Spectra Of SO Research Articles

Theoretical studies of absorption cross sections for the C̃ B12-X̃ A11 system of sulfur dioxide and isotope effects

The C (1)B(2)-X (1)A(1) photoexcitation of SO(2) was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections (sigma's) of seven isotopologues ((32)S (16)O(2), (33)S (16)O(2), (34)S (16)O(2), (36)S (16)O(2), (32)S(16)O(17)O, (32)S(16)O(18)O, (34)S(16)O(18)O) were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces of the X and C states, which were calculated using the ab initio molecular orbital configuration interaction method. Numerous wave packet simulations were carried out under the adiabatic approximation and used to calculate the sigma's of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO(2) can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated sigma's are in reasonable agreement with the recent experiment in the 190-228 nm region, and the isotope shifts of the peaks for (33)S (16)O(2) and (34)S (16)O(2) relative to the corresponding peaks for (32)S (16)O(2) are in good agreement with the observed data. Relative to the sigma of (32)S (16)O(2), isotopic substitution shows a significant increment for those of (34)S (16)O(2) and (36)S (16)O(2) in the 190-228 nm region. This trend is consistent with the observed data.

Ab initio calculations of the ionization spectrum of SO2

The ionization spectrum of sulfur dioxide has been successfully studied by using the symmetry-adapted-cluster configuration-interaction (SAC-CI) general-R and SD-R methods and the basis set correlation-consistent polarized valence triple-zeta (cc-pVTZ). The SAC-CI general-R method reproduces the experimental spectrum well for both the main peaks and the satellite peaks of ionization spectrum of SO2. The sequence of ionic states corresponding to main peaks of SO2 has been re-determined according to the SAC-CI conclusions and it is reordered as X̄2A1, Ã2B2, B̄2A2, C̄2B1, D̄2A1, Ē2B2 and F̄2A1. Besides, the equilibrium structures and adiabatic ionization potentials (AIPs) of ionic states of main peaks of SO2 are calculated by using the SAC-CI SD-R method.

Promotional effect of potassium on soot oxidation activity and SO2-poisoning resistance of Cu/CeO2 catalyst

Abstract Potassium nitrate was incorporated to the Cu/CeO2 system to enhance the soot oxidation activity and sulfur-poisoning resistance. The Cu, K/CeO2 catalyst exhibited superior activity for soot oxidation with the lowest Tm at 313 and 359 °C under tight and loose contact modes, respectively. The CO–TPR curves demonstrated that the co-impregnation of copper and potassium effectively shifted the redox process of ceria to lower temperatures, contributing greatly to enhance soot oxidation activity. The IR spectra of SO2 poisoned catalysts implied partial transformation of KNO3 to K2SO4. The activity loss of the binary metal catalysts by SO2 poisoning was less than 70 °C thanks to remained KNO3.

Middle UV to near‐IR spectrum of electron‐excited SO2

We investigated the electron impact–induced fluorescence spectrum of SO2 to provide excitation cross sections for modeling Io's emission spectrum and analyzing Cassini Imaging Science Subsystem observations. The electron‐excited middle‐ultraviolet visible optical near‐infrared (VOIR) emission spectrum of SO2 gas was generated in the laboratory and studied from 2000 to 11,000 Å at a resolution of Δλ ∼ 2.5 Å full width at half maximum (FWHM). The VOIR laboratory spectrum longward of 6000 Å consists entirely of S I, II and O I, II multiplets for electron impact energies above ∼15 eV. Between 2000 and 6000 Å, we find previously identified molecular bands from both SO and SO2. This work represents a significant improvement in spectral resolution over our earlier work done at 18 Å FWHM. From a measurement of the medium‐resolution spectrum, we provide detailed 25‐ and 100‐eV emission cross sections for spectral features from 2000 to 11,000 Å. On the basis of these data, we suggest future ground‐based and satellite telescopic observations in the VOIR that are of promise for understanding Io's atmosphere.

Comparison of a quantum cascade laser used in both cw and pulsed modes. Application to the study of SO2 lines around 9 μm

The same quantum cascade laser spectrometer working around 9 μm was used in both continuous-wave and pulsed modes to compare their own characteristics. The laser emitting in continuous-wave mode was mainly used to study some spectroscopic parameters of SO2 ro-vibrational lines. This work demonstrates the necessity to use new calculations previously developed instead of conventional databases such as HITRAN. In addition, the same laser emitting in pulsed mode with long pulses (600 to 900 ns) was used to record SO2 spectra with the intrapulse technique. This work permits us to make comparisons about those two modes of emission for the development of future spectrometers.

