Temperature Dependence Of Distribution Research Articles

Rapid Characterization of Point Defects in Solid-State Ion Conductors Using Raman Spectroscopy, Machine-Learning Force Fields, and Atomic Raman Tensors.

The successful design of solid-state photo- and electrochemical devices depends on the careful engineering of point defects in solid-state ion conductors. Characterization of point defects is critical to these efforts, but the best-developed techniques are difficult and time-consuming. Raman spectroscopy─with its exceptional speed, flexibility, and accessibility─is a promising alternative. Raman signatures arise from point defects due to local symmetry breaking and structural distortions. Unfortunately, the assignment of these signatures is often hampered by a shortage of reference compounds and corresponding reference spectra. This issue can be circumvented by calculation of defect-induced Raman signatures from first principles, but this is computationally demanding. Here, we introduce an efficient computational procedure for the prediction of point defect Raman signatures in solid-state ion conductors. Our method leverages machine-learning force fields and "atomic Raman tensors", i.e., polarizability fluctuations due to motions of individual atoms. We find that our procedure reduces computational cost by up to 80% compared to existing first-principles frozen-phonon approaches. These efficiency gains enable synergistic computational-experimental investigations, in our case allowing us to precisely interpret the Raman spectra of Sr(Ti0.94Ni0.06)O3-δ, a model oxygen ion conductor. By predicting Raman signatures of specific point defects, we determine the nature of dominant defects and unravel impacts of temperature and quenching on in situ and ex situ Raman spectra. Specifically, our findings reveal the temperature-dependent distribution and association behavior of oxygen vacancies and nickel substitutional defects. Overall, our approach enables rapid Raman-based characterization of point defects to support defect engineering in novel solid-state ion conductors.

Distribution and Characteristics of Ammonia Concentration by Region in Korea

In this study, the characteristics of ammonia and their effects on secondary particulate matter (PM) formation were analyzed by region in Korea in 2020. The NH3 concentration was high in GJ (11.4 ppb), a neighboring agricultural area, followed by DJ (9.0 ppb) and SE (8.6 ppb), which are located in urban areas. On the other hand, BI (2.6 ppb) and JI (4.5 ppb), which are background regions, demonstrated a lower concentration than other areas. Seasonally, ammonia was high in spring and summer, and it generally increased when human activities are active. Therefore, it is believed that the ammonia in the atmosphere not only changes depending on local emissions, but also based on temperature-dependent phase distribution characteristics. For SE and GJ, regions with relatively high ammonia concentrations, investigations into the effect of ammonia on secondary PM formation were conducted. In both regions, the ammonium-to-sulfate mole ratio tended to increase with increasing ammonia or PM2.5 concentration. It can be assumed that the PM2.5 concentration increases as nitrates are formed under the ammonia-sufficient condition. The adjusted gas ratio is generally greater than 4, indicating that there is a lot of free ammonia. Thus, it is estimated that a reduction in ammonia would not be effective to restrain nitrate formation.

Leprous neuropathy.

Leprosy is still an important cause of neuropathy. Late diagnosis is associated with development of severe nerve impairment. early diagnosis and early treatment is essential in order to avoid disability and disease transmission. Recognizing that leprosy is a neurological disease is a fundamental step to the Leprosy zero action proposed by the World Health Organization. leprosy neuropathy manifests as a mononeuropathy or a multiple mononeuropathy with a temperature-dependent distribution. Electromyography, high-resolution sonography serology and PCR help make the diagnosis. Multidrug therapy should be instituted.

Computation of the Spatial Distribution of Charge-Carrier Density in Disordered Media.

The space- and temperature-dependent electron distribution n(r,T) determines optoelectronic properties of disordered semiconductors. It is a challenging task to get access to n(r,T) in random potentials, while avoiding the time-consuming numerical solution of the Schrödinger equation. We present several numerical techniques targeted to fulfill this task. For a degenerate system with Fermi statistics, a numerical approach based on a matrix inversion and one based on a system of linear equations are developed. For a non-degenerate system with Boltzmann statistics, a numerical technique based on a universal low-pass filter and one based on random wave functions are introduced. The high accuracy of the approximate calculations are checked by comparison with the exact quantum-mechanical solutions.

