James D. Kubicki, Dan Sykes, George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, California 91125
Ab initio, molecular orbital calculations have been performed on a variety of hypothetical aluminosilicate molecules to investigate relationships among composition, structure, and infrared spectra of OH. Vibrational analyses of the full-optimized molecular geometries at the 3-21G** lever were performed with Gaussian 92 to determine theoretical infrared spectra. Theoretical infrared OH frequencies v(OH), shift 10 to 100 cm-1 with ionic substitutions. The inverse correlation of theoretical infrared OH intensities with OH stretching frequencies in these aluminosilicate molecules is similar to that observed for aluminosilicate glasses (Paterson 1982). O-H bond lengths, H-bond distances, and H-bond angles correlate with frequency. The dominant factor affecting v(OH) is the H-bond distance, if this distance is less than 2 Å. Beyond H-bond distances of 2 A, structural and compositional effects exert competitive influences on v(OH).