Integrated Absorption Cross-sections Research Articles

Jet-cooled ethylene cavity ring-down spectroscopy between 5880 and 6200 cm−1

Absorption spectra of jet-cooled ethylene (ethene, C2H4) are recorded at three different rotational temperatures (6/8 K, 12 K, 38 K) using cavity ring-down spectroscopy (CRDS) in the 5880–6200 cm−1 spectral region. Rotational cooling is used to determine the various vibrational band centers by simplifying drastically the rotational band structure. A line-by-line assignment, based on a direct comparison with the TheoReTS variational line list and a systematic use of lower state combination difference (LSCD), is performed. Experimental line lists including line position and line integrated absorption cross sections are drawn up. The 6/8 K, 12 K and 38 K spectra contain 668, 1553 and 1679 absorption lines respectively. Overall, 320 rovibrational lines are assigned across 20 interacting vibrational bands. Among the 20 vibrational cold bands identified in this work, 14 had never been observed before. Line intensities are in the range of 10−24 - 10−20 cm/molecule. A direct comparison between our work and the TheoReTS and ExoMol theoretical line lists, as well as with the recent experimental work of Ben Fathallah et al. (2024) is provided.

A new instrumentation for simultaneous terahertz and mid-infrared spectroscopy in corrosive gaseous mixtures.

The correct interpretation of infrared (IR) observations of planetary atmospheres requires an accurate knowledge of temperature and partial and global pressures. Precise laboratory measurements of absorption intensities and line profiles, in the 200-350K temperature range, are, therefore, critical. However, for gases only existing in complex chemical equilibria, such as nitrous or hypobromous acids, it is not possible to rely on absolute pressure measurements to measure absolute integrated optical absorption cross sections or IR line intensities. To overcome this difficulty, a novel dual-beam terahertz (THz)/mid-IR experimental setup has been developed, relying on the simultaneous use of two instruments. The setup involves a newly constructed temperature-controlled (200-350K) cross-shaped absorption cell made of inert materials. The cell is traversed by the mid-IR beam from a high-resolution Fourier transform spectrometer using along a White-cell optical configuration providing absorption path lengths from 2.8 to 42m and by a THz radiation beam (82.5GHz to 1.1THz), probing simultaneously the same gaseous sample. The THz channel records pure rotational lines of molecules for which the dipole moment was previously measured with high precision using Stark spectroscopy. This allows for a determination of the partial pressure in the gaseous mixture and enables absolute line intensities to be retrieved for the mid-IR range. This new instrument opens a new possibility for the retrieval of spectroscopic parameters for unstable molecules of atmospheric interest. The design and performance of the equipment are presented and illustrated by an example of simultaneous THz and mid-IR measurement on nitrous acid (HONO) equilibrium.

Collisions of low- to intermediate-energy electrons with acetonitrile

A systematic investigation was carried out on the elastic scattering of low- to intermediate-energy electrons ( = 0.1–1000 eV eV) by acetonitrile (CH3CN). We calculated differential (DCS), integral (ICS), momentum-transfer (MTCS), and total absorption cross sections from 0.1 to 1000 eV energy range using an absorption-effects-implemented ePolyScat-E3 suite of codes, which applies the Schwinger variational method combined with the Padé-approximants technique. Also, the screen-corrected independent atom model was used to compute DCSs, ICSs, and MTCSs from 10–1000 eV impact energies. Present results are compared to other theoretical and experimental data when available. In general, our DCS and MTCS results show a good agreement with available data, however, the ICSs and the resonance features exhibit fair accordance. Our results show two shape-resonance structures: one at about 3.4 eV and a second at about 7 eV. They are labeled as and , and comprise the and scattering channels, respectively.

