A Low-Field Magnetically Affected Reaction Yield (MARY) Spectrometer with Spectral Fluorescence Resolution.

Applied Magnetic Resonance, February 2013, Volume 44, Issue 1-2, pp 81-96.

Evgeny V. Kalneus, Anatoly R. Melnikov, Valery V. Korolev, Vladimir I. Ivannikov, Dmitri V. Stass.

Institute of Chemical Kinetics and Combustion, 630090, Novosibirsk, Russia

Novosibirsk State University, 630090, Novosibirsk, Russia

Abstract

 

A novel spectrometer for low-field studies in magnetically affected reaction yield (MARY) spectroscopy with fluorescence detection is described. The spectrometer is based on a yoke-free magnetic system containing no ferromagnetic elements, uses X-ray or optical excitation, and includes a monochromator to analyze the spectral composition of luminescence. Using the new setup, the effect of transversal residual magnetic field on zero field MARY line is illustrated, formation of exciplexes under X-irradiation in a naphthalene/N,N-dimethylaniline solution in alkane is demonstrated, a magnetic field effect on the emission spectrum is shown in field-cycling mode, and modulated MARY spectra in the exciplex and the intrinsic luminophor bands are compared to show that magnetic field sensitivity here is provided at the stage of the recombining radical ion pair, while exciplex formation only transforms the luminescence properties.

 

 

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Additional Information

A novel spectrometer for low-field studies in Magnetically Affected Reaction Yield (MARY) spectroscopy with fluorescence detection is described. The spectrometer is based on a yoke-free magnetic system, uses switchable X-ray or optical excitation, and includes a monochromator to analyze the spectral composition of magnetosensitive luminescence.

The heart of the spectrometer is a specialized magnetic system optimized for creating low static homogeneous magnetic fields that can be cleanly swept through zero, described in details in paper “Evgeny V. Kalneus, Dmitri V. Stass, Yuri A.Grishin,  Yoke-free magnetic system for low field studies in magnetically affected reaction yield spectroscopy, Rev. Sci. Instrum. 76, 084102 (2005)”, http://dx.doi.org/10.1063/1.2001646 and schematically shown in the figure. The actually built system creates magnetic field in the range “-50” to “+50” mT in a cylindrical working region 8×1 cm (L x D) with a relative field homogeneity of about 10-4 without using ferromagnetic elements or employing a field-sensing feedback loop. At a distance of 15 cm or more from the center of the system magnetic field does not exceed 10 mT due to active shielding, which allows putting magnetic field-sensitive elements, such as X-ray tube or PMT, that close to the sample.

The system consists of Power, Scanning, Compensation, and Modulation subsystems. The Power system with active shielding has three pairs of coaxial coils and can create field 2 to 50 mT in both directions along the Z axis with rather high efficiency (rated power 850 W at 50 mT), steep field roll-off outside the working region, and calculated relative field homogeneity 4.3×10−6. The Scanning system is built of two pairs of coaxial coils and can continuously sweep through the zero of the field covering the range ±10 mT, providing a better calculated relative field homogeneity of 1.4×10−6 at the expense of lower power efficiency (rated power 300 W at 10 mT) and shallower field roll-off profile. The two system work independently, and their fields add up vectorially in space due to the lack of any ferromagnetic elements. Field stabilization is done solely by stabilizing currents through the coils. The Compensation system cancels residual transversal fields to ensure clean and linear passage through the zero of the total field at the sample location and consists of two pairs of thin rectangular coils. Finally, a pair of coaxial modulation coils is provided to create oscillating field along the sweeping Z axis.

 

A Low-Field Magnetically Affected Reaction Yield (MARY) Spectrometer with Spectral Fluorescence Resolution