Band Of SO Research Articles

Conductor-backed dielectric metasurface thermal emitters for mid-infrared spectroscopy

A conductor-backed dielectric metasurface thermal emitter at mid-IR frequencies with narrowband emissivity is experimentally demonstrated. The metasurface emitter consists of a high permittivity silicon resonator on top of a ground plane, whose resonant mechanism is explained using image theory. The resonator, placed close to a copper ground plane, is designed to produce a magnetic resonance, resulting in a low-profile device with a single emission peak in its subwavelength frequency range. The thermal emitter is next fabricated using common CMOS processes. Frequency dependent optical constants of plasma-enhanced chemical vapor deposited films of Si, SiO2, and evaporated Cu are also reported in the mid-IR range. Narrowband thermal emission is successfully obtained at around 7.22μm (41.5 THz), which corresponds to the absorption band of SO2. The Q-factor of about 37 is achieved with a peak emissivity of 0.65, which is significantly higher compared to the reported Q-factors of state-of-the-art plasmonic resonators.

Ultraviolet imager on Venus orbiter Akatsuki and its initial results

The ultraviolet imager (UVI) has been developed for the Akatsuki spacecraft (Venus Climate Orbiter mission). The UVI takes ultraviolet (UV) images of the solar radiation reflected by the Venusian clouds with narrow bandpass filters centered at the 283 and 365 nm wavelengths. There are absorption bands of SO2 and unknown absorbers in these wavelength regions. The UV images provide the spatial distribution of SO2 and the unknown absorber around cloud top altitudes. The images also allow us to understand the cloud top morphologies and haze properties. Nominal sequential images with 2-h intervals are used to understand the dynamics of the Venusian atmosphere by estimating the wind vectors at the cloud top altitude, as well as the mass transportation of UV absorbers. The UVI is equipped with off-axial catadioptric optics, two bandpass filters, a diffuser installed in a filter wheel moving with a step motor, and a high sensitivity charge-coupled device with UV coating. The UVI images have spatial resolutions ranging from 200 m to 86 km at sub-spacecraft points. The UVI has been kept in good condition during the extended interplanetary cruise by carefully designed operations that have maintained its temperature maintenance and avoided solar radiation damage. The images have signal-to-noise ratios of over 100 after onboard desmear processing.

Night side distribution of SO2 content in Venus’ upper mesosphere

In this paper we present the first night side distribution of SO2 content in Venus’ upper mesosphere (altitudes from 85 to 105km). The dataset is based on the SPICAV UV stellar occultation experiment which took place onboard ESA's Venus Express (VEX) orbiter in 2006–2014. The UV channel of SPICAV spectrometer detected absorption bands of SO2 and CO2 in the spectral range 180–300nm with a resolution of 1–2nm while stellar light was occulted by the mesosphere. Altitude profiles of sulfur dioxide's volume mixing ratio (VMR) could be retrieved in the upper part of the mesosphere covering the whole night side on Venus. In parallel, we have reprocessed the terminator UV solar occultations dataset (Belyaev et al., 2012. Icarus 217, 740–751) in the same altitude range and extended its statistics until 2014. On average the SO2 VMR increases with altitude from 10–30 ppb at 85km to 100–300 ppb at 100km in both regimes of occultation. The midnight SO2 abundance appears to be 3–4 times higher than in the terminator region: 150–200ppbv versus 50pppv at altitude around 95km. These new results were compared with the distribution of oxygen atoms, which are tracers of the global subsolar-antisolar (SS-AS) circulation at ∼100km (the data provided by Soret et al., 2012 Icarus, 217, 849–855). The night time behavior looks similar for SO2 molecules and O atoms with a correlation coefficient Rcorr= 0.73. Moreover, the retrieved SO2 enrichment above 85km appears to correlate with the density of H2SO4 droplets (Luginin et al., 2016; Icarus 277, 154–170).