Spectral studies of Nd3+ doped different fluorophosphate glasses for their aptness in laser applications at 1060 nm

Neodymium doped fluorophosphate (FP:Nd3+) glasses with different chemical compositions (59NH4H2PO4+15ZnO +15BaF2+10X+1·0NdF3 (X=LiF, NaF, CaF2, SrF2, AlF3)) were prepared by melt quenching. Their structures and spectroscopic properties were studied using x-ray diffraction, FTIR, FT-Raman and 31P, 27Al MAS NMR techniques. Various structural groups were identified using FTIR and FT-Raman spectra. The depolymerisation of metaphosphate chains are described by the decrease of Q2 tetrahedral sites allowing the formation of pyrophosphate groups revealed by 31P MAS NMR spectroscopic studies. Optical properties were studied using absorption and photoluminescence spectroscopy. Judd–Ofelt intensity parameters Ωλ (λ=2, 4 and 6) were estimated from absorption spectra. Radiative parameters such as transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βR) were calculated. Two emission lines at 1060 and 1330 nm were observed for Nd3+ in all the fluorophosphate glasses. From the emission spectra, emission characteristics were studied via optical band gains (σe×τR) and gain bandwidths (σe×Δλeff). Fairly large numerical values for peak emission cross-sections (σe) and branching ratios (β) for 4F3/2Æ4I11/2 transition of Nd3+ ion doped calcium fluorophosphate glass were observed. These results are rosy for NIR laser application at 1060 nm.

Pulsed-cavity ring down spectroscopic study of NO2 in 501–506 nm spectral region

Cavity ring-down spectroscopy (CRDS) is a highly sensitive laser absorption spectroscopic technique. In this paper, we report the pulsed CRDS study of nitrogen dioxide (NO 2 ) using an home-built CRDS set-up. Pulsed CRDS measurements of diluted NO 2 gas (0.091% in N 2 ) at various low pressures have been carried out in 501–506 nm spectral range. From the CRDS measurements, molecular spectral features of NO 2 at very low partial pressure, ∼10 mTorr (3.42 × 10 14 molecules/cm 3 ), was evidently observed. CRDS ring-down decay measurements carried out at wavelength of 504.76 nm for various molecular concentrations of NO 2 demonstrate a minimum detectable number density of NO 2 of 8.65 × 10 12 molecules/cm 3 , which would correspond to 350 ppbv under atmospheric condition. 40 ppbv of detection limit of NO 2 is estimated from the standard deviation (1σ) of ring-down decay time measurements at 504.76 nm wavelength. Absorption and integrated absorption cross section of NO 2 are also estimated.

Absolute Absorption Cross Section and Orientation of Dangling OH Bonds in Water Ice

Abstract The absolute absorption cross section of dangling OH bonds in water ice, a free OH stretch mode by three-coordinated surface water molecules, is derived experimentally as 1.0 ± 0.2 × 10−18 cm2 at 3696 cm−1 for amorphous water at 90 K using infrared multiple-angle incidence resolution spectrometry (IR–MAIRS). The integrated absorption cross section (band strength) of the dangling OH bond at 90 K (1.4 ± 0.3 × 10−17 cm molecule−1 at 3710–3680 cm−1) is found to be more than 1 order of magnitude smaller than those in bulk ice or liquid water. This indicates that a lack of hydrogen-bonding significantly decreases the band strength of dangling OH bonds. The present study also provides average molecular orientations of dangling OH bonds at 10 K and 90 K, because both the surface-parallel (in-plane) and surface-perpendicular (out-of-plane) vibration spectra of dangling OH bonds are quantitatively measured by IR–MAIRS. The intensity ratio of the dangling-OH peaks between in-plane to out-of-plane spectra shows the isotropic nature (random orientation) of the two- and three-coordinated dangling OH bonds in microporous amorphous water prepared at 10 K; however, the three-coordinated dangling OH bonds in nonporous amorphous water prepared at 90 K are dominantly located at the top ice surface and oriented perpendicular to it. These findings provide fundamental insights into the relationship between the structure and optical properties of ice surfaces, and aid quantitative understanding of the surface structure of interstellar ices and their laboratory analogs.

