{"id":1457,"date":"2014-03-17T06:28:19","date_gmt":"2014-03-17T04:28:19","guid":{"rendered":"https:\/\/wissen.science-and-fun.de\/chemistry\/?page_id=1457"},"modified":"2014-03-17T06:31:55","modified_gmt":"2014-03-17T04:31:55","slug":"symbols-nmr","status":"publish","type":"page","link":"https:\/\/wissen.science-and-fun.de\/chemistry\/spectroscopy\/symbols-nmr\/","title":{"rendered":"Symbols for NMR"},"content":{"rendered":"\n<table id=\"tablepress-12\" class=\"tablepress tablepress-id-12 tbody-has-connected-cells\" aria-describedby=\"tablepress-12-description\">\n<thead>\n<tr class=\"row-1\">\n\t<th class=\"column-1\">Symbol<\/th><th class=\"column-2\">Meaning<\/th><th class=\"column-3\">Symbol<\/th><th class=\"column-4\">Meaning<\/th>\n<\/tr>\n<\/thead>\n<tbody class=\"row-striping row-hover\">\n<tr class=\"row-2\">\n\t<td colspan=\"4\" class=\"column-1\">Roman alphabet<\/td>\n<\/tr>\n<tr class=\"row-3\">\n\t<td class=\"column-1\">a or A<\/td><td class=\"column-2\">Hyperfine (electron-nucleus) coupling constant<\/td><td class=\"column-3\">A<sub>q<\/sup><sup>l,m<\/sup><\/td><td class=\"column-4\">The <i>m<\/i>th component of an irreducible tensor of order l representing the nuclear spin operator for an interaction of type q<\/td>\n<\/tr>\n<tr class=\"row-4\">\n\t<td class=\"column-1\">B<\/td><td class=\"column-2\">Magnetic Field (strictly the magnetic flux density or magnetic induction)<\/td><td class=\"column-3\">B<sub>0<\/sub><\/td><td class=\"column-4\">Static magnetic field of an NMR spectrometer<\/td>\n<\/tr>\n<tr class=\"row-5\">\n\t<td class=\"column-1\">B<sub>1<\/sub>,B<sub>2<\/sub><\/td><td class=\"column-2\">Radiofrequency magnetic fields associated with frequencies &nu;<sub>1<\/sub>, &nu;<sub>2<\/sub><\/td><td class=\"column-3\">B<sub>L<\/sub><\/td><td class=\"column-4\">Local magnetic field (components B<sub>xL<\/sub>. B<sub>yL<\/sub>, B<sub>zL<\/sub>) of random field or dipolar origin<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-6\">\n\t<td class=\"column-1\"><b>C<\/b><\/td><td class=\"column-2\">Spin-rotation interaction tensor<br \/>\n<\/td><td class=\"column-3\">C<sub>x<\/sub><\/td><td class=\"column-4\">Spin-rotation coupling constant of nuclide X<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-7\">\n\t<td class=\"column-1\"><b>D<\/b><\/td><td class=\"column-2\">Dipolar interaction tensor<\/td><td class=\"column-3\">D<\/td><td class=\"column-4\">Dipolar coupling constant between<br \/>\ntwo nuclei (say 1 and 2),<br \/>\n(&mu;<sub>0<\/sub>\/4&pi;)&gamma;<sub>1<\/sub>&gamma;<sub>2<\/sub>(h\/2&pi;)r<sub>12<\/sub><sup>-3<\/sup>in frequency units (footnote 1).