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Four spectra of methane in natural isotopic abundance in the 4100-4300 cm(-1) region were recorded by using a Fourier transform spectrometer in Reims, France at long paths (202 m, 602 m, 1604 m and 1804 m) and different pressures. Additional spectra of (CH4)-C-12 covering the same region were obtained at 100-123 K for different pressures, 93 m path length at Synchrotron SOLEIL in Paris for different pressures and were used to measure low-J lines. Spectra of (CH4)-C-12 and (CH4)-C-13 obtained at 80 K at JPL in Pasadena were used for additional frequency calibrations. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and analyzed using effective Hamiltonian and effective dipole transition moment models. A new measured line list contains positions and intensities for 12,378 features. Quantum assignments were made for more than 11,520 new transitions, which represent similar to 99% of the integrated line intensity observed in this region. Some of 4556 hot band transitions for (Dyad - Tetradecad) system were assigned. The resulting list of lines is significantly more accurate than previous empirical compilations. All assigned 6963 line positions were fitted to RMS standard deviations of 0.0015 cm(-1). The sum of the observed intensities between 4100 and 4300 cm(-1) falls within 5% of the predicted value from ab initio variational calculations reported in the TheoReTS database (http: //theorets.univ-reims.fr ; http://theorets.tsu.u). (C) 2021 Elsevier Ltd. All rights reserved.

Measuring the concentration of methane in the atmosphere is demonstrated to be very important, since an increase in methane content enhances the greenhouse effect. It is shown that the error in assessing the concentration of CH4 depends on many factors, including the reliability of the parameters of the spectral absorption lines of gases, the accuracy of determining the concentration, the measurement error, etc. The spectroscopic information necessary to detect sources of high methane concentration in the atmosphere using CO and He – Ne lasers is analysed.

The influence of the parameters (laser linewidths and profiles) of the CO2 laser based on the main molecular isotope on the absorption coefficient of a gaseous compound is analyzed using ammonia as an example. Results of application of the CO2 laser for the determination of the gaseous ammonia content are considered and possible errors in calculating the gas concentration caused by the neglect of the specific spectral linewidth of the CO2 laser are analyzed.

The near infrared transmission spectra of nanoporous SiO2/Al2O3 xerogel have been recorded for the first time in the process of filling of nanopores with ammonia and acetone molecules. It has been found that the physical adsorption of these gases results in a reversible increase in the translucence of xerogel samples at the frequencies of vibrational bands of surface OH groups.

The room temperature absorption spectrum of 17O enriched carbon dioxide is investigated by high sensitivity cavity ring down spectroscopy (CRDS) between 5695 and 5850 cm−1. About 1100 lines are measured and assigned to 26 bands of the six 17O containing carbon dioxide isotopologues: 16O12C17O, 16O13C17O, 17O12C18O, 17O13C18O, 12C17O2 and 13C17O2. The set of observed lines are rovibrationnally assigned on the basis of the predictions of the effective Hamiltonian (EH) model. The observed bands belong to the ΔP = 8 and 9 series of transitions where P = 2 V1 + V2 + 3 V3 is the polyad number (Vi being the vibrational quantum numbers). They consist in 12 previously unobserved bands and 14 already-known bands, for which additional high J lines are assigned. Bands of the 12C17O2 and 13C17O2 isotopologues (two for each) are observed for the first time in this spectral interval. The spectroscopic parameters of the upper vibrational levels are determined from a band-by-band fit of the line positions (typical rms deviations are less than 0.001 cm−1). The comparison to the most recent carbon dioxide spectroscopic databases is presented. The reported data will be used to improve the modeling of the line positions of 17O containing carbon dioxide isotopologues.

