Modulation Effects in Multiple Electron Resonance Spectroscopy

Abstract

In the broadest sense, modulation effects can be considered to represent those perturbations or influences on spectroscopic line shapes that arise either (1) from applied coherent (frequency, amplitude, or phase) modulation of the electromagnetic radiation incident upon the sample or modulation of the energy levels (resonance condition) as found, for example, with Stark modulation in microwave spectroscopy(1–6) or Zeeman modulation in magnetic resonance(7–19) or (2) from modulation of the populations of energy levels or of the phase coherence of precessing electric or magnetic dipoles arising from stochastic lattice fluctuations.(19–28) Thus, modulation effects can be classified as either applied and coherent or as molecular and stochastic. Earlier in this volume, Freed has discussed the effects of stochastic lattice fluctuations upon electron and nuclear spin relaxation rates and hence upon magnetic resonance and multiple magnetic resonance line shapes. While we shall explicitly consider both types of modulation effects, we shall do so from the standpoint of examining the importance of applied coherent modulation in determining magnetic resonance and multiple resonance responses. There are three aspects to the utilization of coherent modulation and accompanying phase-sensitive detection