Temperature-induced suppression of structural disproportionation in paramagnetic quantum materials

With the development of electronic structure theory, a new class of materials—quantum ones—has been recognized by the community. Traditionally, it has been believed that the properties of such compounds cannot be described within the framework of modern density functional theory, and indeed, more advanced post-mean-field theory methods are needed. Motivated by this, herein, we develop a fundamental understanding of such complex materials using the example of paramagnetic YNiO3, which is experimentally known to exhibit metal-to-insulator phase transition. We show that this material has a temperature-dependent distribution of local motifs. Thus, while at low temperatures, YNiO3 has distinct structural disproportionation with the formation of large and small octahedra, as the temperature increases, this disproportionation is suppressed. We also explain the paramagnetic monoclinic to paramagnetic orthorhombic phase transition within the double-well to single-well energy profile, predicting the variation in the corresponding energy profile as a function of octahedral size distribution. In this way, we demonstrate a fundamental understanding of structural phase transitions in quantum materials, giving insights into how they can be used for different applications and what minimum level of theory is needed to describe such types of complex materials at finite temperatures.

Revealing the impact of sink strength, injected interstitial and grain growth on the temperature-dependent depth distribution of voids in nanocrystalline Ni

The application of electrodeposited (ED) Ni coating on structural materials of molten salt reactors has emerged as an attractive option for improving the corrosion resistance of the base alloy. However, the radiation response of the Ni coating, especially the void swelling, is an important aspect to be considered for potential in-pile applications. The study investigates depth-dependent void swelling behavior in 20 nm grain-sized ED nanocrystalline (NC) Ni, irradiated with 1.4 MeV Ni+ ion irradiation at 350–550°C to a peak displacement damage of 18.5 dpa. The injected interstitial effect is absent at 350°C; however, it becomes prominent at 450°C and less at 550°C. This is atypical of ion irradiations in coarse-grained Ni, where the effect becomes more pronounced at lower temperatures. The occurrence of voids at all temperatures goes deeper than TRIM predictions; this effect is more significant at 350°C, surpassing any previous findings in coarse-grain systems. Depending on the irradiation temperature, various types of void distributions about grain boundaries are observed: grain boundaries with no void denudations or one-sided and double-sided denudations. Here, we demonstrate that the instability of NC grains due to the combined influence of temperature and irradiation and the high fractions of internal sinks in NC Ni are responsible for void distributions that may be unique to NC systems.

Spring phytoplankton of Lake Onego as a trophic resource for deep-water benthos

In the past few years the relict deep-water crustacean Monoporeia affinis (Lindström, 1855) has become less abundant in Lake Onego, Europe’s second largest lake. Further studies are needed, therefore, to better understand the formation of spring phytoplankton as food for deep-water benthos. The aim of the present project was to study the temperature-dependent vertical distribution of phytoplankton in Petrozavodsk Bay of Lake Onego in the spring season. In May 2019, the total abundance, biomass and species composition of phytoplankton were assessed. The transparency and temperature of Onego water were also measured. The median values of phytoplankton’s total abundance and biomass at various growth stages were 1.15–1.67 M cells/l and 1.96–3.12 mg/l, respectively. The above indices were consistent with the long-term maximum growth of phytoplankton in Petrozavodsk Bay in spring and were not markedly different (p<0.05) from those for spring phytoplankton in 1989-2015, indicating the permanent trophic status of Petrozavodsk Bay in the spring season over the past 30 years. A significant difference (p>0.05) in the vertical distribution of phytoplankton, dominated by Aulacoseira islandica (O. Müll.) Sim diatoms, was found between the stations in May 2019. The reproduction of the relict deep-water crustacean M. affinis, taking place simultaneously with the intensive vegetation and the settling of its major food resource, A. islandica, on the bottom, suggests the formation of favourable feeding conditions for deep-water benthos in Petrozavodsk Bay of Lake Onego.

