DD220132A1 - METHOD AND ARRANGEMENT FOR RESOLUTION IMPROVEMENT IN ELECTRON SPINRESONAZ SPECTROSCOPY - Google Patents

Abstract

The invention relates to the measurement of the parameters of electron spin resonance spectra. The aim of the invention is to improve the analysis of CW electron spin resonance spectra and hydrogen-bombardment with steady-state Bo gradients. The invention is based on the object without irreversible influence of the sample to be measured and without mathematical conversions of the measurement result spectral analysis with less effort than previously possible, in which the measurement result is decoupled during the measurement process. According to the invention, this is achieved by generating additional magnetic fields that are periodically modulated with different step times at the sample location. In phase synchronism, the sign of the measured signal voltage value is reversed. Furthermore, a determination of the nuclear spin quantum numbers is possible. The invention is used to expand the metrological possibilities of CW electron spin resonance spectrometers and can be used in particular in the Zeugmatographie. Fig. 1

Description

Method and apparatus for resolution enhancement in electron spin resonance spectroscopy

Field of application of the invention. '

The invention relates to the measurement of the parameters of electron spin resonance spectra (ESR spectra) as well as to spin-coupled ones. ESR spectra. It can be used to extend the metrological possibilities of continuous wave electron spin resonance spectrometers (CW-ESR spectrometers). The invention is in particular. Especially for the ESR-Zeugmatographie (also known as tomography or imaging) with stationary magnetic field gradient to r Spinentkopplung used. ,.

Characteristic of the known technical solutions.

Solutions are known for spin-coupling in SSR spectroscopy using the electron-nuclear double resonance (ENDOR), which allows to determine the spectral parameters. With this method, it is possible to achieve the Spinentkopplung by additional irradiation of high-frequency electromagnetic energy. The possibilities offered by this method are linked to considerable technical expenditure and to a limited relaxation behavior of the sample to be measured. Thus, in the majority of cases, the measurement temperature must be lowered, so that then the measurement of low-viscosity solutions that are normally present at room temperature, is not possible. Technically, both a strong microwave transmitter and a high-power ultra-short wave transmitter and precision, as well as a spe-

which leads to a considerable collapse of the CW-south ctrometer. "Spinning coupling is also possible after the measurement process." Here a number of numerical methods have been developed> / 2, 3 " ^, 5, 6, TJ The measured spectrum is evaluated according to the respective algorithms, and the spinned spectrum can be calculated All the cited / 3, 4, 5, jö / methods have the disadvantage that they lead to a reduction When using the spectral simulation / jL, TJ with subsequent opektrenunleich • by varying the parameters / _ TJ isx the computational effort very high, and in the majority of cases only on a large computer system with reasonable time feasible . to evaluate Zeugmatogrammen ^with; steady gradient B are noch.kein.e solutions.

Literature. ·.

/ _ _1_ / MM Dorio, JH Freed: Multiple Electron Resonance. Spectroscopy. Plenary Press, New York, London (1979). '

/ _ 2J JD Swalen, HM Gladney: IBd-J. Res. Dev. _8, 515 (1964)

/ _ _3_ / 3. N. Dobryakov: Zh. SrruKt. Chim. o_, 39 (1965)

/ _ ± / R. Newton, KP Scnulz, R_. M. Elofson: Ganad. J. uhem. ^ ±, 752 (1960)

Γ ~ 2 / ^ΰ · ^w · Kirmse: J. Hag. Resonance J_1_, 1 (1973) / _6 / S. Brumby: J. Mag. Resonance y ± _, 317 (1979) / _ T_ / U. Bwert: Dissertation A, Berlin (1979)

• Object of the invention

The aim of the invention is to improve the analysis of CW electron spin resonance spectra and witness stationary trajectories with steady! ^ Gradients.

