Photochemistry of SiCH2O Isomers on the Triplet

HypersurfaceSamuel A. Abrash, Tran T. Doan, Pradeep

Kushwaha, Diomedes Saldaña-GrecoDepartment of Chemistry, University of

Richmond

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.

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

Relative Energies of SiCH2O Singlet and Triplet Isomers

From: Gunter Maier, Hans Peter Reisenauer and Heiko Egenolf, Organometallics 1999, 18, 2155-2161

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

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

-0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

Abs

orba

nce

1000 1500 2000 2500 3000

Wavenumbers (cm-1)

26.4 °C

23.7 °C

21.5 °C

Formaldehyde deposition in Ar matrix – Lowest T yields monomers only

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

-0.00

0.05

Abs

orba

nce

1000 1500 2000 2500 3000

Wavenumbers (cm-1)

42.00 W

58.31 W

76.32 W

92.73 W

Silicon and Formaldehyde Codeposition in Ar MatrixConstant condition of Formaldehyde Deposition: 27.8 °C

1-Silaketene

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

-0.00

0.05

0.10

Abs

orba

nce

1000 1500 2000 2500 3000

Wavenumbers (cm-1)

91.63 W

97.00 W

107.50 W

121.30 W

Silicon and Formaldehyde Codeposition in Ar matrixConstant Condition of Formaldehyde deposition: 33.5 °C

Siloxiranylidene

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

Abs

orba

nce

1000 1500 2000 2500 3000

Wavenumbers (cm-1)

Annealing of the Ar matrix

25 K

35 K

40 K

45 K

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