CO and H2O adsorption and reaction on Au(310)

We have studied desorption of ¹³CO and H₂O and desorption and reaction of coadsorbed, ¹³CO and H₂O on Au(310). From the clean surface, CO desorbs mainly in, two peaks centered near 140 and 200 K. A complete analysis of desorption spectra, yields average binding energies of 21 ± 2 and 37 ± 4 kJ/mol, respectively. Additional desorption states are observed near 95 K and 110 K. Post-adsorption of H₂O displaces part of CO pre-adsorbed at step sites, but does not lead to CO oxidation or significant shifts in binding energies. However, in combination with electron irradiation, ¹³CO₂ is formed during H₂O desorption. Results suggest that electron-induced decomposition products of H₂O are sheltered by hydration from direct reaction with CO.     

Photoacoustic spectroscopy detection and extraction of discharge feature gases in transformer oil based on 1.5 μ tunable fiber laser

Information from the analysis of gasses dissolved in insulating oils is valuable for early a transformer maintenance. By means of dissolved gas analysis (DGA), it is possible to distinguish faults such as partial discharge (corona), overheating (pyrolysis) and arcing in a great variety of oil-filled equipment. Tunable fiber laser-based second harmonic photoacoustic spectroscopy offers a fast and good-noise-immunity technique for the quantitative analysis of trace gases in transformer oil. In this work, the discharge feature gases, such as C₂H₂, CH₄, CO₂ and H₂O, were measured with a tunable laser photoacoustic spectrometer at the 1530.3709 nm transition line, as a typical application of precise measurement of multi-gas, a proposed BSS model based on overcomplete ICA basis and five-point-sampling method based on a created weight-truncation-constraint equation was used to remove noise so that several fault gases can be extracted with a higher detection accuracy and a method detection limit. Experiment shows that within 0.15 nm band near 1530.3709 nm, the four-gas contents have been detected and extracted and the detection accuracy has been improved from available scanning spacing of 0.03 nm to available extracting spacing of 0.0011 nm. At room temperature and atmospheric pressure, this can achieve simultaneous detection for multiple feature gases in discharged transformer oil using laser source with a limited waveband.     

Measurements of H2O2 in low temperature dimethyl ether oxidation

H₂O₂ is one of the most important species in dimethyl ether (DME) oxidation, acting not only as a marker for low temperature kinetic activity but also responsible for the “hot ignition” transition. This study reports, for the first time, direct measurements of H₂O₂ and CH₃OCHO, among other intermediate species concentrations in helium-diluted DME oxidation in an atmospheric pressure flow reactor from 490 to 750 K, using molecular beam electron-ionization mass spectrometry (MBMS). H₂O₂ measurements were directly calibrated, while a number of other species were quantified by both MBMS and micro gas chromatography to achieve cross-validation of the measurements. Experimental results were compared to two different DME kinetic models with an updated rate coefficient for the H + DME reaction, under both zero-dimensional and two-dimensional physical model assumptions. The results confirm that low and intermediate temperature DME oxidation produces significant amounts of H₂O₂. Peroxide, as well as O₂, DME, CO_, and CH₃OCHO profiles are reasonably well predicted, though profile predictions for H₂/CO₂ and CH₂O are poor above and below ～625 K, respectively. The effect of the collisional efficiencies for the H + O₂ + M = HO₂ + M reaction on DME oxidation was investigated by replacing 20% He with 20% CO₂. Observed changes in measured H₂O₂ concentrations agree well with model predictions. The new experimental characterizations of important intermediate species including H₂O₂, CH₂O and CH₃OCHO, and a path flux analysis of the oxidation pathways of DME support that kinetic parameters for decomposition reactions of HOCH₂OCO and HCOOH directly to CO₂ may be responsible for model under-prediction of CO₂. The H abstraction reactions for DME and/or CH₂O and the unimolecular decomposition of HOCH₂O merit further scrutiny towards improving the prediction of H₂ formation.     

