the hyperfine interaction tensor. For molecules experiencing fast restricted orientational motions (molecular librations), this provides a precise tool to determine the motion-averaged << A(XX)>> value. For nitroxides in glycerol and o-terphenyl glasses, the observed << A(XX)>> temperature dependence below 40 K may be readily interpreted as arising from quantum effects in librations, when the thermal energy of a librating molecule becomes comparable with the elementary quantum of the oscillator. The estimated elementary quanta for nitroxide librations, similar to 60 cm(-1) in glycerol and similar to 90 cm(-1) in o-terphenyl, are found to match the characteristic frequencies of the vibrational spectral densities seen in low-frequency Raman scattering for these glasses. Above similar to 80 K in glycerol and above similar to 120 K in o-terphenyl, the << A(XX)>> temperature dependences manifest a kink with a slightly smaller slope than at lower temperatures.

Kulik L.V. , Rapatsky L.L. , Pivtsov A.V. , Surovtsev N.V. , Adichtchev S.V. , Grigor'ev I.A. , Dzuba S.A.
Electron-nuclear double resonance study of molecular librations of nitroxides in molecular glasses: Quantum effects at low temperatures, comparison with low-frequency Raman scattering
Journal of Chemical Physics. 2009. V.131. N6. 064505 . DOI: 10.1063/1.3206909 WOS Scopus РИНЦ

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