Torsional barriers and force fields in H/sub 4/TO/sub 4/ molecules and molecular ions (T = C, B, Al, Si)

Journal Article · Thu Apr 07 04:00:00 EDT 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100318a019· OSTI ID:5129785

Hess, A C; McMillan, P F; O'Keeffe, M

Geometric and vibrational properties of the four isoelectronic species H/sub 4/BO/sub 4//sup -/, H/sub 4/CO/sub 4/, H/sub 4/AlO/sub 4//sup -/, and H/sub 4/SiO/sub 4/ have been calculated by using self-consistent-field theory at the 6-31G* basis level. The harmonic vibrational frequencies have been calculated from a complete set of force constants, which are reported in internal symmetry coordinates. Where experimental data exist, comparisons have been made between the calculated frequencies and force constants and observed frequencies and empirical force constants. All four of the molecules are found to possess S/sub 4/ symmetry in their minimum-energy conformations. There are also two geometrically distinct D/sub 2nd/ transition states, which may be reached from the stable S/sub 4/ conformation by torsional motion of the hydrogens about the TO bond axis. Barrier heights of the two transition states are reported relative to the stable S/sub 4/ conformation for the four molecules. It is found that the execution of the large-amplitude torsional motion has a large effect on the OTO angles of the TO/sub 4/ unit. In H/sub 4/SiO/sub 4/, for example, it is found that one set of OSiO angles change by 13/sup 0/ with only a 13.8 kJmol change in the total molecular energy. Such results suggest that SiO/sub 4/ units are in fact easily deformable as a function of changes in nearest neighbor geometry.

• Research Organization: Arizona State Univ., Tempe (USA)
• OSTI ID: 5129785
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:7; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALUMINATES
ALUMINIUM COMPOUNDS
ANIONS
BORON COMPOUNDS
BORONIC ACIDS
CARBON COMPOUNDS
CARBONIC ACID
CHARGED PARTICLES
DATA
ENERGY LEVELS
EXCITED STATES
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
IONS
MOLECULAR ORBITAL METHOD
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
SILICIC ACID
THEORETICAL DATA
VIBRATIONAL STATES