I need to fit a transient absorption kinetics, starting from -500 fs to 4000 fs. Around time-zero, it has a Gaussian function due to instrument response (region-1) and from about 100 fs (to 4000 fs) it shows the actual exponential kinetics (region-2). I need to fit both the region simultaneously in Origin (i.e. deconvolution around time-zero and exponential growth(/decay) afterwards). Please suggest how do I perform the fit in Origin? Thanks.
You can a bell shape function with the difference of two sigmoids
S(z(x))=exp(z)/(expo(z)+exp(-z))
z(x)=(x-c)/d
S ranges from 0 to 1.
c is the value of x where S=0.5 and
d represent the width of the function (S(c-d/2)=1/(e+1) approx 1/e.
The function is symmetric with respect to x=c.
you can use this expression a1*S1(x)-a2*s2.
If you have problems in the fitting, due to correlation between a1 and a2, you can fix a1=2 or 3 and check again.
Thanks.
The function you suggest, I think can only able to fit the Gaussian instrument response near time-zero (region-1), however I want to fit simultaneously both region-1 and region-2. Is there any suggestion for that?
Yes you are right. Add a third sigmoid for fitting the last part or an exponential function with negative exponent.
you can define your own function in Origin, with condition to switch the equation, i.e. a piecewise function (e.g. in the function file your formula section will be something like this)
[Formula]
if (x < xi)
y = deconvolution(x, ...)
else
y = exponential(x, ...)
where you need to write the proper form of deconvolution and exponential function you want. You can copy the function formulas from the pre-defined functions in Origin.
Tushar Debnath Deconvolution of a composite peak into its individual peaks plays an important role in the interpretation of many types of graphs including XRD, XPS, FTIR, and PL etc. In this video, I have discussed how to deconvolute simple combined peaks, composite peaks and how to correct missing data in a given peak with the help of deconvolution in OriginLab. In the case you want to further ask about it, please do comment on the specific video, I'll respond to it shortly. I have provided the practice files (OriginLab) here. Thanks
https://youtu.be/WX_X3XlbKRA
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