Investigation of the polyhedral structure of Ga0.5In1.5Se3 by analytical methods

The crystal structure and atomic dynamics (vibrational properties) of the [Formula: see text] compound are studied at room temperature and under normal conditions. The monoclinic symmetry crystal structure of the P61 space group is explained by the polyhedral structure. The studies were carried out by the method of Raman spectroscopy. In the spectrum obtained in the frequency range [Formula: see text]–800 cm[Formula: see text], four main vibrational modes were observed: [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] cm[Formula: see text]. The analysis showed that these modes correspond to the vibration of different polyhedra. Modes [Formula: see text] and [Formula: see text] cm[Formula: see text] correspond to vibrations of bipyramids, and modes [Formula: see text] and [Formula: see text] cm[Formula: see text] correspond to vibrations of tetrahedra.

Transmission Infrared Microscopy and Machine Learning Applied to the Forensic Examination of Original Automotive Paint

Alternate least squares (ALS) reconstructions of the infrared (IR) spectra of the individual layers from original automotive paint were analyzed using machine learning methods to improve both the accuracy and speed of a forensic automotive paint examination. Twenty-six original equipment manufacturer (OEM) paints from vehicles sold in North America between 2000 and 2006 served as a test bed to validate the ALS procedure developed in a previous study for the spectral reconstruction of each layer from IR line maps of cross-sectioned OEM paint samples. An examination of the IR spectra from an in-house library (collected with a high-pressure transmission diamond cell) and the ALS reconstructed IR spectra of the same paint samples (obtained at ambient pressure using an IR transmission microscope equipped with a BaF2 cell) showed large peak shifts (approximately 10 cm−1) with some vibrational modes in many samples comprising the cohort. These peak shifts are attributed to differences in the residual polarization of the IR beam of the transmission IR microscope and the IR spectrometer used to collect the in-house IR spectral library. To solve the problem of frequency shifts encountered with some vibrational modes, IR spectra from the in-house spectral library and the IR microscope were transformed using a correction algorithm previously developed by our laboratory to simulate ATR spectra collected on an iS-50 FT-IR spectrometer. Applying this correction algorithm to both the ALS reconstructed spectra and in-house IR library spectra, the large peak shifts previously encountered with some vibrational modes were successfully mitigated. Using machine learning methods to identify the manufacturer and the assembly plant of the vehicle from which the OEM paint sample originated, each of the twenty-six cross-sectioned automotive paint samples was correctly classified as to the “make” and model of the vehicle and was also matched to the correct paint sample in the in-house IR spectral library.

Vibrational Modes and Crystallographic Structure of Cd3As2 and (Cd1-xZnx)3As2 Epilayers

Low-temperature Raman scattering is used to study the crystal structure of molecular-beam epitaxially grown layers of the Dirac semimetal Cd3As2 and its related alloy (Cd1-xZnx)3As2. The combination of narrow-linewidth spectra, multiple growth directions and full polarization analysis allows improved accuracy in identifying the irreducible representation of over 57 Raman-active vibrations. Several disagreements with previous identifications are found. Structurally, the results agree with the centrosymmetric I41/acd space group of bulk-grown Cd3As2 and are clearly distinct from the Raman spectra of nanoscale platelets and wires. 3-fold twinning is seen in (112) Cd3As2 grown on (111) zincblende substrates corresponding to the three possible tetragonal orientations. In dilute (Cd1-xZnx)3As2, phonons have a frequency and scattering amplitude dependence on Zn concentration that is continuous with Cd3As2 but at least one frequency is absent at the alloy endpoint, preventing a simple one-mode description of the alloy phonon.

Analysis of vibronic coupling in a 4f molecular magnet with FIRMS

<p><b>Vibronic coupling, the interaction between molecular vibrations and electronic states, is a pervasive effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to probe vibronic transitions in in [Yb(trensal)] (where H₃trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an “envelope effect” in the vibronic coupling Hamiltonian, and we calculate the vibronic coupling fully <i>ab initio</i> to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C₃ symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.</b></p>

Anharmonic Vibrational Frequencies of Water Borane and Associated Molecules

Water borane (BH3OH2) and borinic acid (BH2OH) have been proposed as intermediates along the pathway of hydrogen generation from simple reactants: water and borane. However, the vibrational spectra for neither water borane nor borinic acid has been investigaged experimentally due to the difficulty of isolating them in the gas phase, making accurate quantum chemical predictions for such properties the most viable means of their determination. This work presents theoretical predictions of the full rotational and fundamental vibrational spectra of these two potentially application-rich molecules using quartic force fields at the CCSD(T)-F12b/cc-pCVTZ-F12 level with additional corrections included for the effects of scalar relativity. This computational scheme is further benchmarked against the available gas-phase experimental data for the related borane and HBO molecules. The differences are found to be within 3 cm−1 for the fundamental vibrational frequencies and as close as 15 MHz in the B0 and C0 principal rotational constants. Both BH2OH and BH3OH2 have multiple vibrational modes with intensities greater than 100 km mol−1, namely ν2 and ν4 in BH2OH, and ν1, ν3, ν4, ν9, and ν13 in BH3OH2. Finally, BH3OH2 has a large dipole moment of 4.24 D, which should enable it to be observable by rotational spectroscopy, as well.

Theory of Non-Equilibrium Heat Transport in Anharmonic Multiprobe Systems at High Temperatures

We consider the problem of heat transport by vibrational modes between Langevin thermostats connected by a central device. The latter is anharmonic and can be subject to large temperature difference and thus be out of equilibrium. We develop a classical formalism based on the equation of motion method, the fluctuation–dissipation theorem and the Novikov theorem to describe heat flow in a multi-terminal geometry. We show that it is imperative to include a quartic term in the potential energy to insure stability and to properly describe thermal expansion. The latter also contributes to leading order in the thermal resistance, while the usually adopted cubic term appears in the second order. This formalism paves the way for accurate modeling of thermal transport across interfaces in highly non-equilibrium situations beyond perturbation theory.