Time-resolved photoelectron imaging with a femtosecond vacuum-ultraviolet light source: Dynamics in the A∼/B∼- and F∼-bands of SO2

Time-resolved photoelectron imaging is demonstrated using the third harmonic of a 400-nm femtosecond laser pulse as the ionization source. The resulting 133-nm pulses are combined with 266-nm pulses to study the excited-state dynamics in the A∼/B∼- and F∼-band regions of SO2. The photoelectron signal from the molecules excited to the A∼/B∼-band does not decay for at least several picoseconds, reflecting the population of bound states. The temporal variation of the photoelectron angular distribution (PAD) reflects the creation of a rotational wave packet in the excited state. In contrast, the photoelectron signal from molecules excited to the F∼-band decays with a time constant of 80 fs. This time constant is attributed to the motion of the excited-state wave packet out of the ionization window. The observed time-dependent PADs are consistent with the F∼ band corresponding to a Rydberg state of dominant s character. These results establish low-order harmonic generation as a promising tool for time-resolved photoelectron imaging of the excited-state dynamics of molecules, simultaneously giving access to low-lying electronic states, as well as Rydberg states, and avoiding the ionization of unexcited molecules.

The vertical distribution of volcanic SO<sub>2</sub> plumes measured by IASI

Abstract. Sulfur dioxide (SO2) is an important atmospheric constituent that plays a crucial role in many atmospheric processes. Volcanic eruptions are a significant source of atmospheric SO2 and its effects and lifetime depend on the SO2 injection altitude. The Infrared Atmospheric Sounding Interferometer (IASI) on the METOP satellite can be used to study volcanic emission of SO2 using high-spectral resolution measurements from 1000 to 1200 and from 1300 to 1410 cm−1 (the 7.3 and 8.7 µm SO2 bands) returning both SO2 amount and altitude data. The scheme described in Carboni et al. (2012) has been applied to measure volcanic SO2 amount and altitude for 14 explosive eruptions from 2008 to 2012. The work includes a comparison with the following independent measurements: (i) the SO2 column amounts from the 2010 Eyjafjallajökull plumes have been compared with Brewer ground measurements over Europe; (ii) the SO2 plumes heights, for the 2010 Eyjafjallajökull and 2011 Grimsvötn eruptions, have been compared with CALIPSO backscatter profiles. The results of the comparisons show that IASI SO2 measurements are not affected by underlying cloud and are consistent (within the retrieved errors) with the other measurements. The series of analysed eruptions (2008 to 2012) show that the biggest emitter of volcanic SO2 was Nabro, followed by Kasatochi and Grímsvötn. Our observations also show a tendency for volcanic SO2 to reach the level of the tropopause during many of the moderately explosive eruptions observed. For the eruptions observed, this tendency was independent of the maximum amount of SO2 (e.g. 0.2 Tg for Dalafilla compared with 1.6 Tg for Nabro) and of the volcanic explosive index (between 3 and 5).

Theoretical assignment of the Clements bands of SO2

The photoabsorption spectrum of SO2 is theoretically investigated in the energy range 3.56–4.05eV (28713–32665cm−1). The lowest vibronic levels of the coupled excited electronic states (11A2/11B1) have been computed using Lanczos diagonalization of the Hamiltonian. The potential energy surfaces and the diabatization scheme used here were already successfully applied to describe the non-adiabatic dynamics of the molecule (Lévêque et al., 2013). The important vibronic states, playing a role in the experimental spectrum, have been analyzed according to their nodal pattern to propose the first theoretical assignment of the low-energy part of the spectrum. The Clements bands A–D have been assigned and exhibit contributions from numerous transitions, in the low resolution spectrum. The overlap of these transitions is shown to provide an “accidental” regularity of the Clements bands with respect to their intensities, while their regular energy spacing (∼220cm−1) results from a unique series (4,n2,1).

Detection and characterization of Io’s atmosphere from high-resolution 4-μm spectroscopy

