1. Photochemistry of SiCH 2 O Isomers on the Triplet Hypersurface Samuel A. Abrash, Tran T. Doan, Pradeep Kushwaha, Diomedes Saldaña-Greco Department of Chemistry, University of Richmond

2. 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 SiH 2, SiH 4, SiN 2, SiCo, and isomers of SiC 2 H 2 and SiHCN.

3. 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 SiCH 2 O experiments on the triplet hypersurface to try to observe new products and to look for changes in yield for species formed in triplet mechanisms

4. Relative Energies of SiCH 2 O Singlet and Triplet Isomers From: Gunter Maier, Hans Peter Reisenauer and Heiko Egenolf, Organometallics 1999, 18, 2155-2161

5. 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

6. 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

7. 26.4 °C 23.7 °C 21.5 °C Formaldehyde deposition in Ar matrix – Lowest T yields monomers only

8. 42.00 W 58.31 W 76.32 W 92.73 W Silicon and Formaldehyde Codeposition in Ar Matrix Constant condition of Formaldehyde Deposition: 27.8 °C 1-Silaketene

9. 91.63 W 97.00 W 107.50 W 121.30 W Silicon and Formaldehyde Codeposition in Ar matrix Constant Condition of Formaldehyde deposition: 33.5 °C Siloxiranylidene

10. Annealing of the Ar matrix 25 K 35 K 40 K 45 K

11. 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