Vibrational analysis of double-walled silicon carbide nano-cones: a finite element investigation

A three-dimensional finite element model is used to investigate the vibrational properties of double-walled silicon carbide nano-cones with various dimensions. The dependence of the vibrational properties of double-walled silicon carbide nano-cones on their length, apex angles and boundary conditions are evaluated. Current model consists a combination of beam and spring elements that simulates the interatomic interactions of bonding and nonbonding. The Lennard-Jones potential is employed to model the interactions between two non-bonding atoms. The fundamental frequency and mode shape of the double-walled silicon carbide nano-cones are calculated.

Structural, spectroscopic properties ant prospective application of a new nitropyridine amino N-oxide derivative: 2-[(4-nitropyridine-3-yl)amino]ethan-1-ol N-oxide

A new nitropyridine amino N-oxide derivative 2-[(4-nitropyridine-3-yl)amino]ethan-1-ol N-oxide was synthesized and its structural and optical properties were described. Its structure obtained from the X-ray diffraction (XRD) studies was related to the Infrared spectroscopy (IR), Raman spectroscopy (RS), electron Ultraviolet-Visible spectroscopy (UV-VIS) and emission spectra measurements. The experimental results were analyzed in terms of theoretical data obtained from quantum chemical Density Functional Theory (DFT) and Natural Bond Orbital (NBO) calculations. The 6-311G(2d,2p) basis set with the B3LYP functional was used to discuss its optimized structure and vibrational properties. Femtosecond excitation was used to recognize the depopulation mechanism of the electron excited states in the studied compound. It was found that the intermolecular interactions strongly influence the physicochemical properties and application of the new nitropyridine amino N-oxide derivative.

Pressure and temperature effects on the Raman spectra of LLM-105

Currently, only one crystal structure of LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) (P21/n) has been discovered, and there are still debates on its phase transition point and phase diagram. Based on previous work, we performed crystal structure, Raman spectra, and vibrational properties calculations on LLM-105 crystal. Our results indicate that the crystal structure of LLM-105 remains stable until compressed to 49 GPa, beyond which it may undergo two phase transitions at pressure intervals of 49.0-49.1 GPa and 51.4-51.5 GPa, respectively. Analysis of Raman shift results suggests that these two phase transitions may be reversible, with an intermediate phase possibly acting as a transition phase. Additionally, based on the quasi-harmonic approximation, we fitted the experimental data of LLM-105 lattice expansion state, obtaining the volume at zero pressure and using it for Raman spectra calculations. The results demonstrated the accuracy of this quasi-harmonic approximation method in describing the redshift of Raman peaks during the heating process and the excitation ratio of Raman peaks in different wavenumber ranges.

Raman spectra and vibrational properties of FOX-7 under pressure and temperature: First-principles calculations

FOX-7 (1,1-diamino-2,2-dinitroethene) as one of the widely studied insensitive high explosives exists five polymorphs (α, β, γ, α', ε) whose crystal structures have been determined by XRD (X-rays Diffraction) and which are investigated by a density functional theory (DFT) approach in this work. The calculation results show that the GGA PBE-D2 method can reproduce the experimental crystal structure of FOX-7 polymorphs better. The calculated Raman spectra of FOX-7 polymorphs were compared in detail and fully with the experimental Raman spectra data and it was found that the calculated Raman spectra frequencies have an overall red-shift in middle band (800-1700 cm^-1), and that the maximum deviation does not exceed 4 % (The maximum point is the mode of CC in plane bending). The high-temperature phase transform path (α → β → γ) and the high-pressure phase transform path (α → α'→ε) can be well represented in the computational Raman spectra. In addition, crystal structure of ε-FOX-7 was performed up to 70 GPa to probe Raman spectra and vibrational properties. The results showed that the NH₂ Raman shift is jittering with pressure (not smooth compared to other vibrational modes) and NH₂ anti-symmetry-stretching appears red-shifted. The vibration of hydrogen mixes in all of other vibrational modes. This work shows that the dispersion-corrected GGA PBE method can reproduce the experimental structure, vibrational properties and Raman spectra very well.

