Effective Dipole Moment Parameters Research Articles

Unrivaled accuracy in measuring rotational transitions of greenhouse gases: THz CRDS of CF4.

Tetrafluoromethane CF4 is the most abundant perfluorocarbon in the atmosphere, where it is designated as PFC-14. This greenhouse gas is very stable, has an atmospheric lifetime of 50 000 years, and a high greenhouse warming potential 6500 times that of CO2. Over the last 15 years, its atmospheric concentration has increased at a rate of 0.8 ppt per year. The accurate quantification of CF4 is key to understanding the contribution of its emissions to the radiative forcing budget, and the most precise spectroscopic parameters possible are hence required. In this study, a novel high finesse THz cavity, providing an interaction length in excess of 1 km, has enabled highly resolved spectra, and quantification of the weak transitions of CF4 by cavity ring-down spectroscopy (CRDS). More than 50 pure rotational P6 - P6 : ν3 - ν3 lines of CF4 have been measured, yielding both position and intensity with unequalled precision. Several tetrahedral splittings are fully resolved and measured with sub-MHz accuracy. Moreover, CRDS-THz allows determining absolute intensities and, using a global fit of the ν2 polyad series, a CF4 dipole parameter, namely 3,3, has been fitted to 106.38(53) mD. This value is in very good agreement with that of the ab initio-based parameter deduced from a dipole moment surface. For the first time, a set of ab initio effective dipole moment parameters is derived for the computation of the transitions of the type Pn - Pn (n = 0,…, 8) and the resulting line list composed of 25 863 transitions can be used to model the whole CF4 rotational spectrum. Finally, the TFMeCaSDa database is updated and is available for future spectroscopic and monitoring activities.

Comparative line position and line strength analysis of the [formula omitted] dyad of [formula omitted] and [formula omitted

A highly accurate ro-vibrational analysis of FTIR spectra (line positions of 13CD4 and line strengths of both the 12CD4 and 13CD4 species) is presented. The high-resolution infrared spectra of both molecules were measured with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.003 cm−1 and analyzed in the regions of 800–1400 cm−1 where the ν2/ν4 dyad is located. The number of 901 transitions with Jmax=23 were assigned to the ν4 and ν2 bands of 13CD4 (this number is about 5.3 times higher in comparison with the number of known assigned transitions for 13CD4). The weighted fit of experimental line positions was made using the Hamiltonian model which takes into account the resonance interactions between the (0001,F2) and (0100,E) vibrational states. As a result, set of 18 fitted parameters of the (0001,F2)/(0100,E) vibrational states of 13CD4 was determined which reproduce the initial 901 experimental ro–vibrational line positions with the drms=2.59×10−4 cm−1, which is close to the experimental uncertainty of the recorded spectra and about 1330 times better in comparison with the reproduction of the same line position values by the use of parameters from Loëte et al. (1983). The analysis of 1557 experimental lines of the dyad of 12CD4 and 131 lines of the dyad of 13CD4 was fulfilled with the Hartmann–Tran profile to simulate the measured line shape and to determine experimental line intensities. Sets of 6/1 varied effective dipole moment parameters of 12CD4/13CD4 are determined which reproduce the initial 1557/131 line strengths with the drms=4.80% and 4.21%. Lists of the assigned line positions and strengths in the studied region are presented as the Supplementary data to this paper.

Effective Dipole Moment Model for Axially Symmetric C3v Molecules: Application to the Precise Study of Absolute Line Strengths of the ν6 Fundamental of CH335Cl.

