C2 Emission Research Articles

An inversion method for cometary atmospheres

Remote observation of cometary atmospheres produces a measurement of the cometary emissions integrated along the line of sight. This integration is the so-called Abel transform of the local emission rate. The observation is generally interpreted under the hypothesis of spherical symmetry of the coma. Under that hypothesis, the Abel transform can be inverted. We derive a numerical inversion method adapted to cometary atmospheres using both analytical results and least squares fitting techniques. This method, derived under the usual hypothesis of spherical symmetry, allows us to retrieve the radial distribution of the emission rate of any unabsorbed emission, which is the fundamental, physically meaningful quantity governing the observation. A Tikhonov regularization technique is also applied to reduce the possibly deleterious effects of the noise present in the observation and to warrant that the problem remains well posed. Standard error propagation techniques are included in order to estimate the uncertainties affecting the retrieved emission rate. Several theoretical tests of the inversion techniques are carried out to show its validity and robustness. In particular, we show that the Abel inversion of real data is only weakly sensitive to an offset applied to the input flux, which implies that the method, applied to the study of a cometary atmosphere, is only weakly dependent on uncertainties on the sky background which has to be subtracted from the raw observations of the coma. We apply the method to observations of three different comets observed using the TRAPPIST telescope: 103P/ Hartley 2, F6/ Lemmon and A1/ Siding Spring. We show that the method retrieves realistic emission rates, and that characteristic lengths and production rates can be derived from the emission rate for both CN and C2 molecules. We show that the retrieved characteristic lengths can differ from those obtained from a direct least squares fitting over the observed flux of radiation, and that discrepancies can be reconciled for by correcting this flux by an offset (to which the inverse Abel transform is nearly not sensitive). The A1/Siding Spring observations were obtained very shortly after the comet produced an outburst, and we show that the emission rate derived from the observed flux of CN emission at 387nm and from the C2 emission at 514.1nm both present an easily-identifiable shoulder that corresponds to the separation between pre- and post-outburst gas. As a general result, we show that diagnosing properties and features of the coma using the emission rate is easier than directly using the observed flux, because the Abel transform produces a smoothing that blurs the signatures left by features present in the coma. We also determine the parameters of a Haser model fitting the inverted data and fitting the line-of-sight integrated observation, for which we provide the exact analytical expression of the line-of-sight integration of the Haser model.

CN and C2 vibrational spectra analysis in molecular LIBS of organic materials

With the objective of investigation of the influence of molecular structure on CN violet and C2 Swan bands system spectra, plasma emissions from different organic materials, including polycyclic aromatic hydrocarbons, aromatic carboxylic acid, aliphatic carboxylic acid, amides and polymers, have been analyzed by laser-induced breakdown spectroscopy (LIBS) technique in air. To evaluate the influence of N2 and O2 molecules concentration on the CN and C2 molecular emissions, LIB spectra of four different samples have been recorded in air (approximately 80 % N2 and 20 % O2), nitrogen, oxygen and argon atmospheres. Experimental results indicate that the main reason for the absence of C2 emission in LIB spectra of samples which do not contain C–C bonds, when measurements were taken in air, is the presence of oxygen which could potentially deplete C2 emission rather than the absence of C–C bonds in their structure. Also, comparisons between experiment and theory spectra are made using a Nelder–Mead temperature program for CN and C2 bands with the ∆ν = 0 sequences from LIB spectra of different samples in various atmospheres. Furthermore, CN and C2 vibrational temperatures in Kelvin (K) are calculated from these spectral fittings. Both CN and C2 vibrational temperatures have highest values in argon atmosphere, and increasing the oxygen concentration in ambient atmosphere decreased those in most cases.

