CALCULATED TRENDS OF OH INFRARED STRETCHING VIBRATIONS WITH COMPOSITION AND STRUCTURE IN ALUMINOSILICATE MOLECULES

Ab initio, molecular orbital calculations have been performed on a var iety of hypothetical aluminosilicate molecules to investigate relation ships among composition, structure, and infrared spectra of OH. Vibrat ional analyses of the full-optimized molecular geometries at the 3-21G * level were performed with Gaussian 92 to determine theoretical infr ared spectra. Theoretical infrared OH frequencies, v(OH), shift 10 to 100 cm-1 with ionic substitutions. The inverse correlation of theoreti cal infrared OH intensities with OH stretching frequencies in these al uminosilicate molecules is similar to that observed for aluminosilicat e glasses (Paterson 1982). 0-H bond lengths, H-bond distances, and H-b ond angles correlate with frequency. The dominant factor affecting vp( OH) is the H-bond distance, if this distance is less than 2 angstrom. Beyond H-bond distances of 2 angstrom, structural and compositional ef fects exert competitive influences on vp(OH).