Physical Chemistry Chemical Physics最新文献

Rovibrational spectra of the open-shell linear cations HCN⁺ (X̃²Π) and HNC⁺ (X̃²Σ⁺) are measured with leak-out spectroscopy in cryogenic 22-pole ion traps. The fundamental ν₁ C-H stretching vibration of HCN⁺ is found at 3056.3412(1) cm^-1 and the lower energy Renner-Teller (RT) component (Σ) of the ν₁ + ν₂ combination band is found at 3340.8480(2) cm^-1. The resulting effective RT vibrational frequency of ≈300 cm^-1 inferred from the comparison of these two bands indicates a large Renner-Teller splitting for HCN⁺. For HNC⁺, the ν₁ N-H stretching vibration is found at 3407.9136(4) cm^-1, much higher than expected from previous matrix work. Thanks to the rotational resolution of these infrared measurements, spectroscopic constants for the electronic fine-structure, molecular rotation, centrifugal distortion, Λ-doubling and spin-rotation interaction have been determined for the vibrational ground and excited states with high confidence. The infrared spectrum of HCN⁺ is rather rich and contains more bands including, e.g., the electronic à ← X̃ transition. The analysis of this band and the pure rotational spectrum of HCN⁺ will be the subject of further publications.

Two-dimensional multiferroic materials, which exhibit both ferroelectricity and ferromagnetism, have drawn significant interest due to their capability to control electronic and magnetic properties via polarization switching. In this work, we designed a multiferroic van der Waals heterostructure (vdWH) made of 2D ferromagnetic Cr₂Cl₃S₃ and ferroelectric Ga₂O₃, and examined its structural, electronic, and magnetic properties through first-principles calculations. The results demonstrate that by manipulating the polarization state of Ga₂O₃, the Cr₂Cl₃S₃(Cl)/Ga₂O₃ vdWH can reversibly switch between semiconductor and half-metal, whereas the Cr₂Cl₃S₃(S)/Ga₂O₃ vdWH can transition reversibly between semiconductor and metal. These reversible transitions are attributed to the shift in band alignment induced by interlayer charge transfer. Notably, as the spintronic properties of the Cr₂Cl₃S₃(S)/Ga₂O₃ vdWH change, its easy magnetization axis also switches from in-plane to out-of-plane. The switchable electrical control of heterostructures by ferroelectric Ga₂O₃ is nonvolatile. These findings are important for understanding ferroelectric control of spintronics and electromagnetic coupling and provide a potential route for developing multiferroic memory devices.

NaNiO₂ is a layered material composed of alternating NaO₆ and NiO₆ octahedra, which undergoes an insulator-metal transition (IMT) from a monoclinic insulating phase to a metallic phase at approximately 480 K. Although this phase transition has been experimentally observed, its microscopic mechanism remains unclear, particularly regarding the role of Jahn-Teller (JT) distortion and the nature of the structural dynamics during the transition. In this work, we carry out a comprehensive first-principles study to address these issues. Our results show that the IMT is primarily driven by the gradual disappearance of the JT distortion of Ni³⁺, which restores the e_g orbital degeneracy and enables electronic delocalization. Furthermore, potential energy surface analysis and phonon spectrum calculations reveal that this process follows a displacive phase transition pathway, consistent with experimental observations. These findings provide, for the first time, a theoretical explanation of the microscopic mechanism underlying the IMT in NaNiO₂, thereby clarifying its structural-electronic interplay and offering new insights into the phase transition behavior of transition-metal oxides for future material applications.