The very weak absorption spectrum of the minor isotopologues of carbon dioxide near 1.74 µm (5702–5879 cm−1) is studied by high sensitivity cavity ring down spectroscopy (CRDS) with an 18O enriched sample. The investigated spectral region corresponds to a transparency window of very weak opacity which is of particular interest for Venus. Very weak lines with intensity value as low as 10−30 cm/molecule at 296 K are measured. On the basis of the predictions of the effective Hamiltonian models, 3202 lines of nine carbon dioxide isotopologues - 12C16O2, 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 17O12C18O, 17O13C18O, 12C18O2 and 13C18O2 - were rovibrationnally assigned to 59 bands, 44 of which were observed for the first time. The accurate spectroscopic parameters of 53 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are 8 × 10−4 cm−1). Three bands are found to be strongly perturbed by resonance first order Coriolis interaction. The new measured line intensities allowed determining or improving the ΔP = 8 sets of the effective dipole moment (EDM) parameters for five non-symmetrical isotopologues - 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O and 17O12C18O - and ΔP = 9 sets for the 16O12C18O and 12C18O2 isotopologues (P = 2V1+ V2+ 3V3 is the polyad number, Vi being the vibrational quantum numbers). The set of EDM parameters available for eleven isotopologues is used to discuss their isotopic dependence. These newly observed bands provide critical validation tests for the most recent spectroscopic databases. The comparison to the Carbon Dioxide Spectroscopic Databank (CDSD-296), HITRAN2016 database and ab initio Ames line list is presented. Deficiency is evidenced for the weak 41104–00001 band of 16O12C18O in the HITRAN2016 list and identified as due to inaccurate CDSD intensities which were preferred to ab initio intensities.

The spectrum of methane is very important for the analysis and modeling of Titan’s atmosphere but its insufficient knowledge in the near infrared, with the absence of reliable absorption coefficients, is an important limitation. In order to help the astronomer community for analyzing high-quality spectra, we report in the present work the first accurate theoretical methane line lists (T = 50–350 K) of 12CH4 and 13CH4 up to 13400 cm ( > 0.75 µm). These lists are built from extensive variational calculations using our recent ab initio potential and dipole moment surfaces and will be freely accessible via the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru). Validation of these lists is presented throughout the present paper. For the sample of lines where upper energies were available from published analyses of experimental laboratory 12CH4 spectra, small empirical corrections in positions were introduced that could be useful for future high-resolution applications. We finally apply the TheoRetS line list to model Titan spectra as observed by VIMS and by DISR, respectively onboard Cassini and Huygens. These data are used to check that the TheoReTS line lists are able to model observations. We also make comparisons with other experimental or theoretical line lists. It appears that TheoRetS gives very reliable results better than ExoMol and even than HITRAN2012, except around 1.6 µm where it gives very similar results. We conclude that TheoReTS is suitable to be used for the modeling of planetary radiative transfer and photometry. A re-analysis of spectra recorded by the DISR instrument during the descent of the Huygens probe suggests that the CH4 mixing ratio decreases with altitude in Titan’s stratosphere, reaching a value of above the 110 km altitude

The absorption spectrum of water vapor in “natural” isotopic abundance has been recorded at room temperature by high sensitivity Continuous Wave Cavity Ring Down Spectroscopy (CW-CRDS) between 7911 and 8337 cm −1 . The investigated region covers most of the 1.25 µm transparency window of importance for atmospheric applications. The recordings were performed with sensitivity on the order of α min ~2×10 –11 cm −1 , more than two orders of magnitude better than previous investigations by Fourier Transform Spectroscopy (FTS). Measured line intensities cover a range of seven orders of magnitude (3×10 –30 –2×10 –23 cm/molecule at room temperature). The experimental line list provided as Supplementary Material includes more than 5000 transitions. As a result of the achieved sensitivity, more than 1150 lines of the experimental list were identified as being due to ammonia present as an impurity at the 5 ppm concentration level in the water sample. Although incomplete, the obtained ammonia line list seems to be the first one in the region. More than 3193 water lines were assigned to 3560 transitions of five water isotopologues (H 2 16 O, H 2 18 O, H 2 17 O, HD 16 O and HD 18 O). The assignments were performed using known experimental energy levels and calculated spectra based on variational calculations by Schwenke and Partridge. The obtained results are compared to the most relevant previous studies by Fourier Transform Spectroscopy in the region and to the exhaustive review of rovibrational line positions and levels performed recently by an IUPAC sponsored task group. Two-hundred and sixty-six levels are newly determined and 46 are corrected by more than 0.015 cm −1 compared to those recommended by the water IUPAC task group. The overall agreement between variational and measured intensities is satisfactory. A complete empirical list of 4473 transitions incorporating all the experimental information at disposal was constructed for water in the studied region. The intensity cut-off was fixed to 1×10 –29 cm/molecule at 296 K. A detailed comparison with the line list as provided by the HITRAN database illustrates the advantages of the new list.

