Far infrared emission spectra from stratospheric hydrogen peroxide

Synthetic emission spectra from two stratospheric altitude observations have been analyzed for the presence of H₂O₂ in the far infrared region. The calculations are made with a high spectral resolution (10^–3 cm^–1 or 10^–4 cm^–1) greater than those in experimental measurements which are in the region of 3.10^–3 cm^–1. Spectra cover a spectral interval between 40 and 120 cm^–1 showing the best features of H₂O₂ susceptible to observation in a stratospheric spectrum. The optimum conditions for identification have been considered. Using the variations in H₂O₂ abundance in the measurement data and photochemical models, the H₂O₂ features detection limits have been studied.     

Detection of minor constitutents of the stratosphere by far infrared emission spectroscopy

The far infrared (30–110 cm^–1) emission spectrum of the lower stratosphere has been measured from balloon altitudes with a high resolution (0.06 cm^–1) rapid-scanning Michelson interferometer on two flights in 1976. The quality and resolution of the spectra obtained from two altitudes have permitted a careful search for emission lines from environmentally important molecules such as HCl, NO₂, OH, H₂O₂, and CO, among the more prominent and well-known features due to H₂O, O₃ and O₂. Column densities have been determined for H₂O and O₃ and upper limit estimates have been made from tentative identifications of several other constituents. However, the large angular field of view observed by the instrument prevented the determination of concentration profiles from atmospheric limb scans to the horizon. The possible future directions of this technique are outlined on the basis of operating experience over a 6 year programme. The viability of this method of monitoring the concentrations of minor constituents in the stratosphere is discussed with respect to other equivalent techniques.     

Detection of elevated tropospheric hydrogen peroxide (H2O2) mixing ratios in atmospheric chemistry experiment (ACE) subtropical infrared solar occultation spectra

We report measurements of hydrogen peroxide (H₂O₂) profiles from infrared solar occultation spectra recorded at 0.02 cm⁻¹ resolution by the atmospheric chemistry experiment (ACE) during 2004 and 2005. Mixing ratios as high as 1.7 ppbv (1 ppbv=1×10⁻⁹ per unit volume) were measured in the subtropical troposphere. Back trajectories, fire count statistics, and simultaneous measurements of other species from the same occultation provide evidence that the elevated H₂O₂ mixing ratios originated from a young biomass-burning plume. The ACE time series show only a few cases with elevated H₂O₂ mixing ratios likely because of the short lifetime of H₂O₂ and the limited sampling during biomass-burning time periods.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.     

Fourier Transform Spectroscopy of theYΣ–XΠiTransition of CuO

TheY²Σ⁺–X²Π_inear-infrared electronic transition of CuO was observed at high resolution for the first time. The spectrum was recorded with the Fourier transform spectrometer associated with the McMath–Pierce Solar Telescope at Kitt Peak. The excited CuO molecules were produced in a low pressure copper hollow cathode sputter with a slow flow of oxygen. Constants for theY²Σ⁺states of CuO are:T₀= 7715.47765(54) cm⁻¹,B= 0.4735780(28) cm⁻¹,D= 0.822(12) × 10⁻⁶cm⁻¹,H= 0.46(10) × 10⁻¹⁰cm⁻¹, γ = −0.089587(42) cm⁻¹, γ_D= 0.1272(79) × 10⁻⁶cm⁻¹,b_F= 0.12347(22) cm⁻¹, andc= 0.0550(74) cm⁻¹. ImprovedX²Π_iconstants are also presented.     

Nitrogen atom detection in low-pressure flames by two-photon laser-excited fluorescence

Nitrogen atoms have been detected in stoichiometric flat premixed H₂/O₂/N₂ flames at 33 and 96 mbar doped with small amounts of NH₃, HCN, and (CN)₂ using two-photon laser excitation at 211 nm and fluorescence detection around 870 nm. The shape of the fluorescence intensity profiles versus height above the burner surface is markedly different for the different additives. Using measured quenching rate coefficients and calibrating with the aid of known N-atom concentrations in a discharge flow reactor, peak N-atom concentrations in these flames are estimated to be on the order of 10¹²–5×10¹³ cm^–3; the detection limit is about 1×10¹¹ cm^–3.     