<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-8\">\n\t<td class=\"column-1\">D<sup>C<\/sup><\/td><td class=\"column-2\">Nuclear receptivity relative to that of the carbon-13 nucleus<br \/>\n<\/td><td class=\"column-3\">D<sup>P<\/sup><\/td><td class=\"column-4\">Nuclear receptivity relative to that of<br \/>\nthe proton (hydrogen-1 nucleus)<\/td>\n<\/tr>\n<tr class=\"row-9\">\n\t<td class=\"column-1\">E<\/td><td class=\"column-2\">Electric field strength<br \/>\n<\/td><td class=\"column-3\">F<\/td><td class=\"column-4\">Spectral width<\/td>\n<\/tr>\n<tr class=\"row-10\">\n\t<td class=\"column-1\">F<sub>1<\/sub>, F<sub>2<\/sub> (or f<sub>1<\/sub>,f<sub>2<\/sub><\/td><td class=\"column-2\">The two frequency dimensions of a two-dimensional spectrum<br \/>\n(use F<sub>3<\/sub> etc., for higher orders)<\/td><td class=\"column-3\"><img decoding=\"async\" src=\"\/images\/f-dach.jpg\"><\/td><td class=\"column-4\"><img decoding=\"async\" src=\"\/images\/f-operator.jpg\"><\/td>\n<\/tr>\n<tr class=\"row-11\">\n\t<td class=\"column-1\">F<sub>G<\/sub><\/td><td class=\"column-2\">Magnetic quantum number associated with <img decoding=\"async\" src=\"\/images\/f-dach.jpg\"><\/td><td class=\"column-3\">g<\/td><td class=\"column-4\">Nuclear or electronic g factor (Land&eacute; splitting factor)<\/td>\n<\/tr>\n<tr class=\"row-12\">\n\t<td class=\"column-1\">G<\/td><td class=\"column-2\">Magnetic field gradient amplitude<br \/>\n<\/td><td class=\"column-3\">H<sub>ij<\/sub><\/td><td class=\"column-4\">Element of matrix representation of Hamiltonian operator (in energy units) ; superscripts indicate the nature of the operator<\/td>\n<\/tr>\n<tr class=\"row-13\">\n\t<td class=\"column-1\">&Icirc;<sub>j<\/sub><\/td><td class=\"column-2\">Nuclear spin operator for nucleus j (components &Icirc;<sub>jx<\/sub>, &Icirc;<sub>jy<\/sub>, &Icirc;<sub>jz<\/sub>)<\/td><td class=\"column-3\">&Icirc;<sub>j+<\/sub>, &Icirc;<sub>j-<\/sub><\/td><td class=\"column-4\">'Raising' and 'lowering' spin operators for nucleus j<\/td>\n<\/tr>\n<tr class=\"row-14\">\n\t<td class=\"column-1\">I<sub>j<\/sub><\/td><td class=\"column-2\">Magnetic quantum number associated with &Icirc;<sub>j<\/sub><\/td><td class=\"column-3\">J<\/td><td class=\"column-4\">Indirect coupling tensor<\/td>\n<\/tr>\n<tr class=\"row-15\">\n\t<td class=\"column-1\"><sup>n<\/sup>J<\/td><td class=\"column-2\">Nuclear spin-spin coupling constant through n bonds (usually given in frequency units). Parentheses may be<br \/>\n used (for example) to indicate the species of nuclei coupled, e.g. J(13C, 1H) or, additionally, the coupling path, e.g. J(POCF). Where no ambiguity arises, the elements involved can be, alternatively, given as subscripts, e.g. J<sub>CH<\/sub>. The nucleus of higher mass should be given first<br \/>\n<\/td><td class=\"column-3\">J(&omega;)<\/td><td class=\"column-4\">Spectral density of  fluctuations at angular  frequency &omega;. Subscripts and superscripts to J may  be used to indicate <br \/>\nthe relevant quantum number change (0, 1 or 2) or the order and <br \/>\ncomponent of the relevant tensor  quantities.