The effects of water dilution on hydrogen,syngas, and ethylene flames at elevated pressure

This work investigates experimentally and numerically the kinetic effects of water vapor addition on the burning rates of H₂, H₂/CO mixtures, and C₂H₄ from 1 atm to 10 atm at flame temperatures between 1600 K and 1800 K. Burning rates were measured using outwardly propagating spherical flames in a nearly constant pressure chamber. Results show good agreement with newly updated kinetic models for H₂ flames. However, there is considerable disagreement between simulations and measurements for H₂/CO and C₂H₄ flames at high pressure and high water vapor dilution. Both experiments and simulations show that water vapor addition causes a monotonic decrease in mass burning rate and the inhibitory effect increases with pressure. For hydrogen flames, water vapor addition reduces the critical pressure above which a negative pressure dependence of the burning rate is observed. However, for C₂H₄ flames, the burning rate always increases with pressure. The results also show that water vapor addition has the same effect as a pressure increase for H₂ and H₂/CO flames, shifting the reaction zone into a narrower window at higher temperatures. For all fuels, water vapor addition increases OH formation via H₂O + O while reducing the overall active radical pool for hydrogen flames. For C₂H₄, the additional HO₂ production pathway through HCO results in a dramatic difference in pressure dependence of the burning rate from that observed for hydrogen. The present work provides important additions to the experimental database for syngas and C₀–C₂ high pressure kinetic model validations.     

Multi-species time-history measurements during n-hexadecane oxidation behind reflected shock waves

Species concentration time-histories were measured during oxidation for the large, normal-alkane, diesel-surrogate component n-hexadecane. Measurements were performed behind reflected shock waves in an aerosol shock tube, which allowed for high fuel loading without pre-test heating and possible decomposition and oxidation. Experiments were conducted using near-stoichiometric mixtures of n-hexadecane and 4% oxygen in argon at temperatures of 1165–1352 K and pressures near 2 atm. Concentration time-histories were recorded for five species: C₂H₄, CH₄, OH, CO₂, and H₂O. Methane was monitored using DFG laser absorption near 3.4 μm; OH was monitored using UV laser absorption at 306.5 nm; C₂H₄ was monitored using a CO₂ gas laser at 10.5 μm; and CO₂ and H₂O were monitored using tunable DFB diode laser absorption at 2.7 and 2.5 μm, respectively. These time-histories provide critically needed kinetic targets to test and refine large reaction mechanisms. Comparisons were made with the predictions of two diesel-surrogate reaction mechanisms (Westbrook et al. [1]; Ranzi et al. [9]) that include n-hexadecane, and areas of needed improvement in the mechanisms were identified. Comparisons of the intermediate product yields of ethylene for n-hexadecane with those found for other smaller n-alkanes, show that an n-hexadecane mechanism derived from a simple hierarchical extrapolation from a smaller n-alkane mechanism does not properly simulate the experimental measurements.     

Ground-based solar absorption studies for the Carbon Cycle science by Fourier Transform Spectroscopy (CC-FTS) mission

Carbon cycle science by Fourier transform spectroscopy (CC-FTS) is an advanced study for a future satellite mission. The goal of the mission is to obtain a better understanding of the carbon cycle in the Earth's atmosphere by monitoring total and partial columns of CO₂, CH₄, N₂O, and CO in the near infrared. CO₂, CH₄, and N₂O are important greenhouse gases, and CO is produced by incomplete combustion. The molecular O₂ column is also needed to obtain the effective optical path of the reflected sunlight and is used to normalize the column densities of the other gases. As part of this advanced study, ground-based Fourier transform spectra are used to evaluate the spectral region and resolution needed. Spectra in the 3950–7140 cm^?1 region with a spectral resolution of 0.0042 cm^?1 recorded at Kiruna (67.84°N, 20.41°E, and 419 m above sea level), Sweden, on 1 April 1998, were degraded to the resolutions of 0.01, 0.1, and 0.3 cm^?1. The effect of spectral resolution on the retrievals has been investigated with these four Kiruna spectra. To obtain further information on the spectral resolution, optical components and spectroscopic parameters required by the future mission, high-resolution solar absorption spectra between 2000 and 15000 cm^?1 were recorded using Fourier transform spectrometers at Kitt Peak (31.9°N, 111.6°W, and 2.1 km above sea level), Arizona, on 25 July 2005 and Waterloo (43.5°N, 80.6°W, and 0.3 km above sea level), Ontario, on 22 November 2006 with spectral resolutions of 0.01 and 0.1 cm^?1, respectively. Dry air volume mixing ratios (VMRs) of CO₂ and CH₄ were retrieved from these ground-based observations. The HITRAN 2004 spectroscopic parameters are used with the SFIT2 package for the spectral analysis. The measurement precisions for CO₂ and CH₄ total columns are better than 1.07% and 1.13%, respectively, for our observations. Based on these results, a Fourier transform spectrometer (maximum spectral resolution of 0.1 cm^?1 or 5 cm maximum optical path difference (MOPD)) operating between 2000 and 15000 cm^?1 is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO₂, CH₄, and O₂ requires new laboratory measurements of the spectroscopic line parameters.     

