Investigation of the broadening effect of ammonia on the S-branch Raman linewidth of nitrogen with time-domain rotational coherent anti-Stokes Raman scattering.

Authors

Mark Kuria, Jonas I Hölzer, Henry Misoi, Nancy Karuri, Thomas Seeger

Published in

Applied optics. Volume 65. Issue 23. Pages 7922-7930. Aug 10, 2026.

Abstract

Ammonia (NH₃) emerges as a promising carbon-free, sustainable fuel, but its integration into technical combustion processes requires accurate, spatially, and temporally resolved diagnostics, obtained through non-invasive techniques like rotational coherent anti-Stokes Raman scattering (RCARS). However, the lack of spectroscopic data for ammonia-containing gas mixtures hinders its integration into advanced RCARS spectral models for data evaluation. In this study, we experimentally investigated the broadening effect of NH₃ on the N₂ S-branch Raman linewidths using the picosecond time-resolved RCARS technique. Experiments were conducted on N₂-NH₃ binary mixtures containing up to 50% NH₃, at atmospheric pressure and temperatures up to 870 K close to the ammonia-air autoignition temperature. The peak intensities of the rotational spectrum of NH₃ are weak compared with the N₂ peak intensity and its rotational coherences decay more rapidly than those of N₂, limiting the direct application of NH₃-based RCARS diagnostics in the presence of intense scatterers and complicating its linewidths determination. Nevertheless, NH₃ was found to induce significant broadening of the N₂ Raman lines, which must be quantified to avoid diagnostic errors in RCARS. The magnitude of the S-branch Raman linewidth, obtained from the coherence decay time constant, increases linearly with NH₃ concentration, indicating a more efficient collisional energy transfer in N₂-NH₃ compared to N₂-N₂ collisions. This behavior enables direct determination of N₂-NH₃ broadening coefficients, providing key spectroscopic parameters for RCARS spectral modeling. We further demonstrate that the inclusion of the newly determined linewidth data for nitrogen thermometry prevents temperature errors from inaccurate linewidth approximations. Thus, the obtained N₂-NH₃ broadening coefficients provide the spectroscopic basis for extending RCARS thermometry and species diagnostics to ammonia-fueled combustion and reactive flow environments.

PMID:
42593464
Bibliographic data and abstract were imported from PubMed on 13 Aug 2026.

Read full publication at:
Please sign in to see all details.

Stats

1-terrible, 9-excellent. How would you rate this publication? Sign in in to submit your rating.

Post a comment

You need to be signed in to post comments. You can sign in here.

Comments

There are no comments yet.