<\/td>\n<\/tr>\n<tr class=\"row-16\">\n\t<td class=\"column-1\"><sup>n<\/sup>K<\/td><td class=\"column-2\">Reduced nuclear spin-spin coupling constant (see the notes concerning <sup>n<\/sup>J), K<sub>jk<\/sub>= 4&pi;<sup>2<\/sup>J<sub>jk<\/sub>\/h&gamma;<sub>j<\/sub>&gamma;<sub>k<\/sub><\/td><td class=\"column-3\">L<\/td><td class=\"column-4\">Angular momentum<\/td>\n<\/tr>\n<tr class=\"row-17\">\n\t<td class=\"column-1\">m<sub>j<\/sub><\/td><td class=\"column-2\">Eigenvalue of &Icirc;<sub>jz<\/sub>  (magnetic component quantum number) (footnote 2)<\/td><td class=\"column-3\">m<sub>tot<\/sub><\/td><td class=\"column-4\">Total magnetic component quantum <br \/>\nnumber for a spin system (eigenvalue<br \/>\nof &Sigma;<sub>j<\/sub>&Icirc;<sub>jz<\/sub>)(footnote 2)<\/td>\n<\/tr>\n<tr class=\"row-18\">\n\t<td class=\"column-1\">m<sub>tot<\/sub>(X)<\/td><td class=\"column-2\">Total magnetic component quantum number for X-type nuclei (footnote 2)<\/td><td class=\"column-3\">M<sub>0<\/sub><\/td><td class=\"column-4\">Equilibrium macroscopic  magnetization per volume of a spin  system in the presence of B<sub>0<\/sub><\/td>\n<\/tr>\n<tr class=\"row-19\">\n\t<td class=\"column-1\">M<sub>X<\/sub>, M<sub>Y<\/sub>, M<sub>Z<\/sub><\/td><td class=\"column-2\">Components of macroscopic magnetization per volume.<\/td><td class=\"column-3\">M<sub>n<\/sub><\/td><td class=\"column-4\"><i>n<\/i>th moment of spectrum (M<sub>2<\/sub> = second moment, etc.)<\/td>\n<\/tr>\n<tr class=\"row-20\">\n\t<td class=\"column-1\">n<sub>&alpha;<\/sub>, n<sub>&beta;<\/sub><\/td><td class=\"column-2\">Populations of the &alpha; and &beta; spin states<\/td><td class=\"column-3\">N<\/td><td class=\"column-4\">Total number of nuclei of  a given type per volume in the sample<\/td>\n<\/tr>\n<tr class=\"row-21\">\n\t<td class=\"column-1\">q<\/td><td class=\"column-2\">Electric field gradient tensor in units of the elementary charge  (principal components q<sub>xx<\/sub>, q<sub>yy<\/sub>, q<sub>zz<\/sub>) (see also <b>V<\/b>)<\/td><td class=\"column-3\">Q<\/td><td class=\"column-4\"><i>e<\/i>Q is the nuclear  quadrupole moment, <br \/>\nwhere <i>e<\/i> is the elementary charge<\/td>\n<\/tr>\n<tr class=\"row-22\">\n\t<td class=\"column-1\">R<sup>X<\/sup><sub>1<\/sub><\/td><td class=\"column-2\">Spin-lattice (longitudinal) relaxation rate constant for nucleus X<br \/>\n<\/td><td class=\"column-3\">R<sup>X<\/sup><sub>2<\/sub><\/td><td class=\"column-4\">Spin-spin (transverse) relaxation rate constant for nucleus X<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-23\">\n\t<td class=\"column-1\">R<sup>X<\/sup><sub>1&rho;<\/sub><\/td><td class=\"column-2\">Spin-lattice relaxation rate constant in the rotating frame for nucleus X<br \/>\n<\/td><td class=\"column-3\">S<\/td><td class=\"column-4\">Signal intensity<\/td>\n<\/tr>\n<tr class=\"row-24\">\n\t<td class=\"column-1\"><img decoding=\"async\" src=\"\/images\/s-dach.jpg\"><\/td><td class=\"column-2\">Electron (or, occasionally, nuclear) spin operator; cf. &Icirc;<\/td><td class=\"column-3\">t<sub>1<\/sub>, t<sub>2<\/sub><\/td><td class=\"column-4\">Time dimensions for two-dimensional NMR<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-25\">\n\t<td class=\"column-1\">T<sub>C<\/sub><\/td><td