Ultrafast Rotation

Abstract

For large angular momentum quantum numbers, a classical description of molecular rotation should be almost as good as quantum mechanical models. This is the starting point for this chapter, where a semi-classical method for the calculation of large angular momentum states in small molecules is discussed. Here, a classical description in terms of the angular momentum vector is extended by a quantization procedure, where path-integral methods are used. This combined method is known for a few decades but we apply it here to a totally quantum mechanical description of vibrational states using a variational approach. The chapter starts with an introduction of path integral methods in general and the formulation of the semi-classical approach to molecular rotation. The latter is also accompanied by a description of how a variational approach to vibrational dynamics can be used to create the rotational energy surface, the starting point for the semi-classical treatment.