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1. http://www.worldofteaching.com/ FT NMR WORKSHOP/===/ S.A.I.F./===/ NEHU/==/ Shillong INTRODUCTORY LECTURE S.ARAVAMUDHAN

2. A PULSED NMR EXPERIMENT Essentially consists of applying a SHORT Intense Pulse (π/2 pulse)and as much as possible bring the Magnetization into XY Plane during the pulsing period. Slide # 2-3 Since after the pulse duration, in the non equilibrium situation, the spins are not in the discrete quantum levels, the deviation from the z-axis causes the Magnetization to precess. Slide # 3-4 This precessing magnetization is made to induce a voltage in a RF coil which will be at the resonance frequency which is amplified and detected. Slide # 4-5 Such detected induction signal, decay from the initial amplitude since the XY magnetization is governed by the transverse relaxation time during which the XY magnetization goes to zero. Elaborated FID in Slide # 6

3. Z Y X PULSED NMR experiment XY - Magnetization induces RF signal in the receiver coil Z - Magnetization along the Field Defocusing and signal decay Output from receiver coil - FID RF Pulse : π/2 pulse to flips the magnetization into xy plane CW Oscillator GATE Receiver- detector Display Monitor Recorder RF Pulse Probe In Magnet DC Pulse generator

4. Z Pulse applied Y Solenoidal sample coil axis Axis- Y Y In XY plane precessing magnetization Precessing magnetization induces rf voltage: NMR signal X Z When relaxation process is effective, the relaxation leads to the decay of the transverse magnetization of XY plane The above picture is for time scales small compared to relaxation time T2 This decay of magnetization due to the transverse relaxation time is because of the defocusing of the magnetization isochromats in XY plane

5. 2 3 4 1 5 Probe & sample Crossed Diodes Transmitter ONtime Receiver Silent or dead time Receiver Receiver OFF time DATA acquisition starts at this time After the RF pulse, the FID is the impulse response from the sample spin system. The pulsing and FID can be repeated and added to acquire the averaged signal for better signal to noise ratio The RF frequency of the pulseisνas given by the equation ‘h ν = g β H’where H is the applied homogeneous magnetic field

6. Z Y X Y Y Y X X X In terms of Angular momenta, Izreplaces‘z’;forrotationabout z-axis= e-iφIz Represents rotation by angle φ about z-axis; Φ can be replaced by frequency of rotation in radians ‘ω’ multiplied by ‘t’ the time lapsed. Rotation about z-axis= e-i ω tIz Viewed from within the rotating frame the RF field appears stationary Z= unit vector along z-axis Rotation about z-axis= e-iφZ Represents rotation by angle φ about z-axis; Φ can be replaced by frequency of rotation in radians ‘ω’ multiplied by ‘t’ the time lapsed. Rotation about z-axis= e-i ω tZ RF field is along –X in the XY plane, the effect caused would be rotation about X-axis,unlike the precession about z-axis An equation representing this rotation would be displayed Repeat pulsing?.....Right Click and choose menu option ‘previous’ and CLICK! CLICK ! CLICK ! CLICK ! Z To repeatthe animated RF depictions “right click” and choose option:‘previous’ Click to end this slide A rotating RF magnetic field results on application of RF at resonance frequency x,y-axes Rotating about Lab Z-axis; frequency same as the precession frequency For a π/2 pulse the value of ‘ω1 t ‘=90º; ω1=γH1 The impulseoff… The impulseon… CLICK ! H1e-iI-xωt H1 e+iI-xωt A Pulse lasts only for a few μ Secs. For proton NMR a H1 of ~25Gauss along ‘-x’ , pulse widths are approximately 10-15μs + 2 H1I-x cos(ωt) = Only one of the rotating component is effective in causing resonance Rotating system viewed from within that system: STATIONARY RF source/ transmitter Connected to coil. Linearly oscillating field along the coil axis (X-axis) The linearly oscillating field can be resolved into two counter rotating components CLICK ! http://www.geocities.com/sankarampadi/eulexp.html

7. Z Z Y Y X X Y X t=0 FID tp Acquisition time ~5T2 Rotating x,y axes :rotation about Lab z-axis A BLUE line for z-Axis indicates the view from within the rotating coordinate system. Viewed from within the rotating frame the RF field appears stationary Tilted Magnetization in xy plane viewed from Lab Frame. Precessing at resonance frequency. No More Clicks ! This show has automatic timings Z After the pulse: at t>0 Y If No T2…….. The F.I.D. Tilting of magnetization Apply the 90º, -X pulse now, P-Xπ/2 Magnetization in XY plane appears stationary when viewed in Rotating Frame from within the rotating frame At the end of pulse, time for F.I.D. begins with t=0 Described in rotating frame: Rotation about the X-axis I(tp) =e-iI-xφIz e+iI-xφwithφ=90º & tp is pulse duration When the XY magnetizationdecays with transverse relaxation time T2, immediately after the pulse…… When PSD reference is in phase off set from Resonance frequency; NMR signal at receiver (RF 300 MHz ) Induced NMR signal at receiver (RF 300 MHz ) When PSD reference is in phase at Resonance frequency; NMR signal at receiver (RF 300 MHz ) CLICK to Transit FreeInductionDecay Signal

8. So acquired Free Induction Decay Signal is subjected to further digitization and data processing in a digital computer to obtain the NMR spectral information “WONDER-SHARE PPT to WMV” Conversion Software