Hi isro1
I have had a look at your data and have tried to fit an exponential decay to the envelope.
You can see on the attachment a plot of the data where I have corrected the zero position on the y axis using the average of the values rather than the median.
median = 1.5822 average = 1.7613
The difference is insignificant compared to the asymmetry of the oscillations which is highlighted
by the plot of y = 28e^(-1.9x)sin(31x-0.1) (in green).
(a) the decay does not follow a simple exponential decay law and
(b) the frequency of the oscillations is not constant.
For these reasons I feel that it will not be possible to find a single exponential to model the peaks and the troughs simultaneously.
Regards