Application of Fourier transform electron paramagnetic resonance in the study of photochemical reactions

Acrylic Polymer Radicals: Structural Characterization and Dynamics

“…The microwave excitation is continuous wave throughout the experiment, even during the production of the radicals, as opposed to pulsed microwave methods such as electron spin echo or Fourier transform (FT) EPR. Significant advantages in sensitivity with similar time response are available with FT-EPR, 48 but there are also disadvantages in terms of spectral width of excitation that limit the application of this technique. The TREPR (CW) method is the most facile and cost-effective method for the observation of field-swept EPR spectra of organic radicals on the submicrosecond timescale.…”

Spin projection chromatography

“…Hence, one could go beyond the standard initial value solution of the Schrödinger equation and include a continuous coherent injection of probability amplitude as is required to describe time dependent transport in mesoscopic and molecular devices [30,31]. Future applications may include the descriptions of the chemical kinetics at low rates of laser pumping into the excited state [32,33,34] and the gradual creation of homonuclear coherence in NMR cross-polarization transfer [8]. Equation (8) allows the evaluation of Eq.…”

Quantitative time-resolved EPR CIDEP study of the photodecomposition oftrans-azocumene in solution

“…However, one of the basic physical quantities involved, the magnitudes of the induced polarizations, have remained unknown in the vast majority of investigations. As they are difficult to measure, accurate information about them is still scarce [1,2,[4][5][6][7][8].…”

“…In one of the simplest cases already, when identical radicals are generated by flash photolysis and their magnetization is detected by time-resolved cw-EPR spectroscopy, at least eight parameters are influencing the time-profile, ir the RPM only is operative: the initial concentration of radicals, their initial z-magnetization, their spin-lattice and spin-spin relaxation times, their rate constant for bimolecular termination, the polarization they gain in nonreactive encounters, as well as the amplitude of the resonant microwave tŸ and the sensitivity factor of the EPR detection system. Evaluation of all these quantities via a multiparameter least-squares flt of the relevant Bloch type differential equations to the experimental data is a hopeless undertaking, as errors in the parameters are mutual compensating and the tŸ are anything but unequivocal, even if a few of the parameters can be measured separately or be taken from literature [6] and (Bl~ittler C., Paul H., unpubl.). Moreover, previous investigations have shown, that the same experimental time-profile may be described about equally well even with different kinetic schemes and CIDEP mechanisms [9,10].…”

“…Therefore, in order to evaluate accurate magnitudes of CIDEP from EPR time-profiles, as many as possible of the other parameters should be determined precisely in separate experiments, and, of course, the kinetics must be known. Though this is basically true for cw-EPR as well as FT-EPR detection, the problem seems to be less severe in the latter technique [6,11,12].…”