Line positions and intensities of acetylene in the 2.2-μm region

More than 440 line positions and intensities of 8 bands of acetylene are measured in the 2.2-μm spectral region. A multispectrum fitting procedure has been applied to retrieve line parameters. The average absolute accuracy of the line parameters obtained in this work is estimated to be ±0.0005 cm⁻¹ for the line positions, and ±5% for the line intensities. Vibrational transition dipole moment and Herman-Wallis coefficients are determined for two of the studied bands. An unusual rotational dependence of the vibrational-rotational transition dipole moment of remaining bands has been found. All measured line intensities are treated simultaneously within the framework of the effective operators approach. The sets of effective dipole moment parameters obtained reproduce the observed line intensities within the experimental uncertainty.     

Emission spectroscopy from optically thick laboratory acetylene samples at high temperature

Recently, a high temperature source has been used to produce high temperature emission spectra of acetylene in the 3 μm spectral range, under Doppler limited resolution, and the complete spectral assignment has been performed using a global rovibrational Hamiltonian [Amyay B, Robert S, Herman M, Fayt A, Raghavendra B, Moudens A et al. Vibration-rotation pattern in acetylene (II): Introduction to Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 μm. J Chem Phys 2009;131:114301]. The present investigation focuses on the relative emission line intensities which are observed to be affected. The strongest lines intensity may be considerably reduced for high column density acetylene samples, hence affecting the 3:1 ortho:para intensity ratio. A radiative model is developed to take into account the effects generated by the strong opacity of the acetylene samples including self-absorption and absorption of the radiation emitted by the hot environment. The model is used to extract the absolute concentration of the high temperature acetylene samples from the observed relative spectral intensities. The relevance of the procedure for infrared remote sensing in high temperature astrophysical environments, such as circumstellar envelopes of cool carbon rich evolved stars, is discussed.     

Effective dipole moment parameters of C2H2 for the 100, 7.7, 1.4, 1.3, 1.2 and 1.0 μm regions

Based on new line intensity measurements collected from the literature, the effective dipole moment parameters of acetylene have been found for the 100, 7.7, 1.4, 1.3, 1.2 and 1 μm spectral regions by least-squares fittings. On average, the experimental uncertainty was obtained in all fits. The new sets of the effective dipole moment parameters combined with those that were previously published allow for the calculation of the line intensities for the majority of the acetylene bands in the spectral range from 100 to 1 μm.     

Absolute line intensities of CO2 in the 3090-3920 cm region

Absolute line intensities of ¹³C¹⁶O₂ were retrieved from high-resolution Fourier transform spectra recorded in the region 3090-3920 cm⁻¹. The uncertainty of the line intensity determination is estimated to be between 3 and 5% for the strong lines. The global fittings of the observed line intensities within the framework of the effective operators approach have been performed, reaching the experimental accuracy. A comparison of newly measured line intensities with those found in the HITRAN database is presented.     

Absolute line intensities of CO2 in the 4200-8500 cm region

The absolute line intensities of ¹³C¹⁶O₂ were retrieved from Fourier-transform spectra recorded in the region 4200-8500 cm⁻¹. The accuracy of the line intensity determination is estimated to be 5% or better for most lines and about 10% for weak ones. The vibrational transition dipole moments squared and Herman-Wallis coefficients have been determined. The global fittings of the observed line intensities within the framework of the effective operators approach have been performed. As the result of the fittings, most line intensities are reproduced within the experimental accuracy. The comparison between the new measured data and the HITRAN database are also carried out.     

Absorption spectra of CO2 and CO2 near 1.05 μm

The absolute line intensities of the Fermi triad 2003i-00001 (i = 1, 2, 3) of ¹²C¹⁶O₂ and ¹³C¹⁶O₂ isotopic species of carbon dioxide were retrieved from Fourier-transform spectra recorded at Doppler limited resolution in the region 9200-9700 cm⁻¹. The accuracy of the line intensity determination is estimated to be better than 15% for most lines. The vibrational transition dipole moments squared and Herman-Wallis coefficients have been determined. The global fittings of the observed line intensities within the framework of the effective operators method have been performed. The fitting results reproduce the data within experimental uncertainty.     

