MAGNETIC-FIELD CONTROL OF MOLECULAR DISSOCIATION-ENERGIES

We show that it is possible to control the dissociation energies of mo lecules with an external magnetic field. We focus our interest on the lowest dissociation channel for which the two atomic and/or molecular products are formed in their ground state. The crucial requirement is the paramagnetic character of at least one of the two dissociation pro ducts. Then, an external magnetic field lowers the energy of the param agnetic species in its lowest Zeeman component and, possibly, the corr esponding energy of dissociation of the parent molecule. This it true for diatomic molecules when at least one of the atoms has an odd numbe r of electrons. This is also true for oxygen and phosphorus atoms whic h have a P-3(2) ground state. The Zeeman energy shift of paramagnetic species is always of the order of 1 cm(-1) per tesla. The main theoret ical difficulty is to determine the correlation diagram existing betwe en the bound states of the parent molecule and the states of the produ cts, or equivalently, how the energy evolves as a function of the inte rnuclear distance corresponding to the dissociation coordinate. Little is known about this evolution, except for diatomic molecules, because the large internuclear distances are difficult to observe experimenta lly. The main part of the information come from ab initio calculations . For diatomic molecules, the dissociation coordinate is also the uniq ue internuclear distance while for polyatomic molecules, the potential energy surface has 3N-6 coordinates and multidimensional effects shou ld be considered. In any case, the singlet-triplet-quintet, etc... (or doublet-quartet, etc...) interactions should play an important role i n the correlation diagram because crossings are expected between singl et and triplet potential energy curves (from short to long internuclea r distances) and these interactions transform the crossings into antic rossings. The specific examples of alkali diatomic molecules (Li-2, Na -2, etc...), of NO2 and of (O-2)(2) are analyzed in details. (C) 1997 John Wiley & Sons, Inc.