Distant Jupiter family Comet P/2011 P1 (McNaught)

The spectra and images obtained through broadband BVRc filters for Jupiter family Comet P/2011 P1 (McNaught) were analyzed. We observed the comet on November 24, 2011, when its heliocentric distance was 5.43AU. Two dimensional long slit spectra and photometric images were obtained using the focal reducer SCORPIO attached to the prime focus of the 6-m telescope BTA (SAO RAS, Russia). The spectra cover the wavelength range of 4200–7000Å. No emissions of C2 and CO+, which are expected in this wavelength region, were detected above 3σ level. An upper limit in gas production rate of C2 is expected to be 1.1×1024mols−1. The continuum shows a reddening effect with the normalized gradient of reflectivity along dispersion of 5.1±1.2% per 1000Å. The color indices (B–V)=0.89±0.09 and (V–Rc)=0.42±0.07 for the nucleus region or (B–V)=0.68±0.12 and (V–Rc)=0.39±0.10 for the coma region, which are derived from the photometric data, also evidence that the color of the cometary nucleus and dust are redder with respect to the Sun. The normalized gradients of 5.9±2.9% per 1000Å and 2.6±1.9% per 1000Å for VRc filters were obtained for the cometary nucleus and the dust coma, respectively. The estimated dust mass production rate is about 12kgs−1 for Rc filter. The dust coma like a spiral galaxy edge-on was fitted using a Monte Carlo model. Since it is expected that the particles forming the dust coma consist of “dirty” ice, Greenberg’s model was adopted to track grains with an icy component that evaporates slowly when exposed to solar radiation. The observed coma was fitted assuming two isolated active zones located at the cometocentric latitudes of −8° and −35° with outflow of the dust within the cones having half opening angles of 8° and 70°, respectively. About, 45% and 55% of the observed dust were originated from the high collimated and low collimated active zones, respectively. The spin-axis of the rotating nucleus is positioned in the comet’s orbit plane. The sizes of the dust particles were ranged from 5μm to 1mm with a power index of −3.0 for the adopted exponential dust size distribution.

Femtosecond Laser-Induced Breakdown Spectroscopy Studies of Nitropyrazoles: The Effect of Varying Nitro Groups.

The technique of femtosecond laser-induced breakdown spectroscopy (FLIBS) was employed to investigate seven explosive molecules of nitropyrazole in three different atmospheres: ambient air, nitrogen, and argon. The FLIBS data illustrated the presence of molecular emissions of cyanide (CN) violet bands, diatomic carbon (C2) Swan bands, and atomic emission lines of C, H, O, and N. To understand the plasma dynamics, the decay times of molecular and atomic emissions were determined from time-resolved spectral data obtained in three atmospheres: air, argon, and nitrogen. The CN decay time was observed to be longest in air, compared to nitrogen and argon atmospheres, for the molecules pyrazole (PY) and 4-nitropyrazole (4-NPY). In the case of C2 emission, the decay time was observed to be the longest in argon, compared to the air and nitrogen environments, for the molecules PY, 4-NPY, and 1-methyl-3,4,5-trinitropyrazole. The intensities of the CN, C2, C, H, O, and N emission lines and various molecular/atomic intensity ratios such as CN/C2, CN(sum)/C2(sum), CN/C, CN(sum)/C, C2/C, C2(sum)/C, (C2 + C) / CN, (C2(sum) + C)/CN(sum), O/H, O/N, and N/H were also deduced from the LIBS spectra obtained in argon atmosphere. A correlation between the observed decay times and molecular emission intensities with respect to the number of nitro groups, the atmospheric nitrogen content, and the oxygen balance of the molecules was investigated. The relationship among the LIBS signal intensity, the molecular/atomic intensity ratios, and the oxygen balance of these organic explosives was also explored.

Laser ablation molecular isotopic spectrometry of carbon isotopes

Quantitative determination of carbon isotopes using Laser Ablation Molecular Isotopic Spectrometry (LAMIS) is described. Optical emission of diatomic molecules CN and C2 is used in these measurements. Two quantification approaches are presented: empirical calibration of spectra using a set of reference standards and numerical fitting of a simulated spectrum to the experimental one. Formation mechanisms of C2 and CN in laser ablation plasma are briefly reviewed to provide insights for implementation of LAMIS measurements. A simulated spectrum of the 12C2 Swan system was synthesized using four constituents within 473.5–476.5nm. Simulation included three branches of 12C2 (1-0), branches R(0-0) and R(1-1), and branch P(9-8) of 12C2. Spectral positions of the tail lines in R(0-0) and R(1-1) were experimentally measured, since they were not accurately known before. The Swan band (1-0) of the isotopologue 13C12C was also simulated. Fitting to the experimental spectrum yielded the ratio 13C/12C=1.08% in a good agreement with measurements by isotope ratio mass spectrometry. LAMIS promises to be useful in coal, oil and shale exploration, carbon sequestration monitoring, and agronomy studies.

