CO Emission Intensity Research Articles

Measurement of absolute CO number densities in CH3F/O2 plasmas by optical emission self-actinometry

CH3F/O2 inductively coupled plasmas at 10 mTorr were investigated using optical emission spectroscopy. A ‘self-actinometry’ method was developed to measure the absolute number density of CO that formed in reactions following dissociation of CH3F and O2 in the plasma. In this method, small amounts of CO were added to the plasma, leading to small increases in the CO emission intensity. By carefully accounting for small perturbations to the plasma electron density and/or electron energy distribution, and by showing that very little of the CO added to the plasma was decomposed by electron impact or other reactions, it was possible to derive absolute number densities for the CO content of the plasma. With equal fractions (0.50) of CH3F and O2 in the feed gas, the CO mole fraction as a function of plasma power saturated at a value of 0.20–0.25. As O2 in the feed gas was varied at a constant power of 100 W, the CO mole fraction went through a maximum of about 0.25 near an O2 feed gas fraction of 0.5. The relative CO number densities determined by ‘standard’ actinometry followed the same functional dependence as the absolute mole fractions determined by self-actinometry, aided by the fact that electron temperature did not change appreciably with power or feed gas composition.

TG–FTIR and kinetics of devolatilization of Sulcis coal

The N2-pyrolysis of low-rank Sulcis coal was investigated by thermogravimetric techniques (TG/DTG) in the temperature range ambient to 1000°C under dynamic heating conditions (50, 75, and 100°Cmin−1 heating rates). Little differences in the mass losses with heating rates were observed. From thermogravimetric analysis it was established that coal pyrolysis consisted of three main stages: water evaporation; devolatilization of thermally labile and more stable volatiles; and char formation. The evolved gas (EGA) by Fourier transform infrared spectrometry (FTIR) coupled to the thermobalance under 100°Cmin−1 heating rate was conducted for the identification of the gaseous species and their evolution profiles during coal thermal degradation. The temperatures of maximum rate of release of H2O, CO2, CO, COS, C2H4, as well volatile fragments originating from breaking of covalent bonds such as alkyl and ether groups, were in agreement with the temperature of maximum mass-loss rate around 466°C. Meanwhile the maximum releasing rates of SO2, CH4, and NH3 took place at 330, 575, and 690°C, respectively. An increase of CO emission intensity at 770°C was indicating in situ gasification with CO2-bearing product of freshly formed char. The kinetic processing of non-isothermal TG data was performed by isoconversional method. In the coal conversion regions α=5–40% the apparent activation energies were almost constant suggesting a single-step reaction path. The calculated average E value was 189kJmol−1. A kinetic compensation effect existed between E and ln A: the linear dependence provided an average pre-exponential factor A0 value of 2×1011min−1. With further increase of conversion degree a complex E dependence on α was evident as the coal thermal degradation process underwent a multi-step reactions.

FAR-ULTRAVIOLET OBSERVATION OF THE AQUILA RIFT WITHFIMS/SPEAR

We present the results of far ultraviolet (FUV) observations of the broad region around the Aquila Rift including the Galactic plane. As compared with various wavelength data sets, dust scattering is found to be the major origin of the diffuse FUV continuum in this region. The FUV intensity clearly correlates with the dust extinction level for E(B – V) 0.2 due to heavy dust extinction combined with the effect of nonuniform interstellar radiation fields. The FUV intensity also correlates well with Hα intensity, implying that at least some fraction of the observed Hα emission could be the dust-scattered light of Hα photons originating elsewhere in the Galaxy. Most of the Aquila Rift region is seen devoid of diffuse FUV continuum due to heavy extinction while strong emission is observed in the surrounding regions. Molecular hydrogen fluorescent emission lines are clearly seen in the spectrum of Aquila-Serpens, while Aquila-East does not show any apparent line features. CO emission intensity is also found to be higher in the Aquila-Serpens region than in the Aquila-East region. In this regard, we note that regions of star formation have been found in Aquila-Serpens but not in Aquila-East.