Line intensities of acetylene: New measurements in the 1.5-μm spectral region and global modelling in the ΔP=10 series

Using the Fourier transform spectra of the acetylene molecule recorded near 1.5-μm, the intensities of 111 lines belonging to seven hot bands of the main isotopologue ¹²C₂H₂ have been retrieved by means of a multispectrum fitting procedure. Considering the density of lines in the spectra, and the fact that the measured bands are the weakest observed, the accuracy of the measurements is around 10%. At first stage, an empirical treatment of these data has been performed, leading to the vibrational transition dipole moment squared and some Herman–Wallis coefficients. Then the measured line intensities of this work and collected ones from the literature have been treated simultaneously within the framework of the effective operator approach.     

Line intensities in the 1.5-μm spectral region of acetylene

Line intensities are measured for 546 transitions belonging to 13 bands of the main isotopologue ¹²C₂H₂ of the acetylene molecule, in the 1.5-μm spectral domain. A multispectrum fitting procedure is used to retrieve line parameters from Fourier transform spectra. Prior to this work, line intensities were known for only 4 bands in this spectral region, from the work of El Hachtouki and Vander Auwera [Absolute line intensities in acetylene: the 1.5 μm region. J Mol Spectrosc 2002;216:355-62]. An excellent agreement is found with the results of these authors, showing that the accuracy of both results is likely better than 1% for the strong bands. However, the spectrum becomes very crowded when one wants to study weaker bands, so that the average accuracy of the intensities reported in the present work is 5%. From these data, vibrational transition dipole moments squared and Herman-Wallis coefficients have been determined for all the bands.     

Raman cross sections of selected hydrocarbons and freons

The Raman spectra of some selected hydrocarbons and freon gases have been measured and are reported here. The observed peak intensities of the strongest line for each hydrocarbon molecule relative to that of the 2331 cm^?1 line of molecular nitrogen range from 14·5 for benzene to 2·6 for 2-pentene. The Raman cross sections of the C-H stretching bands relative to the 2331 cm^?1 nitrogen line range from 46 for hexane to 1·2 for acetylene.     

Infrared Spectra of the OCO and OCO Species of Carbon Dioxide: The Region 500-1500 cm

The effective operator approach is applied to the calculation of the spectra of ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O in the far infrared. Using the eigenfunctions of the effective Hamiltonians previously derived for each of these species, parameters of the corresponding effective dipole moment operators have been fitted to more than 400 observed line intensities of cold and hot bands covering the ν₂ and ν₁ spectral regions. New line intensities measurements in the ν₂ band region of ¹⁶O¹²C¹⁸O have been performed. The new observed line intensities have been also included into the corresponding fit. The fittings have been achieved within the experimental errors. A comparison of calculated line parameters with those provided by the HITRAN and GEISA databases is given.     

New infrared integrated band intensities for HC3N and extensive line list for the ν5 and ν6 bending modes

The infrared spectrum of cyanoacetylene (also called propynenitrile) has been investigated from 400 to 4000 cm⁻¹ at a resolution of 0.5 cm⁻¹. Integrated intensities of the main bands and a number of weaker bands have been obtained with an uncertainty better than 5%. Inaccurate values in previous studies have been identified in particular concerning the intensity of the strong ν₅ stretching band at 663.2 cm⁻¹. Former results on the temperature dependence of integrated intensities have also been revisited.Synthetic spectra calculation has been performed for the ν₅ and ν₆ bands on the basis of the best available high resolution data. It has been shown that the GEISA line parameters for HC₃N are not sufficient to reproduce the band intensities and some hot band features observed in our experimental spectra at room temperature. As a first step, the model spectra has been improved by including a number of missing hot subbands and by calculating accurately the hot band relative intensities. Finally, a perfect agreement between calculated and observed spectra was achieved on the basis of a global analysis of HC₃N levels up to 2000 cm⁻¹ combined with the new integrated intensity measurements. A new extensive line list for the ν₅ and ν₆ bending modes of HC₃N has been compiled.     

