Water Spectra in the Region 4200-6250 cm, Extended Analysis of ν1+ν2, ν2+ν3, and 3ν2 Bands and Confirmation of Highly Excited States from Flame Spectra and from Atmospheric Long-Path Observations

Water vapor infrared spectra have been recorded at room temperature in the range 4200-6250 cm⁻¹ at resolutions (FWHM) between 0.0053 and 0.0080 cm⁻¹. The use of a White-type multireflection cell made large pressure × pathlength products possible up to 31.27 mbar×288.5 m. The high signal-to-noise ratio allowed us to observe lines with intensities as small as 10⁻²⁶ cm⁻¹/molecule cm⁻² at T=296 K. Among about 5100 recorded water lines, about half of which are reported for the first time, 2351 lines have been assigned to the second triad of H₂¹⁶O (bands ν₁+ν₂, ν₂+ν₃, and 3ν₂). This has allowed the determination of line positions and corresponding upper rovibrational states with considerably improved accuracy. The assignments of certain highly excited states have been confirmed by the analysis of flame spectra and hot emission spectra. New values of effective Hamiltonian parameters for the upper states {(110), (030), (011)} have been determined. The generating function model was used in the data reduction to account for the anomalously strong centrifugal distortion of the rovibrational levels and resonance interactions. The RMS standard deviation of the least-squares fit of the assigned H₂O data was 5×10⁻³ cm⁻¹ for line positions and 7×10⁻³ cm⁻¹ for energy levels up to J_max=20 and K_a(max)=13. Particular attention was paid to water lines in the transparency window 4200-5000 cm⁻¹, in which existing databases are not sufficient. In this region, 1395 lines of four isotopic species of water have been recorded and over 900 accurate line positions of nine bands of H₂¹⁶O (ν₁, ν₃, 2ν₂, ν₁+ν₂, ν₂+ν₃, 3ν₂, 4ν₂−ν₂, 2ν₂+ν₃−ν₂, ν₁+2ν₂−ν₂) are reported in this range. A comparison of laboratory spectra with long path atmospheric spectra (20 km slant path in the mountains) in this region shows that many lines missing from available spectroscopic compilations (or considerably shifted compared to observations) are important for a proper interpretation of atmospheric observations. A comparison of the observed data with the best available predictions from the molecular electronic potential energy surface is discussed.     

NO fundamental and first hot ro-vibrational line frequencies from MIPAS/Envisat atmospheric spectra

MIPAS (Michelson Interferometer for Passive Atmosphere Sounding) is a high spectral resolution interferometer (0.035 cm⁻¹ unapodized) covering a very wide spectral range (from 4.16 to 16.4 μm) with high sensitivity that was successfully launched on the 1st of March 2002 on the European Envisat satellite. MIPAS has measured spectra of the Earth’s upper atmosphere in the 4.3 μm region with the highest spectral resolution so far reached in this altitude region. This high spectral resolution permitted to obtain the frequency position of ro-vibrational NO⁺ transitions with an unprecedented accuracy. It has been found that the spectral line positions of the NO⁺ (1-0) ro-vibrational band are shifted by about ∼0.15 cm⁻¹ with respect to those listed in the HITRAN 2004 compilation. Also, spectral line positions of the NO⁺ (2-1) ro-vibrational band are shifted by approximately 0.05-0.1 cm⁻¹ with respect to those listed in the HITRAN 2004 compilation. A new set of Hamiltonian constants for NO⁺ has been derived from MIPAS data which is suggested to be used in future HITRAN compilations.     

Line Parameters for Ozone Hot Bands in the 3.3-μm Spectral Region

Line positions, intensities, and lower state energies have been calculated for eight hot bands of ¹⁶O₃ in the 3.3-μm spectral region. The results are based on spectroscopic parameters deduced in recent high-resolution laboratory studies and improved rotational energy levels of the (103), (004), and (310) vibrational states derived by refitting earlier data and experimental (004) energy levels from measurements of the 4ν₃ - ν₃ hot band. The good quality of the new parameters has been verified through comparisons of line-by-line simulations with high-resolution laboratory spectra. The present work and the results of our analyses of the main bands at 3.6 μm [Smith et al., J. Mol. Spectrosc.139, 171-181 (1990)] and 3.3 μm [Camy-Peyret et al., J. Mol. Spectrosc.141, 134-144 (1990)] provide a complete set of ozone spectroscopic line parameters covering the 3-μm region.     