Imaging polarimetry and spectropolarimetry of comet C/2013 R1 (Lovejoy)

We have obtained imaging polarimetry of the comet C/2013 R1 (Lovejoy) with 2-Channel-Focal-Reducer Rozhen instrument at 2m Ritchey–Chrétien–Coudé telescope of the Bulgarian National Astronomical Observatory Rozhen in two dust continuum filters covering wavelength intervals clear from molecular emissions and centred at 4430Å in blue filter and at 6840Å in red filter. In imaging mode we measured the degree of linear polarisation 17.01±0.09% in the blue and 18.81±0.02% in the red, which is in a very good agreement with measurements of other comets at the similar phase angle. We have also obtained polarisation maps in both filters. We found a strong correlation between the spatial distribution of the polarisation and the dust colour. Spectropolarimetry of the nucleus region shows an increase of the polarisation with wavelength, and a depolarisation in the spectral regions with gas emission lines, most noticeable in C2 emission band, which shows a polarisation of 6.0±1.1%.

Identification of atomic lines and molecular bands of benzene and carbon disulfide liquids by using LIBS

Plasma emission of liquid benzene (C6H6) and carbon disulfide (CS2) have been studied by using the laser-induced breakdown spectroscopy (LIBS) technique in air. Atomic lines of carbon, hydrogen, sulfur, nitrogen, and oxygen and molecular emissions of CN and C2 have been identified. The formation mechanism of C2 and CN molecules has been discussed. The combustion process and high mole fraction of hydrogen in benzene caused a decreasing atomic line intensity of oxygen and an increasing atomic line intensity of hydrogen with respect to the CS2 and air. Additionally, more intense CN molecular bands and weak nitrogen atomic lines in the C6H6 spectrum compared to CS2 have been observed. Furthermore, molecular emissions of C2 have not been observed in the CS2 spectrum. The electron temperature and vibrational temperature have been calculated from the atomic lines and molecular band intensity, respectively. Finally, the validity of the local thermodynamic equilibrium (LTE) assumption in this experiment has been shown.

Spectrum of comet C/2009 P1 (Garradd) in the optical wavelength range

Moderate-resolution spectra of comet C/2009 P1 (Garradd) in the wavelength range from 380 to 540 nm have been analyzed. The spectra were acquired, when the comet was at the distances 1.96 and 1.36 AU from the Sun and the Earth, respectively. The observations were fulfilled in the prime focus of the 6-m BTA telescope (Special Astrophysical Observatory, Russian Academy of Sciences) with the use of the SCORPIO focal reducer. Molecular emissions of C2, C3, CN, CN2, CH, CH+, and CO+ in the cometary coma were identified. In total, 148 emission features were detected. The gas production rate of molecules was determined with the Haser model. The ratios of the gas production rates are log[Q(C2/Q(CN)] = 0.26 and log[Q(C3/Q(CN)] = −1.09. The gas production rates of C2 and C3 molecules are 4.84 × 1026 and 2.16 × 1025 mol/s, respectively.

Elucidation of C2 and CN formation mechanisms in laser-induced plasmas through correlation analysis of carbon isotopic ratio

Laser ablation molecular isotopic spectrometry (LAMIS) was recently reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. With 13C-labeled benzoic acid as a model sample, this research utilized the LAMIS approach to clarify the formation mechanisms of C2 and CN molecules during laser ablation of organic materials. Because the isotopic ratios in the molecular bands could deviate from statistical distribution depending on their formation pathways, the dominant mechanism can be identified through a comparison of the experimental observed isotopic patterns in the molecular emission with the theoretical statistical pattern. For C2 formation, the experimental 12C12C/13C12C ratios not only support a recombination mechanism through atomic carbon at early delay time but also indicate the presence of other operating mechanisms as the plasma evolves; it is proposed that some of the C2 molecules are released directly from the aromatic ring of the sample as molecular fragments. In contrast, the temporal profiles in the 12C/13C ratios derived from CN emission exhibited opposite behavior with those derived from C2 emission, which unambiguously refutes mechanisms that require C2 as a precursor for CN formation; CN formation likely involves atomic carbon or species with a single carbon atom.