Dependence of Judd-Ofelt parameters on integrated absorption coefficient or cross-section of an individual transition of Er3+

Dependences of two factors on Judd-Ofelt (JO) intensity parameters Ω t (t = 2,4,6) have been studied theoretically by exemplifying the widely studied Er 3+ ion, which is doped into Gd 3 Ga 5 O 12 , LiNbO 3 and SrGdGa 3 O 7 bulk single-crystals and β-NaYF 4 powder. The two factors include 1) selection of induced electric-dipole transitions for JO calculation and 2) integrated absorption coefficient (IAC) or integrated absorption cross-section (IACS) of individual electric-dipole transition of Er 3+ . Absolute and relative root-mean-square methods were considered in the JO fits and consistent results were obtained. Ω t depends mainly on strong and medium-intensity transitions. These transitions must be all included in the fit. The exclusion of an individual transition from the fit leads to deviation of Ω t . From the matrix elements [ U (t) ] 2 values, it is possible to rate how the inclusion or not of a transition affects the Ω t . The study also shows that the Ω t changes almost linearly with the IAC or IACS of an individual transition, and the relevant linear slope may have a positive or negative sign, depending on the [ U (t) ] 2 value. Moreover, the larger the [ U (t) ] 2 value is, the larger the corresponding Ω t value is. In addition, the Ω 2 , Ω 4 and Ω 6 are dependent of each other because it is the summation ∑ t Ω t [ U ( t ) ] 2 instead of its component term Ω t [ U ( t ) ] 2 that has a linear relationship to the IAC or IACS.

The coverage dependence of the infrared absorption of CO adsorbed to NaCl(100).

CO adsorbed to NaCl(100) exhibits perhaps the weakest possible coupling between the adsorbate and solid. It is, therefore, an ideal system to observe the influence of adsorbate-adsorbate interactions on infrared absorption. In this work, we report polarized FTIR absorption spectra of CO/NaCl(100) as a function of coverage (0.02 ≤ θ ≤ 1 ML), where the coverage has been quantitatively determined by temperature-programmed desorption and molecular beam dosing. We extend a previous semi-empirical model designed to describe the screening of the local electric field due to dipole-dipole interactions in a CO monolayer. The extended model applies to sub-monolayer coverages and describes properly the electric field of the absorbed radiation at the vacuum-substrate interface. Fitting this model to coverage-dependent IR absorption data allows us to derive the vibrational and electronic polarizabilities [χv = 0.0435(14) Å3, χe = 3.30(36) Å3] and the integrated absorption cross section of 2.51(8) × 10-17 cm/molecule for an isolated CO molecule adsorbed at the NaCl (100) surface. The determined integrated absorption cross section is substantially smaller than that of gas phase CO.

High enthalpy source dedicated to quantitative infrared emission spectroscopy of gas flows at elevated temperatures.

The High Enthalpy Source (HES) is a novel high temperature source developed to measure infrared line-by-line integrated absorption cross sections of flowing gases up to 2000 K. The HES relies on a porous graphite furnace designed to uniformly heat a constant flow of gas. The flow compensates thermal dissociation by renewing continuously the gas sample and eliminating dissociation products. The flowing characteristics have been investigated using computational fluid dynamics simulation confirming good temperature uniformity. The HES has been coupled to a high-resolution Fourier transform spectrometer to record emission spectra of methane at temperatures ranging between 700 and 1400 K. A radiative model has been developed to extract absolute line intensities from the recorded spectra.

He and H2 broadened propane cross sections in the 3 µm region at cold temperatures

Infrared absorption cross sections of pure propane, as well as propane broadened by He or H2, have been obtained from spectra recorded using Fourier transform instruments located at the Old Dominion University (ODU) and at the Canadian Light Source (CLS). Pressure and temperature regimes for He and H2 foreign gas broadening range from 10 Torr to 300 Torr between 298 K and 200 K. The integrated absorption cross sections were compared to reference data obtained from the Pacific Northwest National Laboratory (PNNL) spectroscopic database, with most values lying within ±10% of their expected values.

