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Photochemistry of SiCH 2 O Isomers on the Triplet Hypersurface Samuel A. Abrash, Tran T. Doan,...
Transcript of Photochemistry of SiCH 2 O Isomers on the Triplet Hypersurface Samuel A. Abrash, Tran T. Doan,...
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Photochemistry of SiCH2O Isomers on the Triplet
HypersurfaceSamuel A. Abrash, Tran T. Doan, Pradeep
Kushwaha, Diomedes Saldaña-GrecoDepartment of Chemistry, University of
Richmond
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Introduction I
• In 1997, G. Maier, H.P. Reisenauer and co-workers published the first in a series of elegant papers in which they reported the IR spectra of a number of highly reactive small organic silicon compounds. In time they reported photochemistry and spectra for a large number of species, including SiH2, SiH4, SiN2, SiCo, and isomers of SiC2H2 and SiHCN.
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Introduction II
• This led us to wonder if any work had been done on triplet photochemistry of organosilicon compounds. A literature search showed this was an unexplored area
• We decided to repeat Maier’s SiCH2O experiments on the triplet hypersurface to try to observe new products and to look for changes in yield for species formed in triplet mechanisms
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Relative Energies of SiCH2O Singlet and Triplet Isomers
From: Gunter Maier, Hans Peter Reisenauer and Heiko Egenolf, Organometallics 1999, 18, 2155-2161
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Experimental Approach
• Si Atom Source: Resistive Oven Designed by Maier/Reisenauer Group
• Formaldehyde Source – Flow Pyrolysis of Paraformaldehyde
• Strategy to Reach Triplet Hypersurface: External Heavy Atom Effect – a) Matrix Isolation in Solid Xe; b) Matrix Isolation in Ar doped with 5-20% Xe
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These Spectra Demonstrate Successful Deposition of Si
Silicon Deposition 46.76 W
Silicon Deposition 75.68 W
Silicon Deposition 64.4 W
Silicon Deposition 49.26 W
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Abs
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Wavenumbers (cm-1)
26.4 °C
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Formaldehyde deposition in Ar matrix – Lowest T yields monomers only
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42.00 W
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Silicon and Formaldehyde Codeposition in Ar MatrixConstant condition of Formaldehyde Deposition: 27.8 °C
1-Silaketene
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91.63 W
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Silicon and Formaldehyde Codeposition in Ar matrixConstant Condition of Formaldehyde deposition: 33.5 °C
Siloxiranylidene
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Annealing of the Ar matrix
25 K
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Conclusions
• We have successfully deposited Si atoms at a range of compositions
• We have successfully deposited formaldehyde under a range of conditions from isolated formaldehyde to clusters
• We have not yet discovered the conditions for co-deposition that lead to significant reaction between formaldehyde and Si atoms