Absolute Line Intensities Research Articles

Mid-infrared high-resolution dual-comb spectroscopy: Intensity, broadening, and beyond-Voigt parameters of [formula omitted] and [formula omitted] lines

Using a high-resolution mid-infrared dual-comb spectrometer operating in the 1300 cm−1 spectral region, spectra of acetylene were recorded at room temperature. Spectroscopic parameters were measured in 3 vibrational bands of both 12C2H2 and 13C12CH2. Absolute line intensities (S0) and self-broadening coefficients (γ0self) were determined in the ν4+ν5, 2ν42+ν5−1⟵ν41 and ν41+2ν50⟵ν51 bands. For the main isotopologue, the collisional narrowing coefficients (ν0VC) as well as the speed-dependence of the broadening (γ2) and shifting (δ2) coefficients were measured in the ν4+ν5 band of the main isotopologue of acetylene. Theoretical line-shape models were fitted on experimental profiles using a homemade multi-spectrum fitting procedure to determine spectroscopic parameters. Excellent agreement with the literature was found for self-broadening coefficients and absolute line intensities in the ν4+ν5 band of 12C2H2. For the hot bands, good agreement with the literature is found within experimental uncertainties, while γ0self of those hot bands are also reported for the first time. Similarly, the rotational dependence of ν0VC is found to be close to previous works. γ2 and δ2 of 12C2H2, as well as S0 and γ0self of 13C12CH2 are also reported for the first time in this band.

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.

New line intensities for the far infrared bands of the Trans- and Cis-conformer of nitrous acid (HONO), new determination of the Trans-Cis conformer barrier and its impact on the astrophysical detection of nitrous acid in protostellar clouds

The first goal of this work is to improve the determination of the energy difference (ΔECis-Trans) between the ground vibrational state of the Cis- and Trans-HONO conformers of nitrous acid. For this, high resolution spectra were recorded in the 50–200 cm−1 spectral region at three different temperatures, 240, 270 and 296 K. The relative line intensities for the B-type transitions of pure rotational bands of Trans-HONO and Cis-HONO achieved from our measurements were combined in least squares fit computations to those measured previously by Sironneau et al. [Sironneau V, Flaud JM, Orphal J, Kleiner I, Chelin P. Absolute line intensities of HONO and DONO in the far-infrared and re-determination of the Energy Difference between the trans- and cis-species of nitrous acid. J Mol Spectrosc 2010;259:100–104]. In this way, we can significantly improve the accuracy on the HONO conformer energy difference, with a value for ΔECis-Trans = 95.8 ± 9.2 cm−1 compared to SIRΔECis-Trans = 99 ± 25 cm−1 in the previous study of Sironneau et al. The second goal is to generate a line list with “absolute” line intensities for the pure rotational bands in the far infrared region of Trans-HONO and Cis-HONO, with both A- and B-type transitions. This new line list proved to be more robust for an improved detection of HONO in astrophysical objects [Coutens A, Ligterink NFW, Loison JC, Wakelam V, Calcutt H, Drozdovskaya MN, Jørgensen JK, Müller HSP, Van Dishoeck EF, Wampfler SF. The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium. Astronomy & Astrophysics 2019;623:L13].

ABSOLUTE INTENSITIES OF HELIUM LINES AND SPACE RESOLVED ELECTRON DENSITIES AND ENERGIES IN DISCHARGE WITH A HOLLOW CATHODE IN HE:H2O GAS MIXTURE

In a discharge with a hollow cathode the electron energy distribution functions (EEDFs), electron concentration, and absolute intensities of pure helium and helium mixtures with water vapor at pressures of 2-3 mbar were measured. It was shown that under the experiment conditions, the EEDFs were significantly different from the Maxwellian function since the amount of high-energy electrons in the energy range of 7-24 eV was much larger. As the concentration of water molecules in plasma increased, the amount of high-energy electrons decreased. The absolute intensities of a number of helium lines were calculated in coronal model approximation. It was determined that the lines reasonably agreed with the experimental measurements of the absolute intensities.