Spin-orbit relativistic calculations of the core excitation spectra of SO2

The time dependent density functional theory approach within the two-component zero-order relativistic approximation has been applied to the calculation of the core excitation spectra of SO2 molecule. The results obtained reproduce correctly the high resolution experimental spectra and allow the assignment of the spectral features both of the valence and Rydberg regions in the S 1s and O 1s spectra. For the S 2p threshold a correct description of the spin-orbit coupling as well as of the molecular field splitting appears mandatory for a reliable description of the spectrum and a detailed attribution of the complex Rydberg manifold of core excited states.

Spectroscopic Detection of Sulfur Oxides in the Aircraft Wake

The absorption/emission spectral regions of SO, SO2, SO3, S2O and HSO are analyzed for the range from UV (λ ≥ 0.2 µm) to IR (λ < 30 µm) and are compared with the atmospheric transmission spectrum. It is shown that many vibrational bands of the compounds considered fall into atmospheric transmission windows. For the vibrational bands of SO, SO2, SO3, S2O, and HSO molecules there are some gases which hinder the absorption diagnostics of the indicated compounds. These interfering gases are natural components of atmospheric air as well as specific gases of aircraft engine exhaust. It is found that the least influence of the interference takes place in the 2400–2700 cm−1 IR region. The spectroscopic techniques used for the detection of aircraft engine exhaust compounds are briefly reviewed, with much consideration given to SO2. The IR absorption spectra of SO2 and other gases are calculated for the conditions of the aircraft engine nozzle exit. Narrow spectral intervals suitable for SO2 detection in a hot flow are determined. An analysis is made for the detection capabilities of CO2 lasers (including isotope CO2 lasers) and CO lasers (both fundamental band and first-overtone ones) as applied to SO2 detection in aircraft engine exhaust.

Chemical differentiation along the CepA-East outflows

We present the results of a multiline survey at millimetre wavelengths of the Cepheus A star-forming region. Four main flows have been identified: three pointing in the southwest, northeast and southeast directions and accelerating high-density CS clumps. The fourth outflow, revealed by high-sensitivity deuterated water (HDO) observations, is pointing towards the south and is associated with conditions particularly favourable to a chemical enrichment. At the CepA-East position the emissions due to the ambient clump and to the outflows coexist and different molecules exhibit different spectral behaviours. Some species (C13CH, C3H2, CH2CO, CH3C2H, HC18O+) exhibit relatively narrow lines at ambient velocities (ambient peak). Other molecules (CO, CS, H2S, SiO, SO, SO2) show extended wings tracing the whole range of the outflow velocities. Finally, OCS, H2CS, HDO and CH3OH are associated with wings and, indeed, show wings, and also reveal a bright high-velocity redshifted spectral peak (outflow peak) which can be used to investigate the southern outflows. At ambient velocities the gas is dense (>105 cm−3) and different components at distinct temperatures coexist, ranging from the relatively low kinetic temperatures (≤50 K) measured with H2S, CH3OH, H2CS and CH3C2H, to definitely higher-temperature conditions, ∼100–200 K, obtained from the SiO, SO and SO2 spectra. For the outflow peak we derive densities of between ∼104 and ∼107 cm−3 and high temperatures, ≃100–200 K, indicating regions compressed and heated by shocks. The analysis of the line profiles shows that the SiO molecule dominates at the highest velocities and at the highest excitation conditions, confirming its close association with shocks. H2S, SO2 and SO preferentially trace more quiescent regions than SiO, and, in particular, a lack of bright H2S emission at the highest velocities is found. OCS and H2CS emit at quite high velocities, where the abundances of three shock tracers such as SiO, CH3OH and HDO are higher. These results may indicate that H2S is not the only major sulphur carrier in the grain mantles, and that OCS and H2CS may probably play an important role on the grains, or that alternatively they rapidly form once the mantle is evaporated after the passage of a shock. Finally, the outflow peak emission has been compared with recent time-dependent sulphur chemistry models: the results indicate that, if associated with accurate measurements of the physical conditions, the CH3OH/H2CS column density ratio can be used as an effective chemical clock to date the age of shocked gas.

Widely tunable continuous-wave mid-infrared radiation (55–11 µm) by difference-frequency generation in LiInS_2 crystal

The first demonstration, to the best of our knowledge, of continuous-wave (cw) difference-frequency generation (DFG) in LiInS2 crystal is reported. Wide spectral coverage (5.5-11.3 microm) has been obtained with angle and wavelength tuning for type II (eoe) critically phase-matched parametric interaction. The phase-matching conditions in cw DFG have been investigated, which allowed us to improve the Sellmeier parameters by use of a two-pole dispersion equation. An effective nonlinear coefficient deff = 6.9 +/- 0.8 pm/V has been determined at approximately 7 microm relative to the well-known nonlinear coefficient d36 of AgGaS2, which yields a power-conversion efficiency of approximately 12.4 microW/(W2 cm). We evaluated the high-resolution spectral characteristics of the DFG source by recording C2H2 and SO2 spectra.