We report on high-resolution and spatially-resolved spectra of Io in the 4.0μm region, recorded with the VLT/CRIRES instrument in 2008 and 2010, which provide the first detection of the ν1+ν3 band of SO2 in Io’s atmosphere. Data are analyzed to constrain the latitudinal, longitudinal, and diurnal distribution of Io’s SO2 atmosphere as well as its characteristic temperature. Equatorial SO2 column densities clearly show longitudinal asymmetry, but with a maximum of ∼1.5×1017cm−2 at central meridian longitude L=200–220 and a minimum of ∼3×1016cm−2 at L=285–300, the longitudinal pattern somewhat differs from earlier inferences from Ly α and thermal IR measurements. Within the accuracy of the measurements, no evolution of the atmospheric density from mid-2008 to mid-2010 can be distinguished. The decrease of the SO2 column density towards high latitudes is apparent, and the typical latitudinal extent of the atmosphere found to be ±40° at half-maximum. The data show moderate diurnal variations of the equatorial atmosphere, which is evidence for a partially sublimation-supported atmospheric component. Compared to local noon, factor of 2 lower densities are observed ∼40° before and ∼80° after noon. Best-fit gas temperatures range from 150 to 220K, with a weighted mean value of 170±20K, which should represent the column-weighted mean kinetic temperature of Io’s atmosphere. Finally, although the data include clear thermal emission due to Pillan (in outburst in July 2008) and Loki, no detectable enhancements in the SO2 atmosphere above these volcanic regions are found, with an upper limit of 4×1016cm−2 at Pillan and 1×1017cm−2 at Loki.

Ab initio determination of potential energy surfaces for the first two UV absorption bands of SO2

Three-dimensional potential energy surfaces for the two lowest singlet (Ã(1)B1 and B̃(1)A2) and two lowest triplet (ã(3)B1 and b̃(3)A2) states of SO2 have been determined at the Davidson corrected internally contracted multi-reference configuration interaction level with the augmented correlation-consistent polarized triple-zeta basis set (icMRCI+Q∕AVTZ). The non-adiabatically coupled singlet states, which are responsible for the complex Clements bands of the B band, are expressed in a 2 × 2 quasi-diabatic representation. The triplet state potential energy surfaces, which are responsible for the weak A band, were constructed in the adiabatic representation. The absorption spectrum spanning both the A and B bands, which is calculated with a three-state non-adiabatic coupled Hamiltonian, is in good agreement with experiment, thus validating the potential energy surfaces and their couplings.

Excitation band dependence of sulfur isotope mass-independent fractionation during photochemistry of sulfur dioxide using broadband light sources

Ultraviolet photolysis of sulfur dioxide (SO2) is hypothesized to be the source of the sulfur isotope mass-independent fractionation (S-MIF) observed in Archean sulfate and sulfide minerals and modern stratospheric sulfate aerosols. A series of photochemical experiments were performed to examine the excitation band dependence of S-MIF during the photochemistry of SO2 under broadband light sources (a xenon arc lamp and a deuterium arc lamp). Optical filters (200±35nm bandpass and 250nm longpass filters) were used to separately access two different excitation bands of SO2 in the 190–220nm and the 250–330nm absorption regions, respectively.UV irradiation of SO2 in the 190–220nm and 250–330nm regions both produced elemental sulfur (S0) and sulfur trioxide (SO3) as end products but yielded very different sulfur isotope signatures. The elemental sulfur products from direct photolysis in the 190–220nm region were characterized by high δ34S values (154.7–212.0‰), modest Δ33S anomalies of 21±3‰, and relatively constant 33λ (=ln(δ33S+1)/ln(δ34S+1)) values of 0.64±0.3, all with respect to the initial SO2. Photoexcitation in the 250–330nm region produced elemental sulfur with δ34S values of 7.7–29.1‰ and Δ33S values of 15.0±1.6‰. In both excitation regions, the SO3 products were mass dependently fractionated relative to the SO2 reservoir. The two different absorption regions produced contrasting Δ36S/Δ33S signatures in the elemental sulfur products, with Δ36S/Δ33S=−1.9±0.3 and 0.64±0.3 for the 190–220nm and 250–330nm bands, respectively.Our results provide several critical constraints on the origin of the S-MIF signatures observed in modern stratospheric aerosols and in the Archean geological record. A lack of S-MIF in the sulfate product and positive Δ36S/Δ33S ratios for the elemental sulfur from SO2 photo-oxidation demonstrate that photoexcitation in the 250–330nm region is not a likely source for the S-MIF observed in modern stratospheric aerosols. Large δ34S fractionation, 33λ values, and Δ36S/Δ33S ratios observed for the 190–220nm band are qualitatively consistent with predictions from synthetic isotopologue-specific cross sections. These isotope patterns, however, are not compatible with the Archean rock record. We explore the possibility that S-MIF from both the 190 to 220nm and the 250 to 330nm absorption bands could have contributed to the Archean S-MIF signatures.