Modeling midwave infrared muzzle flash spectra from unsuppressed and flash-suppressed large caliber munitions

Time-resolved infrared spectra of firings from a 152 mm howitzer were acquired over an 1800–6000 cm^?1 spectral range using a Fourier-transform spectrometer. The instrument collected primarily at 32 cm^?1 spectral and 100 Hz temporal resolutions. Munitions included unsuppressed and chemically flash suppressed propellants. Secondary combustion occurred with unsuppressed propellants resulting in flash emissions lasting ～100 ms and dominated by H₂O and CO₂ spectral structure. Non-combusting plume emissions were one-tenth as intense and approached background levels within 20–40 ms. A low-dimensional phenomenological model was used to reduce the data to temperatures, soot absorbances, and column densities of H₂O, CO₂, CH₄, and CO. The combusting plumes exhibit peak temperatures of ～1400 K, areas of greater than 32 m², low soot emissivity of ～0.04, with nearly all the CO converted to CO₂. The non-combusting plumes exhibit lower temperatures of ～1000 K, areas of ～5 m², soot emissivity of greater than 0.38 and CO as the primary product. Maximum fit residual relative to peak intensity are 14% and 8.9% for combusting and non-combusting plumes, respectively. The model was generalized to account for turbulence-induced variations in the muzzle plumes. Distributions of temperature and concentration in 1–2 spatial regions demonstrate a reduction in maximum residuals by 40%. A two-region model of combusting plumes provides a plausible interpretation as a ～1550 K, optically thick plume core and ～2550 K, thin, surface-layer flame-front. Temperature rate of change was used to characterize timescales and energy release for plume emissions. Heat of combustion was estimated to be ～5 MJ/kg.     

On the stability of the CO adsorption-induced and self-organized CuPt surface alloy

The stability of the recently discovered CO-induced and self-organized CuPt surface alloy was explored at near ambient pressures of O₂ (200 mbar) at room temperature, in a CO + H₂ mix (P_tot = 220 mbar, 4% CO) from room temperature to 573 K, as well as in a CO + H₂O mix (P_tot = 17 mbar, 50% CO) from room temperature to 673 K. No indications of substantial changes in surface structure were observed under the latter conditions compared to CO alone whereas the O₂ oxidation resulted in CO removal and the build-up of an ultrathin CuO_x-film. However, the oxidized CO/CuPt surface alloy could be regenerated by reducing the CuO_x in 100 mbar CO for 10 min at room temperature. The results show, amongst others, the stability of the CuPt surface alloy in various environments containing CO and how a novel coinage/Pt-group bimetallic surface alloy catalyst induced by CO adsorption can be reactivated before use in applications such as electrochemistry at ambient temperatures.     

Resourceful synthesis of pyrazolo[1,5-a]pyrimidines under ultrasound irradiation

Pyrazolo[1,5-a]pyrimidines were synthesized via the ultrasonic sonochemical method using the cyclocondensation reaction of 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones [CF₃C(O)CH = C(R)(OMe) – where R = Me, Bu, i-Bu, Ph, 4-Me–C₆H₄, 4-F–C₆H₄, 4-Cl–C₆H₄, 4-Br–C₆H₄, naphth-2-yl and biphen-4-yl] – with 3-amino-5-methyl-1H-pyrazole in the presence of EtOH for 5 min. This methodology has several advantages, for example, it is a simple procedure, it has an easy work-up, mild conditions, short reaction times (5 min) and produces satisfactory yields (61–98%).     

A near-infrared acetylene detection system based on a 1.534 μm tunable diode laser and a miniature gas chamber

A near-infrared (NIR) dual-channel differential acetylene (C₂H₂) detection system was experimentally demonstrated based on tunable diode laser absorption spectroscopy (TDLAS) technique and wavelength modulation spectroscopy (WMS) technique. A distributed feedback (DFB) laser modulated by a self-developed driver around 1.534 μm is used as light source. A miniature gas chamber with 15 cm path length is adopted as absorption pool, and an orthogonal lock-in amplifier is developed to extract the second harmonic (2f) signal. Sufficient standard C₂H₂ samples with different concentrations were prepared, and detailed measurements were carried out to study the detection performance. A good linear relationship is observed between the amplitude of the 2f signal and C₂H₂ concentration within the range of 200–10,000 ppm, and the relative measurement error is less than 5% within the whole range. A long-term monitoring lasting for 20 h on a 1000 ppm C₂H₂ sample was carried out, and the maximum concentration fluctuation is less than 2%. Due to the capability of using long-distance and low-loss optical fiber, the gas-cell can be placed in the filed for remote monitoring, which enables the system to have good prospects in industrial field.     