Diode laser measurements of NH3, ν2-band spectral lines

High-resolution absorption spectra of the NH₃, ν₂ band in the 800- to 1200-cm^?1 region have been measured using ir tunable diode lasers. One hundred lines of 18sP-, aP-, aQ-, sQ-, aR-, and sR-branch multiplets have been resolved. Absorption line separations have been measured and line frequencies assigned using high-precision literature data. For all the transitions observed, relative line intensities have been calculated and compared to literature data; for three lines, the absolute intensities have been measured.     

High-sensitivity CRDS absorption spectroscopy of acetylene between 5851 and 6341 cm−1

The absorption spectrum of acetylene has been recorded at room temperature (297 K) using high-sensitivity cavity ring-down spectroscopy (α_min ～ 5×10^?11 cm^?1) in the 5851 and 6341 cm^?1 interval corresponding to a region of very weak absorption. A list of about 10,700 absorption features with estimated absolute line intensities was constructed. The smallest intensities are of the order of 5×10^?29 cm molecule^?1. The line list includes about 2500 absorption lines of ethylene present at the ppm level in the acetylene sample and identified on the basis of a high-resolution Fourier transform spectrum specifically recorded. A total of more than 2700 lines of ¹²C₂H₂ were rovibrationally assigned in comparison with accurate predictions provided by a global effective operator model. Overall, the present effort adds about 2260 new assignments to the set of about 500 assigned transitions available in the literature. The new assignments correspond to 45 new bands and 17 already-known bands, for which additional J lines were assigned. Spectroscopic parameters were derived for the upper vibrational levels from a band by band fit of the line positions (typical root mean square deviation values are of the order of 0.001 cm^?1). A few of the analysed bands were found to be affected by rovibrational perturbations, which are discussed. The new data will be valuable to refine the parameters of the global effective Hamiltonian and dipole moments of ¹²C₂H₂.     

13C(16)O(2): Global Treatment of Vibrational-Rotational Spectra and First Observation of the 2nu(1) + 5nu(3) and nu(1) + 2nu(2) + 5nu(3) Absorption Bands

The effective operator approach is applied to the calculation of both line positions and line intensities of the (13)C(16)O(2) molecule. About 11 000 observed line positions of (13)C(16)O(2) selected from the literature have been used to derive 84 parameters of a reduced effective Hamiltonian globally describing all known vibrational-rotational energy levels in the ground electronic state. The standard deviation of the fit is 0.0015 cm(-1). The eigenfunctions of this effective Hamiltonian have then been used in fittings of parameters of an effective dipole-moment operator to more than 600 observed line intensities of the cold and hot bands covering the nu(2) and 3nu(2) regions. The standard deviations of the fits are 3.2 and 12.0% for these regions, respectively. The quality of the fittings and the extrapolation properties of the fitted parameters are discussed. A comparison of calculated line parameters with those provided by the HITRAN database is given. Finally, the first observations of the 2nu(1) + 5nu(3) and nu(1) + 2nu(2) + 5nu(3) absorption bands by means of photoacoustic spectroscopy (PAS) is presented. The deviations of predicted line positions from observed ones is found to be less than 0.1 cm(-1), and most of them lie within the experimental accuracy (0.007 cm(-1)) once the observed line positions are included in the global fit. Copyright 2000 Academic Press.     

Observation of Coriolis Coupling between nu(2) + 4nu(4) and 7nu(4) in Acetylene &Xtilde;(1)Sigma(+)(g) by Stimulated Emission Pumping Spectroscopy

Stimulated emission pumping (SEP) spectroscopy has been used to examine a low energy region (E(vib) approximately 4400 cm(-1)) of &Xtilde;(1)Sigma(+)(g) acetylene at higher resolution than was possible in previous dispersed fluorescence studies. The expected bright state, nu(2) + 4nu(4), is observed to be coupled to the nearly degenerate 7nu(4) state by a Coriolis mechanism. A least-squares analysis yields values for zero-order vibrational energies, rotational constants, and a Coriolis-coupling coefficient that are all consistent with expectations. Calculated relative intensities of SEP transitions, accounting for interference due to axis-switching effects, are also consistent with observations. Implications of the observed Coriolis resonance with regard to global acetylene vibrational dynamics are also discussed. Copyright 2000 Academic Press.     

