Vibration-rotation Lines Research Articles

Expert Assessment of the Accuracy of Determining the Intensities of Vibrational-rotational Lines of Water Vapor in the HITRAN Database in the Range 2500–6500 cm–1

Expert Assessment of the Accuracy of Determining the Intensities of Vibrational-rotational Lines of Water Vapor in the HITRAN Database in the Range 2500–6500 cm–1

Isotopic Shifts of Vibrational-Rotational Lines of SO2

Isotopic Shifts of Vibrational-Rotational Lines of SO2

Pressure broadening in Raman spectra of CH4–N2, CH4–CO2, and CH4–C2H6 gas mixtures

Different molecular environments change the spectrum of a given gas sample involved in a mixture compared to the spectrum of a pure gas. It is necessary to account for this effect to improve the accuracy of the analysis of the natural gas composition by Raman spectroscopy. First, the change in the main components of natural gas (methane, nitrogen, carbon dioxide, and ethane) must be considered. This work is devoted to the mutual influence of CH4–N2, CH4–CO2, and CH4–C2H6 on their characteristic Raman bands in the range of 300–2500 cm−1. The half-width and asymmetry of the Q branches of N2, CO2, and C2H6 as a function of methane concentration were obtained in the range of 1–50 bar. The averaged broadening coefficients of the rotational-vibrational lines of the ν2 band of CH4 perturbed by N2, CO2, and C2H6 are measured. A high-sensitivity spectrometer with a resolution of 0.5 cm−1 based on spontaneous Raman scattering was used to obtain reliable results. The algorithm and all the necessary parameters for simulating the effect of various molecular environments on the Raman bands of the main components of natural gas are presented.

Analysis of the first infrared spectrum of quasi-bound H2 line emission in Herbig-Haro 7

Context. Highly excited molecular hydrogen (H2) has been observed in many regions of shocked molecular gas. A recently published K-band spectrum of Herbig-Haro 7 (HH7) contains several vibration-rotation lines of H2 from highly excited energy levels that have not been detected elsewhere, including a line at 2.179 μm identified as arising from the v = 2, J = 29 level, which lies above the dissociation limit of H2. One emission line at 2.104 μm in this spectrum was unidentified. Aims. We aim to complete the analysis of the spectrum of HH7 by including previously missing molecular data that have been recently computed. Methods. We re-analysed the K-band spectrum, emphasising the physics of quasi-bound upper levels that can produce infrared emission lines in the K band. Results. We confirm the identification of the 2 − 1 S(27) line at 2.1785 μm and identify the line at 2.1042 μm as due to the 1−0 S(29) transition of H2, whose upper level energy is also higher than the dissociation limit. This latter identification, its column density, and the energy of its upper level further substantiate the existence of a hot thermal component at 5000 K in the HH7 environment. Conclusions. The presence of the newly identified 1 − 0 S(29) line, whose quasi-bound upper level (v = 1, J = 31) has a significant spontaneous dissociation probability, shows that dissociation of H2 is occurring. The mechanism by which virtually all of the H2 in levels with energies from 20 000 K to 53 000 K is maintained in local thermodynamic equilibrium at a single temperature of ∼5000 K remains to be understood.

