Knowledge Bank

Because of the long-range behavior (e.g., $C6/R6$) of the potential representing the interaction between two atoms, there are often a certain number of closely spaced vibrational-rotational levels near dissociation with large vibrational amplitudes and long classical vibrational periods (most of which are spent at large $distance).1$ Because the properties of molecules in such levels are quite exotic and nonintuitive (although quite simply related to long-range forces), we shall refer to them as ``long-range molecules”, and symbolize them $AB00$ The existence of such molecules has been conclusively established spectroscopically. We shall discuss the radiative (and non-radiative) properties of such isolated molecules, with particular emphasis on electronic transitions. Molecules discussed will include $H2,LiH,$ and $I2$.