Zero-energy bound or quasibound states and their implications for diatomic systems with an asymptotic van der Waals interaction

Using an l-insensitive quantum defect theory, we derive a set of universal properties, both spectral and scattering, that are shared by diatomic systems with an asymptotic van der Waals interaction and having a zero-energy bound or a quasibound state of angular momentum l(b). The Cs-133 dimer is studied as an example. Systems that are close to having a bound or a quasibound state at the threshold are also discussed.