Coherent Raman and Infrared Studies of Sulfur Trioxide

High-resolution (0.001 cm⁻¹) coherent anti-Stokes Raman scattering (CARS) was used to observe the Q-branch structure of the IR-inactive ν₁ symmetric stretching mode of ³²S¹⁶O₃ and its various ¹⁸O isotopomers. The ν₁ spectrum of ³²S¹⁶O₃ reveals two intense Q-branches in the region 1065–1067 cm⁻¹, with surprisingly complex vibrational–rotational structure not resolved in earlier studies. Efforts to simulate this with a simple Fermi-resonance model involving ν₁ and 2ν₄ states do not reproduce the spectral detail, nor do they yield reasonable spectroscopic parameters. A more subtle combination of Fermi resonance and indirect Coriolis interactions with nearby states, 2ν₄(1=0, ±2), ν₂+ν₄(1=±1), 2ν₂(1=0), is suspected and a determination of the location of these coupled states by high-resolution infrared measurements is under way. At medium resolution (0.125 cm⁻¹), the infrared spectra reveal Q-branch features from which approximate band origins are estimated for the ν₂, ν₃, and ν₄ fundamental modes of ³²S¹⁸O₃, ³²S¹⁸O₂¹⁶O, and ³²S¹⁸O¹⁶O₂. These and literature data for ³²S¹⁶O₃ are used to calculate force constants for SO₃ and a comparison is made with similar values for SO₂ and SO. The frequencies and force constants are in excellent agreement with those obtained by Martin in a recent ab initio calculation.     

Line strength measurements of carbonyl sulfide (OCS) in the 2v3, v1+2v2+v3, and 4v2+v3 bands

To support planetary studies of the Venus atmosphere, we measured line strengths of the 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ bands of the primary isotopologue of carbonyl sulfide (¹⁶O¹²C³²S), whose band centers are located at 4101.387, 3937.427, and 4141.212 cm⁻¹, respectively. For this, infrared absorption spectra in normal carbonyl sulfide (OCS) sample gas were recorded at an unapodized resolution of 0.0033 cm⁻¹ at ambient room temperatures using a Bruker Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory. The FTS instrumental line shape (ILS) function was investigated, which revealed no significant instrumental line broadening or distortions. Various custom-made short cells and a multi-pass White cell were employed to achieve optical densities sufficient to observe the strong 2v₃ and the weaker bands in the region. Gas sample impurities and the isotopic abundances were determined from mass spectrum analysis. Line strengths were retrieved spectrum by spectrum using a non-linear curve fitting algorithm adopting a standard Voigt line profile, from which Herman–Wallis factors were derived for the three bands. The band strengths of 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ of ¹⁶O¹²C³²S (normalized at 100% of isotopologue) are observed to be 6.315(13)×10⁻¹⁹, 1.570(2)×10⁻²⁰, and 7.949(20)×10⁻²¹ cm⁻¹/molecule cm⁻², respectively, at 296 K. These results are compared with earlier measurements and the HITRAN 2004 database.     

Study of processes of translational,rotational, and vibrational relaxation based on CARS spectra line shapes

This paper reviews the various physico-chemical processes responsible for actual linewidths encountered in high-resolution coherent anti-Stokes Raman spectroscopy (CARS). Most of the experimental data are based on linewidth measurements using a pulseamplified CARS spectrometer with an emission bandwidth (FWHM) of 2×10^–3 cm^–1. Detailed rotational and vibrational relaxation constants have been obtained from the analysis of theQ-branch profiles of C₂H₂, N₂, CH₄, and SiH₄.     