Study of water vapor line parameters in the region around 1.1 µm by tunable diode laser spectroscopy

AbstractTo analyze the absolute line intensities, as well as the coefficients of air‐ and self‐broadening of water vapor, 31 transition lines were measured using an external‐cavity diode laser (ECDL) in the range of 9090–9750 cm−1. A multispectrum fitting (MSF) program was used in conjunction with a quadratic speed‐dependent Voigt profile (qSDVP) and a Voigt profile (VP) to extract the line intensities and self‐ and air‐broadening coefficients. Values at room temperature (296 K) were then compared with the HITRAN2016 and HITRAN2020 database. The analysis results show that the line intensities and air‐broadening coefficients are more consistent with the database while also verifying that the self‐broadening coefficients obtained based on qSDVP are larger than those based on VP.

Экспериментальные интенсивности линий колебательно-вращательных переходов в полосах ν1+ ν2 и ν2+ ν3 молекулы D234S

The study of the absolute line intensities in the high-resolution spectrum of the D234S molecule in the range 2300-2900 cm-1 has been carried out for the first time. As a result of the analysis, about 800 experimental intensities of vibrational-rotational transitions were obtained for the v 1 + v 2 and v 2 + v 3 bands, and a set of 6 parameters of the effective dipole moment was calculated, which reproduces the initial experimental line intensities with drms = 9.7%. A list of transitions with frequencies and line intensities in the range under study has been compiled.

Measurements of the absolute intensities of spectral lines of Kr, Ar, and O ions in the wavelength range of 10 – 18 nm under pulsed laser excitation

We have measured the absolute intensities of the spectral lines of Kr, Ar, and O ions (CO2 gas), which are of interest for reflectometry, microscopy, and lithography in the wavelength range of 10 – 18 nm. We have used pulsed excitation by an Nd : YAG laser with an output wavelength λ = 1064 nm, a pulse energy of 0.8 J, a pulse duration of 5.2 ns and a pulse repetition rate of 10 Hz. The targets are formed during gas outflow through a pulsed supersonic conical nozzle for an inlet gas pressure of 3.5 bar. A spectrometer based on X-ray multilayer mirrors and its calibration procedure are described in detail. The absolute intensities of the spectral lines of Kr IX (λ = 11.5 nm; number of photons: N = 9.3 × 1012 photons pulse−1), Ar VIII (λ = 13.84 nm, N = 3 × 1012 photons pulse−1), and O VI (λ = 12.98 nm, N = 5.17 × 1012 photons pulse−1). The results are compared with the data obtained for Xe ions under the same experimental conditions at the same wavelengths.

Towards the intensity consistency of the ozone bands in the infrared range: Ab initio corrections to the S&MPO database

Accurate knowledge of line parameters, and particularly line intensities is of primary importance for satellite, ground based and balloon measurements of the ozone concentration in the atmosphere. Self-consistency in absolute band intensities of ozone in various spectral intervals is necessary to avoid discrepancies in the atmospheric ozone retrieval from different windows. Difficulties in precise experimental characterization of absolute line intensities of this unstable molecule are well known leading to many significant deviations in published intensity values and in spectroscopic compilations. Ab initio intensities computed from the dipole moment functions of our previous works (Tyuterev et al. JCP 2017;146:064304; JCP 2019;150:184303) have permitted achieving a consistency between Stark-effect measurements and various databases in 10 and 5 µm in a good agreement with the most accurate recent experiments. In this paper we extend ab initio corrections to available line lists of ozone band intensities in wider IR range up to the bands with four vibrational quanta. About 40% of intensities were corrected in the 0 - 4122 cm−1 range for thirty cold and hot bands of the main ozone 16O3 isotopologue. Most of them, but not all, were obtained using band specific scaling factors ranging from 0.75 to 1.17 making quite significant changes in the absolute values. The full line lists containing corrected line intensities in the spectral intervals considered in the paper are provided in the Supplementary material for this work. The resulting line list is now available on the web site of the “Spectroscopy and Molecular Properties of Ozone” (S&MPO) information system (http://smpo.iao.ru; http://smpo.univ-reims.fr). A large part of this line list including the ab initio correction reported in this work will be used in the future HITRAN20 update.