A temporally and spatially resolved validation of emission inventories by measurements of ambient volatile organic compounds in Beijing, China

Abstract. Understanding the sources of volatile organic compounds (VOCs) is essential for ground-level ozone and secondary organic aerosol (SOA) abatement measures. We made VOC measurements at 27 sites and online observations at an urban site in Beijing from July 2009 to January 2012. Based on these measurement data, we determined the spatial and temporal distribution of VOCs, estimated their annual emission strengths based on their emission ratios relative to carbon monoxide (CO), and quantified the relative contributions of various sources using the chemical mass balance (CMB) model. These results from ambient measurements were compared with existing emission inventories to evaluate the spatial distribution, species-specific emissions, and source structure of VOCs in Beijing. The measured VOC distributions revealed a hotspot in the southern suburban area of Beijing, whereas current emission inventories suggested that VOC emissions were concentrated in downtown areas. Compared with results derived from ambient measurements, the annual inventoried emissions of oxygenated VOC (OVOC) species and C2–C4 alkanes may be underestimated, while the emissions of styrene and 1,3-butadiene may be overestimated by current inventories. Source apportionment using the CMB model identified vehicular exhaust as the most important VOC source, with the relative contribution of 49%, in good agreement with the 40–51% estimated by emission inventories. The relative contribution of paint and solvent utilization obtained from the CMB model was 14%, significantly lower than the value of 32% reported by one existing inventory. Meanwhile, the relative contribution of liquefied petroleum gas (LPG) usage calculated using the CMB model was 6%, whereas LPG usage contribution was not reported by current emission inventories. These results suggested that VOC emission strengths in southern suburban area of Beijing, annual emissions of C2–C4 alkanes, OVOCs and some alkenes, and the contributions of solvent and paint utilization and LPG usage in current inventories all require significant revisions.

The emission rates of CH, CD and C2 spectral bands and a re-evaluation of the chemical sputtering yield of the JT-60U carbon divertor plates

The CH photon emission rate, defined as the number of photons over a dissociation and/or ionization event of CH4, has been determined from the ratio of the measured emission intensity of the CH spectral band over the CH4 injection rate into the divertor plasma of JT-60U. Similar photon emission rates of CD for CD4, and CH and C2 for C2H4 and C2H6, have also been determined. Interestingly, the C2 spectral band intensity is found to increase during the CH4 and CD4 injection, suggesting that the injected CH4 reacts with the carbon divertor plates to form heavier hydrocarbons. Previously published chemical sputtering yields (Nakano et al 2002 Nucl. Fusion 42 689) evaluated with the photon efficiencies determined in PISCES-A (Pospieszczyk et al 1989 UCLA Report UCLA-PPG-1251) have been re-evaluated using the measured emission rates. By applying the photon emission data found here and taking into account the C2 emission process originating from CH4, the re-evaluated total chemical sputtering yield becomes lower (∼7%) compared to the original in (Nakano et al 2002 Nucl. Fusion 42 689) (∼8%), and the dependence on the incident ion flux and energy becomes weaker.

Multibubble sonoluminescence as a tool to study the mechanism of formic acid sonolysis

Sonoluminescence spectra collected from 0.1 to 3.0M aqueous solutions of formic acid sparged with argon show the OH(A2Σ+−X2Πi) and C2(d3Πg→a3Πu) emission bands and a broad continuum typical for multibubble sonoluminescence. The overall intensity of sonoluminescence and the sonochemical yield of HCOOH degradation vary in opposite directions: the sonoluminescence is quenched while the sonochemical yield increases with HCOOH concentration. By contrast, the concentration of formic acid has a relatively small effect on the intensity of C2 Swan band. It is concluded that C2 emission originates from CO produced by HCOOH degradation rather than from direct sonochemical degradation of HCOOH. The intensity of C2 band is much stronger at high ultrasonic frequency compared to 20kHz ultrasound which is in line with higher yields of CO at high frequency. Another product of HCOOH sonolysis, carbon dioxide, strongly quenches sonoluminescence, most probably via collisional non-radiative mechanism.