Enhancement of optical emission from laser-induced plasmas by combined spatial and magnetic confinement

To enhance optical emission in laser-induced breakdown spectroscopy, both a pair of permanent magnets and an aluminum hemispherical cavity (diameter: 11.1 mm) were used simultaneously to magnetically and spatially confine plasmas produced by a KrF excimer laser in air from pure metal and alloyed samples. High enhancement factors of about 22 and 24 in the emission intensity of Co and Cr lines were acquired at a laser fluence of 6.2 J/cm2 using the combined confinement, while enhancement factors of only about 11 and 12 were obtained just with a cavity. The mechanism of enhanced optical emission by combined confinement, including shock wave in the presence of a magnetic field, is discussed. The Si plasmas, however, were not influenced by the presence of magnets as Si is hard to ablate and ionize and hence has less free electrons and positive ions. Images of the laser-induced Cr and Si plasmas show the difference between pure metallic and semiconductor materials in the presence of both a cavity and magnets.

Study of the factors determining anomalous variability of carbon dioxide total column amount over St. Petersburg

Results of spectroscopic measurements of the carbon dioxide total column amount near St. Petersburg during forest fires in the period from August to September 2002 are analyzed. The HYSPLIT model is used to calculate air-mass trajectories and CO distribution on a mesoscale in this period. The HYSPLIT model simulations and measurements of carbon dioxide total column amount yield an estimate of the specific intensity of CO emission in a Pskov forest fire on August 28–September 8, 2002, equal to 0.17–0.26 kg m2. This estimate can be used for an estimation of the integral CO emission from fires in northwestern Russian forests and for model simulations of atmospheric CO concentration fields. The estimate of the CO emission from forest fires that is obtained from ground-based measurements can also be made on the basis of satellite measurements if they contain information on CO in the lower tropospheric layers (0 to 2 km).

248-nm Laser Photolysis of CHBr3/O-Atom Mixtures: Kinetic Evidence for UV CO(A) Chemiluminescence in the Reaction of Methylidyne Radicals with Atomic Oxygen

The 4th positive and Cameron band emissions from electronically excited CO have been observed for the first time in 248-nm pulsed laser photolysis of a trace amount of CHBr(3) vapor in an excess of O atoms. O atoms were produced by dissociation of N(2)O (or O(2)) in a cw-microwave discharge cavity in 2.0 Torr of He at 298 K. The CO emission intensity in these bands showed a quadratic dependence on the laser fluence employed. Temporal profiles of the CO(A) and other excited-state products that formed in the photoproduced precursor + O-atom reactions were measured by recording their time-resolved chemiluminescence in discrete vibronic bands. The CO 4th positive transition (A(1)Pi, v' = 0 --> X(1)Sigma(+), v' ' = 2) near 165.7 nm was monitored in this work to deduce the pseudo-first-order decay kinetics of the CO(A) chemiluminescence in the presence of various added substrates (CH(4), NO, N(2)O, H(2), and O(2)). From this, the second-order rate coefficient values were determined for reactions of these substrates with the photoproduced precursors. The measured reactivity trends suggest that the prominent precursors responsible for the CO(A) chemiluminescence are the methylidyne radicals, CH(X(2)Pi) and CH(a(4)Sigma(-)), whose production requires the absorption of at least 2 laser photons by the photolysis mixture. The O-atom reactions with brominated precursors (CBr, CHBr, and CBr(2)), which also form in the photolysis, are shown to play a minor role in the production of the CO(A or a) chemiluminescence. However, the CBr(2) + O-atom reaction was identified as a significant source for the 289.9-nm Br(2) chemiluminescence that was also observed in this work. The 282.2-nm OH and the 336.2-nm NH chemiluminescences were also monitored to deduce the kinetics of CH(X(2)Pi) and CH(a(4)Sigma(-)) reactions when excess O(2) and NO were present.

Reaction of CH radical with O2 by time-resolved FTIR spectroscopy

The reaction of CH radical with O2 has been experimentally investigated by time-resolved Fourier transform IR emission spectroscopy. CH radicals were generated by multi-photon UV laser photolysis of bromoform (CHBr3) in gaseous phase. Highly vibrationally excited product CO (v =1-12) with a near Boltzmann distribution was observed after the reaction. The vibrational temperature of CO is estimated as high as 14400±1400 K and the averaged vibrational energy is about 25.8 kcal=·mol−1. The emission intensity of CO is not sensitive to the quenching gas, which indicates that there is no early barrier in the reaction of CH+O2. However, the theoretically predicted product CO2 has not been found in the experiment.