Explanation of the essence of the invention

The invention is based on the object, without irreversible influence on the sample to be measured and without mathematical conversions of the measurement result, a spectra analysis with less effort than. previously allow, in which the measurement result is decoupled during the measurement process. According to the invention, this is achieved in a method for increasing the resolution of spectra in the ultrasound spin resonance spectroscopy, in which an effect modulation is performed and by time-dependent additional magnetic fields influencing the spectra, in that step-shaped additional periodically modulated with different step times at the sample location. · Liehe magnetic fields, 'are generated by a control voltage of a function generator, successively different spectral ranges are excited by these magnetic fields and designed the generated level voltages and stage times so. are that the couplings to be eliminated average out in the central spectral range. In phase synchronism with this, a reversal of the sign of the voltage value, which is characteristic of the measurement signal, is carried out via a second control voltage of the function generator before the time-based evaluation of the measurement signal in the low-pass filter of the detection unit. This sign reversal is in the following text as phase switching to \

the amount ¥ = 180 °

 ζ

In the detection unit, a spin-coupled electron spin resonance spectrum is measured separately from occurring edge lines. Measurement of the mean noise amplitude within the measured spectrum between the region in which the undocked spectrum occurs and the region of the edge lines occurs with variation of the amplitude the additional

dulation by the assignment of minima of the mean noise amplitude to the hyperfine coupling constants a determination of the amount of these hyperfine coupling constants for a 'corresponding nuclear spin quantum number. , '-. The control voltages generated by the punctuation generator lead in dependence on the nuclear spin quantum number I .. and the corresponding coupling cohort A for Spinentkopplung high-resolution multi-line BPH-Speütren. The method is applicable when: the high field approximation; '

, H. »A ₁ ZH. . ' \. , (1)

is valid for all H. and A. and anisotropic Tertne are negligible, so that. all lines of the spectrum can be described by the same line.nform function with the same line width :, but different resonance field strength and intensity, and the resonance field strengths H: of the lines are calculated as follows:

H. = H + Υ "" At _T (2)

All possibilities of value combinations ^s of m. _T v

i. '-! '11 11

consider the transitions:

The symbols mean: ·. '

H. - resonance field strength of the value combination j ^;

H - Resonance field strength of the spectrum (without hyperfine structure).

A. ~ hyperfine coupling constant for the core i

I. - Nuclear spin quantum number for the, core i.

r.z - · number of magnetic cores

At the step times At, during a period

speaking additional magnetic fields and phase values ^ f of the detection unit realized via the function generator. Pure integer I.s leads to the following periodic additional modulation for decoupling:

B ₇ = ζ., A. (5)

= At / T ₊ OL-2) ei _{/ Τζ} _ _{Ό modulo (M} ) _ _{χ 7} _7 (6)

χ ι

% = 130 »d ^ zO _{modulo (M.} ) _Y . ; (7) z = 0, 1, · 2,. .-. , η (8)

It applies to. ·,

"(11)

V = ^B -z

For fractional nuclear spin quantum numbers:

ζ - ^zA i - A _± / 2 ) modulo (M. χ = At / T + (M.-2) cT _lTz _ ^ ₀ = o M ₁ ) - (I ₊ O, ζ ^{= 18O} ° / Tz-1) modulo ( z = 1,2, , , , , η

It applies to

B ₂ - B_ ₂ ,. (17)

At = At .. (18)

The value for η results from

ⁿ min ^{= M} i ^{entier C} Ä- ^ M ~ ⁾ -. ^entier ^ i - P »'5) '. (20)

η = η. , ν. , +1. η. +2, ..

 .mm ', mm' mm

In general: · '

M ₁ = 2L * + 1. : (21)

Sr- £ 7 = 1 if a = O ". \ - (22)

<f / -jT = O if a £ O (23)

modulo: a = c modulo b V (24)

a = b (^ - entier ^) ^ . (25)

animal: 'a = entier b. (26)

a is equal to the integer part of b

SB: spectral width. , ,

The number η of the additional fields B to be generated during a period over the time ΰχ , and with the. Phase angle H * should be greater than or equal to η .. If η is chosen too large, the signal / noise ratio drops sharply. If η is chosen to be too small, a superimposition of the decoupled spectrum with the boundary lines, which result from the limited number of samples within one additional modulation period, results. The order of generation of the individual B values within

