In recent years, the need for a complete collection of information relevant to diatomic molecules has become evident. Several excellent collections of this type of information have been available for many years (Refs. 1–3); however, the state of our collective knowledge has been considerably expanded since their publication. To this end, a comprehensive compendium of spectroscopic information relevant to selected heteronuclear diatomic molecules was compiled and disseminated by us during FY 74 (Ref. 4). At present, however, if recent information concerning a specific homonuclear species is desired, it is still necessary to institute a time-consuming library search to collect the required information from the large number of sources in which it may have been presented. If information concerning an entire isoelectric molecular series is required, the time involved in collecting the information can be considerable.