Scientists have reported the direct measurement of reactions of a gas-phase Criegee intermediate – carbonyl oxides – with the help of photoionization mass spectrometry.
This research has been done by researchers from Sandia’s Combustion Research Facility, the University of Manchester and Bristol University, and published online in January 13 issue of the journal Science.
In the year 1950, Rudolph Criegee proposed that ozonolysis of alkenes take place through carbonyl oxide biradicals, which are now called as Criegee intermediates. Criegee intermediates are used in autoignition chemistry and are very important atmospheric reactants but up till now we had only indirect knowledge of their reaction kinetics.
Through this research, scientists have made direct measurement for the first time by using formaldehyde oxide (CH2OO) i.e. one of the Criegee species. The measurements were made to determine rate co-efficients with the key species such as sulfur dioxide (SO2) and nitrogen dioxide (NO2) and give new insight into the reactivity of these transient molecules.
Researchers have used a special apparatus made by Sandia researchers to detect and measure Criegee intermediate reactions. That unique apparatus uses light from a third-generation synchrotron user facility, Lawrence Berkeley National Laboratory’s Advanced Light Source, to research on chemical reactions critical in hydrocarbon oxidation. This allowed the researchers to detect different isomeric species and in this case they were able to differentiate CH2OO from HCOOH because of different thresholds to photoionization.
The Manchester and Bristol researchers have also found that this apparatus could also work for elucidation of tropospheric oxidation processes, such as ozonolysis i.e. the cleavage of carbon-carbon double bonds through reaction with ozone.
Scientists “report direct photoionization mass spectrometric detection of formaldehyde oxide (CH2OO) as a product of the reaction of CH2I with O2. This reaction enabled direct laboratory determinations of CH2OO kinetics. Upper limits were extracted for reaction rate coefficients with NO and H2O. The CH2OO reactions with SO2 and NO2 proved unexpectedly rapid and imply a substantially greater role of carbonyl oxides in models of tropospheric sulfate and nitrate chemistry than previously assumed.”
This capability breakthrough was funded by the Office of Basic Energy Sciences (BES) within the Office of Science in the U.S. Department of Energy, and conducted using the Advanced Light Source, a scientific user facility supported by BES.
Oliver Welz, John D. Savee, David L. Osborn, Subith S. Vasu, Carl J. Percival, Dudley E. Shallcross, Craig A. Taatjes, (2012). Direct Kinetic Measurements of Criegee Intermediate (CH2OO) Formed by Reaction of CH2I with O2. Science, DOI: 10.1126/science.1213229