Determination of the gap distribution in YBa2Cu3O7 using a far-infrared reflection-Fabry-Pérot device

This paper reports on far-infrared measurements of YBa₂Cu₃O₇ films oriented with the c-axis perpendicular to the surface, by using a silicon reflection Fabry-Pérot interferometer as a multireflection device. From these we could derive the dielectric function, the refractive index, the field penetration depth and the surface impedance of the material. The one order of magnitude higher sensitivity of the method compared to a direct reflectance measurement allowed to find an almost continuous gap distribution in the 70–215 cm^–1 region together with a separate gap at about 330 cm^–1. A quasizero gap absorption is found down to 20 cm^–1 even at low temperatures (10 K).     

Carrier concentration and shallow electron states in In-doped hydrothermally grown ZnO

Single-crystal ZnO has been hydrothermally grown with additional In₂O₃ in the solution. Schottky barrier contacts have been deposited by electron beam evaporation of Pd onto the face. Capacitance–voltage measurements have been performed to reveal the carrier concentration as a function of the In₂O₃ content in the solution, and secondary-ion mass spectrometry was used to measure the resulting In concentration in the samples. For an In₂O₃ content of 2×10¹⁹ cm⁻³, the average free electron concentration increased to 5×10¹⁸ cm⁻³ compared to 4×10¹⁷ cm⁻³ for the non-doped material. An increase of the In₂O₃ content to 4×10¹⁹ cm⁻³ leads to a measured carrier concentration of approximately 1×10¹⁹ cm⁻³; however, only up to a quarter of the incorporated In became electrically active. From thermal admittance spectroscopy measurements two prominent electronic levels are found, and compared with to the non-doped material case, the freeze-out of the shallow doping in the In-doped samples takes place at lower temperatures (below 80 K).     

CW-Cavity Ring Down Spectroscopy of O3. Part 3: Analysis of the 6490–6900 cm region and overview comparison with the O3 main isotopologue

This paper is devoted to the third part of the analysis of the very weak absorption spectrum of the ¹⁸O₃ isotopologue of ozone recorded by CW-Cavity Ring Down Spectroscopy between 5930 and 6900 cm⁻¹. In the two first parts [A. Campargue, A. Liu, S. Kassi, D. Romanini, M.-R. De Backer-Barilly, A. Barbe, E. Starikova, S.A. Tashkun, Vl.G. Tyuterev, J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.02.012 and E. Starikova, M.-R. De Backer-Barilly, A. Barbe, Vl.G. Tyuterev, A. Campargue, A.W.Liu, S. Kassi, J. Mol. Spectrosc. (2009) doi: 10.1016/j.jms.2009.03.013], the effective operators approach was used to model the spectrum in the 6200–6400 and 5930–6080 cm⁻¹ regions, respectively. The analysis of the whole investigated region is completed by the present investigation of the 6490–6900 cm⁻¹ upper range. Three sets of interacting states have been treated separately. The first one falls in the 6490–6700 cm⁻¹ region, where 1555 rovibrational transitions were assigned to three A-type bands: 3ν₂ + 5ν₃, 5ν₁ + ν₂ + ν₃ and 2ν₁ + 3ν₂ + 3ν₃ and one B-type band: ν₁ + 3ν₂ + 4ν₃. The corresponding line positions were reproduced with an rms deviation of 18.4 × 10⁻³ cm⁻¹ by using an effective Hamiltonian (EH) model involving eight vibrational states coupled by resonance interactions. In the highest spectral region – 6700–6900 cm⁻¹ – 389 and 183 transitions have been assigned to the ν₁ + 2ν₂ + 5ν₃ and 4ν₁ + 3ν₂ + ν₃ A-type bands, respectively. These very weak bands correspond to the most excited upper vibrational states observed so far in ozone. The line positions of the ν₁ + 2ν₂ + 5ν₃ band were reproduced with an rms deviation of 7.3 × 10⁻³ cm⁻¹ by using an EH involving the {(054), (026), (125)} interacting states. The coupling of the (431) upper state with the (502) dark state was needed to account for the observed line positions of the 4ν₁ + 3ν₂ + ν₃ band (rms = 5.7 × 10⁻³ cm⁻¹).The dipole transition moment parameters were determined for the different observed bands. The obtained set of parameters and the experimentally determined energy levels were used to generate a complete line list provided as Supplementary Materials.The results of the analyses of the whole 5930–6900 cm⁻¹ spectral region were gathered and used for a comparison of the band centres to their calculated values. The agreement achieved for both ¹⁸O₃ and ¹⁶O₃ (average difference on the order of 1 cm⁻¹) indicates that the used potential energy surface provides accurate predictions up to a vibrational excitation approaching 80% of the dissociation energy. The comparison of the ¹⁸O₃ and ¹⁶O₃ band intensities is also discussed, opening a field of questions concerning the variation of the dipole moments and resonance intensity borrowing by isotopic substitution.     

