QUANTUM REFLECTION

Recent experimental and theoretical results concerning the sticking co efficient at ultralow energy are described. The need for an accurate t reatment of long range forces, including retardation, is emphasized. T he system involving H atoms incident on liquid helium provides the fir st clear evidence of quantum reflection. New results are reported for the sticking of D atoms incident on helium. The energy upper bound for the regime of quantum reflection for alkali atoms is found to be extr emely low, but ultimately achievable.