Temperature effect on vibrational properties of crystalline Dibenz[a,h]anthracene

Vibrational properties associated with the intra- and intermolecular bonding of the crystalline Dibenz[a,h]anthracene at low temperatures are investigated by Raman scattering. A complete characterization of phonon spectra is given for this material. In the 120-150 K temperature region, several lattice modes show abrupt changes of splitting and the discontinuities in the temperature shift, but no emergence of new modes. Moreover, the intensity ratio of I₆₈/₃₈ is greater than 1 below 130 K. Meanwhile, the aromatic C-C stretching modes exhibit anomalous behaviors in frequencies, widths, and intensities at about 130 K. These spectroscopic results demonstrate a disorder-order transition occurred at about 130 K. However, the modes, corresponding to C-H out-of-plane bending, C-H in-plane bending, and/or C-H rocking, have no significant change in the whole temperature range. It indicates that the transition mainly results from the change of the tilt angle between the molecules. Our work is of great significance to understand the internal vibrational properties of Dibenz[a,h]anthracene, and it also provides considerable supports for the further study of this material.

The study of spectroscopy and vibrational assignments of high nitrogen material 1,1'-azobis-1,2,3-triazole

Benefiting from the new strategy of oxidative azo coupling of the N-NH₂ moiety, a series of energetic nitrogen-rich molecules with long catenated nitrogen chains have been successfully synthesized. As one of them, the synthesized 1,1'-azobis-1,2,3-triazole shows excellent thermal stability, great explosive performance, and special photochromic properties, which has caused widespread concern. To further characterize its performance, the structural, electronic, vibrational, mechanical, and thermodynamic properties of 1,1'-azobis-1,2,3-triazole were investigated based on the first-principles density functional theory calculations. The obtained structural parameters are consistent with previous results. We used the band structure, density of states, Mulliken charges, bond populations, and electron density to analyze the electronic properties and chemical bonding. The vibrational frequency regions (396.51-3210.12 cm^-1) were assigned to the corresponding vibrational modes. Furthermore, mechanical properties of 1,1'-azobis-1,2,3-triazole are also calculated. Finally, the thermodynamic properties of 1,1'-azobis-1,2,3-triazole were calculated, including the specific heat at constant volume C_v, temperature*entropy TS, enthalpy H, Gibbs free energy G, and Debye temperature Θ_D.

First-principles calculation of electronic, vibrational, and thermodynamic properties of triaminoguanidinium nitrate

In recent years, the important energetic material triaminoguanidinium nitrate (TAGN) has been widely used, and the process of synthesizing TAGN has become more and more perfect. However, there are relatively few theoretical studies on TAGN. This paper uses first-principles calculations to more systematically study the crystal structure, and electronic, vibrational, and thermodynamic properties of TAGN. The calculation results show that the calculated unit cell parameters are relatively consistent with the values obtained through X-ray diffraction experiments. This article describes in detail the state density of the valence electrons of each atom. By analyzing the vibrational properties of TAGN crystal, the vibration mode corresponding to each optical wave is obtained. At the same time, the vibration mode of each peak in the Raman spectrum and the infrared spectrum is described in detail. Then, the calculated value is compared with the experimental value; it can be seen that the error is relatively small. According to the vibration characteristics, a series of thermodynamic functions such as enthalpy (H), Debye temperature (Θ), free energy (F), and entropy (S) are calculated. These thermodynamic functions can provide a certain reference for future research.

Temperature effect on vibrational properties of crystalline p-quaterphenyl

Vibrational properties of the crystalline p-quaterphenyl at low temperature are investigated by Raman scattering. The temperature dependent vibrational behaviors associated with the intra- and intermolecular terms are analyzed in detail. The order-disorder transition makes significant impacts on the energies, widths, and intensities of the vibrational modes, and the drastic splits of the modes mainly result from the sudden decline of the peak widths. Meanwhile, the intensity ratio of the 1280-cm^-1 and 1220-cm^-1 mode exhibits anomalous tendency around the transition temperature, as well as the frequency separations between them and between the higher energy mode and the lower energy mode around 1600 cm^-1. Thus, they still can well indicate the molecular planarity in the low temperature conditions. However, the intensity ratio of the two modes around 1600 cm^-1 is no longer to be a good indicator of this transition due to the bare anomalous behavior around the transition temperature. Our work is of important significance for understanding the internal vibrational properties of p-quaterphenyl, and it also provides considerable supports for the further study of this material.

