How to write a function of intensity as a function of frequency
rwwhite
I'm extremely new to Igor and am carrying out an experiment to determine the rotational barrier in N,N - dimethylacetamide.
I have used Macnuts to fourier transform the data from the NMR machine and to carry out some phasing. This data was then exported and used to create a graph in Igor.
Now In order to determine the rate constant I need to create a function as described in the subject. Using this function I can fiddle with particular variables to make this graph match the graph from the macnuts data.
My problem is how to write out the following expression:
g(v) = Kτ(υA – υB)2 / [0.5.{(υA – υB) - υ}]2 + 4π2τ2.(υA – υB)2 .(υB-υ) 2
Where the 2's are squaring, (υA – υB) and τ are the variables to be fiddled with.
Wave w
Variable u
//CurveFitDialog/ These comments were created by the Curve Fitting dialog. Altering them will
//CurveFitDialog/ make the function less convenient to work with in the Curve Fitting dialog.
//CurveFitDialog/ Equation:
//CurveFitDialog/ f(u) = Kt*(uA-uB)^2/(((uA-uB)-u)/2)^2 + 4*pi*2*TT^2*(uA-uB)^2*(uB-u)^2
//CurveFitDialog/ End of Equation
//CurveFitDialog/ Independent Variables 1
//CurveFitDialog/ u
//CurveFitDialog/ Coefficients 3
//CurveFitDialog/ w[0] = uA
//CurveFitDialog/ w[1] = uB
//CurveFitDialog/ w[2] = TT
Variable Kt = <replace this with the actual number>
return Kt*(w[0]-w[1])^2/(((w[0]-w[1])-u)/2)^2 + 39.4784176043574*w[2]^2*(w[0]-w[1])^2*(w[1]-u)^2
End
This isn't really very well written- repeated expressions so that they are computed only once. The number 39.4784176043574 is 4*pi^2.
Please pull down the Help menu and take a look at the Getting Started help. The Guided Tour that's the majority of Getting Started will introduce you to Igor's main concepts. It includes a couple of sections on curve fitting as well.
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
September 19, 2011 at 09:21 am - Permalink