class=\"column-2\">Coalescence temperature for signals in an NMR spectrum<br \/>\n<\/td><td class=\"column-3\">T<sup>X<\/sup><sub>1<\/sub><\/td><td class=\"column-4\">Spin-lattice (longitudinal) relaxation<br \/>\n time of the X nucleus  (further subscripts <br \/>\nrefer to the relaxation <br \/>\nmechanism)<\/td>\n<\/tr>\n<tr class=\"row-26\">\n\t<td class=\"column-1\">T<sup>X<\/sup><sub>2<\/sub><\/td><td class=\"column-2\">Spin-spin (transverse) relaxation time of the X nucleus (further subscripts refer to the relaxation mechanism)<\/td><td class=\"column-3\">T<sup>*<\/sup><sub>2<\/sub><\/td><td class=\"column-4\">Net dephasing time for M<sub>X<\/sub> or M<sub>y<\/sub> (including contribution from magnetic field inhomogeneity)<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-27\">\n\t<td class=\"column-1\">T<sup>X<\/sup><sub>1&rho;<\/sub><\/td><td class=\"column-2\">Spin-lattice relaxation time of the X nucleus in the frame of reference rotating with <b>B<sub>1<\/sub><\/b><br \/>\n<\/td><td class=\"column-3\">T<sub>d<\/sub><\/td><td class=\"column-4\">Pulse (recycle) delay<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-28\">\n\t<td class=\"column-1\">T<sub>ac<\/sub><\/td><td class=\"column-2\">Acquisition time<\/td><td class=\"column-3\">T<sup>(l,m)<\/sup><sub>q<\/sub><\/td><td class=\"column-4\">The <i>m<\/i>th component of an irreducible tensor of order l representing the strength of an interaction of type q<\/td>\n<\/tr>\n<tr class=\"row-29\">\n\t<td class=\"column-1\"><b>V<\/b><\/td><td class=\"column-2\">Electric field gradient tensor.  V = eq,<br \/>\nwhere e is the elementary charge<\/td><td class=\"column-3\">V<sub>&alpha;,&beta;<\/sub><\/td><td class=\"column-4\">Elements of Cartesian electric field gradient tensor<\/td>\n<\/tr>\n<tr class=\"row-30\">\n\t<td class=\"column-1\">W<sub>0<\/sub>, W<sub>1<\/sub>,W<sub>2<\/sub><\/td><td class=\"column-2\">Relaxation rate constants (transition <br \/>\nprobabilities per time) between energy <br \/>\nlevels differing by 0, 1, and 2 (respectively) in m<sub>tot<\/sub> especially, but not uniquely, for systems of two spin 1\/2 nuclei <\/td><td class=\"column-3\">W<sub>r<\/sub><\/td><td class=\"column-4\">Transition probability between spin states r and s<\/td>\n<\/tr>\n<tr class=\"row-31\">\n\t<td colspan=\"4\" class=\"column-1\">Greek alphabet<\/td>\n<\/tr>\n<tr class=\"row-32\">\n\t<td class=\"column-1\">&alpha;<\/td><td class=\"column-2\">Nuclear spin wavefunction (eigenfunction of &Icirc;<sub>jz<\/sub>) for the m<sub>I<\/sub>=+1\/2 state of a spin-1\/2 nucleus<\/td><td class=\"column-3\">&alpha;<sub>E<\/sub><\/td><td class=\"column-4\">The Ernst angle (for optimum sensitivity)<\/td>\n<\/tr>\n<tr class=\"row-33\">\n\t<td class=\"column-1\">&beta;<\/td><td class=\"column-2\">Nuclear spin wavefunction (eigenfunction of &Icirc;<sub>jz<\/sub>) for the m<sub>I<\/sub>=-1\/2 state of a spin-1\/2 nucleus<\/td><td class=\"column-3\">&gamma;<sub>X<\/sub><\/td><td