Identification of the incommensurate structure transition in biphenyl by Raman scattering

Raman scattering measurements are performed on crystalline biphenyl at low temperatures. The properties of the vibrational modes focused on the intra- and intermolecular terms are analyzed in detail. Nearly all of the vibration modes exhibit hardening and simultaneously sharpen with decreasing temperature, whereas the modes at around 250 cm^-1 and 1280 cm^-1 soften their energies as temperature is decreased. Moreover, all the internal modes have anomalous reversals at around 45 K on the frequencies, widths, and intensities, and below 45 K, several new internal modes appear. Results of the analyses indicate that the reemergence of the interring tilt angle of the molecules at 45 K has a significant impact on the vibrational properties of biphenyl. Our work thus paves interesting and essential groundwork for the further study of biphenyl.

Spectroscopy of the Surface Polaritons in the CdXZn(1-X)P2 Solid Solutions

Here we report on the analysis of the effect of the doping of CdP₂ single crystals by ZnP₂ nanoclusters on the dispersion of the surface polaritons (SP). The ATR spectroscopic technique has been applied to excite the SP in the Cd_XZn_(1-X)P₂ system. Analysis of the obtained spectra has shown that the doping of CdP₂ single crystals by ZnP₂ nanoclusters result in the position and the width of the dispersion branches of the SP. This effect is more pronounced in the low frequency dispersion branches. These SP branches are originated from phonons which correspond to the motion of the cation sublattice.

Accurate spectroscopic calculations of the 21 Λ-S states and 42 Ω states of the SiB radical

The potential energy curves were calculated for the 21 Λ-S states, which were generated from the first two dissociation channels, Si(³P_g)+B(²P_u) and Si(¹D_g)+B(²P_u), of the SiB radical. The potential energy curves were computed for the 42 Ω states, which arose from the 21 Λ-S states. The calculations were done using the CASSCF method, which was followed by the icMRCI approach. Of these 21 Λ-S states, the D⁴Σ^-, i²Σ⁺, j²Π, 5²Π, and 1²Φ states had double wells. The D⁴Σ^-, a²Π, A⁴Π, e²Π, j²Π, 5²Π, h²Δ, and 1²Φ states were inverted with the spin-orbit coupling effect taken into account. The 3²Δ state and the second wells of D⁴Σ^- and 1²Φ states were weakly bound. Core-valence correlation correction, scalar relativistic correction and Davidson correction were included. The spectroscopic parameters were determined and the vibrational properties of some weakly-bound states were predicted. The spin-orbit coupling effect on the spectroscopic parameters was evaluated. Comparison with available experimental data shows that the methodology used is highly accurate for the SiB radical.

Optical and Vibrational Spectra of CsCl-Enriched GeS2-Ga2S3 Glasses

Optical and FTIR spectroscopy was employed to study the properties of 80GeS2-20Ga2S3-CsCl chalcohalide glasses with CsCl additives in a temperature range of 77-293 K. It is shown that CsCl content results in the shift of fundamental absorption edge in the visible region. Vibrational bands in FTIR spectra of (80GeS2-20Ga2S3)100 - х (СsCl) x (x = 5, 10, and 15) are identified near 2500 cm(-1), 3700 cm(-1),, around 1580 cm(-1), and a feature at 1100 cm(-1). Low energy shifts of vibrational frequencies in glasses with a higher amount of CsCl can be caused by possible thermal expansion of the lattice and nanovoid agglomeration formed by CsCl additives in the inner structure of the Ge-Ga-S glass.

The Role of ZnP2 Nanoclusters in the Vibrational Properties of Cd x Zn(1 - x)P2 Solid Solutions

This study reports an analysis of the IR reflectance and Raman spectra of Cd x Zn(1 - x)P2 solid solutions. We have analyzed the effect of the doping of the CdP2 single crystal by the ZnP2 nanoclusters on the vibrational properties of studied samples: ε 0, ε inf, phonon frequencies, and strengths. These dependencies might be used as an alternative non-destructive way for the control of the Cd x Zn(1 - x)P2 composition. The obtained results show that variation of the concentration of ZnP2 nanoclusters opens a space to design the tailored material properties for the industrial applications.