Energy transfer cross-polarisation

Polarisation effects should be relatively more important when the activation barrier is small or unimportant (i.e. the reactants diffuse together to form the encounter pair, as discussed in ref. 87b) than when the activation barrier is large (i.e. the reactants diffuse together and then have to obtain considerable energy to cross from the reactant to product potential energy surface). Clearly, much more work in this area is required and it is especially appropriate to consider these ideas when discussing proton transfer reactions. 

The addition of a chemical species with a large dielectric constant to induce desired microwave effects in matrices devoid of such substances, or lacking substances with significantly different dielectric constants, can be compared, on a conceptual basis, to cross-polarisation experiments carried out in nuclear magnetic resonance spectroscopy (see Chapter 6). In that case, a nucleus that relaxes relatively rapidly is excited selectively and allowed to transfer that excitation energy to neighbouring nuclei with low or relatively lower relaxation rate (e.g., nuclei being cross-polarised to nuclei). 

Dialysis and diffusion dialysis are membrane processes that consumes generally not much energy. The energy consumption Ep is determined by the pumps to circulate the feed and permeate (dialysate) stream along the membrane (eq. VIII - 87). If concentration polarisation becomes severe higher cross-flow velocities may be required to increase the solute mass transfer coefficient and consequently the energy consumption will increase. 

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