Infrared Excess and Molecular Gas in the Galactic Worm GW 46.4+5.5

We have carried out high-resolution (~3') H I and CO line observations along one-dimensional cuts through the Galactic worm GW 46.4+5.5. By comparing the H I data with IRAS data, we have derived the distributions of I100 excess and τ100 excess, which are, respectively, the 100 μm intensity and 100 μm optical depth in excess of what would be expected from H I emission. In two observed regions, we were able to make a detailed comparison of the infrared excess and the CO emission. We have found that τ100 excess has a very good correlation with the integrated intensity of CO emission, WCO, but I100 excess does not. There are two reasons for the poor correlation between I100 excess and WCO: first, there are regions with enhanced infrared emissivity without CO, and second, dust grains associated with molecular gas have a low infrared emissivity. In one region, these two factors completely hide the presence of molecular gas in the infrared. In the second region, we could identify the area with molecular gas, but I100 excess significantly underestimates the column density of molecular hydrogen because of the second factor mentioned above. We therefore conclude that τ100 excess, rather than I100 excess, is an accurate indicator of molecular content along the line of sight. We derive τ100/N(H) = (1.00 ± 0.02) × 10-5 (1020 cm-2)-1, and X ≡ N(H2)/WCO 0.7 × 1020 cm-2 (K km s-1)-1. Our results suggest that I100 excess could still be used to estimate the molecular content if the result is multiplied by a correction factor ξc ≡ I100/N(H)H I/I100/N(H)H2 (2 in the second region), which accounts for the different infrared emissivities of atomic and molecular gas. We also discuss some limitations of this work, which could stem from using single-temperature model and the IRAS 60 μm intensity in estimating the dust optical depth along the line of sight.

Molecular Gas in the Magellanic Clouds

The molecular gas content in the Magellanic Clouds has been studied, with different spatial coverage and resolution, through obervations of CO(1-0) line emission. In the LMC and the SMC the molecular gas is dominated by clouds whose properties are different from those of their Galactic counterparts. The relation between the intensity of CO emission and molecular hydrogen column density, or the conversion factor X, is different than that of molecular clouds in our Galaxy and depends on the ambient physical conditions. Studying the molecular gas through observations in the H2 emission line may prove an alternative way to determine the molecular content associated with star forming regions in the Magellanic Clouds. In particular, results obtained towards 30 Doradus in the LMC are presented.

Direct introduction of powder samples for inductively coupled plasma atomic emission spectrometry: effect of particle size on emission intensity

The direct determination of trace elements in finely divided solids by ICP-AES and ICP-MS is subject to errors if the efficiency of the process leading to analyte volatilization, emission or ionization is a function of particle size. Direct transport of weighed quantities of powders into a plasma at constant total carrier gas flow is possible using a fluidized-bed powder delivery system. Emission intensity derived from known masses of Cu, Mn, Co, Ti and Cd carried to the plasma chelated (silica-immobilized 8-hydroxyquinoline) to 21, 24, 34 and 43 μm diameter particles was compared. Copper emission intensity was independent of particle size, and varied linearly with mass flow rate of powder. Copper was shown to be suitable as an internal standard element with which to monitor the particle-size dependence of the emission of several other elements. At constant rate of transport of powder to the plasma, the emission intensity of Si and Zn (particle matrix) appeared to be inversely related to the diameter of the particles, whereas the emission intensity of Co, Mn and Cd (constrained to surface) appeared to be a function of the surface concentration of analyte. These results were consistent with partial volatilization of the particles.

