The introduction essentially reports molecular theories and equations, on the basis of which most of the evaluated data are established. Specific comments related to some of the molecules considered in the subvolumes II/20B1-4 are retained in the present introduction due to their possible general applicability. Additional information of practical interest (list of symbols with their definitions, units, table of conversion factors, notations for the bands and energy levels, table of energy-related units and selected fundamental constants, etc.) is also given.
The tables are preceded by an additional index to help the search for specific information. In order to keep their consistency and their optimum ability to reproduce data, molecular constants are reported when possible from the same calculation of a given set of measurements. The subvolume ends with a reference section.