The effective dipole moment model for molecules of axial C3v symmetry is derived on the basis of the symmetry properties of a molecule which, on the one hand, is of the same order of efficiency (but much simpler and clearer in applications) as the analogous models derived on the basis of the irreducible tensorial sets theory, and, on the other hand, mathematically more correct in comparison with concepts like the Herman-Walles function used in the models. As an application of the general results obtained, we discuss high-resolution infrared spectra of CH335Cl, recorded with the Zürich prototype ZP2001 (Bruker IFS125 HR) Fourier transform infrared spectrometer at a resolution of 0.001 cm-1 and analyzed in the region of 880-1190 cm-1 (ν6 bending fundamental centered at ν0 = 1018.070790 cm-1). Absolute strengths of more than 2800 transitions (2081 lines) were obtained from the fit of their shapes both with Voigt and Hartmann-Tran profiles, and parameters of the effective dipole moment of the ν6 band were determined by the computer code SYMTOMLIST (SYMmetric TOp Molecules: LIne STrengths), created on the basis of a derived theoretical model. As the first step of the analysis of the experimental data, assignments of the recorded lines were made. A total of 5124 transitions with Jmax = 68, Kmax = 21 were assigned to the ν6 band. The weighted fit of 2077 upper energy values obtained from the experimentally recorded transitions was made with a Hamiltonian which takes into account different types of ro-vibrational effects in doubly degenerate vibrational states of the C3v-symmetric molecule. As the result, a set of 25 fitted parameters was obtained which reproduces the initial 2077 upper "experimental" ro-vibrational energy values with a root mean square deviation drms=4.7×10-5 cm-1. At the second step of the analysis, the computer code SYMTOMLIST was used for determination of the parameters of the derived effective dipole moment model. Six effective dipole moment parameters were obtained from the weighted fit procedure which reproduces absolute experimental strengths of the 2804 initial experimental transitions with a relative drms=3.4%.

New acetylene line list near 3.8-µm - Part I

Two acetylene spectra were recorded between 2350 and 2750 cm−1 with Fourier Transform Spectrometer (FTS) using high optical path length. 14 bands were observed for the first time including one cold band. The positions and the intensities of the lines have been measured for 824 transitions of the 12C2H2 isotopologue. The band centers, the band strengths, the upper level spectroscopic constants and the Herman-Wallis parameters were retrieved for all bands. The effective dipole moment parameters of the ΔP = 4 region were refined, P being the polyad number defined as P = 5V1 + 3V2 + 5V3 + V4 + V5, where Vi are the vibrational normal mode principal quantum numbers, with i = 1 − 5. An updated line list for the ∆P = 4 series of transitions is proposed as supplementary data in order to improve the spectroscopic databases such as HITRAN or GEISA.

The ν3 band of 16O14N18O: Line positions and intensities

The Fourier transform IR spectra of samples prepared by mixing two gaseous species 18O2/14N16O (1:2) have been recorded in the region of the ν3 band of nitrogen dioxide. The spectra contain the lines corresponding to the ν3 band of the 16O14N18O isotopologue within the 1540–1640 cm−1. In total 1795 lines of the ν3 band of this isotopologue were assigned with the rotational quantum numbers N and Ka up to 51 and 12, respectively, what corresponds to 3487 electron spin-rotation-vibration transitions. The overall measured set of the line positions was used to fit the effective Hamiltonian parameters. The fitted set of the parameters reproduces the observed line positions with an rms of 3.6 × 10−3 cm−1. A selected set of the measured line intensities was used to determine the effective dipole moment parameters describing the line intensities of the ν3 band. The rms deviation of the fit is 5.0%. It was found that the lines with the ΔKa = ±1 are very weak compared to those with the ΔKa =0. At attained sensitivity only few lines with the ΔKa = ±1 were assigned. The measured line intensities lead to the small value of the dipole moment derivatives ratio |(∂μx/∂q3)(∂μz/∂q3)|≈0.139.

