Non-thermal microwave effects or specific microwave effects have been posited in order to explain unusual observations in

microwave chemistry Microwave chemistry is the science of applying microwave radiation to chemical reactions. Microwaves act as high frequency electric fields and will generally heat any material containing mobile electric charges, such as polar molecules in a solvent ...

. The main effect of the absorption of microwaves by most materials is heating; the random motion of the constituent molecules is increased. Non-thermal effects are effects that are not due to the increase of thermal energy of the material. Instead, the microwave energy itself directly couples to energy modes within the

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

lattice Lattice may refer to: Arts and design * Latticework, an ornamental criss-crossed framework, an arrangement of crossing laths or other thin strips of material * Lattice (music), an organized grid model of pitch ratios * Lattice (pastry), an orna ...

. Non-thermal effects in liquids are almost certainly non-existent,Stuerga, D.; Gaillard, P. ''

Journal of Microwave Power and Electromagnetic Energy The ''Journal of Microwave Power and Electromagnetic Energy'' is a quarterly peer-reviewed scientific journal covering industrial, medical, and scientific applications of electromagnetic and microwaves from 0.1 to 100 GHz, including topics such a ...

'', 1996, 31, 101-113. http://jmpee.org/JMPEE_temp/31-2_bl/JMPEEA-31-2-Pg101.htmStuerga, D.; Gaillard, P. Journal of Microwave Power and Electromagnetic Energy, 1996, 31, 87-99. http://jmpee.org/JMPEE_temp/31-2_bl/JMPEEA-31-2-Pg87.htm as the time for energy redistribution between molecules in a liquid is much less than the period of a microwave

oscillation Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

. A 2005 review has illustrated this in application to organic chemistry, though clearly supports the existence of non-thermal effects.''Microwaves in organic synthesis. Thermal and non-thermal microwave effects'', Antonio de la Hoz, Angel Diaz-Ortiz, Andres Moreno, Chem. Soc. Rev., 2005, 164-178. It has been shown that such non-thermal effects exist in the reaction of O + HCl(DCl) -> OH(OD) + Cl in the gas phase and the authors suggest that some mechanisms may also be present in the condensed phase.''Strong Acceleration of Chemical Reactions Occurring Through the Effects of Rotational Excitation on Collisional Geometry'', Adolf Miklavc, ChemPhysChem, 2001, 552-555. Non-thermal effects in solids are still part of an ongoing debate. It is likely that through focusing of

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

s at particle interfaces, microwaves cause

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

formation and enhance

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

in solidsWhittaker, A.G., Chem. Mater., 17 (13), 3426 -3432, 2005. via second-order effects.Booske, J. H.; Cooper, R. F.; Dobson, I. Journal of Materials Research 1992, 7, 495-501.Booske, J. H.; Cooper, R. F.; Freeman, S. A. Materials Research Innovations 1997, 1, 77-84.Freeman, S. A.; Booske, J. H.; Cooper, R. F. J. Appl. Phys., 1998, 83, 5761. As a result, they may enhance solid-state

sintering Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

processes. Debates continued in 2006 about non-thermal effects of microwaves that have been reported in solid-state phase transitions.Robb, G.; Harrison, A.; Whittaker, A. G. Phys. Chem. Comm., 2002, 135-137 A 2013 essay concluded the effect did not exist in organic synthesis involving liquid phases. A 2015 perspective discusses the non-thermal microwave effect (a resonance process) in relation to selective heating by Debye relaxation processes.

References

{{Reflist, 2 Chemical kinetics Microwave chemistry