Spin Systems and Pulse Programs

File NMR Wizard Edit Parameters Go Utilities Options 

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The current spin system and pulse program can be changed using the file selection box. 

In the first section of this chapter spin systems and pulse sequences are discussed. Starting with the definition of a spin system and a description of the various spin parameters used by NMR-SIM. Using suitable examples the correct definition of spin system parameters, how to reduce the number of spin system parameters and the application of variable spin system parameters is illustrated. Following on, pulse sequences are discussed in some detail and the difference between a pulse sequence and a pulse program is emphasized. The pulse program language of NMR-SIM should be familiar to users of Bruker NMR spectrometers as it uses the same syntax. However, because this is not covered in the NMR-SIM manual, pulse sequence elements such as pulses, phases and delays are explained in detail and illustrated using a variety of examples. 

After the software installation two new directories will have been created in the root directory of the local PC. Assuming that the default pathway was used in the installation the program directory C Teach. .. has the directory structure shown in Fig. 1.2. The second directory C NMRSIM SESSION created contains all the pulse programs, spin systems and experimental set-ups files in the subdirectories C . .. CONFIG configuration files, C . .. HAM spin system files, C . .. PP pulse program files, C . .. WAVE pulse shape files, C . .. LIST lists files and C . .. JOB job files. Table... 

In the context of the NMR-SIM simulation, the recording of a one-dimensional experiment consists of the definition of the spin system, the pulse sequence and the experiment parameters. The result of the simulation is a FID that is loaded into the ID WIN-NMR processing program. Both the time domain and the frequency domain data may be processed using a variety of domain specific mathematical functions. 

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. 

Load the configuration file dsweep.cfg. Open the spin system file (Edit Spin system...) and note the spin system variable definition. Examine the pulse sequence (Edit Pulse program...) and note the additional loop command to increment the chemical shift. Using the GolRun Experiment command simulate the spectrum which corresponds to the excitation profile of a 90° TOPHAT pulse. In 1D WIN-NMR process the FID using zero filling of Sl(r+i) 32/cand an exponential window function with a LB value of 2 Hz. 

Simulations of solid-state NMR experiments can provide the user with information about the spin system or the pulse sequence. The programs take a given pulse sequence and parameters for a nuclear spin system as input, and their output allow extraction of information about stmcture and dynamics for the molecular system or evaluation... 

The main window of NMR-SIM is subdivided in the title bar with the program name, the menu bar with the pull-down menu commands File, NMR-Wizard, Edit etc., the rf channel option bar with two accessible rf channel combo boxes and the main status window, see Fig. 1.3. Each command in the menu bar opens a pull-down menu that may contain sub-menus or commands that can be selected and opened/executed. The rf channel option bar uses isotope identifier to assign a specific nucleus and hence NMR frequency to the FI or F2 channel. The main status window is built up in line order and shows the pulse program name, spin system name and other optional files associated with the current simulation. 

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). 

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