Infrared spectra of 16O3 in the 900 - 5600 cm−1 range revisited: Empirical corrections to the S&MPO and HITRAN2020 line lists

The paper presents the results of the analysis of experimental FTS infrared vibration-rotation spectra of 16O3 ozone isotopologue recorded in Reims University in the range from 900 to 5600 cm−1, which was used for the current version of the S&MPO database and web-accessible information system (http://smpo.iao.ru; http://smpo.univ-reims.fr). The majority of the reported data is related to the accurate determination of line positions. New parameters of effective Hamiltonian (EH) models for three polyads of vibrational states {(001), (100)}, {(011), (110)} and {(002), (101), (030), (200)} obtained from accurate fits of observed spectra in 900 – 2200 cm−1 range, have also been described. Further, at the higher wavenumber range 2700 – 5600 cm−1, various perturbations in the observed spectra due to accidental ro-vibrational resonances and which have been at the root of a lack of accuracy in certain regions of the previously published line lists were identified. We have applied empirical corrections to line positions and to corresponding energy levels in cases where the EH models did not provide the target accuracy of 10−3 cm−1 given of more complex polyad structures, which in turn allowed the use of corrected energy levels to compute improved line positions for the hot bands. In terms of line intensities, we publish here the effective dipole moment parameters and the line lists with empirically-determined absolute intensities for the ν1/ν3 dyad which are consistent with recent ab initio calculations for the strongest bands. For the higher wavenumber range, the empirical corrections are applied for relative intensities of some series of individual transitions in order to improve the simulation of observed spectra. A significant part of the reported data is included in the 2020 release of the HITRAN database.

Line strengths, widths and shifts analysis of the [formula omitted][formula omitted] and [formula omitted] bands in [formula omitted]SiH[formula omitted][formula omitted]SiH[formula omitted] and [formula omitted]SiH[formula omitted

The high resolution infrared spectra of SiH4 in its natural abundance were recorded with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.003 cm−1 and analyzed in the region of 1600–2100 cm−1 where the first bending overtone 2ν2,2ν4 and combinational ν2+ν4 bands are located. A line strength analysis of the 2018 (1636/211/171) experimentally recorded transitions of the 28SiH4,29SiH4, and 30SiH4 species was made by the fit of their line shapes with the Hartmann-Tran profile and 9 effective dipole moment parameters (7/1/1 fitted parameters for the 28SiH4,29SiH4 and 30SiH4 species, respectively) were obtained from the weighted fit which reproduce initial experimental line strengths of 28SiH4,29SiH4 and 30SiH4 with the drms=3.65%,3.77% and 3.46%. Self–broadening coefficients of 1064 lines (typically lying between (8 and 10)×10−2 cm−1·atm−1) and self–shift coefficients of 785 lines (typically lying between (5 and 10)×10−3 cm−1·atm−1) of all three isotopologues of silane were determined from the multi–spectrum analysis of these lines.

Line strength analysis of the second overtone [formula omitted] band of D[formula omitted

The high resolution infrared spectrum of di–deuterated hydrogen sulfide D2S was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and analyzed in the region of 2400–2900 cm−1 where ro–vibrational bands of the so–called second triad of D2S are located. The present study is focused on the line strength analysis of the weak 3ν2 band which is made for the first time. The strength analysis comprise 300 lines (376 transitions) with maximum values of the quantum numbers Jmax = 18 and Kamax = 9 and was performed by the fit of the experimental line shapes with a Hartmann–Tran profile. The six effective dipole moment parameters of the 3ν2 band were obtained from the weighted fit which reproduce the initial experimental line strengths with the drms=3.1%.

Comprehensive study of the pentad bending triad region of germane: Positions, strengths, widths and shifts of lines in the [formula omitted][formula omitted] and [formula omitted] bands of [formula omitted]GeH[formula omitted][formula omitted]GeH[formula omitted][formula omitted]GeH[formula omitted][formula omitted]GeH[formula omitted][formula omitted]GeH[formula omitted

