Measurements of isotope effects in the photoionization of N2 and implications for Titan's atmosphere Page: 10 of 15
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
Finally, we note that the very large differences in isotopic fractionation arising from
photoionization versus photodissociation of N2 suggested by the isotope-specific J-values modeled
here for Titan's atmosphere might potentially provide a means of determining the relative
importance of chemical pathways for the production of organic compounds and aerosol (or tholins)
on Titan in future missions. Cassini measurements reveal two distinct mechanisms for organic
synthesis (see recent reviews by Waite et al. (2009) and Cravens et al. (2009)): a new synthesis
process that is largely driven by ion chemistry occurs in the ionosphere of Titan, above 1000 km, in
addition to the neutral chemistry that occurs lower in the atmosphere (Yung et al. 1984). Figure 3
shows that the isotopic fractionations by photoionization and photodissociation of N2 the starting
points of these two synthetic processes are distinct. Hence, measurements of the nitrogen
isotopic composition of organic compounds and tholins, when this becomes feasible, could
potentially offer a means to discriminate between their origins.
In summary, while isotopic fractionation of nitrogen in the atmosphere of Titan due to
neutral chemistry has been modeled by Liang et al. (2007a), a similar study of isotopic fractionation
of nitrogen due to ion chemistry has not been done. The experimental and modeling results
presented here provide a strong motivation to pursue such a modeling study, to measure the near-
threshold photoionization features for 1N2 and "N14N at higher resolution, and to measure isotope
effects in the dissociative photoionization of N2. More generally, these first measurements of
isotope effects in the non-dissociative photoionization of N2 demonstrate that this reaction could in
principle play a previously ignored and potentially important role in isotopic fractionation in
planetary atmospheres and other environments in which N2 and VUV radiation are present.
We gratefully acknowledge support from NASA Planetary Atmospheres grant
NNX08AE69G to UC Berkeley and a Dreyfus Teacher-Scholar Award for KAB; from the Director,
Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division of the
U.S. Department of Energy under contract No. DE-AC02-05CH11231 for OK, MA, and the ALS;
from NSC grant 98-2111-M-001-014-MY3 to Academia Sinica for MCL; and NASA grant
NX09AB72G to the California Institute of Technology for YLY.10
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Croteau, Philip; Randazzo, John B.; Kostko, Oleg; Ahmed, Musahid; Liang, Mao-Chang; Yung, Yuk L. et al. Measurements of isotope effects in the photoionization of N2 and implications for Titan's atmosphere, article, December 30, 2010; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc829751/m1/10/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.