Laser-induced fluorescence instrument for measuring atmospheric SO2

Abstract We report on the development of a high-sensitive detection system for measuring atmospheric SO2 using a laser-induced fluorescence (LIF) technique at around 220 nm. Second harmonics of a tunable broad-band optical parametric oscillator (OPO) pumped by the third harmonic of a Nd:YAG laser is used as a fluorescence excitation source. The laser wavelength is alternatively tuned to the peak and the bottom wavelengths in the photoabsorption spectrum of SO2 at 220.6 and 220.2 nm, respectively, and the difference signal at the two wavelengths is used to extract the SO2 concentration. This procedure can give a good selectivity for SO2 and avoid interferences of fluorescent or particulate species other than SO2 in the sample air. The SO2 instrument developed has a sensitivity of 5 pptv in 60 s and S / N = 2 . The practical performance of the detection system is tested in the suburban area. The inter-comparisons between the LIF instrument and a commercial instrument using Xe flash lamp excitation for the fluorescence detection have been performed. The correlation between two instruments is measured up to 70 ppbv. A good linear relationship between the LIF measurements and commercial instrument measurements is obtained.

A theoretical and experimental study of the SO2(2+) dication.

The double photoionization spectrum of SO2 has been measured using the TOF-PEPECO technique and contains one resolved band. Detailed electronic structure calculations and experimental comparisons allow the resolved band to be identified as the A 1A2 state of the SO2(2+) dication, with its adiabatic ionization energy at 35.284+/-0.02 eV. According to the most accurate calculations, the ground state level of SO2(2+) must be located near 33.48 eV, well below the range accessed by vertical transitions from neutral SO2. Transient SO2 (2+) molecules detected by mass spectrometry may be identified either as the sharp levels of the A 1A2 state or as ground state levels populated by nonvertical ionization pathways.

Degenerate Four-Wave Mixing in SO2 in Free Jets

A rotational excitation spectrum of SO2 [Ã 1A2(511)←X̃ 1A1(000)] at about 33331 cm−1in free jets was observed by using the forward degenerate four-wavemixing (DFWM). Twelve lines of the G band and 11 ones of the Eband were marked based on the rotational constants according to Hamada'sresult [Can. J. Phys. 53 (1975) 2555]. The relation between theDFWM signal intensity and the pressure of the buffer gas in free-jetswas experimentally investigated.

Zero kinetic energy photoelectron study of SO2+(X2A1) using coherent extreme ultraviolet radiation.

Using our newly built extreme ultraviolet (XUV) photoelectron and photoion spectrometer, we have obtained the pulsed field ionization zero kinetic energy (ZEKE) photoelectron spectra of SO2+(X2A1)<--SO2(X1A1) by coherent XUV radiation in the energy range of 12.29-12.82 eV. The adiabatic ionization potential (IP) of SO2 is 12.3458+/-0.0002 (eV), which was determined by comparing the partially resolved rotational branch contour with the simulated one. Besides the bending vibrational mode (upsilon2) which was found to be exclusive in the photoelectron spectra (PE) reported previously, we also observed the other two modes: the symmetric stretching (upsilon1) and the antisymmetric stretching (upsilon3) vibrations. The fundamental of the symmetric stretching (upsilon(1)) is 1057 cm(-1) and the overtone of the antisymmetric stretching (2upsilon(3)) is 2494 cm(-1). The new vibrational progressions (upsilon(1)00)+, (1upsilon(2)0)+, (2upsilon(2)0)+, and (0upsilon(2)2)+ have also been observed, and these new observations suggested that the irregular structure of (0upsilon(2)0)+ assigned to the previous PE spectra should be reconsidered. The comparison of the intensities of these vibrational bands with the calculated Franck-Condon factors with harmonic approximation was also made.

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.

Multiple-scattering and DV-Xα theoreticaldetermination of the local structure of SO2/Pd(111)

We have calculated the sulfur 1s near-edge x-ray absorptionfine-structure (NEXAFS) spectra of SO2 adsorbed onPd(111) in terms of the multiple-scattering cluster andself-consistent field DV-Xα method. The physical originof the resonances in the NEXAFS spectra has been unveiled. Bythe multiple-scattering calculation we have for the first timeidentified two weak features appearing in S K-shell NEXAFS ofSO2/Pd(111), which locate near the π* andσ* resonances respectively. Meanwhile, aself-consistent DV-Xα cluster calculation has beenperformed to confirm the above conclusion. Our calculationresults for the local structure of SO2/Pd(111) arebroadly in agreement with those of Fourier-transform analysis ofthe surface-extended x-ray absorption fine structure.

