Usually the direction of the static magnetic field is chosen as z axis, and the magnetic quantum number mr often called mz, since it describes the size of the spins component in units of h/2T [2-1] resulting in a magnetic moment H =yI [2-2] Hz=myh/2 [2-3] y being the isotope-specific gyromagnetic / magnetogyric constant(ratio) The interaction energy of a spin state described by m, with a static magnetic field Bo in z direction can then be described as E=-HBo=uBo cos o [2-4] E=μ2YBoh2π For the two possible spin states of a spin-n nucleus(mz=+/2)the energies are 5yhBo E 0.5hB [2-6b The energy difference E Ei2-E-In=hv =o h/2T corresponds to the energy that can be absorbed or emitted by the system, described by the larmor frequency o E=YBoh2π The Larmor frequency can be understood as the precession frequency of the spins about the axis of the magnetic field Bo, caused by the magnetic force acting on them and trying(Iz is quantized!) to turn them completely into the field's direction (like a toy gyroscope"feeling"the pull of gravity)8 Usually the direction of the static magnetic field is chosen as z axis, and the magnetic quantum number mI often called mz, since it describes the size of the spin's z component in units of h/2p: Iz = mz h/2p [2-1], resulting in a magnetic moment m: m = g I [2-2] mz = mz gh/2p [2-3] g being the isotope-specific gyromagnetic / magnetogyric constant (ratio). The interaction energy of a spin state described by mz with a static magnetic field B0 in z direction can then be described as: E = -mB0 = mB0 cos Q [2-4] E = mz g B0 h/2p [2-5] For the two possible spin states of a spin-1 /2 nucleus (mz = ± 1 /2) the energies are E1/2 = 05 2 0 . g p hB [2-6a] E-1/2 = - 05 2 0 . g p hB [2-6b] The energy difference DE = E1/2-E-1/2 = hn = w h/2p corresponds to the energy that can be absorbed or emitted by the system, described by the Larmor frequency w: DE = g B0 h/2p [2-7] w0 = gB0 [2-8] The Larmor frequency can be understood as the precession frequency of the spins about the axis of the magnetic field B0, caused by the magnetic force acting on them and trying (Iz is quantized!) to turn them completely into the field's direction (like a toy gyroscope "feeling" the pull of gravity)