Diborane, Dialane, and Digallane: Accurate geometries and vibrational frequencies

Abstract

Optimum equilibrium geometries, harmonic vibrational frequencies, and infrared intensities within the double harmonic approximation are computed for diborane, B{sub 2}H{sub 6}, dialane, Al{sub 2}H{sub 6}, and digallane, Ga{sub 2}H{sub 6}, at both the SCF level of theory and the second-order perturbation theory [E(2)] using three large basis sets: 6-311G(d,p), 6-311G(2d,2p), and 6-311G(2df,2p). In particular, the results obtained with the latter basis set make this present work the first study to include f-type polarization functions in a systematic investigation of the molecular structure and properties of all three molecules in the series. Because of the good agreement of the present theoretical results with experimental data and with previous theoretical studies which employed a higher treatment of electron correlation, this study serves to show that large basis sets can in part compensate for the lack of a more advanced treatment of electron correlation in these electron-deficient systems. In addition, this study establishes the level of basis set needed for future work on these systems including a thorough description of the total electronic density at a correlated level.