Fluorine Abundances in the Galactic Nuclear Star Cluster

Abstract Abundances of fluorine (19F), as well as isotopic ratios of 16O/17O, are derived in a sample of luminous young (∼107–108 yr) red giants in the Galactic center (with galactocentric distances ranging from 0.6–30 pc), using high-resolution infrared spectra and vibration-rotation lines of H19F near λ2.3 μm. Five of the six red giants are members of the Nuclear star cluster that orbits the central supermassive black hole. Previous investigations of the chemical evolution of 19F in Galactic thin and thick-disk stars have revealed that the nucleosynthetic origins of 19F may be rather complex, resulting from two, or more, astrophysical sites; fluorine abundances behave as a primary element with respect to Fe abundances for thick-disk stars and as a secondary element in thin-disk stars. The Galactic center red giants analyzed fall within the thin-disk relation of F with Fe, having near-solar, to slightly larger, abundances of Fe (〈[Fe/H]〉 = +0.08 ± 0.04), with a slight enhancement of the F/Fe abundance ratio (〈[F/Fe]〉 = +0.28 ± 0.17). In terms of their F and Fe abundances, the Galactic center stars follow the thin-disk population, which requires an efficient source of 19F that could be the winds from core-He burning Wolf–Rayet stars, or thermally pulsing AGB stars, or a combination of both. The observed increase of [F/Fe] with increasing [Fe/H] found in thin-disk and Galactic center stars is not predicted by any published chemical evolution models that are discussed, thus a quantitative understanding of yields from the various possible sources of 19F remains unknown.

Global modeling of the 12C32S2 line positions within the framework of the non-polyad model of effective Hamiltonian

The global modeling of 12C32S2 line positions in the 240 – 12 000 cm−1 region has been performed using the non-polyad model of effective Hamiltonian. The effective Hamiltonian parameters were fitted to the measured line positions collected from the literature. The fitted set of 99 effective Hamiltonian parameters allowed reproduction of more than 13 000 measured line positions with the dimensionless weighted standard deviation of 1.65. The root-mean-square of errors of the fitted high-resolution rotation-vibration line positions in the 240 - 466 cm−1 range is 0.0013 cm−1. A comparison of the calculated line positions based on the fitted model with HITRAN2020 is presented and discussed.

Experimental and quantum-chemical characterization of heavy carbon subchalcogenides: Infrared detection of SeC3Se

High-resolution infrared studies of laser ablation products from carbon-selenium targets have revealed a new vibrational band at 2057 cm−1 that is identified as the ν3 vibrational fundamental of the SeC3Se cluster. Because of the rich isotopic composition of selenium and the heavy nuclear masses involved, the vibrational band shows a relatively compact and complex structure despite the simple linear geometric arrangement. Overall, rotational-vibrational lines of six isotopologues could be assigned and fitted permitting the derivation of an accurate selenium-carbon bond length.Spectroscopic analysis has been greatly supported by high-level quantum-chemical calculations of the molecular structure and the harmonic and anharmonic force fields performed at the CCSD(T) level of theory. Scalar-relativistic effects on the molecular structure were also considered but found of little importance.

Уширение и сдвиг линий основной колебательно-вращательной полосы молекул фтористого водорода молекулами SF-=SUB=-6-=/SUB=- и H-=SUB=-2-=/SUB=-

Foreign gas broadening and shift of the vibration-rotation lines in the fundamental band of hydrogen fluoride have been investigated. Using mathematical modeling of measuring the absorption of radiation of an electric discharge HF laser, the possibility of correct calculations of both broadening and shift of HF lines by foreign gases were determined. Measurements for two foreign gases (Ar and N2 for which there are literature data) were made in order to test this approach. The obtained results have been well matched with existing literature data. After that, measurements were carried out on two transitions P(7) and P(8) for SF6 (for which neither broadening nor the shift are known) and for H2 (only broadening is known for overtone band). The obtained results were compared with scarce literature data.

Doppler velocimeter based on dual-comb absorption spectroscopy

The determination of airflow parameters is essential to the research of critical information on environment monitoring, chemical kinetics, and aerodynamic and propulsion applications. During the past few decades, tunable diode laser absorption spectroscopy has become a common and efficient tool for the flow velocity measurement based on the Doppler shift of the absorption line. Dual-comb absorption spectroscopy (DCAS), as a state-of-the-art Fourier-transform broadband spectroscopic technique, not only can detect multiple trace molecules in parallel but also can extract Doppler shifts to derive the flow velocity through the analysis of dozens of molecular absorption lines simultaneously with high precision. Here, we report a proof-of-principle demonstration of the velocity measurements of acetylene at various flow velocities by means of a high-resolution and broadband DCAS. Mode-resolved Doppler-shifted rotational-vibrational lines in the P branch of acetylene molecules are obtained. A model for multiline Doppler frequency determination is investigated and experimentally verified. The flow velocity measurements with a measuring uncertainty down to the submeter per second over the range from 8.7 m/s to 44.8 m/s at an effective time resolution of 1 s and a measuring uncertainty of 1.97 m/s at 0.1 s are demonstrated. With broadband mid-infrared frequency combs covering atmospheric transmission windows, the open-path measurement for monitoring diffusion of the weak pollutant source would be realized.