Measurement and extrapolation modeling of PAH laser-induced fluorescence spectra at elevated temperatures

The laser-induced fluorescence technique is widely used in the measurement of polycyclic aromatic hydrocarbons (PAHs) in sooting flames. One of the main limitations is the absence of the PAH fluorescence spectra at elevated temperatures. In this study, fluorescence spectra and photophysical properties of five typical PAHs were experimentally studied in the temperature range of 673–1373 K in an optical cell. The experimental results indicated that the fluorescence spectra of PAHs were greatly sensitive to PAH structures and were likely to shift to the red and became broader as temperature increases. Further, we also observed that absorption cross sections of PAHs increased linearly as a function of temperature. Fluorescence quantum yields, which were calculated using integral fluorescence intensities and absorption cross sections, decreased monotonically with increasing temperature. However, the descent gradients of different PAHs were quite different, e.g., naphthalene, fluoranthene and fluorene were more sensitive to temperature, and their fluorescence production was much lower at elevated temperature compared with phenanthrene and pyrene. In order to investigate the fluorescence quantum yields at higher temperatures (up to 2000 K), which cannot be measured in the optical cell, a multistep decay model was established and optimized based on experimental results. At temperatures between 1373 and 2000 K, the extrapolation results indicated that fluorescence quantum yields of phenanthrene and pyrene would be two orders of magnitude higher than those of naphthalene, fluorene and fluoranthene. This contributed to explaining that the PAH fluorescence signals emitted from phenanthrene and pyrene were stronger than those emitted from naphthalene in flames, although the concentrations of phenanthrene and pyrene were much lower than that of naphthalene in flames.

Cr L-Edge X-ray Absorption Spectroscopy of CrIII(acac)3 in Solution with Measured and Calculated Absolute Absorption Cross Sections.

X-ray absorption spectroscopy at the L-edge of 3d transition metals is widely used for probing the valence electronic structure at the metal site via 2p-3d transitions. Assessing the information contained in L-edge absorption spectra requires systematic comparison of experiment and theory. We here investigate the Cr L-edge absorption spectrum of high-spin chromium acetylacetonate CrIII(acac)3 in solution. Using a transmission flatjet enables determining absolute absorption cross sections and spectra free from X-ray-induced sample damage. We address the challenges of measuring Cr L absorption edges spectrally close to the O K absorption edge of the solvent. We critically assess how experimental absorption cross sections can be used to extract information on the electronic structure of the studied system by comparing our results of this CrIII (3d3) complex to our previous work on L-edge absorption cross sections of MnIII(acac)3 (3d4) and MnII(acac)2 (3d5). Considering our experimental uncertainties, the most insightful experimental observable for this d3(CrIII)-d4(MnIII)-d5(MnII) series is the L-edge branching ratio, and we discuss it in comparison to semiempirical multiplet theory and ab initio restricted active space calculations. We further discuss and analyze trends in integrated absorption cross sections and correlate the spectral shapes with the local electronic structure at the metal sites.

Influence of F– on stark splitting of Yb3+ and the thermal expansion of silica glass

A local phosphate/fluoride environment of Yb3+ was created in silica glass using a multi-step method. The influence of F- on the Stark splitting of Yb3+ in Al3+/P5+/F- co-doped silica glass was studied at room-temperature, in addition to its effect on the thermal expansion performance of the glass matrix. The results indicate that Yb3+ ions in Al3+/P5+/F- co-doped silica glass have a larger Stark splitting energy of 2F7/2 compared to Al3+/P5+ co-doped silica glass. Moreover, a larger integrated absorption cross-section (34.58 pm2 × nm), stimulated emission cross-section (0.63 pm2), and better thermal expansion performance (1.3062 × 10−6 K- at 100 °C) are achieved in Al3+/P5+/F- co-doped silica glass. Finally, different function mechanisms of F- in silica and phosphate glasses were analyzed and the F-Si bond was used to explain the results in silica glass. The combination of low refractive index, large Stark splitting energy of 2F7/2, and small thermal expansion makes Al3+/P5+/F- co-doped silica glass a preferred material for large mode area fibers for high-power laser applications.

A quantum-mechanical perspective on linear response theory within polarizable embedding.

We present a derivation of linear response theory within polarizable embedding starting from a rigorous quantum-mechanical treatment of a composite system. To this aim, two different subsystem decompositions (symmetric and nonsymmetric) of the linear response function are introduced and the pole structures as well as residues of the individual terms are discussed. In addition to providing a thorough justification for the descriptions used in polarizable embedding models, this theoretical analysis clarifies which form of the response function to use and highlights complications in separating out subsystem contributions to molecular properties. The basic features of the presented expressions and various approximate forms are illustrated by their application to a composite model system.