Z '

half of a period i'st 'if the assignment to. zit

and π is preserved. Bs.but no B until the period ζ ζ

be omitted at the end. In the case of corresponding values for 3 values which have to be realized longer than At, it is possible to realize these values several times at the sample location within a period, whereby the stated total time must be maintained with the corresponding phase position. The size At, from which the period length can be calculated, can be varied in relatively large ranges. The total period length - must be less than that. Time constant of the detection tract (generally preselected), so that no additional baseline modulation of the spectrum; arises. , , "The lower, limit for At is generally through the. technical realization given that the rise times of the legal

eckmodulatior, must be much smaller than / yc, in order to obtain no line broadening, which counteract the dissolution-improving effect. Since the additional modulation through the mediation of sample to be measured and cavity resonator has the same effect as a rectangular frequency modulation, the modulation index of the fundamental (period) can be used as a criterion for the upper limit frequency of the additional modulation. A small module. tion index leads to a broadening of the LIA or additional splitting. In the X-band, At-ranges of several milliseconds have been successfully applied.

An inventive arrangement for resolution enhancement of spectra in the electron spin resonance spectroscopy with a resonator containing a sample which is located in a magnetic field and associated with a microwave bridge and a detection unit, is characterized in that a function generator with additional coils, the Resonator associated with it, which may be required to generate the effect modulation coils or mix without additional coils with mixture of additional and effect modulation, and that the function generator is further associated with a phase switch or inverter, the before Low pass the detection unit is arranged.

Depending on the substance to be measured, the spectroscopist selects an additional modulation function which corresponds to the nuclear spin of the nucleus to be decoupled. At the output amplifier of the function generator leading to the auxiliary coils, the amplitude is set according to the hyperfine constant A. Is A '. unknown, by varying the amplitude of the additional modulation (= A.) and subsequent spectral comparison of the amount of A-. be determined. This is possible if the spectrum is observed in the video display or registered for each set value. Furthermore, the average noise amplitude between the resonant region (resbnanter range) can be used as a criterion for determining the A. s by ^λ variation of the additional modulation amplitude.

H last line - H. first line) and the marginal lines, which exclude "*. 3

Outside, the spectrum occur, used. ' become. In this case, it is necessary to leave η constant, η must be so large that a sufficient range between resonant. A noise minimum is in each case a criterion, for a certain A .. with the nuclear spin quantum number I., which was set by the corresponding additional modulation function, thus it is possible to use only a few function types (for the majority of the problems 2 function types) by varying the functional amplitude to analyze JESR spectra.

If decoupling from several cores is required, two additional modulation functions must be superimposed, with the phase relationships associated with B being added. The total period of the second or η-th additional modulation function must be / yt. correspond to the first or n-1-th. If this variant technically / · '' ^. '

becomes too expensive, another modulation function can be calculated, with repeating B values then only once with a correspondingly longer a. At present (possibly phase change during a. ZVt necessary).

If the same B, values with opposite phase position (H *) occur within a period vpr, the corresponding a. At values are subtracted from each other.

This possibility of multiple spin coupling allows, with a corresponding reduction of the signal-to-noise ratio, the decoupling of a high-resolution CW-EPR spectrum with the validity of the high field approximation and constant line width of all

Single lines to one _; single-line. "

The invention makes it possible to simplify the evaluation of CW-ESR spectra by influencing the measuring process. A special advantage is that the signal-to-noise ratio of the spectrometer and the spine-coupled representation are simultaneously possible, and the spectroscopist can determine the hyperfine coupling constants as well as represent the simplified spectra Interpretation, because after decoupling the spectrum is no longer complicated by the known coupling sizes.

