Pulse Check program

Each Check it is usually based on a configuration file which contains the complete experimental set-up (Fig. 1.6). After starting the simulation the reader will be prompted to define the output file to which the calculated data is stored. If no configuration file exists the pulse program, rf channels, spin system, acquisition and processing parameters have to be chosen by the reader before the simulation is run (Fig. 1.6 left hand side). 

Load the configuration file ch3234b.cfg. Check the pulse program for the delay d10 between last pulse and start the acquisition process. Exit from the pulse program and run the simulation processing the data in exactly the same manner as part a. Note the symmetrical phase error of all the signals about the centre of the spectrum at 3.75 ppm illustrating the frequency dependence of the first order phase distortion. 

Phase cycling is an important part of any pulse program enabling signal selection and the suppression of artefacts. To help in setting up an experiment, particularly a 2D experiment, the minimum number of scans required for the correct phase cycling is usually listed in the commentary section of the pulse program. Check it 3.3.1.5 briefly... 

This chapter can be used either as an introduction to spin system definition and pulse programming or as a reference section. In either case the emphasis is on "learning by doing" and to this end there are numerous examples and Check its to follow. It is recommended that readers unfamiliar with simulation experiments refer to sections 2.2.2 and 2.3.2 before starting this chapter. This teaching version of NMR-SIM does not have all the features of the full version, consequently some topics that appear in the full version may not appear in this text and in these cases the NMR-SIM manual should be consulted for further information. 

Using the File I Pulse program... command load the pulse program cp121.seq into NMR-SIM. Open the file (Edit I Pulse program...) from c nmrsim session pp ppfrag and examine the text file for the execution commands sample, ihc and lo to. The pulse sequence is shown on the left-hand side of this Check it. 

For all the examples the development of the pulse sequence should be checked using the pulse sequence viewer utility (Utilities I Show Pulse program...). 

The common representation of a pulse sequence, including the phase cycling program, is shown above. The sequence can be used for any NMR active nucleus the correct rf frequency is set by the experiment parameters. In Check it 4.L2.6(a) the first elements of the pulse sequence are entered starting with the delay and pulse as line ordered commands. 

As explained in section 2.3.3 for time averaging experiments the pulse phase and the receiver phase are cycled. One major reason for phase cycling is that the performance of the electronic devices used to detect the x- and y-components of coherence for quadrature detection are not identical. In Check it 4.1.2.6(b) the most common phase cycling procedure is listed. In both NMR-SIM and the BRUKER pulse program language phase ph31 is recommended exclusively for the receiver phase. 

Open the pulse program ppexaml.seq created in the Check it 4.1.2.6(a) using the Edit I Pulse program command. Add the two phase program lines after the lines for d1 and (p1 ph1) f1. Using the FiielSave As... command save the file with the new name ppexam2.seq. 

To check that the new pulse program works correctly complete Check it 4.1.2.6 (d). 

Open the pulse program ppexamS.seq using the Edit I Pulse program command and replace p2 by p1 2 and place the simultaneous pulses p1 / p4 and p2 / p5 on the same line as shown below. Save the file as ppexamS.seq us ng File Save as. Using the command Utilities I Show pulse program... compare the pulse program scheme with the scheme from Check it 4.1.2.8(a). 

It is now possible to use the DEPT pulse program just created to simulate the DEPT135 13C 1H spectrum of bromomethylcrotonate using the spin system created in Check it 4.1.1.3. 

Load the configuration file st13cde.cfg (File I Experiment Setup I Load from file...) and replace the spin system file either with the file examS.ham previously created in Check it 4.1.1.3 or the file exam3p.ham delivered with the program. Load the pulse program ppexam/.seq from the Check it 4.1.2.8(c). Run a simulation (GolRun Spectrum) and process the FID with zero filling (Sl(r+i) = 32k) and an exponential window function (LB value of 2 Hz). Phase the spectrum as shown in the result file. 

If variable spin system parameters are used the increment step HS1...32, the start value HV1...32 and the loop limit L0...L31 must be assigned. The range over which a variable parameter is varied depends upon the increment step size and the loop limit. If required by the pulse program these parameters will appear the Go Check Experiment Parameters dialog box. As discussed in previous sections, loop definitions are not only restricted to spin system variable incrementation. 

---