Structural and luminescence properties of Dy3+ doped bismuth phosphate glasses for greenish yellow light applications

Different compositions of (5, 10, 15 and 20 mol%) of bismuth and different concentrations (0.5, 1.0, 1.5 and 2.0 mol%) of Dy3+ ion doped bismuth phosphate (BiP) glasses were synthesized by melt-quenching technique. The structural characterization was accomplished by XRD, SEM with EDS, FTIR, FT-Raman and 31P MAS NMR spectroscopy. The optical properties were studied using absorption and photoluminescence spectroscopy. Different structural groups were identified using FTIR and FT-Raman spectra. The depolymerization of metaphosphate chains are described by the decrease of Q2 tetrahedral sites allowing the formation of pyrophosphate groups (Q1) revealed by 31P MAS NMR spectroscopic investigations.Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6) were evaluated from absorption spectra. Radiative parameters such as radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βR) were calculated using Judd-Ofelt intensity parameters. From photoluminescence spectra, experimental branching ratios (βexp) and stimulated emission cross-sections (σP) were calculated for all the observed emission transitions of prepared glasses. The decay profiles for 4F9/2 level were recorded and fit exponential for 0.5 mol% and non-exponential for higher concentrations of Dy3+ due to non-radiative energy transfer among excited Dy3+ ions. The CIE chromaticity co-ordinates have been calculated from the luminescence spectra which confirmed greenish yellow light emission.

Preparation and laser properties of Yb3+-doped microstructure fiber based on hydrolysis-melting technique

The Yb3+-doped silica glass was prepared by the SiCl4 hydrolysis doping and powder melting technology based on high frequency plasma. The absorption and emission characteristics of the Yb3+-doped silica glass are studied at room temperature. The integrated absorption cross section, stimulated emission cross section and fluorescence lifetime are calculated to be 8.56×104 pm3, 1.39 pm2 and 0.56 ms, respectively. The Yb3+-doped microstructure fiber (MSF) was also fabricated by using the Yb3+-doped silica glass as fiber core. What’s more, the laser properties of the Yb3+-doped MSF are studied.

Optical properties and spectroscopic study of different modifier based Pr3 +:LiFB glasses as optical amplifiers

In this paper, we report the preparation and optical characterization of Pr3+ doped lithium fluoro borate (LiFB) glasses for six different chemical compositions of Li2B4O7-BaF2-NaF-MO (where M=Mg, Ca, Cd and Pb), Li2B4O7-BaF2-NaF-MgO-CaO and Li2B4O7-BaF2-NaF-CdO-PbO. The structural and optical properties of these glasses were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), optical absorption and photoluminescence techniques. The optical absorption spectra of Pr3+ ions in LiFB glasses have been recorded in the UV–VIS-NIR region. The optical absorption data are used to calculate various spectroscopic parameters such as Racah (E1, E2, E3) and spin-orbit interaction (ξ4f) parameters. Judd-Ofelt (J-O) (Ωλ where λ=2, 4 and 6) intensity parameters were determined by applying J-O theory, which in turn used to calculate the radiative properties such as radiative transition probabilities (A), radiative lifetimes (τR), integrated absorption cross-sections (Σ) and branching ratios (βr) for all emission levels of Pr3+ ion in different LiFB glass matrices. By using the J-O theory and luminescence parameters, stimulated emission cross sections (σp) of prominent transitions, 3P0→3H4 and 1D2→3H4 of Pr3+ ion in all LiFB glasses were calculated. 3P0→3H4 possesses higher branching ratios and stimulated emission cross-sections for the Pr3+:LiFB(Mg-Ca) glass, which can be used as a best laser excitation. The optical gain parameter (σpxτR) was noticed higher in Pr3+:LiFB(Mg-Ca) and Pr3+:LiFB(Cd-Pb) glasses for the transition 3P0→3H4 transition, and these glasses have potential for optical amplification at 488 nm wavelength.

