UV absorption probing of the conformer-dependent reactivity of a Criegee intermediate CH₃CHOO

We measure the UV absorption spectrum of a Criegee intermediate acetaldehyde oxide, CH3CHOO, using time-resolved broadband cavity-enhanced spectrometry. We separate the spectra of the two possible structural isomers, syn- and anti-CH3CHOO, based on their different reactivity towards H2O and SO2. Despite significant overlap, the spectra of the two conformers are sufficiently separated to allow direct conformer-specific probing of the reactions of CH3CHOO with other important tropospheric species.