Measurements of isotope effects in the photoionization of N2 and implications for Titan's atmosphere

PDF Version Also Available for Download.

Description

Isotope effects in the non-dissociative photoionization of molecular nitrogen (N2 + h nu -> N2+ + e-) may play a role in determining the relative abundances of isotopic species containing nitrogen in interstellar clouds and planetary atmospheres but have not been previously measured. Measurements of the photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV (65.6-80.0 nm) using the Advanced Light Source at Lawrence Berkeley National Laboratory show large differences in peak energies and intensities, with the ratio of the energy-dependent photoionization cross-sections, sigma(14N2)/sigma(15N14N), ranging from 0.4 to 3.5. Convolving the cross-sections with the solar flux ... continued below

Creation Information

Croteau, Philip; Randazzo, John B.; Kostko, Oleg; Ahmed, Musahid; Liang, Mao-Chang; Yung, Yuk L. et al. December 30, 2010.

Context

This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided by UNT Libraries Government Documents Department to Digital Library, a digital repository hosted by the UNT Libraries. More information about this article can be viewed below.

Who

People and organizations associated with either the creation of this article or its content.

Publisher

Provided By

UNT Libraries Government Documents Department

Serving as both a federal and a state depository library, the UNT Libraries Government Documents Department maintains millions of items in a variety of formats. The department is a member of the FDLP Content Partnerships Program and an Affiliated Archive of the National Archives.

Contact Us

What

Descriptive information to help identify this article. Follow the links below to find similar items on the Digital Library.

Description

Isotope effects in the non-dissociative photoionization of molecular nitrogen (N2 + h nu -> N2+ + e-) may play a role in determining the relative abundances of isotopic species containing nitrogen in interstellar clouds and planetary atmospheres but have not been previously measured. Measurements of the photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV (65.6-80.0 nm) using the Advanced Light Source at Lawrence Berkeley National Laboratory show large differences in peak energies and intensities, with the ratio of the energy-dependent photoionization cross-sections, sigma(14N2)/sigma(15N14N), ranging from 0.4 to 3.5. Convolving the cross-sections with the solar flux and integrating over the energies measured, the ratios of photoionization rate coefficients are J(15N14N)/J(14N2)=1.00+-0.02 and J(15N2)/J(14N2)=1.00+-0.02, suggesting that isotopic fractionation between N2 and N2+ should be small under such conditions. In contrast, in a one-dimensional model of Titan's atmosphere, isotopic self-shielding of 14N2 leads to values of J(15N14N)/J(14N2) as large as ~;;1.17, larger than under optically thin conditions but still much smaller than values as high as ~;;29 predicted for N2 photodissociation. Since modeled photodissociation isotope effects overpredict the HC15N/HC14N ratio in Titan's atmosphere, and since both N atoms and N2+ ions may ultimately lead to the formation of HCN, estimates of the potential of including N2 photoionization to contribute to a more quantitative explanation of 15N/14N for HCN in Titan's atmosphere are explored.

Source

  • Journal Name: Astrophysical Journal Letters

Language

Item Type

Identifier

Unique identifying numbers for this article in the Digital Library or other systems.

  • Report No.: LBNL-4202E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 1004410
  • Archival Resource Key: ark:/67531/metadc829751

Collections

This article is part of the following collection of related materials.

Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

What responsibilities do I have when using this article?

When

Dates and time periods associated with this article.

Creation Date

  • December 30, 2010

Added to The UNT Digital Library

  • May 19, 2016, 3:16 p.m.

Description Last Updated

  • July 26, 2016, 5:52 p.m.

Usage Statistics

When was this article last used?

Yesterday: 0
Past 30 days: 0
Total Uses: 9

Interact With This Article

Here are some suggestions for what to do next.

Start Reading

PDF Version Also Available for Download.

International Image Interoperability Framework

IIF Logo

We support the IIIF Presentation API

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. (digital.library.unt.edu/ark:/67531/metadc829751/: accessed July 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.