class=\"column-4\">Magnetogyric ratio of nucleus X<\/td>\n<\/tr>\n<tr class=\"row-34\">\n\t<td class=\"column-1\">&delta;<sub>X<\/sub><\/td><td class=\"column-2\">Chemical shift (for the resonance) of nucleus of element X (positive when the sample resonates to high frequency of the reference). Usually in ppm (footnote 3). Further information regarding solvent, references or nucleus of interest may be given by superscripts or subscripts or in parentheses.<\/td><td class=\"column-3\">&Delta;n<\/td><td class=\"column-4\">Population difference between nuclear<br \/>\nstates (&Delta;n<sub>0<\/sub> Boltzmann equilibrium)<\/td>\n<\/tr>\n<tr class=\"row-35\">\n\t<td class=\"column-1\">&Delta;&delta;<\/td><td class=\"column-2\">Change or difference in &delta;<\/td><td class=\"column-3\">&Delta;&nu;<sub>1\/2<\/sub><\/td><td class=\"column-4\">Full width in frequency units of a resonance line at half-height<br \/>\n<\/td>\n<\/tr>\n<tr class=\"row-36\">\n\t<td class=\"column-1\">&Delta;&sigma;<\/td><td class=\"column-2\">Anisotropy in &sigma; [&Delta;&sigma; = &sigma;<sub>zz<\/sub> - 1\/2(&sigma;<sub>xx<\/sub> + &sigma;<sub>yy<\/sub>] (footnote 4). (see also &zeta;<\/td><td class=\"column-3\">&Delta;&chi;<\/td><td class=\"column-4\">(i) Susceptibility anisotropy (&Delta;&chi; = &chi;<sub>||<\/sub> - &chi;<sub>&perp;<\/sub><br \/>\n(II) difference in electronegativities<\/td>\n<\/tr>\n<tr class=\"row-37\">\n\t<td class=\"column-1\">&epsilon;<sub>0<\/sub><\/td><td class=\"column-2\">Permittivity of a vacuum<br \/>\n<\/td><td class=\"column-3\">&zeta;<\/td><td class=\"column-4\">Anisotropy in shielding (footnote 4), expressed as &sigma;<sub>zz<\/sub> - &sigma;<\/sub>iso<\/sub>. (see also &Delta;&sigma;) <\/td>\n<\/tr>\n<tr class=\"row-38\">\n\t<td class=\"column-1\">&eta;<\/td><td class=\"column-2\">(i) Nuclear Overhauser enhancement (so that the nuclear Overhauser effect is 1 + &eta;);<br \/>\n(ii) tensor asymmetry factor (e.g. in &sigma;);<br \/>\n(iii) viscosity<\/td><td class=\"column-3\">&kappa; <\/td><td class=\"column-4\">Skew of a tensor. (See also footnote 7)<\/td>\n<\/tr>\n<tr class=\"row-39\">\n\t<td class=\"column-1\">&amp;theta:<\/td><td class=\"column-2\">Angle, especially for that between a given vector and B<sub>0<\/sub><\/td><td class=\"column-3\"><b>&mu;<\/b><\/td><td class=\"column-4\">(i) Magnetic dipole moment (component &mu;<sub>z<\/sub> along B<sub>0<\/sub>);<br \/>\n(ii) electric dipole moment<\/td>\n<\/tr>\n<tr class=\"row-40\">\n\t<td class=\"column-1\">&sigma;<sub>0<\/sub><\/td><td class=\"column-2\">Permeability of a vacuum<\/td><td class=\"column-3\">&sigma;<sub>B<\/sub><\/td><td class=\"column-4\">Bohr magneton<\/td>\n<\/tr>\n<tr class=\"row-41\">\n\t<td class=\"column-1\">&sigma;<sub>N<\/sub><\/td><td class=\"column-2\">Nuclear magneton<\/td><td class=\"column-3\">&nu;<sub>j<\/sub><\/td><td class=\"column-4\">Larmor precession frequency of nucleus j (usually given in MHz)<\/td>\n<\/tr>\n<tr class=\"row-42\">\n\t<td