Optical emission spectroscopy of CF4+O2 plasmas using a new technique

Optical emission intensities in the sheath region are not the same as those in the plasma region. This is because not only the electron density, but also the electron temperature, is different between the two regions. In this study a Cu rod is inserted into the plasma, and the rod potential is altered from the ground potential to a negative potential with a frequency of 20 Hz. The optical emission ray comes from the sheath region when the negative potential is applied, but comes form the plasma region at the ground potential. We can immediately detect the difference of the emission intensities between the plasma and the sheath regions by a lock-in amplifier. The pre-amplifier is placed prior to the lock-in amplifier. By using this pre-amplifier the output signal of the lock-in amplifier can be adjusted to zero for any emission line. the emission spectra from a CF4+O2 plasma are measured. A small amount of Ar gas and/or N2 gas is added and the output signal of the lock-in amplifier is adjusted to zero for either the Ar emission line or the N2 emission line. In a fluorine-contained plasma the F emission intensity normalized by the Ar one has been widely used in order to obtain the F density. This validity is confirmed by the present experiment. It is also confirmed that the CO emission intensity normalized by that of N2 is proportional to the CO density. The metastable states play an important role in the optical emission intensities of CO and N2 molecules.

Carbon monoxide as an extragalactic mass tracer

The validity of integrated CO emission intensity as a tracer of molecular cloud mass in external galaxies is examined critically. By modeling extragalactic CO emission with an ensemble of independently emitting clouds, each of which obeys the virial theorem, it is demonstrated that, on average, there exists a linear relationship between integral CO intensity and the mass surface density of emitting cloud material lying within a radio telescope's antenna beam. Using molecular cloud parameters typical of the Milky Way, a ratio of mass surface density to integrated CO intensity is found which is within a factor of 2 of those frequently used to interpret extragalactic carbon monoxide observations. 28 references.

Mixed liganded species in Native β-helix p-hemocyanin

It is known that addition of low concentrations of cyanide to oxy hemocyanin causes a rapid bleaching of the absorption band, which has been related to the displacement of oxygen [1–3]. Removal of copper is known to require higher concentrations of cyanide and occurs with different kinetics in the presence or absence of other ligands at the site [4,5]. In this communication, preliminary results of a study concerning the competition between O 2, CO and CN − for the active site of Helix p-hemocyanin are reported. The replacement of these ligands occurs in different ways and may be related to the different modes of binding at the active site. In the case of oxygenated hemocyanin a hyperbolic displacement of oxygen by cyanide is observed, the apparent partition coefficient being independent of hemocyanin concentration in the range 10–50 μ M. In the case of CO displacement by cyanide, the shape and position of the curve depend on protein concentration and at higher hemocyanin concentration a ‘lag-phase’ followed by a hyperbolic displacement is observed. This behaviour has been tentatively interpreted assuming that at low concentration of cyanide binding of the ligand to CO-saturated hemocyanin may occur to one of the two metals in a site, while CO remains bound to the other. The results of experiments in which the addition of small amounts of KNC to hemocyanin partially saturated with O 2 and CO causes an increase of CO-emission intensity and a concomitant decrease of O 2copper absorption band are fully consistent with this hypothesis. The mixed-liganded species displays luminescence properties similar to those of CO-saturated hemocyanin [6] and the formation of the complex is reversible on dialysis or oxygenation. Since mixed-liganded intermediates have also been observed in the case of half-met hemocyanin, in which one of the metals is cupric [7], it is suggested that the geometries of the active site of such species and of native hemocyanin may be quite similar.

CHEMICAL REACTIONS IN ELECTRICAL DISCHARGES: I. THE SPECTRUM OF THE METHANE–OXYGEN SYSTEM AT LOW PRESSURE IN THE POSITIVE COLUMN OF A D-C. GLOW DISCHARGE

A technique is described which permits the study of changes in the spectra emitted by fast flowing reacting gas mixtures in the plasma of the positive column of a weak d-c. glow discharge. In certain cases a quantitative relationship is shown to exist between the concentration of a species and the intensity of emission of its spectrum. In particular such a correlation exists between the emission intensity of CO and its concentration. Use of this fact is then made to follow the rate of formation of carbon monoxide in methane–oxygen mixtures flowing through a discharge. The mechanism of formation of the various emitters either by means of a chemical reaction or by electron impact on molecules or radicals is discussed. It is concluded that to account for the rate of formation of CO, at least in the early stages of the presence of the gases in the discharge, before the steady state concentrations of atoms, radicals, and molecules have been approached, most of the energy of the electrons is used in breaking chemical bonds. The electric Held values needed to impart the necessary amount of energy to the electrons are of the same magnitude as those measured in this laboratory (~60 V cm−1).