Fourier-transform spectroscopic study of the rotational intensity distribution in the first positive BΠg-AΣu band system of the nitrogen molecule

In the present work we have studied the rotational intensity distribution in the 0-0, 0-1 and 1-3 bands of the B³Π_g-A³Σ_u⁺ system of N₂ recorded on a Fourier transform spectrometer. The effective Hamiltonian used by Roux et al. (J. Mol. Spectrosc. 97 (1983) 253) for reduction of the experimental line position data to molecular parameters, is found to be adequate in reproducing the observed line intensities. To enhance the accuracy of the theoretical line intensity calculations, it proved necessary to use rotation-dependent Frank-Condon factor. Using the calculated intensities, it was possible to identify certain rotational lines belonging to the weakest branches Q₁₃ and Q₃₁, not reported before.     

CO2: Global Treatment of Vibrational–Rotational Spectra and First Observation of the 2ν1 + 5ν3 and ν1 + 2ν2 + 5ν3 Absorption Bands

The effective operator approach is applied to the calculation of both line positions and line intensities of the ¹³C¹⁶O₂ molecule. About 11 000 observed line positions of ¹³C¹⁶O₂ selected from the literature have been used to derive 84 parameters of a reduced effective Hamiltonian globally describing all known vibrational–rotational energy levels in the ground electronic state. The standard deviation of the fit is 0.0015 cm⁻¹. The eigenfunctions of this effective Hamiltonian have then been used in fittings of parameters of an effective dipole-moment operator to more than 600 observed line intensities of the cold and hot bands covering the ν₂ and 3ν₂ regions. The standard deviations of the fits are 3.2 and 12.0% for these regions, respectively. The quality of the fittings and the extrapolation properties of the fitted parameters are discussed. A comparison of calculated line parameters with those provided by the HITRAN database is given. Finally, the first observations of the 2ν₁ + 5ν₃ and ν₁ + 2ν₂ + 5ν₃ absorption bands by means of photoacoustic spectroscopy (PAS) is presented. The deviations of predicted line positions from observed ones is found to be less than 0.1 cm⁻¹, and most of them lie within the experimental accuracy (0.007 cm⁻¹) once the observed line positions are included in the global fit.     

Ro-vibrational spectra of C2H2 based on variational nuclear motion calculations

A published ab initio-based potential energy surface and newly constructed dipole moment surface of acetylene have been used to compute vibrational band intensities. The line intensity calculations employed the variational nuclear motion code WAVR4 for computation of wave functions and energy levels, and a newly developed code DIPOLE4 for computation of dipole transitions. Owing to the high computational cost of J > 0 transitions using direct variational methods only J = 0 and J = 1 states and transitions have been computed variationally. The intensities of J > 1 transitions were extrapolated from J = 0 and J = 1 using Hönl–London coefficients. The resulting effective rotational constants B and transition intensities are compared with experimental data for the (3ν₄ + ν₅) combination band, the ν₃ and the ν₅ fundamental band. The prospects of using this procedure for extensive calculations of a hot line list, important for cool stars and extrasolar planets are discussed.     

High sensitivity cavity ring down spectroscopy of 13C16O2 overtone bands near 806 nm

The absorption spectrum of ¹³C¹⁶O₂ near 806 nm has been recorded with a continuous-wave cavity ring-down spectrometer. Two cold bands and one associated hot band are observed in this region. The line positions of these bands are determined with an accuracy of 0.003 cm^?1. The absolute line intensities have also been retrieved with an estimated accuracy of 4% for majority of the unblended lines. The vibrational transition dipole moment squared values and the empirical Herman–Wallis coefficients are determined for all the three bands. The comparison of the retrieved line positions and intensities to those given in the Carbon Dioxide Spectroscopic Databank shows large deviations in the line intensities of the 10052–00001 band. The effective dipole moment parameters describing the line intensities of ¹³C¹⁶O₂ near 806 nm are fitted according to the observed line intensities.