Classification of vegetable oils based on their concentration of saturated fatty acids using laser induced breakdown spectroscopy (LIBS)

Spectrochemical analyses of organic liquid media such as vegetable oils and sweetened water were performed with the use of LIBS. The aim of this work is to study, on the basis of spectral analyses by LIBS technique of “Swan band” of C2 emitted by different vegetable oils in liquid phase, the characteristics of each organic media. Furthermore this paper proposes, as a classification, a single parameter that could be used to determine the concentration of saturated fatty acids of vegetable oils. A Nd:YAG operating at λ=532nm and an energies per pulse of 30mJ was focused onto the surface of the liquid in ambient air. Following ablation of vegetable oils and sweetened water, we find that vibrational bonds of C2 were released from the molecule containing carbon–carbon bonds linear. In the case of vegetable oils, we find a clear relationship between C2 emission from the plasma and the concentration of saturated fatty acids in the oil.

Influence of Molecular Structure on the Laser-Induced Plasma Emission of the Explosive RDX and Organic Polymers

A series of organic polymers and the military explosive cyclotrimethylenetrinitramine (RDX) were studied using the light emission from a femtosecond laser-induced plasma under an argon atmosphere. The relationship between the molecular structure and plasma emission was established by using the percentages of the atomic species (C, H, N, O) and bond types (C-C, C═C, C-N, and C≡N) in combination with the atomic/molecular emission intensities and decay rates. In contrast to previous studies of organic explosives in which C2 was primarily formed by recombination, for the organic materials in this study the percentage of C-C (and C═C) bonds was strongly correlated to the molecular C2 emission. Time-resolved emission spectra were collected to determine the lifetimes of the atomic and molecular species in the plasma. Observed differences in decay rates were attributed to the differences in both the molecular structure of the organic polymers or RDX and the chemical reactions that occur within the plasma. These differences could potentially be exploited to improve the discrimination of explosive residues on organic substrates with laser-induced breakdown spectroscopy.

Shock Initiation of Nano-Al + Teflon: Time-Resolved Emission Studies

Laser-launched flyer plates were used to impact-initiate reactive materials consisting of Al nanoparticles (50 nm) and Teflon microparticles (3 μm). The initiation process was probed with time- and wavelength-resolved emission spectroscopy. Teflon particle and Teflon foil samples without Al fuel were also studied. During ∼15 ns duration shocks produced by 50 μm thick flyers, Teflon was heated to a greater extent than Al. Al/Teflon underwent explosive chemical reactions lasting ∼500 ns at an impact velocity threshold of 1.0 ± 0.1 km/s. The Teflon samples emitted a continuum spectrum attributed to triboluminescence. C2 emission (Swan bands) from the powder Teflon could be detected at impact velocities of 0.7 km/s, after a few microseconds, presumably from gases trapped between the decomposing sample and the observation window, indicating that Teflon can be at least partially decomposed to carbon and fluorine. During the 15 ns shock, the Al/Teflon had almost the same emission temporal and spectral profile an...

Atmospheric Pressure Acetylene Detection by UV Photo-Fragmentation and Induced C2 Emission

Detection of C(2)H(2) via UV photo-fragmentation, followed by monitoring the C(2) d(3)Π(g)-a(3)Π(u) fluorescence, is explored at atmospheric pressure and at temperatures of 295 K, 600 K, and 800 K, for excitation wavelengths 210 to 240 nm using a broadband laser source (~3 cm(-1) fwhm). At the lower temperature, C(2) emissions correlate closely with C(2)H(2) Ã ← X absorption bands, and the excitation spectra suggest a higher-transition probability for the v(″)(4) = 2 and 3 states than for the v(″)(4) = 0 and 1 states. As temperature increases, the excitation spectra exhibit a higher nonresonant background.

Decay of C60 by delayed ionization and C2 emission: Experiment and statistical modeling of kinetic energy release

C(60) molecules highly excited in the nanosecond regime decay following ionization and dissociation by emitting a series of carbon dimers, as well as other small fragments if excitation is strong enough. The fragmentation mass spectrum and kinetic energy release of all charged fragments obtained in these experiments are interpreted within the framework of the Weisskopf theory, using a realistic Monte Carlo procedure in which the rates of all relevant decay channels are modeled using Arrhenius expressions. Comparison between the measurements and the simulated spectra allows the distribution of deposited energy to be accurately estimated. The dependence of the fragment kinetic energies on the laser fluence, found in the simulation but not observed in the experimental results, indicates that the small fragments are not necessarily emitted from small fullerenes resulting from C(60) by sequential decay. Rather, direct multifragmentation of C(60) is invoked to interpret the observed patterns. The possible role of post-ionization of neutral emitted fragments is discussed.