Theoretical study of the Cu2+-glycine interaction in ammonia and temperature effects

In this study, we have investigated the potential energy of surfaces of the various glycine tautomers, also the interaction between Cu2+ cation with these glycine tautomers in both the gas and solvent phases and for the first time, the glycine-Cu2+(NH3)n=3−6 clusters in the gas-phase. For the studied clusters, we reported their temperature-dependent conformer distributions, along with the binding energies per ammonia molecule and clustering energies. After comparing the binding energies obtained computationally by using the DLPNO-CCSD(T)/CBS level of theory to those obtained from ten DFT functionals (M06, M06HF, M06-2X, M08HX, MN15, MN12SX, ωB97XD, PW6B95D3, TPSSH, APFD), as well as from the ab initio MP2 method, we selected the DFT functional, M08HX, in conjunction with the aug-cc-pVDZ basis set, as our method of choice. Evidence emerged from our study that the solvation medium and the presence of the Cu2+ cation influence the stability of glycine tautomers. The relative stability of Gly-Cu2+(NH3)n clusters in the gas phase is influenced by the coordination of the Cu2+ cation. The study of the relative population in the gas phase of the Gly-Cu2+(NH3)n=3−6 clusters, predicts that for cluster size n=4, the structure of the more compact penta-coordinated Cu2+ ion dominates at low temperatures. Conversely, the conformers for the less compact tetra-coordinated Cu2+ cation are prevalent at high temperatures. For cluster size n=6 with more ammonia molecules per cluster, the conformers containing the compacted is penta-coordinated Cu2+ cation, are predominant at all temperatures. Binding energies computed for ionic interactions of the Gly-Cu2+ complexes, resulted in the following values at room temperature: the binding electronic energy (ΔEn), binding enthalpy (ΔHn) and binding free energy (ΔGn) of ionic interaction are respectively -218.3, -218.4, -211.6 kcal/mol in the gas phase and -93.8, -94.9, -85.2 kcal/mol in the solvent phase. In order to extrapolate this also to the Gly-Cu2+ ammonia clusters, a suitable function of best fit was applied. The computational prediction of binding electronic energy, binding enthalpy and binding free energy, per ammonia molecule in the gas phase, at saturation, produced the values -25.9, -26.1 and -17.0 kcal/mol, respectively. We therefore recommend this function fit for further study of such systems.

Investigation on nano-grinding process of GaN using molecular dynamics simulation: Nano-grinding parameters effect

Nano-grinding is an essential step in ultra-precision machining for brittle material semiconductor workpieces in order to improve the surface quality and preserve strength prior to practical application. This study utilizes molecular dynamics (MD) method to conduct single-crystal gallium nitride (GaN) nano-grinding simulations under varying parameters. The damage mechanism of the surface/subsurface on the nanometer scale is explored through atomic displacement analysis, radial distribution function (RDF), phase transition, dislocation analysis, processing force, temperature distribution, and residual stress distribution. The machined surface quality and crystal structure distribution in the subsurface damage layer (SDL) are also examined, and a strong correlation is found between the parameters in nano-grinding. The nano-grinding speed is closely associated with the post-processing surface morphology, crystal phase transition, and temperature distribution in the GaN workpiece. Additionally, the ambient temperature has a considerable effect on the surface morphology and crystal phase transition. Moreover, the nano-grinding depth has a considerable influence on the surface morphology, phase transition, dislocation, processing force, and the temperature-dependent distribution of the residual stress in the GaN workpiece. This work reveals the relationship between the parameters and the mechanical properties of the machined surface in nano-grinding, and elucidates the damage mechanism of the subsurface, thus providing a helpful guide to the optimization of ultra-precision machining.

Ab Initio Thermochemistry of Highly Flexible Molecules for Thermal Decomposition Analysis.

