Resonances, nuclear-excited Feshbach

Figure 1. Schematic illustration of (a) shape and (b) nuclear-excited Feshbach resonances. The symbols 0> and i > designate, respectively, the electronic ground state of the neutral molecule and the NIS (1).

As a result of these calculations, it is concluded that the SFg molecule will not bind two electrons to form SF. However, the formation of SF5 in an electronically excited state cannot be dismissed easily. Nuclear-excited Feshbach resonances, in which the kinetic energy of the incident electron is absorbed solely into the nuclear motion of the molecule, occur in the electron attachment process of various molecular species The SF " species studied by Henis and... 

Mabie had a lifetime of about 0,5 ms. A lifetime of 0.03 ms, shorter than the value reported by Henis and Mabie, has been discussed and used for equipment calibrations by Hadjiantoniou, Christophorou and Carter It is conceivable that nuclear-excited Feshbach resonances also may participate in the formation of the SFfi " ion and other doubly-charged negative ions. 

Such doubly excited states are familiar in nuclear physics as compound state, or Feshbach, resonances, and In atomic spectroscopy as autolonizlng, or Auger, states of atoms and molecules (33). Just as In the atomic case (33.34), sequences of states with quantum numbers of the form (n,n-t-m) do not necessarily have shorter lifetimes as a function of Increasing m, in contradistinction to statistical expectations. This follows from the Increase In period of the local bond modes as dissociation Is neared, and the detuning of any near frequency resonances as m increases in a sequence of (n,n+m) states. 

The theory of isolated resonances is well understood and is discussed below. Some initial work has been done on the theory of overlapping resonances (Remade et al., 1989 Desouter-Lecomte and Culot, 1993 Someda et al., 1994a,b) and its relation to experiment (Reid et al., 1994). Much of the research of overlapping resonances has its origins in nuclear physics, where the dissociation of a compound nucleus is treated (Ericson, 1960, 1963 Satchler, 1990 Rotter, 1991). For example, fluctuations in product state populations, called Ericson fluctuations (Satchler, 1990 Rotter, 1991), may arise from coherent excitation of overlapping resonances. However, more work needs to be done to develop a complete theory of overlapping resonances and this topic is not discussed here. Mies and Krauss (1966, 1969) and Rice (1971) were pioneers in treating unimolecular rate theory in terms of the decomposition of isolated Feshbach resonances. 

The properties of unstable negative-ion states of the kind which play the intermediate complex role in associative-detachment have been the subject of a great deal of attention in recent years, primarily because of their role in electron-molecule collisions. An excellent discussion of such resonances is given by Bardsley and Mandl. " The long-lived N02 intermediate in (29), stabilized on a curve such as 3 in Fig. 8 due to rotational excitation of the NO, is again a nuclear-excited Feshbach resonance. 

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