Pulsed laser photoacoustic detection of SO_2 near 2257 nm

A trace concentration of SO(2) near 225.7 nm has been detected with a master-oscillator power-oscillator laser system for the first time, to our knowledge. A photoacoustic absorption spectrum of SO(2) has been recorded on the (1)A(2)-(1)B(2) (pi-pi*) transition. Parametric dependence of the photoacoustic signal has been investigated. A detection limit (signal-to-noise ratio of 1) of 1.3 parts in 10(9) [1.3 ppbv (parts per billion by volume)] for SO(2) have been determined at 1 atmospheric pressure inside a photoacoustic cell.

Superexcitation and subsequent decay of triatomic molecules studied by two-dimensional photoelectron spectroscopy

Photoionization and photodissociation processes of SO2 and CS2 in vacuum UV are studied by using two-dimensional photoelectron spectroscopy with a monochromatized synchrotron radiation source. The principal focus is on the mechanisms of autoionization and neutral dissociation of superexcited states. Photoelectron spectra of SO2 exhibit characteristic peaks at the electron kinetic energy below 1.8 eV which are assigned as resulting from autoionizing transitions of excited atomic sulfur, S*, into the ground S+(4S°) state. These S* atoms are in the singlet Rydberg states converging to S+(2D°). The precursor molecular states, SO2*, are considered to be multiple-electron excited Rydberg states lying at the photon energy above ∼22 eV. The onset of the photoelectron yield due to the atomic autoionization accords with that expected from the thermochemical threshold for the formation of S* through three-body dissociation SO2*→S*+O+O. The two-dimensional photoelectron spectrum of CS2 provides tangible evidence for the formation of a dipole-forbidden Rydberg state (6σg)−1(3dσg)11Σg+ at the photon energy of 14.88 eV which autoionizes into the v3=1 vibrational state of the antisymmetric stretch ν3 mode of CS2+ (X2Πg,Ω, Ω=1/2 and 3/2). This Rydberg state is expected to borrow substantial oscillator strength from the (6σg)−1(5pσu)11Σu+ state through vibronic coupling involving the ν3 vibration.

The Rotational Spectrum of SO2 and the Determination of the Hyperfine Constants and Nuclear Magnetic Shielding Tensors of 33SO2 and SO17O

Precise frequencies for the 111–202 transition of 33SO2 and SO17O in natural isotopic abundance have been obtained near 12 GHz by microwave Fourier transform spectroscopy in order to yield improved hyperfine constants. Nuclear spin–rotation coupling constants have been determined experimentally for 33SO2 for the first time. The spin–rotation constants have been used to derive nuclear magnetic shielding parameters. These parameters are compared with values for the isoelectronic O3 molecule. The transition mentioned above was also measured for 32SO2, 34SO2, SO18O, and vibrationally excited (v2 = 1) 32SO2. For 33SO2, some transitions with large hyperfine splitting were also recorded in the millimeter-wave region. Continuing our investigations of the rotational spectra of SO2 in the submillimeter region, several transitions of SO17O have been recorded with the Cologne terahertz spectrometer between 540 and 840 GHz with J and Ka up to 63 and 16, respectively. Transitions with high Ka, up to 28, have been recorded with the JPL laser sideband spectrometer between 1.8 and 3.2 THz.

Quantum calculations of highly excited vibrational spectrum of sulfur dioxide. III. Emission spectra from the C̃ 1B2 state

We report quantum mechanical calculations of the X̃←C̃ emission spectra of SO2 at the red wing of the C̃ absorption band. The near equilibrium potential energy surface of the C̃ 1B2 state is deduced by fitting experimental vibrational frequencies using an exact quantum mechanical Hamiltonian. Low-lying vibrational eigenenergies on this double minimum potential agree well with experimental frequencies and the corresponding eigenstates show some interesting features. Both spectral positions and intensities of the X̃←C̃ transitions are obtained up to 16 000 cm−1 using a Chebyshev based spectral method, which does not explicitly construct vibrational eigenfunctions in the X̃ state. The emission spectra are in reasonably good agreement with experimental measurements.

Quantum calculations of highly excited vibrational spectrum of sulfur dioxide. II. Normal to local mode transition and quantum stochasticity

We report a quantum mechanical calculation of highly excited vibrational spectrum of SO2 up to 25 000 cm−1, using a filter-diagonalization method based on the Chebyshev propagation. Our results indicate a graduate transition from a normal mode regime at low energies to a local mode regime near 25 000 cm−1, which is marked by a decreasing energy gap between the (n1,0,0) and (n1−1,0,1) states and bifurcation of the corresponding wave functions. Approximately 4700 vibrational levels are found below 25 000 cm−1 and statistical analysis reveals that the SO2 vibration in this energy range is largely regular although the existence of chaos cannot be excluded.