Pyrolysis is a promising technology for chemical recycling of waste plastics, since it enables the generation of high-value chemicals with low capital and operating cost. The calculation of thermodynamic equilibrium composition using the Gibbs free energy minimization approach can determine pyrolysis operating conditions that produce desired products. However, the availability of thermochemical data can limit the application of equilibrium calculations. While density functional theory (DFT) calculations have been commonly used to produce accurate thermochemical data (e.g., enthalpies of formation) of small molecules, the accuracy and computational cost of these calculations are both challenging to handle for large, flexible molecules, exhibiting multiple conformations at elevated (i.e., pyrolysis) temperatures. In this work, we develop a computational framework to calculate accurate, temperature-dependent thermochemistry of large and flexible molecules by combining force field based conformational search, DFT calculations, thermochemical corrections, and Boltzmann statistics. Our framework produces accurately calculated thermochemistry that is used to predict equilibrium thermal decomposition profiles of octadecane, a model compound of polyethylene. Our thermochemistry results are compared against literature data demonstrating a great agreement, and the predicted decomposition profiles rationalize a series of pyrolysis experimental observations. Our work systematically addresses entropic contributions of large molecules and suggests paths for accurate and yet computationally feasible calculations of Gibbs free energies. The first-principles-based thermodynamic equilibrium analysis proposed in this work can be a significant step toward predicting temperature-dependent product distributions from plastic pyrolysis and guide experimentation on chemical plastic recycling.

Direct Growth of Patterned Vertical Graphene Using Thermal Stress Mismatch between Barrier Layer and Substrate

Vertical graphene (VG) combines the excellent properties of conventional graphene with a unique vertical nanosheet structure, and has shown tremendous promise in the field of electronics and composites. However, its complex surface morphology brings great difficulties to micro-nano fabrication, especially regarding photolithography induced nanosheet collapse and remaining chemical residues. Here, we demonstrate an innovative method for directly growing patterned VG on a SiO2/Si substrate. A patterned Cr film was deposited on the substrate as a barrier layer. The VG was synthesized by PECVD on both the patterned Cr film and the exposed SiO2/Si substrate. During the cooling process, the patterned Cr film covered by VG naturally peeled off from the substrate due to the thermal stress mismatch, while the VG directly grown on the SiO2/Si substrate was remained. The temperature-dependent thermal stress distribution in each layer was analyzed using finite element simulations, and the separation mechanism of the Cr film from the substrate was explained. This method avoids the contamination and damage caused by the VG photolithography process. Our work is expected to provide a convenient and reliable solution for the manufacture of VG-based electronic devices.

Quantum states in disordered media. II. Spatial charge carrier distribution

The space- and temperature-dependent electron distribution $n(\mathbf r,T)$ is essential for the theoretical description of the opto-electronic properties of disordered semiconductors. We present two powerful techniques to access $n(\mathbf r,T)$ without solving the Schr\"odinger equation. First, we derive the density for non-degenerate electrons by applying the Hamiltonian recursively to random wave functions (RWF). Second, we obtain a temperature-dependent effective potential from the application of a universal low-pass filter (ULF) to the random potential acting on the charge carriers in disordered media. Thereby, the full quantum-mechanical problem is reduced to the quasi-classical description of $n(\mathbf r,T)$ in an effective potential. We numerically verify both approaches by comparison with the exact quantum-mechanical solution. Both approaches prove superior to the widely used localization landscape theory (LLT) when we compare our approximate results for the charge carrier density and mobility at elevated temperatures obtained by RWF, ULF, and LLT with those from the exact solution of the Schr\"odinger equation.

