Second_Order_Spectra

Second_Order_Spectra - Simulation of Second Order Spectra...

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1 Simulation of Second Order Spectra Using SPINEVOLUTION Spring, 2010 Introduction Although we frequently assume that scalar couplings are small compared to the differences in resonance positions due to chemical shifts and analyze spectra in terms of idealized (first order) multiplet structures, this assumption is often violated. It is therefore useful to understand the effects that violation can have on spectra (second order effects). It is also useful to have tools that allow one to extract chemical shifts and coupling constants from spectra in which they cannot be measured directly from positions of multiplet peaks. There are many tools for doing this, including tools based on density matrix calculations (GAMMA, for example, S.A. Smith et. al, J. Magn. Reson.106A, 75- 105 (1994)). This particular approach has the advantage of being able to simultaneously simulate the effects of complex pulse sequences, evolution under various Hamiltonians, and spin relaxation. The program SPINEVOLUTION, which we will use in this exercise, falls in this general class of tools. SPINEVOLUTION was written by M.Veshtort and R.G.Griffin primarily with the intent of simulating a whole variety of complex NMR experiments, including solids NMR experiments, something in which the Griffin lab specializes. However, it will simulate simple second order 1D experiments and we will use this capability to illustrate some of the principles discussed in class. The published article describing the software is: J. Magn. Reson., 178 (2006) 248-282. There is a support website with examples and other information at: http://web.mit.edu/fbml/cmr/griffin-group/SPINEVOLUTION/index.htm Downloads for a variety of platforms are available at: http://web.mit.edu/fbml/cmr/griffin-group/SPINEVOLUTION/Download.htm SPINEVOLUTION is implemented through the command “spinev” followed by the name of a script containing a series of definitions and commands. The program would normally begin with an equilibrium density matrix, transform it according to a given pulse sequence, and extract observables from density matrices at various points of time in an observation domain. For X and Y magnetization this is presented as a list of real and imaginary pairs of numbers – essentially an FID. However, SPINEVOLUTION also has conventional processing tools including weighting functions and a FFT (fast Fourier transform). When commands for these operations are included in a simulation script, the output is a frequency domain spectrum. You can look at this output file with a LINUX command like “more filename”, but we will opt to display the file with a standard LINUX graphics utility, gnuplot.
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This note was uploaded on 11/07/2011 for the course CHEM 8853R taught by Professor Gelbaum during the Fall '11 term at Georgia Tech.

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Second_Order_Spectra - Simulation of Second Order Spectra...

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