Ab initio quantum scattering calculations and a new potential energy surface for the HCl(X1Σ+X^1\Sigma^+)-O2_{2}(X3Σg−X^3\Sigma^-_g) system: collision-induced line-shape parameters for O2_{2}-perturbed R(0) 0-0 line in H35^{35}Cl

The remote sensing of abundance and properties of HCl -- the main atmospheric reservoir of Cl atoms which directly participate in ozone depletion -- are important for monitoring the partitioning of chlorine between "ozone-depleting" and "reservoir" species. Such remote studies require knowledge of the shapes of molecular resonances of HCl, which are perturbed by collisions with the molecules of the surrounding air. In this work, we report the first fully quantum calculations of collisional perturbations of the shape of a pure rotational line in H$^{35}$Cl perturbed by an air-relevant molecule (as the first model system we choose the R(0) line in HCl perturbed by O$_2$). The calculations are performed on our new highly-accurate HCl($X^1\Sigma^+$)-O$_2$($X^3\Sigma^-_g$) potential energy surface. In addition to pressure broadening and shift, we determine also their speed dependencies and the complex Dicke parameter. This gives important input to the community discussion on the physical meaning of the complex Dicke parameter and its relevance for atmospheric spectra (previously, the complex Dicke parameter for such systems was mainly determined from phenomenological fits to experimental spectra and the physical meaning of its value in that context is questionable). We also calculate the temperature dependence of the line-shape parameters and obtain agreement with the available experimental data. We estimate the total combined uncertainties of our calculations at 2% relative RMSE residuals in the simulated line shape at 296~K. This result constitutes an important step towards computational population of spectroscopic databases with accurate ab initio line-shape parameters for molecular systems of terrestrial atmospheric importance.Comment: 15 pages, 7 figures, The following article has been accepted by The Journal of Chemical Physics. After it is published, it will be found at https://pubs.aip.org/aip/jc

Revisiting the rovibrational (de-)excitation of molecular hydrogen by helium

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TiCoCrFeMn (BCC + C14) High-Entropy Alloy Multiphase Structure Analysis Based on the Theory of Molecular Orbitals

High-entropy alloys (HEA) are a group of modern, perspective materials that have been intensively developed in recent years due to their superior properties and potential applications in many fields. The complexity of their chemical composition and the further interactions of main elements significantly inhibit the prediction of phases that may form during material processing. Thus, at the design stage of HEA fabrication, the molecular orbitals theory was proposed. In this method, the connection of the average strength of covalent bonding between the alloying elements (Bo parameter) and the average energy level of the d-orbital (parameter Md) enables for a preliminary assessment of the phase structure and the type of lattice for individual components in the formed alloy. The designed TiCoCrFeMn alloy was produced by the powder metallurgy method, preceded by mechanical alloying of the initial elementary powders and at the temperature of 1050 °C for 60 s. An ultra-fine-grained structured alloy was homogenized at 1000 °C for 1000 h. The X-ray diffraction and scanning electron microscopy analysis confirmed the correctness of the methodology proposed as the assumed phase structure consisted of the body-centered cubic (BCC) solid solution and the C14 Laves phase was obtained

Ab initio investigation of the line-shape parameters for atmosphere-relevant molecular systems

International audienceWe demonstrate the results of the first ab initio investigation of the line-shape parameters for two molecular systems important for atmospheric studies CO-N2 and O2-N2. We provide the pressure broadening and shift coefficients with their speed dependencies for purely rotational lines, calculated from highly accurate potential energy surfaces with the close-coupling scheme. This is the first, fully quantum approach to the problem of determination of the spectral line shapes for the systems important for terrestrial atmospheric measurements

Ab initio calculations of collisional line–shape parameters and generalized spectroscopic cross-sections for rovibrational dipole lines in HD perturbed by He

International audienceWe report ab initio calculations of generalized spectroscopic cross-sections for hydrogen deuteride perturbed by helium. From these calculations, collisional line-shape parameters are deduced for the HD electric dipole transitions from R(0) to R(5) and from P(1) to P(6) in the 0–0 to 5–0 bands. These parameters are necessary for a proper interpretation of HD spectra from the atmospheres of gas giants. We demonstrate that the centrifugal distortion cannot be ignored, not only for pure rotational lines but also for rovibrational lines when one aims at sub–percent accuracy of the collisional line–shape parameters

First-principles calculations of pressure broadening for the case of N 2 -perturbed 118 GHz fine-structure line in O 2 (X 3 Σ –g )

International audienceBecause of its high molecular abundance in Earth’s atmosphere, nitrogen N2 plays a prominent role in perturbing the shape of the spectral distribution of radiation emitted or absorbed by other molecular species present. Of particular importance are its interactions with the molecular oxygen O2, which is the second most abundant constituent of our planet’s atmosphere.The oxygen spectral bands formed by transitions to its excited electronic states, such as the A- and B-band, are studied extensively due to their application in, e.g., the determination of cloud-top heights and coverage, optical thickness of aerosols, concentration of the pollutant gases such as CO2, and monitoring of the greenhouse gases and vegetation fluorescence.Many such applications involve also purely rotational transitions occurring within the ground electronic (and vibrational) 3Σ–g term of O2. Due to spin-spin interactions of the two unpaired valence electrons in this state, the rotational levels (labeled necessarily with odd quantum numbers) are split into a triplet of fine-structure sub-levels, the transitions between which result in the presence of a strong 60-GHz spectral band and a single isolated line at about 118 GHz. These spectral features have been studied extensively due to their applications in remote sensing and temperature profiling. Here we report the results of the first fully quantum calculations of O2-N2 scattering and its influence on the pressure broadening of the single 118 GHz fine-structure line in the ground-state oxygen.1 Our fully ab initio approach is based onthe new potential energy surface for O2-N2, calculated using the explicitly correlated unrestricted coupled-cluster theory with all electrons correlated and extrapolated to the complete basis set limit. In our approach we make use of the angular momentum recoupling methods,2,3 which allow for expressing the total S-matrix as a linear combination of the spin-free S-matrices. We include the speed-dependence of the broadening parameter in our calculations and obtain a good agreement with the experimental data. Our study is the first step toward the accurate theoretical study of collisional perturbations of the fine structure and rotational lines of O2(X3Σ– g ) due to molecular species of atmospheric importance, such as N2. Such investigations are of great importance for studies of the Earth’s atmosphere and remote sensing applications, and populating spectroscopic databases such as HITRAN or GEIS