Ultrasound-induced emulsification of subcritical carbon dioxide/water with and without surfactant as a strategy for enhanced mass transport

Pulsed ultrasound was used to disperse a biphasic mixture of CO₂/H₂O in a 1 dm³ high-pressure reactor at 30 °C/80 bar. A view cell positioned in-line with the sonic vessel allowed observation of a turbid emulsion which lasted approximately 30 min after ceasing sonication. Within the ultrasound reactor, simultaneous CO₂-continuous and H₂O-continuous environments were identified. The hydrolysis of benzoyl chloride was employed to show that at similar power intensities, comparable initial rates (1.6 ± 0.3 × 10^–3 s^–1 at 95 W cm^–2) were obtained with those reported for a 87 cm³ reactor (1.8 ± 0.2 × 10^–3 s^–1 at 105 W cm^–2), demonstrating the conservation of the physical effects of ultrasound in high-pressure systems (emulsification induced by the action of acoustic forces near an interface). A comparison of benzoyl chloride hydrolysis rates and benzaldehyde mass transport relative to the non-sonicated, ‘silent’ cases confirmed that the application of ultrasound achieved reaction rates which were over 200 times faster, by reducing the mass transport resistance between CO₂ and H₂O. The versatility of the system was further demonstrated by ultrasound-induced hydrolysis in the presence of the polysorbate surfactant, Tween, which formed a more uniform CO₂/H₂O emulsion that significantly increased benzoyl chloride hydrolysis rates. Finally, pulse rate was employed as a means of slowing down the rate of hydrolysis, further illustrating how ultrasound can be used as a valuable tool for controlling reactions in CO₂/H₂O solvent mixtures.     

Kinetics for the reactions of phenyl with methanol and ethanol: Comparison of theory and experiment

The kinetics of the C₆H₅ reactions with CH₃OH and C₂H₅OH has been measured by pulsed-laser photolysis/mass-spectrometry (PLP/MS) employing acetophenone as the radical source. Kinetic modeling of the benzene formed in the reactions over the temperature range 306–771 K allows us to reliably determine the total rate constants for H-abstraction reactions. In order to improve our low temperature measurements down to 304 K we have also applied the cavity ring-down spectrometric technique using nitrosobenzene as the radical source. Both sets of data agree closely. A weighted least-squares analysis of the two complementary sets of data for the two reactions gave the total rate constants k(CH₃OH) = (7.82 ± 0.44) × 10¹¹ exp [?(853 ± 30)/T] and k(C₂H₅OH) = (5.73 ± 0.58) × 10¹¹ exp [?(1103 ± 44)/T] cm³ mol^?1 s^?1 for the temperature range studied. Theoretically, four possible product channels of the C₆H₅ + CH₃OH reaction producing C₆H₆ + CH₃O, C₆H₆ + CH₂OH, C₆H₅OH + CH₃ and C₆H₅OCH₃ + H and five possible product channels of the C₆H₅ + C₂H₅OH reaction producing C₆H₆ + C₂H₅O, C₆H₆ + CH₂CH₂OH, C₆H₆ + CH₃CHOH, C₆H₅OH + CH₃CH₂ and C₆H₅OCH₂CH₃ + H have been computed at the G2M//B3LYP/6?311+G(d, p) level of theory. The hydrogen abstraction channels were predicted to have lower energy barriers than those for the substitution reactions and their rate constants were calculated by the microcanonical variational transition state theory at 200–3000 K. The predicted rate constants are in good agreement with the experimental values. Significantly, the rate constant for the CH₃OH reaction with C₆H₅ was found to be greater than that for the C₂H₅OH reaction and both reactions were found computationally to be dominated by H-abstraction from the hydroxyl group attributable to the affinity of the phenyl toward the OH group and the predicted lower energy barriers for the OH attack.     