The high resolution infrared spectra of GeH4 in its natural abundance were recorded with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.003 cm−1 and analyzed in the region of 1400–2000 cm−1 where the first bending overtone 2ν2,2ν4 and combinational ν2+ν4 bands are located. Ro–vibrational line positions and energies of the 70GeH4 species were analysed for the first time and line positions and energies of the 72GeH4 and 74GeH4 species were improved considerably in comparison with the preceding studies. The numbers of 2316/2406/873/3007/2257 transitions with Jmax = 21/23/18/22/19 of the 2ν2 (A1− and E−type sub–bands), 2ν4 (A1−,E− and F2−type sub–bands) and ν2+ν4 (F1− and F2−type sub–bands) bands of the 70GeH4,72GeH4,73GeH4,74GeH4, and 76GeH4 molecules were used in the joint weighted fit of experimentally assigned transitions with the Hamiltonian model which takes the resonance interactions between the seven, (0200,A1),(0200,E),(0101,F1),(0101,F2),(0002,A1),(0002,E) and (0002,F2), vibrational states into account. From our preceding studies 5563 hot band transitions were also taken into account. As the result of a joint fit, a set of 129 fitted parameters was obtained which reproduce the initial 16422 experimental (including “hot”) transitions of five isotopologues with the drms=3.26×10−4 cm−1. A line strength analysis of the 1697 experimentally recorded transitions of all species was made by the fit of their line shapes with the Hartmann-Tran profile and 13 effective dipole moment parameters were obtained from the weighted fit which reproduce the initial experimental line strengths with the drms=3.4%. Self–broadening coefficients of 993 lines and self–shift coefficients of 674 lines were determined from the multi–spectrum analysis of these lines.

Quantitative analysis of ro–vibrational spectra of ethylene: Line strengths of the [formula omitted] and [formula omitted] bands of [formula omitted]C[formula omitted]H[formula omitted]D[formula omitted]-cis

For the 12C2H2D2-cis molecule a line strength analysis of 1473/400 transitions of the ν12/ν3 bands was performed by the fit of their line shapes with the Hartmann–Tran profile. Ten effective dipole moment parameters (six parameters for the ν12 band and four parameters for the ν3 band) were obtained from the weighted fit which reproduce the initial experimental 1473 transition strengths of the ν12 band with the drms=3.11%. For the very weak ν3 band 400 experimental transitions are reproduced with the drms=7.72%. The results of the analysis are presented as the Supplementary material to this paper.

Ro–vibrational analysis of the first hexad of hydrogen sulfide: Line position and strength analysis of the 4ν2 band of H232S and H234S for HITRAN applications

The high resolution infrared spectrum of hydrogen sulfide H232S was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and analyzed in the region of 4400–5400 cm−1 where ro–vibrational bands of the so–called first hexad of hydrogen sulfide are located. The present study is focused on the weak 4ν2 band. The 505 transitions with maximum values of the quantum numbers Jmax=17 and Kamax=8 (Jmax = 9 and Kamax=7 in the preceding studies) were assigned in the experimental spectrum. On this basis, 132 upper ro–vibrational energies (which is 2.5 times as high as in the preceding studies) were obtained. These data were used in the weighted fit of the Watson Hamiltonian parameters. The 28 varied parameters reproduce the 132 initial energy values with the root mean square deviation drms=3.5×10−4 cm−1. Strength analysis of the 287 strongest experimentally recorded transitions was made by the fit of their line shapes with the Hartmann-Tran profile. The eight effective dipole moment parameters of the 4ν2 band were obtained from the weighted fit which reproduce the initial experimental line strengths with the drms=3.1%. A comparison of the obtained results with the results of variational calculations and HITRAN data is presented. For the first time, transitions of the 4ν2 band of H234S were assigned in the experimental spectrum.

Fourier transform CO spectra near 1.6 μm

The absorption spectra of carbon monoxide have been recorded in the 6000–6450 cm−1 wavenumber regions using the Bruker IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White-type optical system. The spectra were recorded at spectral resolution of 0.008–0.012 cm−1, path length up to 1058 m, and at pressure range from 30 to 320 mbar. The temperature was about 301 K. The lines of the 3-0 bands of six isotopologues 12C16O, 13C16O, 12C18O, 12C17O, 13C18O, 13C17O and the lines of the hot 4-1 band of 12C16O were assigned in the spectra. The line intensities and the self-broadening coefficients were measured. In the case of the principal isotopologue the line intensities were determined for the lines with the angular momentum quantum number J up to 41. The effective dipole moment parameters describing the line intensities of the observed bands were fitted to the observed values of the line intensities. The uncertainty of the line intensity measurements for the strong unsaturated and unblended lines of the principal isotopologue varies between 2% and 2.5%. The comparison of our measured line intensities to those of other authors and of the HITRAN2016 database is given.

