Hyperfine state spin orientation

If the laser bandwidth is small enough to resolve the hyperfine structure, a specific hfs component can be selectively populated. This can result in a nuclear spin orientation as illustrated in Fig. 5.5 for the Na atom with a nuclear spin 7 = 3/2. The laser selectively populates the F = 2 component in the upper 2 P /2 state. The fluorescence from this state terminates at both the F" = 1 and F" = 2 components in the 3 5i/2 state. The F = 1 component is again excited into the 3 P f2 state. 

The spin orientation order in the sample is created and monitored using standing wave optical pumping of the ground state hyperfine levels of the Tm" 2 ion (see Fig. 1). These levels have a magneto-optic susceptibility which depends on the electron spin orientation. The absorption constant for right or left circularly polarized light can be written as... 

The PAC experiment makes use of a nucleus which decays through successive gamma radiations yj and yj- The observation of yj in a fixed direction determines the spin orientation of the nucleus and the subsequent radiation j2 then has a definite angular correlation with respect to the direction of yj. If in the intermediate state of the gamma-ray cascade the nucleus is under the influence of a magnetic hyperfine interaction, the second radiation y2 carries with it information on this interaction. Hence the relaxation of the environment within the lifetime of the intermediate state of the nucleus manifests itself in a time-dependent magnetic hyperfine interaction. 

OIDEP usually results from Tq-S mixing in radical pairs, although T i-S mixing has also been considered (Atkins et al., 1971, 1973). The time development of electron-spin state populations is a function of the electron Zeeman interaction, the electron-nuclear hyperfine interaction, the electron-electron exchange interaction, together with spin-rotational and orientation dependent terms (Pedersen and Freed, 1972). Electron spin lattice relaxation Ti = 10 to 10 sec) is normally slower than the polarizing process. 

Let us first discuss a system which is traditional for optical pumping in the Kastler sense [106, 224, 226], namely an optically oriented alkali atom A (see Fig. 1.1) in a noble gas X buffer surrounding. It is important to take into account the fact that in alkali atoms, owing to hyperfine interaction, nuclear spins are also oriented. However, in a mixture of alkali vapor with a noble gas alkali dimers A2 which are in the 1SJ electronic ground state are always present. There exist two basic collisional mechanisms which lead to orientation transfer from the optically oriented (spin-polarized) atom A to the dimer A2 (a) creation and destruction of molecules in triple collisions A + A + X <—> A2 + X (6) exchange atom-dimer reaction... 

The nuclear hyperfine interaction splits the paramagnetic states of an electron when it is close to a nucleus with a magnetic moment. For a random orientation of spins and nuclei, the tensor quantities in Eq. (4.11) are replaced by scalar distributions, and the resonance magnetic field is shifted from the Zeeman field // by... 

ESR spectra of La Cs2/ Y Cs2, Ho Cs2, and Tm C82 taken from the solid soot extract were reported by Bartl et al. (1994, 1995a,b, 1996) and showed low resolved but split hyperfine structure, indicating that the metal atoms exist in ionic form in the fullerene cage also in the solid state. The research group also reported (Knorr et al., 1998) the principal values of the hyperfine tensor A and the relative orientation of g and A tensors of M C82 (M = Sc, Y, La) applying three- and four-pulse electron spin-echo envelope modulation techniques (ESEEM). 

In the general case, both isotropic and anisotropic hyperfine interachons contribute to the experimental spectrum. The whole interaction is therefore dependent once again on orientation and must be expressed by a tensor. The effechve spin Hamiltonian for this more reahstic descriphon of a paramagnehc species in the solid state was given earher in Equahon 1.28. Nevertheless the A tensor may be split into its component isotropic and anisotropic parts as follows ... 

Interaction between the magnetic field of the electrons and the nuclear spin is the basis for various techniques that are broadly applied in chemistry, atomic physics, nuclear physics and solid-state physics. The magnetic field of the electrons is due to their spin and orbital angular momentum and much larger than the magnetic field of the nucleus. Consequently, the nuclear spin is oriented in relation to the field produced by the electron shell. This leads to hyperfine spectra which can be resolved by means of optical spectrometers of very high resolution. 

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