The structure and extinction of nonpremixed methane/nitrous oxide and ethane/nitrous oxide flames

Knowledge of combustion of hydrocarbon fuels with nitrogen-containing oxidizers is a first step in understanding key aspects of combustion of hypergolic and gun propellants. Here an experimental and kinetic-modeling study is carried out to elucidate aspects of nonpremixed combustion of methane (CH₄) and nitrous oxide (N₂O), and ethane (C₂H₆) and N₂O. Experiments are conducted, at a pressure of 1 atm, on flames stabilized between two opposing streams. One stream is a mixture of oxygen (O₂), nitrogen (N₂), and N₂O, and the other a mixture of CH₄ and N₂ or C₂H₆ and N₂. Critical conditions for extinction are measured. Kinetic-modeling studies are performed with the San Diego Mechanism. Experimental data and results of kinetic-modeling show that N₂O inhibits the flame by promoting extinction. Analysis of the flame structure shows that H radicals are produced in the overall chain-branching step 3H₂ + O₂ ? 2H₂O + 2H, in which molecular hydrogen is consumed. Hydrogen is also consumed in the overall step N₂O + H₂ ? N₂ + H₂O where stable products are formed. Inhibition of the flames by N₂O is attributed to competition between these two overall steps.     

Infrared spectra of acetylene–water complexes: C2D2–H2O,C2D2–HDO,and C2D2–D2O

Infrared spectra of C₂D₂–water complexes are studied in the 4.1 μm region of the C₂D₂ ν₃ fundamental band using a tunable diode laser source to probe a pulsed supersonic slit jet. Relatively large vibrational red shifts (?27.7 to ?28.0 cm^?1) are observed which are more easily interpretable than for the analogous C₂H₂ vibration thanks to the absence of Fermi resonance effects for C₂D₂. Noticeable homogeneous line broadening leads to estimates of upper state predissociation lifetimes of about 0.5, 0.9 and 1.1 ns for C₂D₂–H₂O, –HDO, and –D₂O, respectively. Transitions involving K_a = 0 and 1 levels are observed for C₂D₂–HDO, but there is a puzzling absence of K_a = 1 for C₂D₂–H₂O and C₂D₂–D₂O.     

Effect of oxide on carbon deposition behavior of CH4 fuel on Ni/ScSZ cermet anode in high temperature SOFCs

This work investigated the effect of oxide in Ni-zirconia cermets on the carbon deposition behavior in internal reforming SOFCs. Within 800–1000 °C, carbon deposition was found to decrease with increasing temperature on Ni/ScSZ cermet anodes at a low oxygen / carbon ratio (O / C = 0.03) during anodic oxidation of methane. On the contrary, an opposite trend was observed on Ni/YSZ under the same conditions, consisting with the temperature dependence of carbon deposition predicted by a thermodynamic equilibrium calculation. Results of temperature-programmed-reduction (TPR) of NiO mixed with YSZ or ScSZ indicated that interaction of Ni with ScSZ is stronger than that with YSZ. The stronger interaction was corroborated by observed tendency of inhibiting Ni agglomeration by both BET specific surface area analysis and SEM observation. It was also found that the dependence of CO₂ production rate monitored by GC on current density showed a similar dependence trend of the equilibrium CO₂ content on O / C ratio. A model in which H₂O_ad enrichment effects on Ni surface by anodic current depend on the interaction between Ni and the oxide in Ni cermet was proposed to explain the different carbon deposition behaviors between Ni/YSZ and Ni/ScSZ cermets.     

Preparation of carbon aerogel in ambient conditions for electrical double-layer capacitor

Carbon aerogels were prepared by polycondensation of resorcinol with formaldehyde using sodium carbonate as a catalyst in ambient conditions, and they were used as an electrode of electrical double-layer capacitor. The effect of resorcinol to catalyst ratio (R/C ratio) on volume shrinkage, BET surface area, and electrochemical property of carbon aerogels was investigated by changing R/C ratio from 50 to 2000. In order to minimize volume shrinkage, solvent exchange was performed with acetone at 50 °C for 1 day. Volume shrinkage was <2% after 2-day gelation in the absence of CO₂ supercritical drying. BET surface area was strongly dependent on R/C ratio. Carbon aerogel prepared at R/C ratio of 500 showed the highest BET surface area (706 m²/g) with average pore diameter of 10.9 nm. Electrochemical property of carbon aerogels as an electrode of electrical double-layer capacitor was investigated by cyclic voltammetry measurement. Specific capacitance of carbon aerogel prepared at R/C ratio of 500 was found to be 81 F/g in 1 M H₂SO₄ electrolyte at the scan rate of 10 mV/s.     

