Nitrogen, known for its rich polymorphism and kinetic barriers, has served as a valuable testbed for evaluating advanced computational methods. In this study, we investigate the infrared absorptions of $\gamma \text{−}{\mathrm{N}}_2$, a crystalline molecular configuration that is only accessible via a low-temperature compression, employing synchrotron radiation. Our results reveal that $\gamma \text{−}{\mathrm{N}}_2$ possesses a simple infrared spectrum consisting of only three far-infrared phononic absorptions: a prominent asymmetric peak made up of two unresolved modes, and a weak higher-frequency peak, all of which could be tracked up to 93 GPa. Critically, no absorption associated with an internal vibrational mode of the ${\mathrm{N}}_2$ molecule was detected up to the highest pressures. Density functional theory (DFT) simulations conducted at 40 GPa demonstrate that these observations align with the $P{2}_1/c$ structural model, reinforcing its compatibility as a candidate complimenting existing Raman and x-ray diffraction results. Finally, our findings, in conjunction with measurements made over 50 years ago, further support that the formerly assigned “anomalous”/$\lambda {\mathrm{N}}_2$-phase is in fact the long-established $\gamma \text{−}{\mathrm{N}}_2$ phase.

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• High-pressure studies
• Molecular spectra
• Molecular solids
• Synchrotron radiation facilities
• Infrared spectroscopy
• Liquid nitrogen cooling
• Raman spectroscopy