ABSTRACT

We begin by stating that it may not be immediately evident from Chapters 4 and 5 that every element in the periodic table that is sufciently abundant either has been or presumably could be formed into an atomic beam. Some are clearly more difcult to form into a beam than others, depending upon the temperature needed for evaporation. So for some elements obtaining a collimated beam has not proved possible. Sometimes the reactivity of the element may cause problems, particularly if a stable beam is needed for many hours of operation. All elements that are naturally diatomic gases can be formed into dissociated beams, as is described in Chapter 6, but obtaining high concentrations of highly dissociated atomic nitrogen has proved particularly challenging. Forming beams of other radicals and molecules does not normally appear to be problematic. However, it is reported by Periquet et al. (2000) that forming a molecular beam of the nucleobase guanine [C5H5N5O] was not readily possible because of isomerisation or decomposition.