The room temperature spectrum of carbon monoxide in natural isotopic abundance is recorded by Cavity Ring Down Spectroscopy between 8094 and 8317 cm −1 . The investigated range covers the low frequency region of the third overtone band centered at 8414 cm −1 . The achieved sensitivity of the recordings corresponds to a noise equivalent absorption, α min ~ 5×10 –12 cm −1 . 94 transitions are measured with intensity ranging between 3×10 –27 and 1×10 –30 cm/molecule. They include the first observation of (i) high J lines of the P branch of the 4-0 band of 12 C 16 O, (ii) the 4-0 band of 13 C 16 O and 12 C 18 O present in natural abundance in the sample (35 and 38 transitions, respectively), (iii) a few lines of the 4-0 band of 12 C 17 O and of the 5-1 hot band of 12 C 16 O. The spectroscopic parameters of the v =4 upper level of 13 C 16 O and 12 C 18 O are obtained from a fit of the measured line positions. The line positions reported with an accuracy of 5×10 −4 cm −1 and the derived line intensities are used for comparison to various theoretical line lists of carbon monoxide available in the literature. The agreement between the obtained experimental data and the most recent theoretical line lists available in the literature is discussed.

The room temperature absorption spectrum of 18O enriched carbon dioxide has been recorded by very high-sensitivity Cavity Ring Down spectroscopy between 6977 and 7918 cm−1 (1.43−1.26 μm). The achieved sensitivity (noise equivalent absorption αmin ~8×10−11 cm−1) has allowed for the detection of more than 8600 lines belonging to 166 bands of eleven carbon dioxide isotopologues. Line intensities of the weakest observed transitions are on the order of 2×10−30 cm/molecule. In this first part, we present the results relative to the 16O12C18O, 16O12C17O, 12C16O2 and 13C16O2 isotopologues. Their absorption lines were rovibrationally assigned on the basis of the predictions of their respective effective Hamiltonian model. Overall 5476 lines were measured and assigned to 93 bands. Forty nine of them, all belonging to 16O12C18O and 16O12C17O, are reported for the first time. The studied spectral region is formed by ΔP=10–12 series of transitions, where P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The spectroscopic parameters of 58 bands of 16O12C18O and 16O12C17O were determined from a fit of the measured line positions. An inter- and an intrapolyad resonance perturbation were identified and analyzed in the 16O12C18O spectrum. The comparison with the line positions and line intensities included in the AMES line list is discussed. Global fits of the line intensities were performed in order to (i) improve the ΔP=10 and 11 sets of the effective dipole moment parameters of 16O12C18O and the ΔP=11 set of parameters of 16O12C17O and (ii) derive for the first time the ΔP=10 and 12 parameters of 16O12C17O and 16O12C18O, respectively.

In this work, we report first-principle theoretical predictions of methane spectral line intensities that are competitive with (and complementary to) the best laboratory measurements. A detailed comparison with the most accurate data shows that discrepancies in integrated polyad intensities are in the range of 0.4%–2.3%. This corresponds to estimations of the best available accuracy in laboratory Fourier Transform spectra measurements for this quantity. For relatively isolated strong lines the individual intensity deviations are in the same range. A comparison with the most precise laser measurements of the multiplet intensities in the 2ν3 band gives an agreement within the experimental error margins (about 1%). This is achieved for the first time for five-atomic molecules. In the Supplementary Material we provide the lists of theoretical intensities at 269 K for over 5000 strongest transitions in the range below 6166 cm−1. The advantage of the described method is that this offers a possibility to generate fully assigned exhaustive line lists at various temperature conditions. Extensive calculations up to 12,000 cm−1 including high-T predictions will be made freely available through the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru) that contains ab initio born line lists and provides a user-friendly graphical interface for a fast simulation of the absorption cross-sections and radiance.

An application of one-dimensional velocity approach to calculation of speed-dependent spectral line profiles was considered. It was shown that a mean deviation of the line profile obtained within this approach from the line profile derived with integrating over three projections of an absorbing molecule's velocity does not exceed 1.1% at mass ratios of perturbing and absorbing molecules ≤9. Analytical approximate expressions for speed-dependent line profiles, including spectral line narrowing and mixing, were obtained for one- and three-dimensional velocity approaches.

