Spin Exchange Reactions

Turner and Schultz (2001) Coupled electron-transfer and spin-exchange reactions [248]. 

Fig. 2. Scattering cross sections for pt with a hydrogen isotope nuclei from Refs. [12,18], showing the Ramsauer-Townsend minimum at around 10 eV for pt+p pt(F) +t cross sections plotted include both elastic and spin exchange reactions, where pt(0) is the singlet state and pt( 1) is the triplet state...

Any p" spin relaxation that occurs within the time window of pSR (several ns several tens of ps) can be measured precisely (Eq. 11). When Mu undergoes a chemical reaction or spin exchange reaction with an additive X, the Mu relaxation function is described by a quasi first-order decay as... 

A particular usefulness of pS Relaxation to chemistry is that it gives a means of distinguishing between two different spin relaxation types spin depolarization and dephasing. By pS Rotation method it is not possible to distinguish between the relaxation due to depolarization, as in the spin exchange reaction... 

Fig. 11. A proposed scheme of Mu formation and reactions in water. Mu is formed by reaction with nearly thermalized p and an excess electron formed by radiolysis (the spur model of Mu formation) with the probability h, and the rest (Iiq) is solvated ttecomeing diamagnetic muon. Mu thus formed can further react with aqueous electrons by spin exchange reaction it is depolarized and the polarization is lost (Pi. By chemical reactions, a fraction of Mu is incorporated into diamagnetic muon while another fraction becomes dephased and forms a part of depending on how fast the reactions proceed. Mu that has not reacted is observed as free Mu (P )...

Although Pj was initially attributed to spin-exchange reaction, formation of dephased diamagnetic muon (MuH below) as a result of reaction... 

Ps is a neutral light particle composed of e and e. Since it is a free radical it may undergo reactions with paramagnetic species and electron acceptors via oxidation, compound formation, and spin exchange reactions. 

Spin exchange reactions between the ions, since the Coulomb force keeps the ions apart ... 

Randolph and Carlier used EPR spectroscopy to study the Heisenberg spin exchange reaction of nitroxide free radicals in supercritical ethane (194). The... 

In the above reaction scheme Solv" ", C-RH+, S represent the solvent cation, cyclohexane cation and hexafluorobenzene (HFB) anion respectively. The spin-dynamics of S and c-RH+ determine the magnetic field effect, since the spin wave-function for the ion pair (S / c-RH+) evolves differently at the different magnetic field strengths. The intensity of recombination fluorescence of the solution is determined by the rate of radiative deactivation of S [reaction (7)], which is accumulated within the simulation program. Although this model is not a complete description of the radiolysis of n-hexane which contains a solution of HFB and cyclohexane, it does however, take into account the most important aspect of the proposed relaxation mechanism, namely cross recombination. A more detailed reaction scheme for the radiolysis of n-dodecane is considered later in this chapter (in Sect. 8.6), which takes into account the excited state chemistry as well as spin-exchange reactions. 

In the first simulation (Fig. 8.18a), the effects of spin-exchange reactions (15), (16) and (17) were taken into consideration indirectly by using the experimentally determined T and T2 values. The purpose of this simulation was to isolate the effect of cross-recombination without complicating the decay of the TR MFE curve by other random processes which can cause relaxation as well. 

The second simulation (Fig. 8.18b) treated spin-exchange reactions (15), (16) and (17) as well as cross-recombination, but did not assume any high field spin-lattice relaxation rate (i.e. T = 00). The purpose of this simulation was to isolate the effect of cross-recombination and spin-exchange reactions on the overall spin relaxation rate. In both simulations, in order to simplify the computation model and make the solution tractable, no Ag mechanism or hyperfine interaction was taken into account. It is found by the experimentalists that direct manifestation of the hyperfine interactions in TNIPD" " is unobservable due to (i) the delay in the formation of TMPD+, (ii) the self-exchange reaction [reaction (27)] and (iii) the long fluorescence lifetime [34, 35]. 

---