Process Control of CVD Deposition of Nanocrystalline Diamond Films by Plasma Diagnostics

Abstract Ultrananocrystalline Diamond (UNCD) Films were deposited by MW-CVD from an Ar/H2/CH4 plasma. The plasma properties were measured in situ by optical emission spectroscopy and mass spectroscopy. The intensity of the C2 emission line was systematically varied as a key plasma parameter and a correlation with resulting film properties was found.

Laser diagnostics of soot precursors in a heavy-duty diesel engine at low-temperature combustion conditions

To better understand in-cylinder soot formation processes for modern, low-emissions, low-temperature combustion (LTC) operating conditions in diesel engines, soot and its precursors are imaged by laser diagnostics in a heavy duty optical engine. Virtually simultaneous images of planar laser-induced incandescence of soot (soot-PLII) using 1064 nm excitation and combined soot-PLII and planar laser-induced fluorescence of poly-cyclic aromatic hydrocarbons (PAH-PLIF) using 532 nm excitation reveal the temporal and spatial evolution of soot and its precursors during combustion. With increasing dilution of the intake air stream by various levels of nitrogen to simulate the use of exhaust-gas recirculation (EGR) to achieve LTC, the residence time of PAH increases as soot formation is delayed. At zero dilution (21% intake oxygen), soot appears nearly simultaneously with PAH, while at higher dilution (12.7% or 9.5% intake oxygen), soot formation is delayed by hundreds of microseconds to a millisecond or more. At all dilution levels, at its onset, PAH rapidly fills most of the downstream cross-section of the jet, with a relatively uniform fluorescence intensity distribution. The spatial evolution of soot, however, shifts from a relatively rapid filling of the downstream head of the jet at low dilution, to inception at the midstream periphery of the jet followed by a gradual progression downstream at high dilution. Effects of fuel-bound aromatics are also explored by comparing soot and PAH formation for a representative diesel fuel containing 27% aromatics by weight to that for neat n-heptane. The residence time of PAH before the onset of soot is slightly longer with the non-aromatic fuel, but otherwise the spatial and temporal evolution of PAH-PLIF and soot-PLII are indistinguishable from that of the diesel fuel at LTC conditions. Spectral analysis shows a characteristic soot emission spectra from 1064 nm excitation, while 532 nm excitation yields significant short-wavelength emission that cannot be attributed solely to soot incandescence, and is likely due to fluorescence of large PAH soot precursors. No narrow spectral features, such as from C2 or C3 emission, are apparent in the spectra, even at high laser fluence.

Methyl chloride and C2–C5 hydrocarbon emissions from dry leaf litter and their dependence on temperature

Emissions of methyl chloride and several C2–C5 hydrocarbons from dry leaf litter at temperatures in the range 20–100 °C are reported for different plant species. The emission rates of ethane, ethene, propane, propene, n-pentane and methyl chloride increased with temperature. Hydrocarbon emission rates up to 0.88 ng gdw−1 h−1 were measured at 20 °C, while methyl chloride emission rates between 0.03 and 0.85 ng gdw−1 h−1 were observed at this temperature. At 70 °C emission rates increased up to 650 ng gdw−1 h−1 for C2–C5 hydrocarbons and up to 18 μg gdw−1 h−1 for methyl chloride. The Arrhenius relation can be used to describe the temperature dependence of methyl chloride emissions, while for hydrocarbon emissions deviations from this relation were observed. The emissions were not due to enzymatic activity, which was indicated by emission rates that continuously increased with increasing temperature, and activation energies higher than 50 kJ mol−1. At constant temperature, the emission rate of both methyl chloride and hydrocarbons from dry leaf litter decreased in time. At high temperatures (80–100 °C) this was noticeable on a timescale of hours, while at low temperatures (20–30 °C) the decrease was very slow and only visible on a timescale of months. Emission of methyl chloride from leaf litter might be significant for its global budget, while temperature induced hydrocarbon emissions from leaf litter are likely insignificant.