class=\"column-1\">&nu;<sub>0<\/sub><\/td><td class=\"column-2\">(i) Spectrometer operating frequency;<br \/>\n(ii) Larmor precession frequency (general, or  of bare nucleus)<\/td><td class=\"column-3\">&nu;<sub>1<\/sub><\/td><td class=\"column-4\">Frequency of  'observing' RF  magnetic Field B<sub>1<\/sub> (to be distinguished from its strength, &gamma;B<sub>1<\/sub>,  for which the symbol &Omega;<sub>1<\/sub> <br \/>\nis recommended)<\/td>\n<\/tr>\n<tr class=\"row-43\">\n\t<td class=\"column-1\">&nu;<sub>2<\/sub><\/td><td class=\"column-2\">Frequency of 'irradiating' RF  magnetic Field B<sub>2<\/sub> (to be distinguished from its strength, &gamma;B<sub>2<\/sub>,  for which the symbol &Omega;<sub>2<\/sub> <br \/>\nis recommended)<\/td><td class=\"column-3\">&Xi;<sub>x<\/sub><\/td><td class=\"column-4\">Resonance frequency for the nucleus of element X in a magnetic Field such <br \/>\nthat the protons in tetramethylsilane <br \/>\n(TMS) resonate at exactly  100 MHz<\/td>\n<\/tr>\n<tr class=\"row-44\">\n\t<td class=\"column-1\">&rho;<\/td><td class=\"column-2\">Density matrix<\/td><td class=\"column-3\"><img decoding=\"async\" src=\"\/images\/rho-dach.jpg\"><\/td><td class=\"column-4\">Density operator<\/td>\n<\/tr>\n<tr class=\"row-45\">\n\t<td class=\"column-1\">&rho;<sub>ij<\/sub><\/td><td class=\"column-2\">Element of matrix representation of <img decoding=\"async\" src=\"\/img\/rho-dach.jpg\"><\/td><td class=\"column-3\"><b>&sigma;<\/b><\/td><td class=\"column-4\">Shielding tensor (footnotes 5  and 6)<\/td>\n<\/tr>\n<tr class=\"row-46\">\n\t<td class=\"column-1\">&sigma;<sub>j<\/sub><\/td><td class=\"column-2\">Isotropic) shielding constant of nucleus j. Usually given  in ppm.  Subscripts may alternatively indicate contributions  to &sigma;<\/td><td class=\"column-3\">&sigma;<sub>||<\/sub>, &sigma;<sub>&perp;<\/sub><\/td><td class=\"column-4\">Components of shielding tensor &sigma; parallel and perpendicular to the  symmetry axis (axially-symmetric case) <br \/>\n(footnote 5)<\/td>\n<\/tr>\n<tr class=\"row-47\">\n\t<td class=\"column-1\"><img decoding=\"async\" src=\"\/images\/sigma-dach.jpg\"><\/td><td class=\"column-2\">Reduced density operator<br \/>\n<\/td><td class=\"column-3\">&tau;<\/td><td class=\"column-4\">(i) Time between RF pulses (general symbol) <br \/>\n(ii) lifetime in dynamic NMR usage<\/td>\n<\/tr>\n<tr class=\"row-48\">\n\t<td class=\"column-1\">&tau;<sub>c<\/sub><\/td><td class=\"column-2\">Correlation time for molecular-level motion, especially for isotropic molecular tumbling<\/td><td class=\"column-3\">&tau;<sub>d<\/sub><\/td><td class=\"column-4\">Dwell time<\/td>\n<\/tr>\n<tr class=\"row-49\">\n\t<td class=\"column-1\">&tau;<sub>null<\/sub><\/td><td class=\"column-2\">Recovery time sufficing to give zero signal after a 180\u00b0 pulse<\/td><td class=\"column-3\">&tau;<sub>p<\/sub><\/td><td class=\"column-4\">Pulse duration<\/td>\n<\/tr>\n<tr class=\"row-50\">\n\t<td class=\"column-1\">&tau;<sub>sc<\/sub><\/td><td class=\"column-2\">Correlation