Real space study of local bonding for zinc structure based on temperature-dependent x-ray pair distribution function analysis

Zinc metal has a hexagonal close packing hcp structure with an unusual axial ratio c/a. This work presents the local atomic structure analysis of elemental zinc using the x-ray atomic pair distribution function (PDF) method and total synchrotron x-ray scattering in the temperature range of 100–300 K. In this PDF study, we determined the evolution of local bonding in zinc structure in the temperature range of 100–300 K by fitting the first two peaks in the radial distribution function (RDF), R(r), with two Gaussian peaks. Our local structure results reveal a piece of evidence for unusual bond length behavior at low temperatures. The PDF analysis revealed that the a-axis varies linearly from 300 to 160 K and remains constant below 160 K. This local structural result indicates that at temperatures below 160 K, the Zn–Zn bonds are no longer thermally contractible in the ab plane, in agreement with standard crystallographic analysis [J. Nuss et al., Z. Anorg. Allg. Chem. 636, 309 (2010)]. Another significant observation is that the local thermal expansion for the a-axis was found to be three times larger than the one obtained using conventional crystallographic methods [U. Wedig et al., Z. Anorg. Allg. Chem. 639, 2036 (2013)]. This PDF result shows the advantage of total scattering PDF methods in studying the local structural features in elemental zinc, which cannot be captured by the crystallographic model. In addition, this PDF study demonstrates that multiple RDF-peak fitting is a useful approach for interpreting the local structural features of such a non-ideal hcp structure.

Analytical solution for solute transport in a triple liner under non-isothermal conditions

Analytical solutions for the transport of contaminant through a 1D triple-layer composite liner system consisting of a geomembrane (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) under non-isothermal conditions are derived using the generalized integral transform technique. The proposed analytical solutions account for the combined effects of molecular diffusion, sorption and thermodiffusion as well as the temperature-dependent distribution coefficient and effective diffusion coefficient. The proposed analytical solutions are successfully validated against the experimental results of thermodiffusion tests and verified against an analytical solution available in the literature and a numerical model based on commercial finite element software. Using the verified analytical solutions, simulations are performed with representative geometry and material properties for a GMB/GCL/CCL liner system. The results indicate that neglecting the effect of non-isothermal condition can underestimate the benzene outflow rate by over 30% when the temperature difference between the surface and bottom of the liner system exceeds 10 K. The temperature-dependent CCL effective diffusion coefficient and CCL distribution coefficient have a significant effect on benzene transport through the GMB/GCL/CCL liner system, whereas the liner thermal conductivity and the temperature-dependent GCL effective diffusion coefficient and GCL distribution coefficient have a negligible effect.

Effects of temperature and oxygen on 137Cs desorption from bottom sediment of a dam lake

The temperature and oxygen environment play important roles in the desorption of 137Cs from freshwater lake sediment to lake water. In this study, 12 quarterly surveys were performed to measure the dissolved 137Cs concentration in surface and bottom lake water, the vertical distribution of water temperature, and the dissolved oxygen (DO) concentration at the upstream, midstream, and downstream sites of the Yokokawa Dam Lake in Fukushima Prefecture, Japan. Higher concentrations of dissolved 137Cs were detected in the bottom water than in the surface water, especially in the summer and midstream lake regions at depths of 8–21 m owing to higher temperatures, which activated the bacterial decomposition of organic matter, and anaerobization, which enhanced the NH4+ in the pore water and 137Cs desorption from mineral particles. To compare the effects of anaerobization and increasing temperature on 137Cs desorption from sediment particles, intact sediment core samples were collected from the lake midstream and incubated for 1–14 days in a chamber under three controlled temperature and oxygen environment conditions: aerobic +10 °C; anaerobic +10 °C; and anaerobic +20 °C. The vertical distribution of 137Cs in the sediment pore water showed a similar profile as NH4+ and K+, and both the increased temperature and reduced DO concentration enhanced the 137Cs desorption. A comparison of the standard partial regression coefficients of temperature and DO concentration in the multiple regression equation for the 137Cs concentration in pore water shows that the reduction of DO from saturation to zero at the water–sediment interface accelerated the desorption of 137Cs more strongly than did the temperature rise from 10 to 20 °C. The experimental results show a nearly inverse proportional relationship between NH4+ and the distribution coefficients of 137Cs after thermodynamic correction, except in the surface layer. These findings indicate that the 137Cs concentration in pore water can be explained by the temperature-dependent chemical distribution between the solid–aqueous phase and its equilibrium with NH4+.

