Dissociative recombination as primary dissociation channel in plasma chemistry

Molecule formation, surface modification and deposition in plasmas can in first order be described as dissociation in the plasma and association of fragments at the surface. In active plasmas ionization and dissociation by electrons is accompanied by excitation. But besides these direct electron processes also a second dissociation channel is active: that by charge transfer followed by dissociative recombination. This latter route is the dominant one in the colder recombining phase of the plasma. Atomic and molecular radicals diffuse or flow to the surface, where new molecules are formed. As a result the original molecules are, after being dissociated in the plasma, converted at the surface to new simple molecules, as H\u3csub\u3e2\u3c/sub\u3e, CO, N\u3csub\u3e2\u3c/sub\u3e, H \u3csub\u3e2\u3c/sub\u3eO, O\u3csub\u3e2\u3c/sub\u3e, NO, NH\u3csub\u3e3\u3c/sub\u3e, HCN, C\u3csub\u3e2\u3c/sub\u3eH \u3csub\u3e2\u3c/sub\u3e, CH\u3csub\u3e4\u3c/sub\u3e, to name a few in C/H/O/N containing plasmas. There is evidence that the molecular fragments resulting from dissociative recombination are ro-vibrationally (and possible electronically) excited. Also the molecules resulting from association at the surface may be ro-vibrationally or electronically excited. This may facilitate follow up processes as negative ion formation by dissociative attachment. These negative ions will be lost by mutual recombination with positive ions, giving again excited fragments. Rotational or other excitation may change considerably plasma chemistry. © 2009 IOP Publishing Ltd. U7 - Export Date: 24 March 2010 U7 - Source: Scopus U7 - Art. No.: 01201

Photon source

A photon source is described comprising a plasma source with at least one cathode and at least one anode, between which a system of one or more mutually sepd. cascade plates is placed, which cascade plates are provided with at least one passage opening, wherein corresponding passage openings of successive cascade plates lie at least substantially mutually in line, with at least one gas inlet for admitting at least during operation a gas to be excited at an inlet pressure and with an outlet opening close to the anode for allowing exit of photons emitted by a generated plasma, wherein an elec. power source is connected at least during operation between the cathode and the anode, characterized in that the power source is able and adapted to generate a modulated current and that, at least during operation, the gas inlet is coupled to gas supply means which are able and adapted to admit the gas to be excited at a modulated, sub-atm. to above-atm. inlet pressure. [on SciFinder (R)

Molecule synthesis in an Ar-CH4-O2-N2 microwave plasma

The formation of new mols. in a microwave plasma, created from a mixt. of Ar, CH4, N2 and O2, is investigated by means of an in-depth study of the mol. abundance in the plasma. The mols. are detected by means of tunable diode laser absorption spectroscopy and by abs. mass spectrometry. Three groups of mols. can be discerned in terms of mol. abundance: CO is predominantly formed, together with H2O, N2 and H2. The mols. CH4 and O2 are significantly depleted, but still abundant in a finite quantity. The third group is formed by several other species like NH3, NO, HCN etc. This tendency is expected to occur in every low temp. plasma contg. C, O, H and N atoms. Furthermore, the combination of both techniques also allows us to make a clear distinction between the etching mode and deposition mode of the microwave reactor. Etching mainly occurs when the ratio of admixed gas flows F(O2)/F(CH4) > 0.5. [on SciFinder (R)

Intercomparison of ethanol, formaldehyde and acetaldehyde measurements from a flex-fuel vehicle exhaust during the WLTC

An intercomparison exercise of the world-harmonized light-duty vehicle test procedure (WLTP) aiming at measuring ethanol, formaldehyde and acetaldehyde emissions from a flex-fuel light-duty vehicle using E85 was conducted in the Vehicle Emission Laboratory (VELA) at the European Commission Joint Research Centre (EC-JRC), Ispra, Italy. The instruments used during the intercomparison allowed online measurements of these compounds directly from the diluted exhaust. Measurements were done either in real time or immediately after the test. The measurement and analysis of exhaust emissions over the world-harmonized light-duty vehicle test cycle was done by means of Fourier transform infrared spectroscopy (FTIR), proton transfer reaction-mass spectrometry (PTR-Qi-ToF-MS), photoacoustic spectroscopy (PAS) and gas chromatography (GC). Results showed that online systems can perform measurements from the vehicle diluted exhaust assuring a good repeatability (within instrument variance) and reproducibility (between instrument variance) of the results. Measurements from all the instruments were in good agreement (|Z-score| < 2). Results showed that online systems can perform measurements from the vehicle diluted exhaust assuring the reproducibility and repeatability of the results. Results obtained measuring at the tailpipe using a FTIR were in good agreement with those acquired measuring at the constant volume sampler (CVS). Considering the low sensitivity of the current technique used to measure hydrocarbons emissions towards oxygenated compounds (flame ionization detector; FID), non-methane organic gases (NMOG) were calculated applying their FID response factors to the measured emissions of ethanol, acetaldehyde and formaldehyde. NMOG resulted to be up to 74% higher than measured non-methane hydrocarbons (NMHC)

