UV Photodissociation Spectroscopy of Oxidized Undecylenic Acid Films

Oxidation of thin multilayered films of undecylenic (10-undecenoic) acid by gaseous ozone was investigated
using a combination of spectroscopic and mass spectrometric techniques. The UV absorption spectrum of the
oxidized undecylenic acid film is significantly red-shifted compared to that of the initial film. Photolysis of
the oxidized film in the tropospheric actinic region (λ > 295 nm) readily produces formaldehyde and formic
acid as gas-phase products. Photodissociation action spectra of the oxidized film suggest that organic peroxides
are responsible for the observed photochemical activity. The presence of peroxides is confirmed by mass-spectrometric analysis of the oxidized sample and an iodometric test. Significant polymerization resulting
from secondary reactions of Criegee radicals during ozonolysis of the film is observed. The data strongly
imply the importance of photochemistry in aging of atmospheric organic aerosol particles.