Thermal dehydrogenation of polysilane

The isochronal thermal decomposition of polysilane, -(SiH₂)_n− has been investigated at temperatures up to 335°C by in situ infrared spectroscopy. The studies were performed, in vacuo, on compressed discs of polysilane in a KBr matrix. Dehydrogenation was measured by the reduction of the infrared stretching ω_s(2100 cm⁻¹), bending ω_b(910 cm⁻¹), wagging ω_w(865 cm⁻¹) and rocking ω_r(650 cm⁻¹) integrated band intensities. The wavenumbers of the infrared-active modes of -(SiH₂)_n− given in parenthesis correspond to room temperature samples. Loss of hydrogen occurs at relatively low temperatures, ca. 140−200°C, and is essentially complete at 335°C. The integrated intensities of each band show an equal decrease with time. However, the peak position of the essentially degenerate symmetric and asymmetric stretching mode shifted systematically to lower wavenumbers in the region 2100 cm⁻¹−2080 cm⁻¹ on dehydrogenation. No shift was effected in the doublet of peaks in the range 800−950 cm⁻¹ under the same conditions. The width (f.w.h.m.) of the 650 cm⁻¹ band decreased with a reduction in the hydrogen content. This band exhibited a slight red shift of 10 cm⁻¹ on dehydrogenation. Preliminary studies of the oxidized polysilane films demonstrated that rearrangement of [SiH₂O] groupings to [SiH₂O₂] groupings takes place at elevated temperatures.