Intercomparison of ethanol, formaldehyde and acetaldehyde measurements from a flex-fuel vehicle exhaust over the WLTC

An intercomparison exercise of the world-harmonized light-duty vehicle test procedure (WLTP) aiming at measuring ethanol, formaldehyde and acetaldehyde emissions from a flex-fuel light-duty vehicle using E85 was conducted in the Vehicle Emission Laboratory (VELA) at the European Commission Joint Research Centre (EC-JRC), Ispra, Italy. The instruments used during the intercomparison allowed online measurements of these compounds directly from the diluted exhaust. Measurements were done either in real time or immediately after the test. The measurement and analysis of exhaust emissions over the world-harmonized light-duty vehicle test cycle was done by means of Fourier transform infrared spectroscopy (FTIR), proton transfer reaction-mass spectrometry (PTR-Qi-ToF-MS), photoacoustic spectroscopy (PAS) and gas chromatography (GC). Results showed that online systems can perform measurements from the vehicle diluted exhaust assuring a good repeatability (within instrument variance) and reproducibility (between instrument variance) of the results. Measurements from all the instruments were in good agreement (|Z-score| < 2). Results showed that online systems can perform measurements from the vehicle diluted exhaust assuring the reproducibility and repeatability of the results. Results obtained measuring at the tailpipe using a FTIR were in good agreement with those acquired measuring at the constant volume sampler (CVS). Considering the low sensitivity of the current technique used to measure hydrocarbons emissions towards oxygenated compounds (flame ionization detector; FID), non-methane organic gases (NMOG) were calculated applying their FID response factors to the measured emissions of ethanol, acetaldehyde and formaldehyde. NMOG resulted to be up to 74% higher than measured non-methane hydrocarbons (NMHC).JRC.C.4-Sustainable Transpor

Intercomparison of in situ measurements of ambient NH3 : instrument performance and application under field conditions

Ammonia (NH3) in the atmosphere affects both the environment and human health. It is therefore increasingly recognised by policy makers as an important air pollutant that needs to be mitigated, though it still remains unregulated in many countries. In order to understand the effectiveness of abatement strategies, routine NH3 monitoring is required. Current reference protocols, first developed in the 1990s, use daily samplers with offline analysis; however, there have been a number of technologies developed since, which may be applicable for high time resolution routine monitoring of NH3 at ambient concentrations. The following study is a comprehensive field intercomparison held over an intensively managed grassland in southeastern Scotland using currently available methods that are reported to be suitable for routine monitoring of ambient NH3. In total, 13 instruments took part in the field study, including commercially available technologies, research prototype instruments, and legacy instruments. Assessments of the instruments' precision at low concentrations ( 0.75). At concentrations below 10 ppb, however, precision decreased, and instruments fell into two distinct groups, with duplicate instruments split across the two groups. It was found that duplicate instruments performed differently as a result of differences in instrument setup, inlet design, and operation of the instrument. New metrological standards were used to evaluate the accuracy in determining absolute concentrations in the field. A calibration-free CRDS optical gas standard (OGS, PTB, DE) served as an instrumental reference standard, and instrument operation was assessed against metrological calibration gases from (i) a permeation system (ReGaS1, METAS, CH) and (ii) primary standard gas mixtures (PSMs) prepared by gravimetry (NPL, UK). This study suggests that, although the OGS gives good performance with respect to sensitivity and linearity against the reference gas standards, this in itself is not enough for the OGS to be a field reference standard, because in field applications, a closed path spectrometer has limitations due to losses to surfaces in sampling NH3, which are not currently taken into account by the OGS. Overall, the instruments compared with the metrological standards performed well, but not every instrument could be compared to the reference gas standards due to incompatible inlet designs and limitations in the gas flow rates of the standards. This work provides evidence that, although NH3 instrumentation have greatly progressed in measurement precision, there is still further work required to quantify the accuracy of these systems under field conditions. It is the recommendation of this study that the use of instruments for routine monitoring of NH3 needs to be set out in standard operating protocols for inlet setup, calibration, and routine maintenance in order for datasets to be comparable