Compositional-dependent properties of Pr3+-doped multicomponent fluoro-phosphate glasses for visible applications: a photoluminescence study

Five fluoro-phosphate (FP) glasses of different compositions, 49.5P2O5–10AlF3–10BaF2–10SrF2–10PbO–10M (M = Li2O, Na2O, K2O, ZnO, and Bi2O3), doped with 0.5 mol% praseodymium were prepared by melt quenching technique. For these glass matrices, structural, thermal, dielectric, electrical, and optical properties have been studied. The structures are characterized by XRD, Fourier transform infrared, Raman spectroscopy, and solid-state 31P and 27Al magic angle spinning nuclear magnetic resonance techniques. The chemical and electronic states of these glass materials are characterized by X-ray photoelectron spectroscopy. The thermal stability for the host glass matrix is estimated from differential scanning calorimetry technique. From the impedance spectroscopy, various parameters, viz. electrical conductivity, dielectric constant (e′), and dielectric losses (tan δ), at various frequencies and temperatures have been measured. X-ray absorption near-edge spectroscopy was used to study the electronic structure of praseodymium in the host glass matrices. By analyzing the absorption spectra with Judd–Ofelt theory, three intensity parameters (Ω λ , λ = 2, 4, 6) are obtained. In turn, these parameters are used to calculate radiative properties such as emission probabilities (A R), radiative lifetimes (τ R), and integrated absorption cross sections (Σ) of different Pr3+ transitions. Luminescence parameters such as stimulated emission cross sections (σ p) and branching ratios (β exp) have been studied through photoluminescence spectra. Further, decay time constants are estimated from the decay profiles of Pr3+-doped different FP glasses.

MIPAS database: new HNO<sub>3</sub> line parameters at 7.6 µm validated with MIPAS satellite measurements

Abstract. Improved line positions and intensities have been generated for the 7.6 µm spectral region of nitric acid. They were obtained relying on a recent reinvestigation of the nitric acid band system at 7.6 µm and comparisons of HNO3 volume mixing ratio profiles retrieved from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) limb emission radiances in the 11 and 7.6 µm domains. This has led to an improved database called MIPAS-2015. Comparisons with available laboratory information (individual line intensities, integrated absorption cross sections, and absorption cross sections) show that MIPAS-2015 provides an improved description of the 7.6 µm region of nitric acid. This study should help to improve HNO3 satellite retrievals by allowing measurements to be performed simultaneously in the 11 and 7.6 µm micro-windows. In particular, it should be useful to analyze existing MIPAS and IASI spectra as well as spectra to be recorded by the forthcoming Infrared Atmospheric Sounding Interferometer – New Generation (IASI-NG) instrument.

Concentration dependent luminescence properties of Dy3+ doped lead free zinc phosphate glasses for visible applications

Dysprosium (Dy3+) doped lead free zinc phosphate glasses with chemical compositions (60 − x) NH4H2PO4 + 20ZnO + 10BaF2 + 10NaF + xDy2O3 (where x = 0.5, 1.0, 1.5, 2.0 mol%) have been prepared by melt quenching technique. The functional groups of vibrational bands have been assigned and clearly elucidated by FTIR and Raman spectral profiles for all these glass samples. Judd–Ofelt (J–O) intensity parameters (Ωλ: λ = 2, 4, 6) have been obtained from spectral intensities of different absorption bands of Dy3+ doped glasses. Radiative properties such as radiative transition probabilities (A R ), radiative lifetimes (τ R ), branching ratios (β R ) and integrated absorption cross-sections (Σ) for different excited states are calculated by using J–O parameters. Luminescence spectra exhibit three emission bands (from 4F9/2 level to 6H15/2, 6H13/2 and 6H11/2) for all the concentrations of Dy3+ ions before and after gamma irradiation. Various luminescence properties have been studied by varying the Dy3+ concentration for the three spectral profiles. Fluorescence decay curves of 4F9/2 level have been recorded. The energy transfer mechanism that leads to quenching of 4F9/2 state lifetime has been discussed by the variation of Dy3+ concentration. These glasses are expected to be useful for yellow luminescent materials.