Microwave Effect in Chemical Reactions

Abstract

Microwave Effect in Chemical Reactions Samuel P. Bowen, David R. Kanis, Christopher McDaniel, Robert C Richter Abstract Time dependent perturbation theory predicts no change in the electronic state probability amplitudes of molecules unless the energy of the applied electromagnetic field matches an electronic energy level difference. Therefore, microwaves should have no non-thermal effect on chemical reactions. However, at low frequencies the oscillating potentials are essentially classical and the relevant question is whether the electronic molecular states evolve adiabatically or non-adiabatically. Time varying potentials can mix excited states into the instantaneous adiabatic ground state as the expectation of the energy changes in response to the potential. This mixing yields a non-zero excited state proba bi l i t y a mp l i t u d e s c n (t). Measurements of these excited states, for example, by reactant collisions, may collapse the instantaneous ground state wave function onto the excited state with a probability |cn (t)|2. This nonadiabatic probability o pe ns a new channel for chemical reactions in addition to the usual thermal Ar r h e n i u s probability. The temperature dependence of the reaction rate from these two channels will exhibit the microwave effects primarily at low temperatures. At high temperatures the Arrhenius probabili ti es wi l l dominate and the microwave effects may be negligible. Most precise laboratory a s s e s s me n t s of non-thermal mi crowave effects appear to have been at high temperatures. Several experiments are reviewed and one is found to have a wide enough temperature range to exhibit the predicted f o rm. Our results also suggest that m i c r o w a v e couplings could induce reactions different from those weighted by the thermal probabilities. Full Text: PDF DOI: 10.15640/jcb.v2n2a1