Engineering the radiative dynamics of thermalized excitons with metal interfaces

As a platform for optoelectronic devices based on exciton dynamics, monolayer transition metal dichalcogenides (TMDCs) are often placed near metal interfaces or inside planar cavities. While the radiative properties of point dipoles at metal interfaces has been studied extensively, those of excitons, which are delocalized and exhibit a temperature-dependent momentum distribution, lack a thorough treatment. Here, we analyze the emission properties of excitons in TMDCs near planar metal interfaces and explore their dependence on exciton center-of-mass momentum, transition dipole orientation, and temperature. Defining a characteristic energy scale k B T c = (ℏk)2/2m (k being the radiative wavevector and m the exciton mass), we find that at temperatures T ≫ T c and low densities where the momentum distribution can be characterized by Maxwell–Boltzmann statistics, the modified emission rates (normalized to free space) behave similarly to point dipoles. This similarity in behavior arises due to the broad nature of wavevector components making up the exciton and point dipole emission. On the other hand, the narrow momentum distribution of excitons for T < T c can result in significantly different emission behavior as compared to point dipoles. These differences can be further amplified by considering excitons with a Bose Einstein distribution at high phase space densities, such as in a condensate phase. We find suppression or enhancement of emission relative to the point dipole case by several orders of magnitude. These insights can help optimize the performance of optoelectronic devices that incorporate 2D semiconductors near metal electrodes and can inform future studies of exciton radiative dynamics at low temperatures. Additionally, these studies show that nanoscale optical cavities are a viable pathway to generating long-lifetime exciton states in TMDCs.

Temperature-dependent local conformations and conformational distributions of cyanine dimer labeled single-stranded-double-stranded DNA junctions by 2D fluorescence spectroscopy.

DNA replication and the related processes of genome expression require binding, assembly, and function of protein complexes at and near single-stranded (ss)-double-stranded (ds) DNA junctions. These central protein-DNA interactions are likely influenced by thermally induced conformational fluctuations of the DNA scaffold across an unknown distribution of functionally relevant states to provide regulatory proteins access to properly conformed DNA binding sites. Thus, characterizing the nature of conformational fluctuations and the associated structural disorder at ss-dsDNA junctions is critical for understanding the molecular mechanisms of these central biological processes. Here, we describe spectroscopic studies of model ss-dsDNA fork constructs that contain dimers of "internally labeled" cyanine (iCy3) chromophore probes that have been rigidly inserted within the sugar-phosphate backbones of the DNA strands. Our combined analyses of absorbance, circular dichroism, and two-dimensional fluorescence spectroscopy permit us to characterize the local conformational parameters and conformational distributions. We find that the DNA sugar-phosphate backbones undergo abrupt successive changes in their local conformations-initially from a right-handed and ordered DNA state to a disordered splayed-open structure and then to a disordered left-handed conformation-as the dimer probes are moved across the ss-dsDNA junction. Our results suggest that the sugar-phosphate backbones at and near ss-dsDNA junctions adopt specific position-dependent local conformations and exhibit varying extents of conformational disorder that deviate widely from the Watson-Crick structure. We suggest that some of these conformations can function as secondary-structure motifs for interaction with protein complexes that bind to and assemble at these sites.

