Theory of pulsed reaction yield detected magnetic resonance

Abstract

We propose pulse sequences for Reaction Yield Detected Magnetic Resonance (RYDMR), which are based on refocusing the zero-quantum coherences in radical pairs by non-selective microwave pulses and using the population of a radical pair singlet spin state as an observable. The new experiments are analogues of existing EPR experiments such as the primary echo, Carr-Purcell, ESEEM, stimulated echo and Mims ENDOR. All pulse sequences are supported by analytical results and numerical calculations. The pulse sequences can be used for more efficient and highly detailed characterization of intermediates of chemical reactions and charge carriers in organic semiconductors.

Theoretical Description of Pulsed RYDMR: Refocusing Zero-Quantum and Single Quantum Coherences

“…We only look at the ρ SS (t) time trace and check whether we obtain echo-like signals. The reason why this treatment is sufficient for understanding the mechanism of the echo formation is described in the previous publication [13]. For an alternative RYDMR detection method we evaluate the difference of the populations, ΔP, of the RP states with parallel Bereitgestellt von | Freie Universität Berlin Angemeldet Heruntergeladen am | 28.08.…”

“…An extension of this treatment was later performed by Shkrob [12], who considered refocusing by two MW-pulses with different phases. In our previous work [13] this possibility of creating "spin echoes" observed via the singlet-state population of an RP has been considered in detail.…”

“…When one monitors the singlet-state population, ρ SS , as a function of time one would see an echo-like signal (a peak) at the instant of time when the ZQC is completely (or partly) refocused. In the previous work [13] we have also considered more complex pulse sequences using non-selective pulses, e.g. pulse sequences, which enable modulation of the spin echo due to different interactions, stimulated echo and electron-nuclear double resonance.…”

Magnetic isotope effect and chemical Zeno effect

“…If and , the dependence of coef ficient on magnetic and kinetic RP parameters can be represented as , (11) where (12)…”

“…Equation (11) does not afford exact w values at which δ reaches a maxi mum. However, numerical calculations show that the maximal isotope enrichment of recombination prod ucts is achieved at , i.e., when geminate recom bination rates are comparable with the HFC constant of the magnetic isotope.…”