The development that brings mathematical problems. Numerical spectra analyzes following the measurement can be omitted in the cases described. The invention does not require a computer for implementation.

exemplary

The invention will be explained in more detail below using an exemplary embodiment. FIG. 1 shows a block diagram of an arrangement for improving the resolution of spectra for CW-BSR spectrometers. Sine microwave bridge M ¥ stimulates a sample in a resonator R. A magnetic power supply MSV is used to generate a static magnetic field. The recorder and video unit TV are connected in a known manner to low-pass filters having a time constant 't for detecting the decoupled' spectra. A function generator FG generates phase-locked voltage to a control voltage supplied to the phase-sensitive detector PSD the additional coils ZS are supplied in such a way that an additional step modulation of the magnetic flux density is produced at the sample location.

To demonstrate the operation of the process, the spectrum of DPPH (1,1-diphenyl-2-picrylhydrazyl dissolved in toluene) was measured in the conventional manner (see FIG. 2). When implementing a periodic additional modulation function, which during a period, the additional fields 3 listed in Table 1 with the corresponding effect

times a. At generated and a control voltage in the Nachz ***

Weiskanal guarantees the associated phase settings ' -f ,

result in spin-coupled spectra.

¹ 10

Table 1: Function values according to Eq. ο ~ 12 and. . ·. 'Gi. 2Ö for DPPH with 1 = 1. and SB = 6.2 mT

~ ö -0 A. ' 1 . 0 -5 -5 ^A i. ; • 2 ·· ' 180 -4- , -4 A. 1 0 -3. _; , -3. A ₁ 1 0 -2 '- -2 ^A i · +2   180 -i. ^A i   1 . 0 +0 O 1 0 1 ^A i 1 0 2 2 ^A i '. 2 180 3, .... 3 ' A., 1 0 4 - , 4 ^A i '- ^: 1 0 5 ' · ..5 ^A i 2 · ' ^: 1SO  6 - , 6 ^A i 1 0

Given A. = 0.7908 mT, the spectrum is given in accordance with FIG. 3a, and given A. = 0.9630 mT, the spectrum is given in accordance with FIG. 3c. Both the spincipulated resulting three-line spectrum, which is typical for radicals with only one N-Kopplur.g, can be seen in the center as well as the boundary lines at the spectral edges. The specification of false values for A. (e ¹ leads to an increase in the baseline oscillations in the region between, decoupled spectrum and boundary lines.) Duren Variation of A. according to Table 1 for the generation of the additional modulation is the determination of the ^s A- of the sample by assignment the smallest oscillations between edge lines and spectrum possible.

Claims (3)

'Invention claim' Method for improving the resolution of spectra in the electron spin resonance spectroscopy, in which by time-dependent additional magnetic fields 'spectral influence, characterized in that' at the sample location step-shaped periodically with different stage times modulated additional magnetic fields are generated by a control voltage of a punctuation generator (PG) - Different spectral ranges are excited by these magnetic fields and the generated level voltages and step times are designed so that the couplings to eliminate in the central spectral range, that phase-synchronized via a second control voltage of the function generator (PG) before the temporal Ausmittlüng the measuring signal in the low-pass filter (T) the detection unit reverses the sign of the voltage value characteristic of the measurement signal, and that in the detection unit is a spin-coupled electron spin resonance spectrum is measured separately from occurring boundary lines, and that when measuring the mean noise amplitude of the measured spectrum, the range between the region in which the undocked spectrum occurs and the region of the boundary lines when the amplitude of the additional modulation is varied by the assignment From the minimum noise amplitude minima to the hyperfine coupling constants, a determination is made of the amount of hyperfine coupling constants and nuclear spin quantum numbers. , 2. Method according to item 1, characterized in that additional magnetic fields which have to be realized for a longer time than At are realized several times at the sample location within a period, wherein the specified total time is maintained with a corresponding phase position. 3. Arrangement for improving the resolution of spectra in electron spin resonance spectroscopy with a resonator, the one. Containing a sample which is located in a magnetic field and to which a microwave bridge and a detection unit are assigned, characterized in that a function generator (FG) with additional coils (ZS) corresponding to the Resonator (R) · are associated, and that the punctuation generator (PG) is further associated with a phase switch or inverter ^1, which is arranged in front of the low-pass filter (Ό the detection unit. For this 3 sheets of drawings