UV absorption spectrum of the C2 Criegee intermediate CH3CHOO

The UV spectrum of CH3CHOO was measured by transient absorption in a flow cell at 295 K. The absolute absorption cross sections of CH3CHOO were measured by laser depletion in a molecular beam to be (1.06 +/- 0.09) x 10(-17) cm(2) molecule-1 at 308 nm and (9.7 +/- 0.6) x 10(-18) cm(2) molecule-1 at 352 nm. After scaling the UV spectrum of CH3CHOO to the absolute cross section at 308 nm, the peak UV cross section is (1.27 +/- 0.11) x 10(-)1(7) cm(2) molecule-1 at 328 nm. Compared to the simplest Criegee intermediate CH2OO, the UV absorption band of CH3CHOO is similar in intensity but blue shifted by 14 nm, resulting in a 20% slower photolysis rate estimated for CH3CHOO in the atmosphere. (C) 2014 AIP Publishing LLC.