High-resolution cw-cavity ring-down spectroscopy of allowed (ν4 + ν5)0 and forbidden (ν4 + ν5)2 bands of C2H2 using external-cavity quantum cascade laser

In this paper, we measured the absolute line intensities and air broadening coefficients of several rotationally resolved lines in the P and R branches of the allowed (ν4 + ν5)0 and forbidden (ν4 + ν5)2 vibrational combinational bands of C2H2 at room temperature 296 K. These measurements were performed using an external-cavity quantum cascade laser (EC-QCL) operating at 7.5 μm coupled with high-sensitive cavity ring-down spectroscopy (CRDS). Rotational level-dependent pressure-broadening coefficients of the resolved spectral lines of the selected transitions from (ν4 + ν5)0 band are reported here. The air broadening coefficients for 5 rotational lines from P-branch of (ν4 + ν5)2 band were also obtained first time with better than 3% uncertainty. The vibrational transition dipole moment squared values of the rotational lines and empirical Herman-Wallis coefficients were also quantified from experimental data. Finally, experimentally obtained all spectroscopic parameters were rigorously compared with previous studies. The new experimental data including several spectroscopic parameters will be useful for atmospheric and astrophysics applications.

Self-absorbed Ca doublet lines for stand-off quantitative analysis by laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) is one of the promising techniques for stand-off detection of element composition. However, it is somewhat limited by quantitative shortage. Absolute line intensity may be influenced by acquisition conditions, environmental variation, and sample surface conditions. Relative intensity may also fluctuate greatly. This study shows that the intensity ratio between Ca II doublet emission lines (393.37 nm and 396.85 nm) is stable, and changes with Ca concentration (or Ca atoms count within the laser spot). This is due to differences in self-absorption between the two transitions. A theoretical calibration shows a linear section for low species density and quadratic section for high species density. Experimental results confirm the linear section after density correction of CaO pellets. However, an equipment factor should be considered for numerical calibration in different laboratories. For Ca-containing samples, quantitative analysis could be based on the detected Ca spectrum. Ca is also shown to be suitable as an internal standard reference to determine other elemental concentration, such as Mg.

Light-reflection-induced changes in the line shape of sputtered atoms

The erosion from plasma-facing components has to be monitored in many kind of laboratory and fusion plasmas. For this purpose, spectroscopy is an essential tool. Under certain conditions the particle flux can be calculated from the absolute line intensities of the sputtered material using so-called S/XB values. The impact of light reflection on the emission induced by sputtered particles at the mirror-grade polished surface of tungsten (W) and aluminum (Al) was investigated in a low-density (ne ≈ 2 × 1012 cm−3) and low-temperature (Te ≈ ) argon (Ar) plasma in the linear plasma device PSI-2 using high-resolution spectroscopy. Using the line shape affected by Doppler shift we show that the light reflection has a considerable impact on the number of measured photons and has to be taken into account for calculating particle fluxes. The Al target was sputtered by Ar ions at the incident ion energy of . The measured profile of the Al I line () was compared with a Doppler-shifted emission model based on the Thompson energy distribution function. In this new model, the instrumental broadening and the impact of the Zeeman effect were also taken into account. The parameter for the high-energy fall-off n of the energy distribution function (), the surface binding energy Eb and the surface reflectance were derived by comparing the experimental and the synthetic spectrum. The W target was sputtered by Ar ions at incident ion energies in the range of –. The influence of the ion impact energy on the energy distribution of the sputtered particles was demonstrated.

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.

Emission Spectroscope Diagnostics of Direct Current Plasma Jets Used for YSZ Equiaxed Structure Coatings

This study combines spectroscope diagnostics of the plasma jet under APS and the characterization of sprayed coatings by using nanoparticles yttria partially stabilized zirconia (YSZ) powder. The absolute intensities of ArⅠneutral species spectrum lines were used to estimate the electron excited temperature of the thermal plasma jets by the Boltzmann method. The effects of the detection distances, current intensities and H2 flow rates on electron temperature were analyzed. The plasma sprayed YSZ coatings were heated to 1200°C for 6 min under the atmosphere, and then the micro-structure of the nanostructured powder and coatings were analyzed by using Field Emission Scanning Electron Microscope. The results showed that the increase of input power and H2 content considerably increased the electron temperature, while the electron temperature decreased a lot with the increase of the detection distance. The coatings were consisted of the equiaxed grains and a small-size grain shape pores.

New spectral reduction algorithm for echelle spectrometer in laser-induced breakdown spectroscopy.

In this work, a new spectral reduction algorithm for the echelle spectrometer was proposed. Unlike conventional approaches, the key concept in this algorithm is to model the spectrogram rather the spectrometer, which makes the algorithm more adaptive to different designs. This algorithm also introduces a dynamic adjusting procedure for generating optimized spectra from laser-induced plasmas. This additional step improved the spectrum stability and absolute line intensity of the spectrum and yielded better quantification performance. Experimental results demonstrated that the quantification results of analyzing aluminum alloy samples were improved using this new algorithm.