IR Reflection of Thin Bi4Ge3O12 Films

The spectra of IR reflection of the systems thin Bi₄Ge₃O₁₂ film–substrate made of molten -SiO₂ quartz in the region 10–1600 cm^–1 at 295 K are investigatedterpretation of fundamental vibrations in the region 10–800 cm^–1 and two phonon processes in the region 800–1600 cm^–1 are considered.     

XeCl-laser-generated ablation products from a nitrogen-rich polymer studied by laser-ionization mass spectrometry

Laser-ionization time-of-flight mass spectrometry has been used to probe laser-ablation products from a nitrogen-rich polymer at a wavelength of 308 nm. The ablation products at a laser fluence of 150 mJ/cm² showed, similar to 532 nm ablation studied previously [18], two strong peaks due to neutral species that were assigned to C⁺ and CN⁺, as well as several weak peaks that were assigned to CH⁺, HCN⁺, HCNH⁺, H_nN–CN⁺ (n=1–3), and H₂N–C=N–CN⁺ or H₂N–C=N–CN⁺. The ablation products at 870 mJ/cm² revealed, in addition to a broad signal due to ionic products generated directly by the ablation laser, several peaks due to neutral products that were assigned to C⁺, C ₂ ⁺ , C ₃ ⁺ , CN⁺, HCN⁺, HCNH⁺, and NCCN⁺. The most probable flight velocities for major neutral products are 5.7×10⁴ cm/s at 150 mJ/cm² and 2.3–2.7×10⁴ cm/s at 870 mJ/cm². The results at a laser fluence of 150 mJ/cm² support the finding that the translational energy of the tragments has importance for the collision-induced product generation in the laser plume, as suggested earlier [18]. Furthermore, the product generation at 870 mJ/cm² is interpreted by the ejection of small neutral and ionic fragments, and subsequent reactions among the fragments.     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

Fourier transform measurements of SO2 absorption cross sections: II.: Temperature dependence in the 29 000–44 000 cm (227–345 nm) region

This paper is the second of a series that reports results on the measurements of the absorption cross section of SO₂ in the UV/visible region at high resolution and that investigates high temperatures in support to planetary applications. Absorption cross sections of SO₂ have been obtained in the 29 000–44 000 cm⁻¹ spectral range (227–345 nm) with a Fourier transform spectrometer at a resolution of 2 cm⁻¹ (0.4500 cm MOPD and boxcar apodisation). Pure SO₂ samples were used and measurements were performed at room temperature (298 K) as well as at 318, 338 and 358 K. Temperature effects in this spectral region are investigated and are favorably compared to existing studies in the literature. Comparison of the absorption cross section at room temperature shows good agreement in intensity with most of the literature data, but shows that most of the latter suffer from inaccurate wavelength scale definition. Moreover, literature data are often given only on restricted spectral intervals. Combined with the data described in the first part of this series of papers on SO₂, this new data set offers the considerable advantage of covering the large spectral interval extending from 24 000 to 44 000 cm⁻¹ (227–420 nm), at the four temperatures investigated.     

