The CH3CO quantum yield in the 248 nm photolysis of acetone, methyl ethyl ketone, and biacetyl

We report measurements of the CH3CO quantum yield, ΦCH3COΦCH3CO, following the 248 nm pulsed laser photolysis of acetone (CH3C(O)CH3), methyl ethyl ketone (CH3C(O)CH2CH3), and biacetyl (CH3C(O)C(O)CH3). CH3CO quantum yields at 248 nm were measured at 296 K, relative to CH3CO reference systems. CH3CO was detected using cavity ring-down spectroscopy at wavelengths between 490 and 660 nm. Measurements were performed between 60 and 670 Torr (He, N2 bath gases) and the obtained CH3CO quantum yields in the low-pressure limit, ΦCH3CO0, were 0.535 ± 0.09, 0.41 ± 0.08, and 0.76 ± 0.11, for acetone, methyl ethyl ketone, and biacetyl, respectively. The quoted uncertainties are 2σ   (95% confidence level) and include estimated systematic errors. An increase in ΦCH3COΦCH3CO with increasing bath gas pressure, which depended on the identity of the collision partner (He, N2), was observed. The present results are compared with previous quantum yield determinations.