Line intensities for the ν6 and 2ν3 bands of methyl iodide (12CH3I)

The goal of this study is to measure for the first time absolute line intensities for the ν6 band of methyl iodide (CH3I) centered at 892.918 cm–1. High-resolution Fourier transform spectra were recorded at various pressures for the whole 500–1450 cm–1 spectral range. Using these spectra, a large set of CH3I individual line intensities was measured for the ν6 band. These experimental intensities were least squares fitted to derive the expansion of the ν6 transition moment operator. The theoretical model used to describe the line positions and intensities accounts for the hyperfine structure in the 61 and ground states and for the vibration-rotation resonances that couple the 61 energy levels with those of the 32 and 21 vibrational states [Perrin et al., J. Mol. Spectrosc. 324 (2016) 28–35]. As the 2ν3 band is extremely weak, its associated transition moment operator was estimated from band strength available in the literature. A comprehensive list of line positions and intensities was generated for the ν6 and 2ν3 bands of CH3I at 11 µm, which should be useful for the possible detection of this species by the future IASI-NG satellite instrument (Infrared Atmospheric Sounding Interferometer New Generation), now under preparation (https://iasi-ng.cnes.fr/en/IASI-NG/index.htm).

Determination of the Absolute Intensities of Spectral Lines of the 12С2H4 Molecule

As a result of analysis of the experimental spectrum of the 12C5H4 molecule, the absolute intensities of some spectral absorption lines in the region 2900–3100 cm–1 are determined.

The multi-spectral imaging diagnostic.

The Multi-Spectral Imaging system is a new diagnostic that captures simultaneous spectrally filtered images from a common line of sight while maintaining a large étendue and high throughput. Imaging several atomic line intensities simultaneously may enable numerous measurement techniques. By making a novel modification of a polychromator layout, the MSI sequentially filters and focuses images onto commercial CMOS cameras while exhibiting minimal vignetting and aberrations. A four-wavelength system was initially installed and tested on Alcator C-Mod and subsequently moved to TCV. The images are absolutely calibrated and spatially registered enabling 2D mappings of atomic line ratios and absolute line intensities. The spectral transmission of the optical system was calibrated using an integrating sphere of known radiance. The images are inverted by cross-referencing points on TCV with a computer-aided design (CAD) model.

Analysis of the Intensities of the Absorption Lines in the υ7 Band of the C2D4 Molecule

Absolute intensities of the absorption lines of the deuterated modification of the ethylene C2D4 molecule, namely, the ν7 band are measured for the first time.

Absolute line intensities and first measurements of self-collisional broadening and shift coefficients in the 2ν4 band of NH3

Absolute line intensities and a first determination of self-broadening and shift coefficients are presented here, deduced from room temperature measurements for 302 rovibrational lines of NH3 in the 2ν4 band, using Fourier transform infrared spectroscopy. These lines, ranging from 1 ≤ J ≤ 11 to 0 ≤ K ≤ 11, are located in the 3060–3580 cm−1 spectral range. The lines were fitted with a single spectrum non-linear least squares fitting procedure. The absence of signature in the residuals suggests that the Voigt profile is well suited to fit the experimental line shapes without the need of taking into account line mixing effects, in the pressure range used. Average absolute accuracies of the measurements are estimated to ±4% for line intensities and self-broadening coefficients and to ±13% for self-shift coefficients. The J and K dependences of the self-broadening coefficients have been observed and modeled using an empirical polynomial expression. The results are compared with previous experimental and calculated data. Our absolute line intensities, S0, are in good agreement with previous work and HITRAN2016 database, but with a reduced uncertainty. The self-broadening coefficients, γ0, as well as the pressure shift coefficients, δ0, are in reasonable agreement with those reported for various vibrational bands in the 3 µm spectral region, which indicates that no obvious vibrational dependence was observed. For shift coefficients, it should be noted that this is not the case in many studies which put in evidence a large dependence with vibrational excitation. This study complements the existing line parameters in the 3 µm spectral region, essential for the analysis of atmospheric spectra. For this purpose, the complete list of measurements is provided as supplementary material.

Studying the Absolute Intensities of the Absorption Lines of 2ν7 and ν2 Bands of the CH2 = CD2 Molecule in the Region 1450–1650 cm–1

As a result of analysis of the high-resolution Fourier spectrum, the absolute intensities of absorption lines of the CH2 = CD2 molecule are measured for the first time.