time for relaxation by the scalar  mechanism<\/td><td class=\"column-3\">&tau;<sub>sr<\/sub><\/td><td class=\"column-4\">Correlation time for spin-rotation relaxation<\/td>\n<\/tr>\n<tr class=\"row-51\">\n\t<td class=\"column-1\">&tau;<sub>||<\/sub>, &tau;<sub>perp<\/sub><\/td><td class=\"column-2\">Correlation times for molecular tumbling  parallel and  perpendicular to the <br \/>\nsymmetry axis (axially  symmetric case)<\/td><td class=\"column-3\">&Chi;<\/td><td class=\"column-4\">(i) Magnetic susceptibility (footnote 7) ;<br \/>\n(ii) nuclear quadrupole coupling constant (&Chi; = e<sup>2<\/sup>q<sub>zz<\/sub>Q\/h)<\/td>\n<\/tr>\n<tr class=\"row-52\">\n\t<td class=\"column-1\">&omega;<sub>j<\/sub>, <br \/>\n&omega;<sub>0<\/sub>,<br \/>\n&omega;<sub>1<\/sub>,<br \/>\n&omega;<sub>2<\/sub><\/td><td class=\"column-2\">As for &nu;<sub>j<\/sub>,  &nu;<sub>0<\/sub>,  &nu;<sub>1<\/sub>,  &nu;<sub>2<\/sub> but for angular frequencies<\/td><td class=\"column-3\">&Omega;<\/td><td class=\"column-4\">Span of a Tensor<\/td>\n<\/tr>\n<tr class=\"row-53\">\n\t<td class=\"column-1\">&Omega;<sub>1<\/sub>, &Omega;<sub>2<\/sub><\/td><td class=\"column-2\">R.f. magnetic Fields, expressed in angular frequency units for  a  nucleus of magnetogyric ratio &gamma; (&Omega;<sub>1<\/sub> = -&gamma;B<sub>1<\/sub>, &Omega;<sub>2<\/sub> = -&gamma;B<sub>2<\/sub><\/td><td class=\"column-3\"><\/td><td class=\"column-4\"><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<span id=\"tablepress-12-description\" class=\"tablepress-table-description tablepress-table-description-id-12\">Magnetic Resonance in Chemoistry, Vol. 36, 145-149 (1998)<br \/>\nParameters and Symbols for Use in Nuclear Magnetic Resonance (IUPAC Recommendations 1997)<br \/>\n<br \/>\n<sup>1<\/sup>Note that confusion might arise when the so-called alphabet expansion is used for <b>D<\/b>, since this includes a term D which is not the dipolar coupling constant.<br \/>\n<sup>2<\/sup>M rather than m is frequently recommended, but most NMR practitioners use m so as to avoid confusion with magnetization.<br \/>\n<sup>3<\/sup>Whereas earlier IUPAC recommendations give a definition of &delta; which requires that the \u201cunit\" ppm is not stated when values are quoted, this is largely ignored and a change of recommendation is under consideration.<br \/>\n<sup>4<\/sup>&zeta; = 2&Delta;&delta;\/3<br \/>\n<sup>5<\/sup>The symbols &sigma; (and related terms for components), &sigma;<sub>j<\/sub>, &sigma;<sub>||<\/sub>, &sigma;<sub>&perp;<\/sub> should refer to shielding on absolute scale (for theoretical work). For shielding relative to a reference, symbols such as &sigma;<sub>||<\/sub> - &amp;sigma<sub>ref<\/sub> should be used.<br \/>\n<sup>6<\/sup> For tensors, doubled subscript <i>capital letters<\/i> X, Y and Z should generally be used for principal components, e.g. &sigma;<sub>XX<\/sub>, &sigma;<sub>YY<\/sub> and &sigma; <sub>ZZ<\/sub>  for shielding. 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