1. 1H{X}
1H and 1H{X} NMR spectra (decoupled from X nucleus, X = 31P–109Ag) give information about chemical shifts and spin-spin coupling constants JHH as well as information about the signal’s integrated intensities.
1. JRES, selective JRES
Correlation between chemical shifts and spin-spin coupling constants. Can be used to separate homo- and hetero-nuclear couplings.
EPR spectra can be detected from samples in all states of matter: solids (crystalline or amorphous), liquids and in gases. For practical reasons, however, it is important to keep in mind that the sample should not exhibit electrical conductivity or macroscopic magnetization. In favorable conditions, the minimal detectable amount of electron spins in the sample is about 1010. The overall mass of the sample can be anywhere from several micrograms to half a gram. EPR is a non-destructive analytical method and the sample can used for further studied afterwards.
At the moment 1D and 2D spectra are recorded using spin echo techniques. Spin-lattice and spin-spin relaxation measurements are possible. The available spectral range is 27-120 MHz and the available temperature range is 4-400 K.
Samples are placed in a glass tube (35 mm high, 5 mm in diameter). In case of small volumes of the sample it has to be somehow fixed in the center of the tube.
Brief description of the method
NQR phenomenon is essentially the resonance absorption of electromagnetic energy due to the transitions between energy levels formed by the interaction between nuclear electric quadrupole and electric field gradient (EFG) at the position of the nucleus. EFG values depend of the charges of all surrounding electrons and nuclei, thus providing the information about the molecular and crystal structure.
1. Magic Angle Spinning (MAS)
The sample is being rotated at high speed (max 24 kHz at CMR) inside the NMR probe under the so-called magic angle (θm=54.74°=54°44´) with respect to the external magnetic field, which averages the anisotropic part of the shielding tensor (and dipole-dipole and quadrupolar interaction tensors as well), leading to the signal narrowing.
It appeared that certain anisotropic interactions could be suppressed to some extent by introducing an artificial motion of the sample – by rotating the sample around an axis oriented at 54°44' by respect to the external magnetic field (Fig. 1, left). This technique is known as Magic Angle Spinning (MAS). However it works effectively only when the spinning frequency is equal or greater than the line width, which can be in order of tens and even hundreds of kHz. Nowadays modern commercially-available MAS NMR probe-heads can spin the sample up to ca. 40 kHz.