Retrieval of sulphur dioxide from the infrared atmospheric sounding interferometer (IASI)

Abstract. Thermal infrared sounding of sulphur dioxide (SO2) from space has gained appreciation as a valuable complement to ultraviolet sounding. There are several strong absorption bands of SO2 in the infrared, and atmospheric sounders, such as AIRS (Atmospheric Infrared Sounder), TES (Tropospheric Emission Spectrometer) and IASI (Infrared Atmospheric Sounding Interferometer) have the ability to globally monitor SO2 abundances. Most of the observed SO2 is found in volcanic plumes. In this paper we outline a novel algorithm for the sounding of SO2 above ~5 km altitude using high resolution infrared sounders and apply it to measurements of IASI. The main features of the algorithm are a wide applicable total column range (over 4 orders of magnitude, from 0.5 to 5000 dobson units), a low theoretical uncertainty (3–5%) and near real time applicability. We make an error analysis and demonstrate the algorithm on the recent eruptions of Sarychev, Kasatochi, Grimsvötn, Puyehue-Cordón Caulle and Nabro.

Experimental examination of flame chemistry in hydrogen sulfide-based flames

Spectroscopic examination of the emission spectra of excited species in hydrogen/air flames both without and with H2S addition and in hydrogen sulfide/oxygen flame are conducted. The baseline case of hydrogen/air flame showed one distinct global peak of OH* at 309.13nm. However, higher resolution spectrum analysis showed the presence of three major OH* peaks at 306.13, 309.09, and 312.9nm. The addition of hydrogen sulfide to hydrogen/air flame resulted in the presence of a bluish cone located at inner regions of the flame. The spectrum of the blue cone showed group of peaks in the 350–470nm spectral range. The addition of H2S drastically reduced the peak value of OH* due to extensive consumption of the hydroxyl group during H2S combustion. The group of peaks in the blue cone spectrum can be divided into three major bands. The first band is formed by SO* within 320–350nm, the second band is attributed to SO3∗ within 350–400nm, and the third band is caused by H* within 400–470nm. However, the distinction of SO3∗ band and H* band around 400nm is an issue that requires further examination. Absorption bands of SH were observed at 324.03nm and 328.62nm. The effect of sulfur dioxide on the spectrum was observed by neither emission bands nor absorption bands because of its reaction with elemental oxygen to produce excited sulfur trioxide. Gas chromatography analysis showed that combustion products did not contain any SO2. The spectra of H2S/O2 flame have also been examined under lean conditions (at Φ=0.5). In contrast to H2/air/H2S flames, the spectra of H2S/O2 showed strong absorption bands of SO2 within 280–310nm. Strong continuum was observed between 280 and 460nm with distinct group of peaks superimposed in the spectra. The continuum is attributed to the afterglow of singlet and triplet SO2. The superimposed peaks are attributed to SO3∗ and H*.

Ash and sulfur dioxide in the 2008 eruptions of Okmok and Kasatochi: Insights from high spectral resolution satellite measurements

Ash particles and sulfur dioxide gas are two significant components of volcanic clouds that are important because of their effects on the atmosphere. Several different satellite instruments are capable of delivering quantitative measurements of ash and SO2, but few can provide simultaneous assessments. High‐spectral resolution (ν/Δν ∼ 1200) infrared satellite data from the Atmospheric Infrared Sounder (AIRS) are utilized to detect volcanic ash within the 8–12 μm window region, and at the same time exploit the 4.0 μm and 7.3 μm bands of SO2 to detect SO2 at two different heights. The purpose is to study the interaction between gas and particles in dispersing volcanic clouds, and investigate the circumstances when the gas‐rich and ash‐rich parts of the plume are collocated and when they separate. Simultaneous retrievals of ash and SO2 in the eruption clouds from Okmok and Kasatochi suggest that the two components were transported together for at least the first 3 days after the initial injection. Later (several days) transport is difficult to infer because of the lack of sensitivity of the ash algorithm to thin, dispersing ash clouds. For Kasatochi and Okmok, AIRS measured maximum masses of approximately 1.21 ± 0.01 Tg and 0.29 ± 0.01 Tg of SO2, and 0.31 ± 0.03 Tg and 0.07 ± 0.03 Tg of fine ash (1 μm < radii < 10 μm), respectively. The retrieval schemes described here are capable of detecting the distribution of SO2 simultaneously with estimates of ash concentrations from the same satellite instrument and represent an important improvement for observations of multispecies dispersing volcanic clouds. Analyses of other volcanic eruptions show that SO2 and ash do not always travel together. Consequently, it is concluded that for dispersing volcanic clouds it is vital to be able to detect both SO2‐rich and ash‐rich clouds simultaneously in order to diagnose their effect on the atmosphere and the aviation hazard.

