Photochemistry of trimethyl arsine at 193 nm

Abstract

The photodecomposition of trimethyl arsine results in fragments/products that exhibit numerous UV overlapping absorptions. Nevertheless, quantum yields of CH3, intramolecular C2H6, As(CH3) and As(CH3)2 production can be obtained as 1.25, 0, 0.25 and 0.75, respectively, employing both quantitative spectroscopic detection of CH3 at 216.4 nm and GC-mass spectral analysis of isotopically labelled ethane end-products. The isotopic experiments employed photolysis of mixtures of As(CH3)3 and (CD3)2CO, the latter providing the actinometric standard. Two absorptions attributed to As(CH3)2 were monitored by kinetic spectroscopy and a schematic mechanism describing the system is proposed. Some distinguishing features of the mechanism include: (1) the quantum yields appear to be independent of pressure, (2) rates of reaction of CH3 with arsenic-containing fragments are slower than that of CH3 combination, (3) a metastable absorption attributed to As(CH3)2 was observed, the rate constant for its quenching by helium to the ground state was measured.