Programme for normal co-ordinate calculations; vibrational analysis of diborane and halides M2X6(M = Al, Ga, or ln)

Abstract

An outline is given of an Algol computer programme for normal co-ordinate analysis. Some improvements in the force-constant refinement process are reported. The spectra of diborane, and of six halides of the formula M₂X₆(M = Al, Ga, or ln), have been analysed. In each case the force field is built up from the SVFF by adding interaction terms one by one, only those that are determined by the data being accepted. Force fields for all of the M₂X₆ molecules can be constructed by choosing 10 or more force constants from a set of 13; the force field for diborane differs considerably from these. A B–B force constant of 2·511 mdynes/Å was found for diborane. In contrast, calculations for the M₂X₆ molecules became unstable when an M–M force constant was included, contrary to a previous report. An error in our previous calculations on auric chloride is corrected.