H -H "
H") = A ( -H)
(2-5)
A precise baseline correction is necessary, and asymmetric spectra require a correction factor to
account for the asymmetry. The nth moment is given by Equation 2-5, where Ho is the center
field, Hj Hj_. is the step size, Hj is the field value for any point j, and yj is the intensity at point
j. Figure 2-16 shows a graphical representation of the determination of these parameters.
A AH B C
Bo
I
I-- r ,-
1HF LF CF
Figure 2-16. Pictorial representation of the determination of common spectral parameters A)
AHpp, B) ILF, ICF, and IHF, and C) second moment (## ).
Pulsed Electron Paramagnetic Resonance Spectroscopy
Introduction
Pulsed EPR was pioneered by W. B. Mims in the 1960s and has since become a valuable
tool used in a wide variety of applications. The specific pulsed technique utilized in this research
is called pulsed electron double resonance (PELDOR), or double electron-electron resonance
(DEER). DEER experiments use two different microwave frequencies to measure the strength of
the coupling between two electron spins; in our case, to measure the distance between two
nitroxide spin labels. This technique can be described by a simplified Hamiltonian, given in
Equation 2-6, comprised of three sets of terms: the Zeeman terms for the spin subsets A and B,
and the dipolar coupling term that relates the two, where Q~ASz is the Zeeman term for the spin