Experimental settings for cw EPR

There are several functions in EasySpin that calculate continuous-wave EPR spectra:

chili (slow-motion regime), garlic (isotropic limit), pepper (solid-state limit).

All of these functions take a common set of experimental parameters that define the spectrometer settings. When calling any of these functions, these settings are given in the second argument Exp. For example,

pepper(Nitroxide,Exp,Opt);

The following table lists the fields in the experiment structure Exp. Of these fields, only very few are mandatory: You need to specify mwFreq for a field sweep, or Field for a frequency sweep.

mwFreq

(For field sweeps only). Spectrometer frequency, in GHz. E.g. Exp.mwFreq = 9.5; for X band. For frequency sweeps, omit this field and use Exp.Field to specify the fixed static field.

CenterSweep

(For field sweeps only). 2-element vector [center, sweep]
Contains center and sweep width of the sweep range. For magnetic field sweeps, values should be in mT, e.g. Exp.CenterSweep=[310 100].

The sweep range can be specified either in CenterSweep or in Range. If both are given, CenterSweep has precedence.

Range

(For field sweeps only). 2-element vector [lo hi]
Contains lower and upper limit of the field sweep range. Values should be in mT, e.g. Exp.Range=[260 360].

The sweep range can be specified either in CenterSweep or in Range. If both are given, CenterSweep has precedence.

Field

(For frequency sweeps only). Static magnetic field, in mT. E.g. Exp.Field = 1000; for a 1 T field. For field sweeps, omit this field and use Exp.mwFreq.

mwCenterSweep

(For frequency sweeps only). 2-element vector [center sweep]
Contains center and sweep width of the frequency sweep range. The values should be in GHz, e.g. Exp.mwCenterSweep=[9 10].

The sweep range can be specified either in mwCenterSweep or in mwRange. If both are given, mwCenterSweep has precedence.

mwRange

(For frequency sweeps only). 2-element vector [lo hi]
Contains lower and upper limit of the frequency sweep range. Values should be in GHz, e.g. Exp.Range=[9 10].

The sweep range can be specified either in mwCenterSweep or in mwRange. If both are given, mwCenterSweep has precedence.

nPoints

Number of points along the horizontal axis (magnetic field for field sweeps, microwave frequency for frequency sweeps). If not given, the default is 1024.

Harmonic

0, 1 (default) or 2

Harmonic of the detection. 1 and 2 specify the first and the second harmonic of the absorption spectrum, detected using field modulation. 0 returns the absorption/dispersion spectrum directly. To explicitly include the effect of field modulation, use Exp.ModAmp.

ModAmp

Modulation amplitude (peak-to-peak), in mT. If not given or set to zero, harmonics are calculated using simple differentiation. This setting is only used for field sweeps. It is not available for frequency sweeps.

mwPhase

The reference microwave phase, in radians. 0 is pure absorption (default value), and pi/2 is pure dispersion. mwPhase allows you to include absorption/dispersion admixture in the simulation.

Temperature

This field specifies the temperature of the spin system in the EPR experiment, in kelvin. E.g., Exp.Temperature = 298 corresponds to room temperature. If given, populations are computed for all energy levels assuming thermal (Boltzmann) equilibrium, and the population differences between two levels are included in the line intensities of the corresponding EPR transition. If not given (or set to NaN), the populations are not calculated, and all transitions are assumed to have equal population difference of 1.

To specify non-equilibrium populations, use the spin system field Sys.initState. See the spin system definition and the user guide on spin polarization for details.