Nuclear Magnetic Resonance ANIMATED ILLUSTRATIONS MS Powerpoint Presentation Files Uses Animation Schemes as available in MS XP or MS 2003 versions A class room educational material File-8 FT NMR-I http://ugc-inno-nehu.com/links_from_web.html 2/24/2019 10:38:15 PM Dr.Aravamudhan

Frequency Domain Spectrum This FID acquisition and the variations are considered in detail in the following slides PULSED NMR Acquire F.I.D. Free Induction Decay NMR detection soon after a strong pulse: precessing nuclear magnetization induces a signal in coil when it is free of the perturbing EM radiation Acquisition is automatically in the digitized form Computer memory Address Contents 1 0000 15 1111 2 0001 14 1110 3 0010 13 1101 4 0011 11 1011 5 0100 8 1000 6 0101 4 0100 7 0110 1 0001 0111 0000 --------- Next Slide Time domain 15 11 DIGITIZE Analogue to Digital Converter A.D.C. F.I.D. Frequency Domain Spectrum Computer output FFT from FID Computer input This one-dimensional FT NMR spectrum is the same information as the C.W. NMR spectrum 2/24/2019 10:38:16 PM Dr.Aravamudhan

The FID2 is acquired after a delay one DW more compared to the FID1 Aquisition Time domain 15 12 14 13 11 10 8 Pulse This delay (after the first pulse/first scan) is called the receiver dead time. This is requirement due to response characteristics of the electronic system. This first FID acquisition can be repeated without any necessities of alterations in delay times. This is typically the single pulse experiment repeated for summing the FIDs to improve signal to noise ratio. FID 1 Receiver dead time/Acquisition delay The FID2 signal from probe is the same. But, the signal received is acquired after a larger delay than for FID1 Time domain 12 14 13 11 10 8 Aquisition FID 2 Pulse The delays of the type in FID2 are set by the experimenter to realize sequences of pulses for the case of multiple-pulse –sequence at the end of which the FID is ACQUIRED. These class of experiments dominate the advanced NMR techniques. The time interval between the dotted (digitized) points is the DWELL (DW) time of the digitizer. The FID2 is acquired after a delay one DW more compared to the FID1 2/24/2019 10:38:16 PM Dr.Aravamudhan

Apply Pulse Acquisition of FID is started by sending a trigger pulse to the A to D converter/digitizer It is possible to increment the delay, and acquire the FID at different phases. Time domain 15 9 12 14 13 11 10 8 different phases Trigger to ADC cos Start acquisition after a delay D1 Time domain 9 12 11 10 8 Acquisition delay D1 Trigger to ADC -sin Trigger to ADC -cos Note D2 > D1 How will be the Fourier transformed frequency domain spectrum of these three time domain signals with different phases? Start acquisition after a delay D2 Acquisition delay D2 2/24/2019 10:38:16 PM Dr.Aravamudhan

Time domain FID data: 32 points Real Imaginary 16 data 16data points points Frequency domain spectrum 2/24/2019 10:38:16 PM Dr.Aravamudhan

t=0 +1 Value between +1 & 0 Provision is made in the data processing system, for routinely applying phase corrections COS Real Imaginary F.T Real Imaginary F.T SIN Real Imaginary F.T Arbitrary Phase fc cos(2πνt) + fs sin (2πνt) with fc2 +fs2 =1 2/24/2019 10:38:16 PM Dr.Aravamudhan

Time domain 15 12 14 13 11 10 8 Time domain 12 14 13 11 10 8 Time domain 9 12 13 11 10 8 Time domain 9 12 11 10 8 Time domain 9 11 10 8 Time domain 9 10 8 Time domain 9 8 Time domain 8 CONSIDER THE KIND OF DETAILS: for the variations in delays, phases and the frequency domain signals. 2/24/2019 10:38:16 PM Dr.Aravamudhan

PURE Cosine Arbitrary Phase with sine and cosine Mostly a negative of cosine Negative cosine and negative sine

Cosine F.T. fC cos + fS sin Sine Cosine Sine Cosine Sine Cosine Subtract out the sine component F.T. Sine Cosine Sine Cosine Sine Cosine Such requirements as subtracting a sine component from the magnetization can be effected by appropriate pulse widths and phases at the required time.

There has been no MULTIPLE PULSE SEQUENCE considered in this illustration. This only to illustrate the spectrometer settings required while setting up multiple pulse experiments. Two dimensional spectra contain rich information if the spin system is allowed to evolve under multiple pulse perturbations before acquisition of FID.

Preparation pulse: facilitates the following…….. Free evolution of spin system Free evolution of spin system FFT Spectrum Spin Echo Fourier Transform Spectroscopy x z y Preparation pulse (π/2-pulse) Echo x z y Τ secs Τ secs Refocussing (Mixing?) pulse Inverting pulse (π-pulse) 180° pulse 90° pulse F.I.D Refocus Defocus t2 acquisition The refocus period is somewhat similar to the Mixing Time in the pulse sequences for 2-dimensional NMR Spectra. However the Mixing period is held fixed while varying the t1 period for 2D, as described in the next slide. Rotating x,y axes :rotation about Lab z-axis Preparation pulse: facilitates the following…….. Z X Y Magnetization in XY plane appears stationary when viewed in Rotating Frame from within the rotating frame X Y X Y Z Rotating system viewed from within that system: STATIONARY X Y The description above of the spin echo spin system evolution was with the magnetization vectors in a rotating coordinate system Transforming to Rotating coordinate system

tm t1 t2 Acquisition for duration t2 ω1 ω2 Evolution period t1 Mixing period tm (Fixed duration) t1 tm Acquisition for duration t2 t2 Depends on the choice of the type of 2D experiment ω2 ω1 2D Spectrum Contour plot 2D NMR pulse sequence structure