Experimental line strengths of the 5ν2 band of H[formula omitted]S in comparison with the results of “variational” calculation and HITRAN database

The strengths of 176 transitions of the 5ν2 band of H232S were experimentally recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and theoretically analyzed. The seven effective dipole moment parameters of this band were obtained from the weighted fit which reproduce the initial experimental line strengths with the drms = 3.4%. A comparison of the obtained results with the results of variational calculation and HITRAN data is presented.

Fourier transforms CO spectra near 1.19 µm

The absorption spectra of carbon monoxide have been recorded in the 8150–8466 cm−1 wavenumber regions using the IFS 125 HR Fourier transform spectrometer and a 30 m multipass cell with the White-type optical system. The spectra were recorded at spectral resolution of 0.012–0.014 cm−1, path length up to 1058 m, and at pressure range from 196 to 492 mbar. The temperature of the recordings was about 302 K. The lines of the 4–0 band of three isotopologues 12C16O, 13C16O and 12C18O were assigned. The effective dipole moment parameters describing the line intensities of the 4–0 band of 12C16O were fitted to the observed values of the line intensities. Then using the isotopic substitution equations they were recalculated to those of the minor isotopologues including the radioactive ones. The accuracy of the line intensity measurements varies between 2% and 3% for the strong unblended lines. The comparison of our measured line intensities to those of other authors and to HITRAN2016 database is given.

Line strengths analysis of germane in the 1100–1350 cm[formula omitted] region: the [formula omitted][formula omitted][formula omitted] and [formula omitted] “hot” bands of MGeH4 (M = 70, 72, 73, 74, 76)

The infrared spectrum of MGeH4 (M=70,72,73,74,76) was measured at the temperature of (296.75 ± 0.1) K with a Bruker Fourier transform infrared spectrometer IFS125 and analyzed in the region of 1100–1350 cm−1 where the ν1−ν4,ν3−ν4,ν3−ν2 and ν1−ν2 “hot“ bands of GeH4 are located. The strengths of 133, 203, 40, 274 and 53 experimentally recorded spectral lines of the 70GeH4, 72GeH473GeH4, 74GeH4 and 76GeH4 isotopologues with the value of quantum number Jmax = 16, 16, 12, 16 and 14 were determined from the fit of their line shapes with a Hartmann–Tran line profile and were used then in the weighted fit for determination of the effective dipole moment parameters of the studied “hot“ bands. The obtained set of 10 fitted parameters for the 74GeH4 isotopologue and only one of the main fitted parameters for the 72GeH4 and 70GeH4 species (in this case, the values of all other effective parameters were fixed to the values of corresponding parameters of the 74GeH4 species) reproduce the initial experimental line intensities with the mean drms=3.54%. The 72GeH4 and 70GeH4 species are also analysed. A list of transitions of the four studied “hot“ bands with their line intensities is generated in the HITRAN format up to the value of quantum number J=23.

Extended analysis of the lowest bands of 12C2H4: Line strengths, widths, and shifts in the ν7, ν10, and ν4 bands

The high–resolution infrared spectra of 12C2H4 were analyzed in the region of 600 – 1200 cm−1, where the ν7, ν10, and ν4 bands are located. 2259 line strengths (3369 transitions) were determined from the fit of their line shapes with a Hartmann–Tran profile (Jmax=46 and Kamax=19) which is about two times higher than in preceding studies. These data were used in the fit of the effective dipole moment parameters and eight such parameters (5 parameters of the ν7 band and 3 parameters of the ν10 band) were obtained in the frame of the improved effective dipole moment model which reproduce the strengths of the initial lines with the drms=4.18%. Pressure self–broadening coefficients of 594/303 lines and self–shift coefficients of 344/227 lines for the ν7 and ν10 bands were determined from the multi–spectrum analysis. The line list of 3369 transitions with the experimental line positions and strengths is documented.

