EPR Practical
Prepare sample of 10 M IASL in water in 50 L capillary (Wilmad)
Record all spectra on the hardcopy plotter and store them on the disk, you will need to process them later.
power dependence
collect spectra as a function of microwave power: 1, 4, 9, 16, 25, 36 mW
plot the peak-to-peak height of center line of each spectrum as a function of square root of power
modulation field
collect the spectra as a function of modulation amplitude: 0.1, 0.5, 1, 2, 4, 8 Gauss
plot the peak-to-peak height of each spectrum as a function of modulation amplitude
plot the peak-to-peak width of center line of each spectrum as a function of modulation amplitude
time constant
record the spectra with the integration time of 10 ms/point and vary the time constant (TC) between 1; 4; 10; 40; 80
ms.
plot the noise at the baseline as a function of the time constant;
plot the position of baseline crossover for the central peak as function of TC;
number of scans
with a visible noise (10 seconds scans with 10 ms TC) record:
- single spectrum;
- 4 spectra;
- 9 spectra;
- 25 spectra;
plot signal-to-noise ratio a function of number of scans
data analysis
integration
using LABVIEW or Sim_Exp integrate and print out the integrals of the spectra obtained in the power dependence
(1, 4 and 144 mW) and plot the integrals v. the square root of power;
integrate spectra of the modulation dependence and plot the integrals obtained at Hm = 0.1; 1; 4 Gauss.
P. Fajer
Instruments
subtraction
subtract the Hm=0.1 G spectrum from 1 G spectrum
subtract the Hm=0.1 G spectrum from 2 G spectrum
Data Analysis
You will need to average spectra to improve the signal/noise ratio; integrate to obtain the spin concentration; fit
peaks to find resonance amplitudes e.t.c.
There is a number of programs you can use: WinEPR, Origin, Excel however, we have developed in the lab two
EPR analysis suites specifically tailored to our needs:
Sim_Exp - DOS program written by PF over the years - very good for batch analysis of many spectra. Powerful
recording utility which allows you to process many spectra in identical fashion. For tutorials see Lab/EPR/Demo
directory. Demos is self playing programs using *.in files which you can print out/examine with Notepad.
LabVIEW - Mikolai's program written in the National Instruments graphical programming language - very flexible
with great graphics capabilities. See our WEB page for explanation of the particular routines.
If you want to use any other program you have to convert the Bruker format (reverse bit binary) to ASCII first, both
Sim_Exp and LabVIEW allow you to do that.