High sensitivity CW-cavity ring down spectroscopy of CO2 near 1.35 μm (I): line positions

The absorption spectrum of carbon dioxide in natural isotopic abundance has been investigated by CW-cavity ring down spectroscopy with a new setup based on fibred distributed feedback (DFB) laser diodes. By using a series of 25 DFB lasers, the CO₂ spectrum was recorded in the 7123–7793 cm⁻¹ region with a typical sensitivity of 3×10⁻¹⁰ cm⁻¹. A 2125 transitions with intensities as low as 1×10⁻²⁹ cm/molecule were detected and assigned to the ¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O isotopologues. For comparison, only 357 of them were previously reported from Venus spectra and 344 transitions were included in the 2004 version of the HITRAN database. The band by band analysis has led to the determination of the rovibrational parameters of 28, 2 and 6 bands for the ¹²C¹⁶O₂, ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O isotopologue, respectively. While the uncertainty on the experimental line positions is on the order of 5×10⁻⁴ cm⁻¹, the average deviation from the ¹²C¹⁶O₂ calculated values provided by the most recent version of the carbon dioxide spectroscopic databank (CDSD) is −2.8×10⁻³ cm⁻¹ with an root mean square (rms) deviation of 3.5×10⁻³ cm⁻¹. Maximum deviations in the order of 0.02 and 0.12 cm⁻¹ were evidenced for some bands of the ¹⁶O¹²C¹⁷O and ¹⁶O¹²C¹⁸O minor isotopologues. The obtained results improve significantly the previous measurements from Venus spectra and will be valuable to refine the sets of effective Hamiltonian parameters used to generate the CDSD database.     

Rotational temperature measurement in high-temperature air using KrF laser-induced O2 fluorescence

Rotational temperature of O₂ has been measured in an atmospheric-air furnace using KrF laser-induced fluorescence. Average measurement errors of 10.7% and 5.1% over a temperature range of 1325–1725K were observed using two- and four-line excitation techniques, respectively. Ground-state depletion was observed for a spectral laser irradiance greater than approximately 7.5×10⁶ W/cm² cm^–1. This technique is suitable for temperature measurements when the O₂ vibrational population is not in thermal equilibrium.     

Water Vapor Measurements between 590 and 2582 cm: Line Positions and Strengths

This study involves measurements of H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O vapor spectra for the region between 590 and 2582 cm⁻¹. The parameters derived from the data include line positions, energy levels, and linestrengths. The study involves high-resolution line-position measurements with samples at room temperature in the (000)–(000), (010)–(010), and (010)–(000) bands. The experimental frequencies were used along with microwave, far-infrared, and hot water emission measurements in an analysis to obtain high-accuracy rotational energy level values in the (000), and (010) vibrational states of H₂¹⁶O forJ≤ 20. The experimental linestrengths were fitted by least squares to a model in which the dipole moment was represented as a series expansion containing up to 19 dipole moment matrix elements. The measurements in this work were more extensive than reported in prior studies by this author for the (010)–(000) band.     

Absorption spectrum of nitrous acid for the ν1+2ν3 band studied with continuous-wave cavity ring-down spectroscopy and theoretical calculations

We present the high resolution absorption measurements of gaseous HONO at room temperature using continuous-wave cavity ring-down spectroscopy in the near-infrared region between 6017 and 6067 cm⁻¹ at a resolution of 1 pm (0.037 cm⁻¹). For the trans-HONO isomer an extensive analysis of the ν₁+2ν₃ combination band 6045.8089 cm^–1 was performed starting from the results of a previous study for the 1¹ and 3¹ vibrational states [Guilmot J-M, Godefroid M, Herman M. Rovibrational parameters for trans-nitrous acid. J Mol Spectrosc 1993;160:387–400]. The present combination band is perturbed because of the existence of several dark states of HONO which could not be identified unambiguously. The rotational constants achieved for the 1¹3² state deviate slightly from the values which are predicted from the rotational constants achieved in the previous studies for the 1¹ and 3¹ vibrational states of trans-HONO.