Non-covalent interactions in dimethylsulfoxide (DMSO) clusters and DFT benchmarking

Dimethylsulfoxide (DMSO) is one of the most used solvents in industries and in Chemistry. Understanding the dynamics of the solvent is subjected to the understanding of interactions in DMSO clusters. Despite its importance, a very few studies have been reported on DMSO clusters. In this work, we have explored thoroughly the potential energy surfaces (PESs) of the DMSO clusters from dimer to tetramer at the MP2/aug-cc-pVDZ level of theory. In order to understand the non-covalent interactions in DMSO clusters, we have performed a quantum theory of atoms in molecules (QTAIM) analysis. The QTAIM analysis showed that there are eight different types of non-covalent interactions stabilizing the DMSO clusters. The CH⋯O hydrogen bonding and H⋯H bonding are found to be the strongest and the weakest non-covalent interactions in DMSO clusters, respectively. In addition, we have reported the temperature-dependent isomer distribution of all the investigated clusters for temperatures ranging from 50 to 500 K. To allow affordable investigations of medium and large sized DMSO clusters in future investigations, we have assessed the performance of ten functionals of the density functional theory (DFT) in calculating the binding energies of the DMSO clusters. The ten DFT functionals (M05, M05-2X, M06, M06-2X, M08HX, PBE0, ωB97XD, PW6B95D3, APFD and MN15) have been benchmarked to MP2/CBS and DLPNO-CCSD(T)/CBS. The functionals PW6B95D3 and ωB97XD are recommended for further affordable investigations of the DMSO clusters.

Pressure Effects on the Relaxation of an Excited Ethane Molecule in High-Pressure Bath Gases.

We use molecular dynamics to calculate the rotational and vibrational energy relaxation of C2H6 in Ar, Kr, and Xe bath gases over a pressure range of 10-400 atm and at temperatures of 300 and 800 K. The C2H6 is instantaneously excited by 80 kcal/mol randomly distributed into both vibrational and rotational modes. The computed relaxation rates show little sensitivity to the identity of the noble gas in the bath. Vibrational relaxation rates show a nonlinear pressure dependence at 300 K. At 800 K the reduced range of bath gas densities covered by the range of pressures does not yet show any nonlinearity in the pressure dependence. Rotational relaxation is characterized with two relaxation rates. The slower rate is comparable to the vibrational relaxation rate. The faster rate has a linear pressure dependence at 300 K but an irregular, nonlinear pressure dependence at 800 K. To understand this, a model was developed based on approximating the periodic box used in the molecular dynamics simulations by an equal-volume collection of cubes where each cube is sized to allow only single occupancy by the noble gas or the molecule. Combinatorial statistics then leads to a pressure- and temperature-dependent analytic distribution of the bath gas species the molecule encounters in a collision. This distribution, the dissociation energy of molecule/bath gas complexes and bath gas clusters, and the computed energy release per collision combine to show that only at 300 K is the energy release sufficient to dissociate likely complexes and clusters. This suggests that persistent and pressure-dependent clusters and complexes at 800 K may be responsible for the nonlinear pressure dependence of rotational relaxation.

Laser-Based Primary Thermometry: A Review

Laser-based primary thermometry was initiated almost 15 years ago by the proposal to determine the absolute temperature of a gas at thermodynamic equilibrium through the Doppler width of an associated absorption transition, exploiting the potentially very accurate measurement of an optical frequency to infer the elusive thermal energy of a molecular or atomic absorber. This approach, commonly referred to as Doppler broadening thermometry, has benefited across the years from substantial improvements, of both technical and fundamental nature, eventually reaching an accuracy of about 10 ppm on the temperature determination in the best cases. This is sufficient for Doppler broadening thermometry to play a significant role in the practical realization of the new kelvin, which follows the 2019’s redefinition from a fixed value of the Boltzmann constant, and to tackle the challenge, among others, to quantify and possibly fix systematic uncertainties of the international temperature scale of 1990. This paper reviews and comparatively analyzes methods and results achieved so far in the field of laser-based primary thermometry, also including spectroscopic approaches that leverage the temperature-dependent distribution of line intensities and related absorbances across the rovibrational band of a molecular sample. Although at an early stage of development, these approaches show a promising degree of robustness with respect to the choice of the line-shape model adopted for the fitting of the absorption spectra, which is a delicate aspect for all laser-based thermometers. We conclude by identifying possible technical and scientific evolution axes of the current scenario.