Browsing by Author "Morrow, B. A."

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    Infra-red Studies of Reactions on Oxide Surfaces: Part 1.— Boron Trifluoride on Silica
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (3), 1972) Morrow, B. A.; Devi, A.
    Infra-red spectroscopy has been used to study the adsorption of boron trifluoride on silica. On highly dehydroxylatcd samples chemisorption is rapid and the major product initially appears to be a surface SiOBF2 species. This species is also formed when BF3 interacts wtih totally dehydroxylatcd silicas which have been prepared by heating silica in vacuum at about 1250cC. Spectroscopic evidence indicates that on highly or totally dehydroxylatcd silica, BF3 preferably reacts with a new reactive site, probably a siloxane bridge site, which is formed as a result of the removal of the surface silanol groups during heating. Only after the reaction is complete on the “ siloxane ” sites docs chemisorption take place with silanol groups if these are present. During prolonged evacuation the surface SiOBF2 groups react further with trace amounts of water to produce (SiO)2BF groups; the latter arc also produced during the initial stages of chemisorption when the silanol concentration is high. When water or air is admitted after chemisorption of BF3, a spectrum characteristic of boric acid is observed.
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    Infra-red Studies of Reactions on Oxide Surfaces: Part 2.—Methanol on Silica
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (08), 1974) Morrow, B. A.
    Infra-red spectroscopy has been used to investigate the structure of the chemisorbed species which are formed when CH3OH, CH2DOH, CHD-OH and CD3OH react with silica. Force constant calculations utilizing only the CH and CD stretching modes have been used to show that the strongest spectral features can be assigned to an unsymmetrical surface SiOMe group which has one strong and two weak CH bonds. Some additional spectral features which reversibly grew in intensity with increasing sample temperatures have been assigned to a symmetrical SiOMe species which exists in equilibrium with unsymmetrical SiOMe. It has been suggested that the infra-red bands of sym metrical SiOMe are probably hot bands arising from transitions from the first vibrationally excited state of the SiOC bending mode such that rapid flipping of the SiOC bond can occur in this excited state.