Photolysis of tetramethylstannane vapour at 185 nm

Abstract

The study was made in a static mercury-free, system using a low-pressure mercury arc. At 25°C the major gaseous product is ethane; some methane is formed with traces of other hydrocarbons. Solid polymer and metallic tin deposit on the cell window. The decomposition increases with temperature and at 150°C several other tin alkyls were found in the products. The quantum yields at 25°C are C₂H₆, 1.75 and CH₄, 0.05. They are reduced by addition of nitrogen or carbon dioxide. Nitric oxide reduces the ethane yield to nearly zero but does not affect the methane yield.

The major primary reaction is Sn(CH₃)₄+hν(λ= 185 nm)→ Sn(CH₃)+3CH₃(ϕ= 0.95). The methyl radicals combine to form ethane, tin and polymer or abstract either (a) hydrogen or (b) another methyl radical from the alkyl. The rate constants are log₁₀(k_a/l.mol^–1s^–1)= 8.07–34.1 kJ/2.3 RT and log ₁₀(k_b/1.mol^–1s^–1)= 4.41–5.5 kJ/2.3 RT. At longer wavelengths (λ∼220. nm) only two methyl radicals are detached in the primary reaction and no metallic tin is formed. The effect of added gases is to deactivate by collision one of the two excited state precursors of the breakdown.