Combination of soot pyrometry and [formula omitted] emission spectroscopy for temperature measurement during combustion of hydrocarbons

Flame emission spectroscopy emerged as a technique for gas flow temperature monitoring in combustion chambers. The measurement could be based on soot emission or C2∗ electronic vibrational–rotational lines. However, during the exploitation of a gas turbine, it is hard to resolve emission spectra sufficiently to differentiate rotational levels whereas soot emission does not provide satisfactory accuracy. This study proposes a method of measuring a gas flow temperature based on the combination of soot emission and C2∗ electronic-vibrational spectra. C2∗ vibrational temperatures are obtained with the help of electronic-vibrational lines. The variance between the C2∗ vibrational temperatures obtained through the use of different emission bands are applied to correct the calculated value of the soot temperature and to find the gas flow temperature. The experimental study has demonstrated that the gas flow temperature in the primary zone of the combustion chamber varies from 2064 to 2318 K, with standard deviations from 0.3% to 1.5% of the measured value.

Investigation of the Spectral Line Intensities of the ν9 Band of the Trans-Conformer of Ethylene

The intensities of 740 vibrational-rotational lines of the ν9 fundamental band in the IR spectrum of the trans-C2H2D2 molecule are first analyzed. The Hartmann–Tran profile is used to fit the line contour. More than 2700 spectral transitions are assigned using the ground state combination difference method and the isotopic substitution theory. The special features of the spectral line broadening and the influence of the parameters of the Hartmann–Tran line profile on the accuracy of line contour reconstruction are considered.

Collisional Broadening of Vibrational-Rotational CO2 Lines by Buffer Gases

Unsaturated absorption coefficients in pure CO2 and binary mixtures of CO2 with buffer gases Mj (He, Ar, Kr, Xe, N2, O2, CO, N2O, 13C16O2) were measured with a tunable CO2 laser at the central frequencies of the R(8), R(22), R(34), P(8), P(22), and P(36) CO2 spectral lines of the 1000–0001 transition at a temperature of 300–700 K. A technique is described and the coefficients of self-broadening and broadening of CO2 spectral lines by a buffer gas Mj are calculated. It is shown that the efficiency of the CO2 interaction with diatomic and triatomic molecules is determined by the electric moment; in the case of inert gases, the mass factor plays the major role. It is ascertained that the temperature dependences of the collisional broadening of CO2 spectral lines can be highly accurately approximated by power functions with two different exponents.

The high-temperature rotation-vibration spectrum and rotational clustering of silylene (SiH2)

A rotation-vibration line list for the electronic ground state (X˜1A1) of SiH2 is presented. The line list, named CATS, is suitable for temperatures up to 2000 K and covers the wavenumber range 0–10 000 cm−1 (wavelengths > 1.0 µm) for states with rotational excitation up to J=52. Over 310 million transitions between 593 804 energy levels have been computed variationally with a new empirically refined potential energy surface, determined by refining to 75 empirical term values with J ≤ 5 and a newly computed high-level ab initio dipole moment surface. This is the first, comprehensive high-temperature line list to be reported for SiH2 and it is expected to aid the study of silylene in plasma physics, industrial processes and possible astronomical detection. Furthermore, we investigate the phenomenon of rotational energy level clustering in the spectrum of SiH2. The CATS line list is available from the ExoMol database (www.exomol.com) and the CDS database.

