 |
| Titel |
Hydrogen isotope fractionation in the photolysis of formaldehyde |
| VerfasserIn |
T. S. Rhee, C. A. M. Brenninkmeijer, T. Röckmann |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 5 ; Nr. 8, no. 5 (2008-03-07), S.1353-1366 |
| Datensatznummer |
250005798
|
| Publikation (Nr.) |
 copernicus.org/acp-8-1353-2008.pdf |
|
|
|
|
|
| Zusammenfassung |
| Experiments investigating the isotopic fractionation in the formation of
H2 by the photolysis of CH2O under tropospheric conditions are
reported and discussed. The deuterium (D) depletion in the H2 produced
is 500(±20)‰ with respect to the parent CH2O. We also observed
that complete photolysis of CH2O under atmospheric conditions produces
H2 that has virtually the same isotope ratio as that of the parent
CH2O. These findings imply that there must be a very strong concomitant
isotopic enrichment in the radical channel (CH2O+hν → CHO+H) as
compared to the molecular channel (CH2O+hν → H2+CO) of the
photolysis of CH2O in order to balance the relatively small isotopic
fractionation in the competing reaction of CH2O with OH. Using a 1-box
photochemistry model we calculated the isotopic fractionation factor for the
radical channel to be 0.22(±0.08), which is equivalent to a 780(±80)‰
enrichment in D of the remaining CH2O. When CH2O is in
photochemical steady state, the isotope ratio of the H2 produced is
determined not only by the isotopic fractionation occurring during the
photolytical production of H2 (αm) but also by overall
fractionation for the removal processes of CH2O (αf), and is
represented by the ratio of αm/αf. Applying the isotopic
fractionation factors relevant to CH2O photolysis obtained in the
present study to the troposphere, the ratio of αm/αf varies from
~0.8 to ~1.2 depending on the fraction of CH2O that reacts
with OH and that produces H2. This range of αm/αf can render
the H2 produced from the photochemical oxidation of CH4 to be
enriched in D (with respect to the original CH4) by the factor of 1.2–1.3 as anticipated in the literature. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|