COMPUTATIONAL CHEMISTRY AND COMPUTATIONAL VIBRATION SPECTROSCOPY OF AEROSIL

Spherical aerosil particles of 160 Å and more in diameter consist of an amorphous silica core that is neutral to chemical reactions, and an active surface. The chemistry of aerosil is the chemistry of its surface. This phenomenon, from the modern computational chemistry point of view, is considered in three steps: model simulation, methods of calculation and an analysis of the results obtained. Model simulation is based on a cluster approximation. The cluster consisting of up to 150 atoms is considered. The model for the core and surface of silica as well as for adsorbed molecules of water, methane, anthracene and other compounds is considered. The primary choice of a model is made with molecular mechanics methods. Optimized structures, binding energies and force-field constants are obtained with the program CLUSTER-Z1 based on the AM1 method of Dewar. Vibrational spectra are calculated with the program COSPECO. The obtained data are used to fit experimental spectra of inelastic neutron scattering. The fitting has resulted in making a choice of the most reliable model

COMPUTATIONAL CHEMISTRY AND COMPUTATIONAL VIBRATION SPECTROSCOPY OF AEROSIL

Spherical aerosil particles of 160 Å and more in diameter consist of an amorphous silica core that is neutral to chemical reactions, and an active surface. The chemistry of aerosil is the chemistry of its surface. This phenomenon, from the modern computational chemistry point of view, is considered in three steps: model simulation, methods of calculation and an analysis of the results obtained. Model simulation is based on a cluster approximation. The cluster consisting of up to 150 atoms is considered. The model for the core and surface of silica as well as for adsorbed molecules of water, methane, anthracene and other compounds is considered. The primary choice of a model is made with molecular mechanics methods. Optimized structures, binding energies and force-field constants are obtained with the program CLUSTER-Z1 based on the AM1 method of Dewar. Vibrational spectra are calculated with the program COSPECO. The obtained data are used to fit experimental spectra of inelastic neutron scattering. The fitting has resulted in making a choice of the most reliable model

NEUTRON SPECTROSCOPY OF WATER ADSORBED AT AEROSIL

Computational and real neutron scattering experiments are presented. The computational one is based on the modern cluster approximation of a computational chemistry. A few models for water molecule deposition at the aerosil surface are considered. The core and surface of aerosil are simulated by clusters with up to 150 atoms. The active centre is selected. It is shown that water molecules join willingly to a silicon atom forming a group of four coordinated molecules. Additionally these molecules attract other ones forming a “subcluster” (up to 8–10 molecules) bound to one centre. Optimized structure, electron density distribution, binding energy and force field constants are calculated. Basing on these data weighted densities of vibrational states are obtained. The results are in good agreement with experimental inelastic neutron scattering spectra recorded at 10, 80 and 290 K at Dubna for aerosil A380OHH2O and A380ODD2O (A380 means aerosil with a specific area of 380 (m2 g−1)

NEUTRON SPECTROSCOPY OF WATER ADSORBED AT AEROSIL

Computational and real neutron scattering experiments are presented. The computational one is based on the modern cluster approximation of a computational chemistry. A few models for water molecule deposition at the aerosil surface are considered. The core and surface of aerosil are simulated by clusters with up to 150 atoms. The active centre is selected. It is shown that water molecules join willingly to a silicon atom forming a group of four coordinated molecules. Additionally these molecules attract other ones forming a “subcluster” (up to 8–10 molecules) bound to one centre. Optimized structure, electron density distribution, binding energy and force field constants are calculated. Basing on these data weighted densities of vibrational states are obtained. The results are in good agreement with experimental inelastic neutron scattering spectra recorded at 10, 80 and 290 K at Dubna for aerosil A380OHH2O and A380ODD2O (A380 means aerosil with a specific area of 380 (m2 g−1)