WHAT HAPPENS WHEN PROTONS ABSORB 60 MHz RADIO-FREQUENCY ENERGY (NMR) SPECTROSCOPY

                         

Nuclei in the lower energy state undergoing transitions to the higher energy levels state, the population of the two states may approach equality and if this arises no further total net absorption of frequency can occurred, and the observed resonance signals will fading out. This situation is called as the " saturation of the signal". In the total population of the two spin states don't become equal : because they high energy nuclei are constantly returning to the lower energy spin states by the following two radiationless processes.

1) SPIN - LATTICE RELAXATION :-

                                

                             The higher energy level nucleus can undergo energy loss or relaxation by transferring  ∆E to some electromagnetic vector is present in the surrounding environment. For example, a nearby solvent molecule, undergoing continues rotational and vibrational changes, will have associated magnetic and electrical changes, which may be properly oriented of the correct dimension to absorb is  ∆E, since the nucleus, may be surrounded by a whole array of neighbours atoms. But in the same molecule or in solvent molecules, etc. This relaxation process is called " spin lattice relaxation" where lattice implies the entire framework or aggregate of neighboring atoms.

2) SPIN - SPIN RELAXATION :-

                                     The relaxation process involving transferring  ∆E  to the neighboring nucleus, it's providing that the particular value of ∆E is common to both nuclei : this mutual exchange of spin energy is called " spin - spin relaxation. While one nucleus loses energy, the other nucleus gains energy, so that no net changes in population of the two spin states are involved.

                       The rates of relaxation by this processes are important, and in particular the rate of the spin- lattice relaxation determining the rate at which the net adsorption of 60 MHz energy can occurs.

                The means half - life of the spin - lattice relaxation process is designed T₁, and that the spin - Spin relaxation process T₂.  If T₁ and T₂ are very small, then lifetime of the excited nucleus is too short, and it have been found that this giving rise to very broad absorption lines in the nmr spectroscopy. If T₁ and T₂ are very large, perhaps of the order of 1 second, then sharp spectral lines arises.

                         For nonviscus liquids and that includes solutions of solids in nonviscus solvents, and molecular orientation are randomly, and transfer of energy by spin - lattice relaxation is always inefficient. In consequence T₁ is very largely and this is one reason why sharp signals are obtained in NMR studies on nonviscus systems.

                       The ¹⁴N nucleus possesses and an electric quadruple, it's therefore able to intearcting with the magnetic and electric field gradients, which causes the nucleus to tumble rapidly : spin - lattice relaxation is very highly effective and therefore T₁ is small. Since T₁ is small, nmr signals for the

  ¹⁴N nucleus are very broad indeed and for the same reason the nmr signals for the most protons attached to  ¹⁴N in N- H groups are broadened.