Collisional broadening of vibrational-rotational CO2 lines by buffer gases

Collisional broadening of vibrational-rotational CO2 lines by buffer gases

Коэффициенты самоуширения и сдвига колебательно-вращательных линий КР азота и кислорода в диапазоне давлений 1-50 атм

Коэффициенты самоуширения и сдвига колебательно-вращательных линий КР азота и кислорода в диапазоне давлений 1-50 атм

Fluorine Abundances in the Galactic Disk

Abstract The chemical evolution of fluorine is investigated in a sample of Milky Way red giant stars that span a significant range in metallicity from [Fe/H] ∼ −1.3 to 0.0 dex. Fluorine abundances are derived from vibration-rotation lines of HF in high-resolution infrared spectra near 2.335 μm. The red giants are members of the thin and thick disk/halo, with two stars being likely members of the outer disk Monoceros overdensity. At lower metallicities, with [Fe/H] < −0.4 to −0.5, the abundance of F varies as a primary element with respect to the Fe abundance, with a constant subsolar value of [F/Fe] ∼ −0.3 to −0.4 dex. At larger metallicities, however, [F/Fe] increases rapidly with [Fe/H] and displays a near-secondary behavior with respect to Fe. Comparisons with various models of chemical evolution suggest that in the low-metallicity regime (dominated here by thick-disk stars), a primary evolution of 19F with Fe, with a subsolar [F/Fe] value that roughly matches the observed plateau, can be reproduced by a model incorporating neutrino nucleosynthesis in the aftermath of the core collapse in Type II supernovae. A primary behavior for [F/Fe] at low metallicity is also observed for a model including rapidly rotating low-metallicity massive stars, but this overproduces [F/Fe] at low metallicity. The thick-disk red giants in our sample span a large range of galactocentric distance (R g ∼ 6–13.7 kpc) yet display a roughly constant value of [F/Fe], indicating a very flat gradient (with a slope of 0.02 ± 0.03 dex kpc−1) of this elemental ratio over a significant portion of the Galaxy having ∣ Z ∣ > 300 pc away from the Galaxy midplane.

Theoretical electronic structure with rovibrational and dipole moment calculation of the SiS Molecule

The quantitative distribution of the molecular abundances in the universe is a classical problem in astronomy, astrophysics and cosmo-chemistry. Astrophysicists are interested in determining the abundances of molecular species in order to: (1) Know the primordial composition of the solar system, and its relation to the past and present composition of the earth. (2) Have a complete understanding of physical and chemical processes taking place in the stellar atmospheres and the interstellar medium (3) Test the hypotheses that have been proposed for element formation. To investigate the presence of astronomical sources, experimental astrophysicists usually study the wavelength and intensity of light that they emit. Many diatomic molecular species are present in various astrophysical sources, however, the theoretical studies on such species are not enough and information is missing in that area. Knowledge of the electronic structure, Franck-Condon factors (FCFs), and other related quantities for a band system of a diatomic molecule is essential to arrive at its astrophysically significant parameters such as kinetics of the energy transfer, radiative lifetimes, band intensity, vibrational temperature, etc. In this view, the spectroscopic and ro-vibrational constants, FCFs of several electronic states of the diatomic molecule SiS electronic have been evaluated in this work. We performed theoretical calculation of the low-lying electronic state, of the molecule SiS by using the Complete Active Space Self Consistent Field (CASSCF) method followed by the Multi Reference Configuration Interaction with Davidson correction MRCI+Q. The potential energy along with the dipole moment curves of these states have been calculated along with the spectroscopic constants Re, ωe, Be, and Te. Additionally, the Rotation-vibration lines for the considered electronic states were obtained by direct solution of the nuclear motion Schrödinger equation using the canonical approach with program Rovib-1

Theoretical electronic structure with rovibrational and dipole moment calculation of SiN Molecule