Впервые зарегистрированы спектры поглощения молекул CO, находящихся в нанопорах гибридного SiO2/Al2O3-ксерогеля. Определены значения полуширин спектральных линий CO, проанализирована их зависимость от вращательного квантового числа J, проведено сопоставление полученных результатов с данными, имеющимися в литературе.

Впервые зарегистрированы спектры поглощения молекул CO, находящихся в нанопорах гибридного SiO2/Al2O3-ксерогеля. Определены значения полуширин спектральных линий CO, проанализирована их зависимость от вращательного квантового числа J, проведено сопоставление полученных результатов с данными, имеющимися в литературе.

Systematic errors inherent in the Voigt line profile are analyzed. Molecular spectrum processing with the Voigt profile is shown to underestimate line intensities by 1–4%, with the errors in line positions being 0.0005 cm−1 and the decrease in pressure broadening coefficients varying from 5% to 55%.

The sizes of aerogel nanopores from the measured broadening of rotational-vibrational CO lines caused by collisions with nanopore walls have been determined. It has been shown that the sizes of nanopores with a diameter of 15–25 nm can be reliably assessed from the half-widths of spectral lines measured on a high-resolution Fourier spectrometer and agree well with the experimental data found from the low-temperature adsorption of nitrogen.

Пособие восполняет существенный недостаток в учебной литературе по теоретической астрофизике. В этом пособии рассматриваются вопросы теории образования спектральных линий в спектрах звезд, излагаются механизмы уширения линий, даются методы решения уравнения переноса излучения с учетом поглощения в линиях. Приведены главные результаты использования спектральных линий для диагностики звездных атмосфер (определение температур, давлений, химического состава, вращения). Приведены сведения о звездных ветрах, микро и макро турбуленции. Теоретическая астрофизика

The line positions and intensities of carbon dioxide isotopologues have been retrieved between 5900 and 6400 cm−1 region from Fourier transform spectra of 17O- and 18O-enriched carbon dioxide recorded in LADIR (Paris, France) with the Bruker IFS 125-HR. In total 1634 line positions and intensities of 20 bands of the 5 major CO2 isotopologues present in our sample 16O12C17O (39.48%), 17O12C17O (27.73%), 16O12C16O (15.20%), 16O12C18O (7.32%) and 17O12C18O (8.25%) are retrieved. All studied bands belong to the ΔP=8 (only for asymmetric species) and 9 series of transitions, where P = 2 V 1 + V 2 + 3 V 3 is the polyad number (Vi are vibrational quantum numbers). The accuracy of the line position determination is about 0.3×10−3 cm−1 for the unblended and not very weak lines and the accuracy for the line intensities varies from 4% to 30% depending on the intensity of the line and on the extent of the line overlapping. For the 16O12C17O, 17O12C17O, 16O12C18O and 17O12C18O isotopologues the systematic comparisons have been performed with the recent CRDS measurements.

Разработана высокотемпературная база данных (БД) параметров спектральных линий диоксида азота (14N16O2). Вычисления центров и интенсивностей вращательных и колебательно-вращательных линий осуществлены с учетом спин-вращательного взаимодействия. Обсуждаются результаты моделирования спектральных характеристик 14N16O2, полученные line-by-line методом на основе предлагаемой БД и БД HITRAN2012 при высоких температурах.

Получена алгебраическая аппроксимация контура спектральных линий, при выводе которого одновременно учтены столкновения с рассеянием на большие и малые углы. В области практически значимых параметров отклонения приближенного контура от точного расчетного не превышают десятой доли процента. Показано, что слабые столкновения с рассеянием на классические малые углы уменьшают эффект столкновительного сужения линий, за счет чего контур линии становится более плоским по сравнению с контуром в модели сильных по скоростям столкновений. Относительная разность максимальных амплитуд этих контуров может достигать 15%, что приводит к необходимости учета слабых столкновений наряду с сильными столкновениями в количественной обработке спектров высокого разрешения в условиях неоднородного уширения линий.

