Question

1. what do you mean by ESR spectrescopy? write the selection rule of observing ESR spectra?

2. what is hyperfine interaction? discuss by taking a suitable example

3. what do you mean by g factor? what is its significance

Answer 1

1. ESR spectroscopy is an absorption spectroscopy which involves the absorption of radiation in the microwave region (10⁴-10⁶ MHz) by substances containing one or more unpaired electrons. This absorption of microwave radiation takes place under the influence of an applied magnetic field. The substances with one or more unpaired electrons are paramagnetic and exhibit ESR. Thus, ESR spectroscopy is also called electron paramagnetic resonance (EPR) spectroscopy or electron magnetic resonance spectroscopy.

Selection rules: Splitting can occur only when the electron is in a state with non-zero total angular momentum, i.e. electrons in atoms with closed atomic shells cannot show this behavior. The term ESR refers specifically to the case in which the spins of the electrons absorbing the radiation are only weakly interacting ("weakly coupled") with each other.

2. Hyperfine interaction: The total electron angular momentum quantum number (J) is just the spin quantum number (S) in this case. The nuclear angular momentum quantum number (L) is determined by the net spin of the nucleus. The first term is the hyperfine interaction, and in this case (L = 0) is the "Fermi Contact" term. The second term is the electronic Zeeman term due to the effect of the applied magnetic field (H₀) on the electron spin. The third term is the nuclear Zeeman term due to the effect of the magnetic field on the nuclear spin. Since N is much smaller than '', this last term is small. The magnetic field (H_N) seen by the nucleus may be modified by the electron system. '' and 'N' are the electron and nuclear "magnetons" beta = eh/(4mc).

3. The electron's 'g' factor is given by the Lande rule for the vector model of the atom. The nuclear 'g' factor, (g_N), is obtained from a knowledge of the structure of the nucleus.