Atomic and molecular data are at the origin of the atmospheres of planetary and stellar objects discoveries. Based on the laboratory astrophysics and the computational molecular spectroscopy, the interpretation of this data can give the chemical compositions and temperatures of these astrophysical systems. The detection and the identification of the SiN radical in the interstellar medium has drawn the attention to the gas phase chemistry and the evidence of a link between the interstellar chemistry of silicon and that of nitrogen. The quantum chemistry methods used to predict the spectroscopic properties of the SiN molecule can be calibrated with some available experimental results. In order to obtain reliable theoretical data that may help in the interpretation of interstellar or laboratory spectra concerning the SiN molecule, we performed theoretical calculation of 31 low-lying electronic state, below 66000 cm−1, of the molecule SiN by using the Complete Active Space Self Consistent Field (CASSCF) method followed by the Multi Reference Configuration Interaction with Davidson correction MRCI+Q. The potential energy along with the dipole moment curves of these states have been calculated along with the spectroscopic constants Re, ωe, Be, and Te. The Rotation-vibration lines for the considered electronic states of SiN molecule were obtained by direct solution of the nuclear motion Schrödinger equation using the canonical approach with program Rovib-1. By comparing our investigated values of the calculated vibrational energy Ev, the rotational constant Bv and the turning points Rmin and Rmax. with those available in literature shows a very good agreement. To the best of our knowledge nine new electronic states have been studied here for the first time that have not been observed yet.

The HH 212 Interstellar Laboratory: Astrochemistry as a Tool To Reveal Protostellar Disks on Solar System Scales around a Rising Sun

The investigation of star-forming regions has enormously benefited from the recent advent of the ALMA interferometer working in the millimeter- and submillimeter-wavelength spectral windows. More specifically, the unprecedented combination of high-sensitivity and high-angular resolution provided by ALMA allows one to shed light on the jet/disk systems associated with a Sun-like mass protostar. In this context, astrochemistry also possesses the possibility to analyze complex spectra obtained using large bandwidths: several interstellar complex organic molecules (iCOMs; C-bearing species with at least six atoms) have been detected and imaged around protostars, often thanks to a large number of rotational–vibrational lines. This in turn boosted the study of the astrochemistry at work during the earliest phases of star formation paving the way to the chemical complexity in planetary systems where Life could emerge. There is mounting evidence that the observations of iCOMs (e.g., CH3CHO or NH2CHO) can be used as unique tools to shed light on Solar System scales (<50 au) on the molecular content of protostellar disk. The increase of iCOMs abundance occur only under very selective physical conditions, such as those associated low-velocity shocks found where the infalling envelope is impacting the rotating accretion disk. The imaging of these regions with simpler molecules such as CO or CS is indeed paradoxically hampered by their high abundances and consequently high line opacities which do not allow the observers to disentangle all the emitting components at these small scales. In this respect, we review the state-of-the art of the ALMA analysis about the standard Sun-like star forming region in Orion named HH 212, associated with a pristine jet-disk protostellar system. We enrich the discussion with unpublished ALMA data sets, showing (i) how all of the physical components involved in the formation of a Sun-like star can be revealed only by observing different molecular tracers, and (ii) how the observation of iCOMs emission, observed to infer the chemical composition of star-forming regions, can be used also as a unique tracer to image protostellar disks on Solar System scales, that is, where planets will eventually form.

Theoretical rotation-vibration spectroscopy of cis- and trans-diphosphene (P2H2) and the deuterated species P2HD.

Growing astronomical interest in phosphorous (P) chemistry is stimulating the search for new interstellar P-bearing molecules, a task requiring detailed knowledge of the microwave and infrared molecular spectrum. In this work, we present comprehensive rotation-vibration line lists of the cis- and trans-isomers of diphosphene (P2H2). The line lists have been generated using robust, first-principles methodologies based on newly computed, high-level ab initio potential energy and dipole moment surfaces. Transitions are considered between states with energies up to 8000 cm-1 and total angular momentum J ≤ 25. These are the first-ever line lists to be reported for P2H2, and they should significantly facilitate future spectroscopic characterization of this system. The deuterated species trans-P2HD and the effect of its dynamic dipole moment on the rovibrational spectrum are also discussed.