7/23/2015 12:59:31 AMRefresher course in Chemistry; Sept.20-Oct.12, 2007 1 Magnetic Resonance Phenomenon is a manifestation due to the presence of INTRINSIC. - презентация

1 7/23/ :59:31 AMRefresher course in Chemistry; Sept.20-Oct.12, Magnetic Resonance Phenomenon is a manifestation due to the presence of INTRINSIC SPIN angular momentum and the associated Magnetic Moment characteristically in electrons and Nuclei When the experimental conditions are set for the NUCLEI to resonate, then it is the Nuclear Magnetic Resonance. A definition:

2 7/23/ :59:31 AMRefresher course in Chemistry; Sept.20-Oct.12, Spin and Magnetic moment: Nucleus rotates about an axis within itself, which is referred to as the spinning of nuclei. The spinning object acquires an angular momentum The NUCLEI thus possess angular momentum; and the angular momentum in atomic system are quantized. Due to this quantization, the angular momentum component in any chosen direction can take only specified discrete values. Spin Angular momentum Nucleus has electrical Charge. Thus a rotating charge has associated magnetic moment. For protons: Spin quantum number=1/2 The angular momentum and magnetic moment are in the same direction because of the positive charge of the nucleus Illustration:

3 7/23/ :59:31 AMRefresher course in Chemistry; Sept.20-Oct.12, When there is no magnetic field, then the Nuclear moment can be in any direction since in all orientations its potential energy would be the same When a magnetic field is externally applied………. The magnetic moment would tend to align along the direction of the magnetic field The nuclear magnetic moment is present along with the spin angular momentum which, as mentioned before, cannot take any arbitrary orientation. Thus the orientation of magnetic moment is restricted to only the orientations which are the possible orientations of angular momentum Interaction in presence of applied magnetic field

4 7/23/ :59:31 AMRefresher course in Chemistry; Sept.20-Oct.12, Thus even while the magnetic moment tends to align exactly along the magnetic field, the associated presence of angular momentum allows only discrete directions and the magnetic moment subtends a non-zero angle with the direction of the magnetic field. X Not possible Because of the fact that the complete alignment is not possible, a precession of the system of magnetic moment-angular momentum occurs in presence of the magnetic filed.