Validation of a structural candidate for 𝛾-N2 by synchrotron far-infrared spectroscopy
Year: 2025
Authors: Dalladay-Simpson P., Capitani F., Gorelli F.A.
Autors Affiliation: Ctr High Pressure Sci Technol Adv Res, 1690 Cailun Rd, Shanghai 201203, Peoples R China; Synchrotron SOLEIL, Dept 128, F-91192 St Aubin, France; Consiglio Nazl Ric CNR INO, Inst Nazl Ott, I-50019 Sesto Fiorentino, Italy; Shanghai Adv Res Phys Sci SHARPS, Shanghai, Peoples R China.
Abstract: 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 -N2, a crystalline molecular configuration that is only accessible via a low-temperature compression, employing synchrotron radiation. Our results reveal that gamma -N2 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 higherfrequency peak, all of which could be tracked up to 93 GPa. Critically, no absorption associated with an internal vibrational mode of the N2 molecule was detected up to the highest pressures. Density functional theory (DFT) simulations conducted at 40 GPa demonstrate that these observations align with the P21/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/) N2-phase is in fact the long-established gamma -N2 phase.
Journal/Review: PHYSICAL REVIEW B
Volume: 112 (1) Pages from: 14102-1 to: 14102-7
More Information: The authors acknowledge SOLEIL synchrotron and the SMIS beamline for their support during the experiments conducted under Proposal No. 20240376.KeyWords: Nitrogen; Raman; Phase; TemperatureDOI: 10.1103/q4v6-v7y7
