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 ...