Infrared Absorption Spectroscopy Measurement of SOx using Tunable Infrared Laser

The absorption characteristics of sulfur dioxide (SO2) and sulfur trioxide (SO3) in the infrared region were measured using a quantum cascade laser and an absorption cell of length 1 m heated to 150°C. The laser was scanned over the wavelength range 6.9-7.4 μm, which included the absorption bands of SO2 and SO3. Measurement results showed that the absorption bands of SO2 and SO3 partially overlapped, with peaks at 7.28 μm and 7.35 μm for SO2 and 7.14 μm and 7.25 μm for SO3. These results showed the possbility of using infrared laser absorption spectroscopy for measurement of sulfur oxides (SOx) in flue gas. For SO3 measurement, infrared absorption spectroscopy was shown to be more suitable than ultraviolet absorption spectroscopy. The absorption characteristics of open air in the same wavelength region showed that the interference due to water vapor must be efficiently removed to perform SOx measurement in flue gas.

An Experimental and Theoretical Study of NSCl Decomposition in the Presence of Trace Amounts of Water

An experimental and density functional theory study of the decomposition reaction of NSCl with water molecule(s) into NH 3 and SO 2 is described. Experiments involving the decomposition of NSCl in the presence of trace amounts of water showed that the formation of both HNSO and SO 2 is faster when the cell and the cell surface are fresh and more likely to be coated in adsorbed water. The density functional theory computational results suggest that the decomposition involves two main steps: reactions 1 NSCl + nH 2O --> HNSO + ( n - 1) H 2O + HCl and 2 HNSO + nH 2O --> NH 3 + SO 2 + ( n - 1)H 2O. The barrier for reaction 1 in which NSCl decomposes to form HNSO becomes substantially lower when the explicit hydrogen bonding of water molecules is considered. The water assisted decomposition reaction mechanism can help account for the experimentally observed conversion of NSCl to produce HNSO in the presence of water. The calculated barrier of reaction 2 (the decomposition of HNSO into NH 3 and SO 2) can also explain the experimental observation of SO 2 bands from the decomposition of NSCl in the presence of water.

First observations of SO2 above Venus' clouds by means of Solar Occultation in the Infrared

Solar Occultation in the Infrared (SOIR) is a part of the Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus (SPICAV)/SOIR occultation experiment on board Venus Express dedicated to the study of gaseous and aerosol vertical structure of Venus' mesosphere. SOIR is an echelle spectrometer with acoustooptic selection of diffraction orders operating in the wavelengths range of 2.2–4.3 μm at high spectral resolution (λ/Δλ ∼ 20,000). Detection of minor constituents such as CO, H2O, HDO, HCl, HF, and SO2, at altitudes between 65 and 130 km has been demonstrated. We report results from a series of six occultations with observations of the 4‐μm SO2 band at latitudes 69°–88°N and 23°–30°N. It is the first time when the vertical distribution of SO2 is retrieved above the clouds with the help of solar occultation direct method. The sulfur dioxide transmission spectrum is measured on a background of strong CO2 absorption. Each retrieved vertical profile of SO2 is characterized by few points; the mixing ratio of SO2 being ∼0.1 ppm with scale height 1 ± 0.4 km for polar measurements (evening observations) and ∼1 ppm with scale height 3 ± 1 km at low latitudes (morning observations) at the altitude of about 70 km. Upper limits of <∼0.05 ppm are established around 75 km.

Spectroscopic study of the ν1 band of SO2 using a continuous-wave DFB QCL at 9.1 μm

We report results of spectroscopic measurements with a continuous-wave distributed-feedback quantum-cascade laser (DFB QCL). Line intensities and self-broadening coefficients were measured in the ν1 band of SO2 between 1088 and 1090 cm-1. The self-broadening coefficients in this paper confirm the typical decrease of γself with increasing rotational quantum number Ka′′. The line intensities determined here are smaller than those in the HITRAN 2000 database. Several lines found in this study were not present in the database.