Line intensities of the radioactive isotopologues of carbon monoxide

The isotopic substitution relations for the effective dipole moment parameters of a heterogenic diatomic molecule have been derived. These equations are applied to the calculations of the line intensities of the minor carbon monoxide isotopologues, including the radioactive ones. The comparisons of the calculated line intensities of the minor isotopologues to those observed and to those earlier calculated are given. These comparisons show that the used method has potential of predicting intensities of the minor isotopologues of carbon monoxide within 2–10%. The comparison of our calculated line intensities for the radioactive isotopologues of the carbon monoxide molecule to those from Li et al. (2015) is also given.

High resolution analysis of GeH4 in the dyad region: Ro-vibration energy structure of 70GeH4 and line strengths of MGeH4 (M = 70, 72, 73, 74, 76)

The infrared spectrum of MGeH4 (M=70,72,73,74,76) was measured at the temperature of (294.5 ± 0.3) K in the 740-960 cm−1 region with a Bruker Fourier transform infrared spectrometer IFS125 and analyzed. The line positions of the ν2/ν4 bands and the ro-vibrational energy structure of corresponding upper vibrational states of 70GeH4 were analyzed. The strengths of 1079 experimentally recorded spectral lines (243/270/152/262/152 lines for the isotopologues 70GeH4/72GeH4/73GeH4/ 74GeH4/76GeH4) with the value of quantum number Jmax = 19 were determined from the fit of their line shapes with a Hartmann–Tran line profile and were used then in the weighted fit for determination of the effective dipole moment parameters of the ν4 band. The obtained sets of parameters reproduce the initial experimental line intensities with the drms=3.46/3.12/3.21/3.38/3.45/% for the 70GeH4/72GeH4/73GeH4/ 74GeH4/76GeH4 species, respectively. A list of transitions with their line intensities is generated in the HITRAN format up to the value of quantum number J=40.

Extended analysis of the ν12 band of 12C2H4 for astrophysical applications: Line strengths, widths, and shifts

The high-resolution infrared spectra of 12C2H4 were analyzed in the region of 1360 – 1530 cm−1, where the strong ν12 band is located. 998 line strengths (1491 transitions) were determined from the fit of their line shapes with a Hartmann–Tran profile (Jmax=48 and Kamax=17) which is about two times more than in the preceding studies. These data were used in the fit of the effective dipole moment parameters and six such parameters were obtained which reproduce the strengths of the 998 initial lines (1491 transitions) with the drms=2.31%. Self–broadening and self-shift coefficients were determined from the multi–spectrum analysis for sets of lines (JKa=Ka′Kc)←(J′Ka′Kc′),Ka′=0,1,2,3,4,5 (in general, 253 lines for determination of self-broadening coefficients and 225 lines for determination of self-shift coefficients). The line list of 19186 transitions is documented.

Extended analysis of the ν3 band of HD32S: Line positions, energies, and line strengths

The HD32S high resolution infrared spectrum was recorded and analyzed in the ν3 fundamental band region (2000–3000 cm−1) with a Bruker IFS 125HR Fourier transform infrared spectrometer (Zurich prototype ZP2001). 1533 transitions (about 3.4 times more compared to 446 transitions in earlier studies) were assigned to the ν3 band in the experimental spectra. For the first time, an analysis of the line strengths of this band was made and effective dipole moment parameters were obtained. A special analysis was performed with the goal to obtain the partial pressures of all components (HDS, D2S, H2S, H2O, D2O, HDO, CO2) presented in the sample. A line list of the transitions and strengths of the ν3 band has been generated.