Tutorial Tuesday: Characterizing Polycyclic Aromatic Hydrocarbons Using Infrared Microspectroscopy

There are several spectroscopic techniques that are routinely used to characterize polycyclic aromatic hydrocarbons (PAHs).

In this “Tutorial Tuesday” clip, Pavi Sundararajan, who is a postdoctoral research associate at the National Aeronautics and Space Administration (NASA)’s Ames Research Center, discusses one of these techniques in detail, and that is infrared microspectroscopy.¹ The IR region reveals molecular vibrations, and since each molecule has a unique vibrational "fingerprint," this spectral region is called the fingerprint region. Because many ground- and space-based telescopes also operate in the infrared, spectra measured in the laboratory can be directly compared to astronomical observations, making infrared microspectroscopy useful for connecting laboratory measurements to space-based data.

Pavi Sundararajan: The first characterization technique is the infrared microspectroscopy. So, the infrared region is where we observe the vibrational characteristic of molecules. Each molecule has a unique vibrational fingerprint, and hence, it is called the fingerprint region. So, the infrared spectra generated in the laboratory can directly be compared with the astronomical observations, as many ground-based and space-based telescopes operate in the infrared region.

Sundarajan recently presented her team’s research at the American Chemical Society (ACS) Fall 2026 Meeting in Chicago, Illinois. Her talk, which was titled, “Infrared Spectroscopy of Carbon Grains Formed from Nitrogen substituted Polycyclic Aromatic Hydrocarbons Precursors Under Astrophysical Conditions: Implications for Space Return Samples,“ discussed the cosmic carbon that underlies prebiotic chemistry, existing in space as both simple diatomic molecules and complex polycyclic aromatic hydrocarbons (PAHs).² Sundarajan’s presentation explored how she and her team synthesized carbon grains from PANH precursors using NASA Ames' COSmIC facility before analyzing them through multiple spectroscopic techniques.² The techniques that were used included infrared (IR) micro-spectroscopy, optical constant measurements (OCF), scanning electron microscopy (SEM), and Raman spectroscopy.²

What is Tutorial Tuesday?

“Tutorial Tuesday” is an ongoing multimedia series that offers bite-sized overviews of key spectroscopic techniques and topics. These clips are designed to encourage viewers to explore the topics presented in the videos.

All “Tutorial Tuesday” clips are produced as shorts, which viewers can access on the main homepage.

References

(1) Wetzel, W. Why Spectroscopists Should Attend the ACS Fall 2026 Conference. Spectroscopy Online, 2026. https://www.spectroscopyonline.com/view/why-spectroscopists-should-attend-the-acs-fall-2026-conference (accessed August 11, 2026).

(2) Sundararajan, P. Infrared Spectroscopy of Carbon Grains Formed from Nitrogen substituted Polycyclic Aromatic Hydrocarbons Precursors Under Astrophysical Conditions: Implications for Space Return Samples. Presented at the American Chemical Society, Chicago, Illinois, August 26, 2026. Available at: https://acs.digitellinc.com/live/37/session/596644