Investigation of the ν8 and ν21 bands of propane CH3CH2CH3 at 11.5 and 10.9 µm: evidence of large amplitude tunnelling effects

ABSTRACT

We present the first investigation of the ν₈ band (C–C symmetric stretch at 870.3137?cm^?1), together with an extended analysis of the neighbouring ν₂₁ band (CH₃ rock at 921.3756?cm^?1) of propane (C₃H₈). Our previous investigation of the ν₂₁ A-type band [A.Perrin, F. Kwabia-Tchana, J.M.Flaud, L.Manceron, P.Groner, W.J.Lafferty. J. Mol. Spectrosc. 315, 55 (2015)] revealed that the rotational energy levels of 21¹ are split because of interactions with the internal rotations of the methyl groups, leading to the identification of AA, EE, AE and EA torsional components. In this work, a similar behaviour was observed for the B-type ν₈ band and the analysis of the ν₂₁ band was greatly extended. One of the results of the present study is to show that these torsional splittings are due to the existence of anharmonic and Coriolis resonances, coupling the 21¹ and 8¹ rotational levels to nearby highly excited levels of the two internal rotations of the methyl groups. Accordingly, an effective ‘vibration – torsion- rotation’ Hamiltonian model was built in the G₃₆ symmetry group which accounts for both types of resonances. In parallel, a code computing the line intensities was developed to allow unambiguous torsional component assignments. The line assignments were performed using a high resolution (0.0015?cm^?1) infrared spectrum of propane, recorded with synchrotron radiation at the SOLEIL French light source facility coupled to a Bruker IFS-125 Fourier transform spectrometer. Finally, a linelist of positions and intensities which can be used for the detection of propane in the Earth and outer planets atmospheres was produced.     

Experimental intercomparison of the absorption cross-sections of nitrous acid (HONO) in the ultraviolet and mid-infrared spectral regions

Nitrous acid, HONO, is an important trace gas in tropospheric photochemistry, because it is a source of OH radicals. In order to obtain HONO concentrations from spectroscopic measurements, the knowledge of accurate absorption cross-sections is essential. Furthermore, the ultraviolet absorption cross-sections of HONO determine its atmospheric photolysis rates, which are still being debated. In particular, in a recent field study focusing on the photolysis frequency of HONO, the absolute values of the ultraviolet absorption cross-sections have been proposed as a potential source for systematic errors. For these reasons, we have compared the absorption cross-sections for HONO in the infrared (IR) and ultraviolet (UV) by performing simultaneous measurements in both spectral regions. Assuming that the IR cross-sections (that show good agreement between different studies) are correct, our study shows a good agreement between the consistent infrared studies and some selected accurate UV spectra published previously (about 6%) while a rather large disagreement (about 22%) is observed when using other UV data sets.     

The first high-resolution analysis of the 10-μm absorption of thioformaldehyde

The 10 μm region of thioformaldehyde (H₂CS) has been recorded at high resolution (0.005 cm⁻¹) using a Fourier transform spectrometer. H₂CS was produced by low-pressure pyrolysis of a gas flow of C₃H₅SCH₃ in Ar at 560 °C or CH₃SCl at 1150 °C, which was introduced into a multipass White cell with an optical path length of 32 m. Forty scans were recorded for the range 750-1400 cm⁻¹ at a total pressure of 0.15 mbar. A thorough analysis of the three lowest wavenumber fundamental bands, ν₃, ν₄ and ν₆, which fall in this region, has been carried out using a Hamiltonian model, which takes explicitly into account the numerous resonances affecting the ro-vibrational energy levels; especially the massive A-type Coriolis resonance between the out-of-plane wagging mode, ν₄, and the in-plane rocking mode, ν₆. These two modes are only separated by 0.83 cm⁻¹, and they are thoroughly mixed. From the fittings, the following band centers were derived: ν_o (ν₄)=990.18213(40) cm⁻¹, ν_o (ν₆)=991.02021(50) cm⁻¹ and ν_o (ν₃)=1059.20476 (30) cm⁻¹ where the uncertainties are one standard deviation. In addition, a number of relative line intensities were measured permitting the determination of relative values of the first-order transition moments and therefore relative band intensities for all three bands. Finally, a comprehensive list of line wavenumbers and relative intensities has been generated.