Quantitative analysis of dilute mixtures of SO 2 in N 2 at 7.4 ?m by difference frequency spectroscopy

We describe a 7.4-μm source based on difference frequency generation with 6.5 mW of 1278-nm radiation from an extended cavity laser and 66 mW of 1544-nm radiation from another extended cavity laser, amplified in an erbium-doped fibre amplifier. Optimum focusing of the input beams in the 5×5×10-mm3 AgGaSe2 crystal, and the spatial and temporal characteristics of the output beam, are determined. The source is used for accurate determination of line parameters for selected lines of the ν3 band of SO2, centred at 1361 cm-1. Subsequently, these lines are used for performing quantitative analysis of gas mixtures containing SO2 at concentration levels down to 4 ppm without relying on any calibration with certified gas mixtures. This demonstrates the potential of infrared spectroscopy as a primary method for low-concentration gas analysis.

Middle ultraviolet and visible spectrum of SO2 by electron impact

Electron‐impact‐induced fluorescence spectra of SO2 in the middle ultraviolet and visible wavelength regions (200–600 nm) have been measured in the laboratory using a crossed beam experiment at three electron impact energies. The emission spectra at 8, 18, and 98 eV exhibit a broad and continuous emission region extending from 225 to near 600 nm with a peak emission close to 330 nm. The quasicontinuous SO2 bands arise primarily from direct excitation of SO2. At 18 and 98 eV, simultaneous excitation and dissociation of SO2 produces distinct vibrational bands from SO and from atomic emission lines from S I, S II, O I, and O II that are superimposed on the SO2 electronic transitions. The laboratory spectra were compared to green/violet color ratios obtained at Io by the Galileo Orbiter Solid State Imaging experiment. The laboratory spectra were also applied to the Cassini Imaging Subsystem to determine which filter combinations are particularly sensitive to electron energy, if the atmospheric gas present in the auroral atmosphere is solely or primarily SO2.

Line intensity and self-broadening investigations in the ν1 and ν3 bands of SO2

Line intensities and self-broadening coefficients were measured for 37 transitions in the ν1 band of SO2 between 1072 and 1149cm−1 in the rotational quantum number range between 3≤J″≤44 and 0≤Ka″≤23 and for 12 transitions in the ν3 band of SO2 near 1321cm−1 in the rotational quantum number range between 50≤J″≤61 and 2≤Ka″≤18. The experiments were carried out with a dual-channel lead–salt diode-laser spectrometer, which was operated in pulsed mode. The spectroscopic parameters for the individual lines were determined from the analysis of spectra measured in the pressure range between 1 and 12Torr. The measured data of a complete pressure series were analyzed at once. Therefore, the fit delivered directly the self-broadening coefficients and the line intensities. The determined self-broadening coefficients are within the uncertainties in good agreement with previously published data and confirm the typical decrease of the self-broadening coefficient γSO2–SO2 with increasing rotational quantum number Ka″. The broadening coefficients decrease from a γSO2–SO2 by about 0.4cm−1/atm for lines with small Ka″down to values of about 0.2cm−1/atm for lines with a Ka″>18. The line intensities determined here were slightly smaller compared to the data listed in the HITRAN 1996 database. The deviations do not show any remarkable quantum number dependence. The average values of the ratio SiExp/SiHITRAN 1996 were calculated to 0.83±0.02 (ν1 band) and 0.75±0.03 (ν3 band). The integrated band intensities were determined to (3.41±0.11)×10−18cm−1/moleculecm−2 for the ν1 band and to (2.40±0.15)×10−17cm−1/moleculecm−2 for the ν3 band, respectively.

Proton impact excitation of SO2

Because of the interest in atomic emissions observed from the Io plasma torus, we have investigated the spectrum produced by proton impact on SO2 in the wavelength region of 380–800 nm. The proton energy was varied from 50 to 225 keV. The spectrum shows numerous S, O, S+, and O+ lines. A weak series of SO2 bands has also been tentatively identified. In addition, Balmer series lines are seen, which indicates charge‐transfer ionization of the SO2 target. Preliminary absolute emission cross sections on the order of 10−18 cm2 have been measured for the most dominant line in the spectrum, an oxygen triplet at 777 nm.