SU1693500A1 - Method for identification of spectrum of nuclear quadrupole resonance - Google Patents

Abstract

The invention relates to radio spectroscopy and can be used to study the structure and properties of chemical compounds. The purpose of the invention is to increase the sensitivity and increase accuracy. The method includes a two-frequency impulse effect on a sample, containing a core with a multilevel non-equidistant energy spectrum, recording echo signals on excited transitions, and correlating lines on the variation of the echo amplitude. The frequency modulation of the pulses is carried out on one of the transitions so that the entire constellation of the line is excited. 3 il.

Description

The invention relates to radio spectroscopy and can be used to study the structure and properties of organic and inorganic compounds.

The purpose of the invention is to increase the sensitivity and increase accuracy.

Fig.1.2 shows the time diagrams of the excitation pulses on the 1st and 2nd channels, respectively, where o) 2 is the average filling frequency of the chirp pulses, GJ23 is the filling frequency of the RF pulses; Fig. 3 is a schematic of the device implementing the method.

The device consists of a control unit 1, a generator of 2 radio pulses, a generator of 3 chirp pulses, a two-frequency sensor 4 with a sample, amplifiers 5, 6 of echo signals and a two-beam oscilloscope 7.

The method is carried out as follows.

8, the instant t 0 b.ok 1 of control 1 generates a pulse arriving at the input of the generator 2 radio pulses, from the output of which the radio pulse is fed to the input of the first circuit of the dual-frequency sensor 4 with the sample.

At time t and ha, control unit 1 produces pulses arriving at the input of the chirp 3 generator, from which chirp pulses are output to the input of the second circuit of the dual-frequency sensor 4.

The signals generated by the excitation of the sample come from the outputs of the first and second circuits of the sensor 4 to the inputs of the amplifiers 5, 6 of the echo signals, respectively. The output of amplifier 5 is connected to

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the first, and the output of the amplifier b - to the second input of a two-beam oscilloscope 7.

When the distance between the chirp pulses is less than the transverse relaxation time of each line and the signal parameters provide the excitation of the entire set of lines, the echo-response is a series of signals, each of which carries information about a particular line.

If, when this echo response is observed, the filling frequency of the radio pulse applied at time t 0 changes, then if it coincides with the transition frequency, which has a common energy level with an excited transition, the echo amplitude will increase, which will indicate that the specific transition frequency lines.

A further change in the frequency of filling of the exciting radio pulse makes it possible to identify in turn the various lines in the sample,

Consider, for example, the excitation of potassium perrhenate (KReCM). The rheni nuclei on which resonance is observed have two isotopes — 185Re and 87Re (spin I 5/2).

Two signals are observed on the 1S5Re isotope: on the 1/2 - 3/2 transition (frequency 29.386 MHz) and on the 3 / 2-5 / 2 transition (frequency 58.746 MHz). Two signals are also observed on the 18T Re isotope: on the 1/2 - 3/2 transition (frequency 28.839 MHz) and on the 3/2 - 5/2 transition (55.651 MHz frequency). Frequencies are given at 77 K.

Exciting a sample of chirp pulses with a center frequency of 57.5 MHz with an increasing modulation law, a deviation of 4 MHz and durations not exceeding the transverse relaxation time of the transitions (Tn T2), we will observe two echo signals, each of which is formed by the cores of one of the isotopes. Moreover, on a time scale (on the oscilloscope screen) these signals will be spaced apart

If we give a radio pulse to the second loop of the two-frequency sensor at the time point preceding the first chirp pulse, we will change its filling frequency within 27 and 30 MHz. With

This will observe an alternate increase in the amplitude of the first first and then the second echo signals. Moreover, such a change in the echo amplitude will occur only when the excitation of transitions of one isotope.

Measuring the frequency of filling the radio pulse (when the maximum amplitude is observed) and the frequency of the echo signal, the amplitude

which increases, it is possible to carry out the assignment of lines.

The ability to simultaneously observe two echo signals, which need to be assigned to the line, allows

more accurately identify the spectrum. In addition, the echo amplitudes of two isotopes are simultaneously observed, their relative quantities can be determined by their relative intensities (i.e.

Spread).

Claims (1)

The invention of the method for identifying a nuclear quadrupole resonance spectrum, including a dual-frequency pulsed effects on a sample containing a core with a multilevel energy spectrum, recording echo signals on excited transitions, and identifying lines by changing the echo amplitude, are also distinguished by the fact that, in order to increase sensitivity and increase accuracy, two-frequency pulse effects are performed by radio frequency ( RF) pulse on one of the excited transitions and after a time less than the transverse relaxation time, with two frequency-modulated pulses with a time interval y between them, which is less than the longitudinal relaxation time, and with an average filling frequency, the frequency of the neighboring transition, and then identifying the lines by the amplitudes of the individual signals echo when changing the frequency of filling RF pulse, with the deviation of the frequency-modulated pulses is chosen such that the entire set of lines is excited. 50 ABOUT Fm.2 Fm.z