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1. Correlated libration in liquid water

   https://doi.org/10.1063/5.0200094  

   Shelton, David P. (March 2024, The Journal of Chemical Physics)

   The libration spectrum of liquid H2O is resolved into an octupolar twisting libration band at 485 cm−1 and dipolar rocking–wagging libration bands at 707 and 743 cm−1 using polarization analysis of the hyper-Raman scattering (HRS) spectrum. Dipole interactions and orientation correlation over distances less than 2 nm account for the 36 cm−1 splitting of the longitudinal and transverse polarized bands of the dipolar rocking–wagging libration mode, while the intensity difference observed for the bands is the result of libration correlation over distances larger than 200 nm. The coupled rock and wag libration in water is similar to libration modes in ice. The libration relaxation time determined from the width of the spectrum is 36–54 fs. Polarization analysis of the HRS spectrum also shows long range correlation for molecular orientation and hindered translation, bending and stretching vibrations in water. 

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2. Long range correlation of molecular orientation and vibration in liquid CDCl3

   https://doi.org/10.1063/5.0107226  

   Shelton, David_P (October 2022, AIP Advances)

   The polarization dependence of hyper-Rayleigh second harmonic light scattering (SHS) and hyper-Raman light scattering (HRS) measured for liquid CDCl3 show the effect of long-range correlation of molecular orientation and vibration. HRS from the ν1, ν4, and ν5 vibration modes is polarized transverse to the scattering wavevector, whereas HRS from the ν2, ν3, and ν6 vibration modes and SHS from the ν0 orientation mode all show longitudinal polarization. The transverse polarized HRS is accounted for by long range vibration correlation due to dipole–dipole interaction for molecules at 20–400 nm separation. Longitudinal SHS and HRS are due to the combined effect of long range dipole–dipole orientation correlation and the increment in the molecular first hyperpolarizability induced by short range intermolecular interactions. 

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3. Super diffusive length dependent thermal conductivity in one-dimensional materials with structural defects: Longitudinal to transverse phonon scattering leads to κ ∝ L 1/3 law

   https://doi.org/10.1063/5.0267503  

   Burin, Alexander L (April 2025, The Journal of Chemical Physics)

   Structural defects in one-dimensional heat conductors couple longitudinal (stretching) and transverse (bending) vibrations. This coupling results in the scattering of longitudinal phonons to transverse phonons and backward. We show that the decay rate of longitudinal phonons due to this scattering scales with their frequencies as ω3/2 within the long wavelength limit (ω → 0), which is a more efficient scattering compared to the traditionally considered Rayleigh scattering within the longitudinal band (ω2). This scattering results in temperature-independent thermal conductivity, depending on the size as κ ∝ L1/3 for sufficiently long materials. This predicted length dependence is observed in nanowires, although the temperature dependence seen there is possibly because of deviations from pure one-dimensional behavior. The significant effect of interaction of longitudinal phonons with transverse phonons is consistent with the earlier observations of a substantial suppression of thermal energy transport by kinks, obviously leading to such interaction, although anharmonic interaction can also be significant. 

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4. Characterization of the intermolecular vibrational levels bound within the Ar + I2(E, v) potential energy surfaces

   https://doi.org/10.1016/j.cplett.2023.140642  

   Makarem, Camille; Loomis, Richard A. (September 2023, Chemical Physics Letters)

   Two-color, two-photon laser-induced fluorescence experiments were performed to probe the intermolecular interactions within the Ar + I2(E, vE = 0–3) potential energy surfaces. Spectra were recorded using the lowest-energy T-shaped level and an excited intermolecular vibrational level with bending excitation within the Ar + I2(B, vB = 23) potential as intermediate levels to guide the spectral assignments. Progressions of intermolecular stretching and bending levels bound within the Ar + I2(E, vE) potentials were identified, and their vibrational frequencies were determined. The harmonic frequency and anharmonic constant for the bending vibrational mode were determined to be ωe(b) ∼ 34.8 cm−1 and ωeχe(b) ∼ 0.3 cm−1. The frequency and anharmonic constant for the stretching mode were found to be the same as reported previously [V.V. Baturo, et al. Chem. Phys. Lett. 647 (2016) 161], ωe(s) = 37.2(1.1) cm−1 and ωeχe(s) = 1.8(2) cm−1. 

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5. How periodic surfaces bend

   https://doi.org/10.1098/rsta.2024.0016  

   Nassar, Hussein (October 2024, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   A periodic surface is one that is invariant by a two-dimensional lattice of translations. Deformation modes that stretch the lattice without stretching the surface are effective membrane modes. Deformation modes that bend the lattice without stretching the surface are effective bending modes. For periodic piecewise smooth simply connected surfaces, it is shown that the effective membrane modes are, in a sense, orthogonal to effective bending modes. This means that if a surface gains a membrane mode, it loses a bending mode, and conversely, in such a way that the total number of modes, membrane and bending combined, can never exceed 3. Various examples, inspired from curved-crease origami tessellations, illustrate the results. This article is part of the theme issue ‘Origami/Kirigami-inspired structures: from fundamentals to applications’. 

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