The line positions and intensities of carbon dioxide isotopologues have been retrieved in the 4681–5337 cm−1 spectral range from Fourier transform spectra of carbon dioxide recorded in LADIR (Paris, France) with the Bruker IFS 125-HR [Jacquemart D, et al., J Quant Spectrosc Radiat Transf 2012;113:961–975]. In total 6386 line positions and intensities of 89 bands of 12 isotopologues 16O12C16O, 16O13C16O, 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 18O12C18O, 17O12C18O, 17O12C17O, 18O13C18O, 17O13C18O, and 17O13C17O have been retrieved. 23 bands were newly assigned. All studied bands belong to the ΔP=7 series of transitions, where P = 2 V 1 + V 2 + 3 V 3 is the polyad number (Vi are vibrational quantum numbers). The accuracy of the line position measurement is about 0.3×10−3 cm−1 for the unblended and not very weak lines. The accuracy of the line intensities varies from 4% to 15% depending on the isotopologue, on the intensity of the line and on the extent of the line overlapping. The observed intensities were used to fit the effective dipole moment parameters for the ΔP=7 series of transitions in 16O12C18O, 16O12C17O, 12C17O2, 17O12C18O, 16O13C17O, 13C17O2 and 17O13C18O isotopologues of carbon dioxide.

The updated methane spectral line list GOSAT-2014 for the 5550–6240 cm −1 region with the intensity cutoff of 5×10 –25 cm/molecule at 296 K is presented. The line list is based on the extensive measurements of the methane spectral line parameters performed at different temperatures and pressures of methane without and with buffer gases N 2 , O 2 and air. It contains the following spectral line parameters of about 12150 transitions: line position, line intensity, energy of lower state, air-induced and self-pressure-induced broadening and shift coefficients and temperature exponent of air-broadening coefficient. The accuracy of the line positions and intensities are considerably improved in comparison with the previous version GOSAT-2009. The improvement of the line list is done mainly due to the involving to the line position and intensity retrieval of six new spectra recorded with short path way (8.75 cm). The air-broadening and air-shift coefficients for the J -manifolds of the 2ν 3 (F 2 ) band are refitted using the new more precise values of the line positions and intensities. The line assignment is considerably extended. The lower state J -value was assigned to 6397 lines representing 94.4% of integrated intensity of the considering wavenumber region. The complete assignment was done for 2750 lines.

Разработан программный комплекс RELAX, который применен для исследования влияния сильного колебательного возбуждения на параметры контура спектральных линий молекул. В комплексе для вычисления полуширины и сдвигов центров линий использован вариант Маиппинга-Буле ударной теории уширения. При определении уровней энергии и волновых функций двухатомных молекул использовался прямой вариационный метод, для трехатомных молекул применялся эффективный вращательный гамильтониан Уотсона, преобразованный по Паде-Борелю. Показано, что существенное изменение внутримолекулярной динамики при колебательном возбуждении приводит к значительным изменениям полуширин и сдвига центров линий, образованных переходами на высоколежащие колебательные состояния двух- и трехатомных молекул.

Представлены результаты вычислений температурной зависимости полуширин и сдвигов центров линий молекул CO, HF в плазме атмосферного давления. Использована теоретическая модель, включающая правильное описание внутримолекулярной динамики высоковозбужденных колебательных состояний молекул. Вычисления проведены с применением программного комплекса RELAX.

Analytical approximate expressions for speed-dependent Rautian-Sobel'man, Voigt, and general line profiles, including spectral line mixing, were obtained. Systematic errors of the approximate profiles are within 0.7% for the mass ratios of perturbing and absorbing molecules mb/ma≤9. The calculation time of the approximate line profiles is much shorter than the time required for calculating exact expressions for the line profiles. An approximate analytical expression for the observable homogeneous line width was derived. A least-square fitting of the singlet methane absorption line centered at 6107.17 cm−1 was performed, using the approximate line profiles obtained.

Представлена теоретическая модель, позволяющая получить расчетные значения полуширины и сдвига центров линий двухатомных молекул для спектральных баз данных и лазерной физики. Достоверность модели подтверждена сравнением с экспериментальными данными для линий полосы 0-3 молекулы СО. Показана хорошая предсказательная способность модели для переходов на высокие колебательные состояния.

В рамках предлагаемой модели проведены расчеты полуширины и сдвига центров спектральных линий, образованных переходами на высоколежащие колебательные состояния молекулы СО вплоть до предела диссоциации. Представленные результаты позволяют исследовать кинетические процессы и характеристики холодной плазмы СО-лазера.