Electrode materials for potentiometric hydrogen sensors

Due to their relatively high sensitivity, improved long-term stability, possibilities for miniaturization and low cost products, mixed potential solid electrolyte sensors can be competitive for the in situ measurement of hydrogen trace concentrations in oxygen containing gases. Their response behavior in non-equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. In this work the sensitivity of electrodes made of composites (Au/MeO) has been investigated in hydrogen containing gases in the concentration range φ(H₂) = 0…800 vol.-ppm using a two-chamber setup with Pt-air reference. Electrodes made of Au/Nb₂O₅ composites show the highest sensitivities of up to 20 mV/vol.-ppm at φ(H₂) = 10 vol.-ppm and the lowest catalytic activity for hydrogen oxidation. Selected composite materials were tested additionally in self-heated solid electrolyte sensors with both electrodes exposed to the same atmosphere (gas-symmetrical sensor).     

Comprehensive visualization of detonation-diffraction structures and sizes in unstable and stable mixtures

The geometry and characteristic length of diffraction and re-initiation during a two-dimensional detonation propagation were revealed by visualization. C₂H₄ + 3O₂ (unstable), 2C₂H₂ + 5O₂ + 7Ar (stable) and 2C₂H₂ + 5O₂ + 21Ar (stable) were used as the test mixtures. Experiments were performed over the deviation angle range from 30° to 150° and the initial pressure range from 15.8 to 102.3 kPa. By self-emitting photography, we confirmed that the geometry and the characteristic length of diffraction are not different among test gases, with the exception of the fan-like structure of re-initiation that occurred regardless of whether the mixture was unstable or stable. We conducted a compensative experiment by changing the deviation angle and initial pressure, and summarized the detonation diffraction by shadowgraph. At deviation angles larger than 60°, we measured the distances from the vertex of the channel corner to the point where the transverse detonation wave reflected on the under wall (= wall reflection distance) and confirmed that wall reflection distances are approximately in the range of 10–15 times the cell width, whether the mixture is unstable or stable.     

Fragmentation of 370 MeV/n 20Ne and 470 MeV/n 24Mg in light targets

Total charge-changing cross sections and cross sections for the production of projectile-like fragments were determined for fragmentation reactions induced by 370 MeV/n ²⁰Ne ions in water and lucite, and 490 MeV/n ²⁴Mg ions in polyethylene, carbon and aluminum targets sandwiched with CR-39 plastic nuclear track detectors. An automated microscope system and a track-to-track matching algorithm were used to count and recognize the primary and secondary particles. The measured cross sections were then compared with published cross sections and predictions of different models. Two models and the three-dimensional Monte Carlo Particle Heavy Ion Transport Code System (PHITS) were used to calculate total charge-changing cross sections. Both models agreed within a few percent for the system ²⁴Mg + CH₂, however a deviation up to 20% was observed for the systems ²⁰Ne + H₂O and C₅H₈O₂, when using one of the models. For all the studied systems, PHITS systematically underestimated the total charge-changing cross section. It was also found that the partial fragmentation cross sections for ²⁴Mg + CH₂ measured in present and earlier works deviated up to 20% for Z = 6–11. Measured cross sections for the production of fragments (Z = 4–9) for ²⁰Ne + H₂O and C₅H₈O₂ were compared with predictions of three different semi-empirical models and JQMD which is used in the PHITS code. The calculated cross sections differed from the measured data by 10–90% depending on which fragment and charge was studied, and which model was used.     

Room-temperature chemisorption of chloroethylenes on Si(1 1 1)7 × 7: formation of surface vinyl,vinylidene and their chlorinated derivatives

Chemisorption of a family of six chloroethylenes (C₂H₃Cl, 1,1-C₂H₂Cl₂, cis-1,2-C₂H₂Cl₂, trans-1,2-C₂H₂Cl₂, C₂HCl₃, and C₂Cl₄) on Si(1 1 1)7 × 7 at room temperature (RT) has been investigated by vibrational electron energy loss spectroscopy (EELS). The characteristic vibrational EELS features have been used to identify the prominent surface species upon RT adsorption. Like ethylene, C₂H₃Cl has been found to predominantly adsorb in a di-σ bonding geometry to the Si surface, while 1,1-C₂H₂Cl₂, cis- and trans-1,2-C₂H₂Cl₂, C₂HCl₃ and, to a lesser extent, C₂Cl₄ appear to undergo dechlorination upon adsorption to form chlorinated vinyl adspecies involving single-σ bonding structures. Evidence of vinylidene (>CCH₂) has been obtained for the first time on a semiconductor surface for the adsorption of 1,1-C₂H₂Cl₂. The present work illustrates that the molecular structure and the Cl content of chloroethylenes play a crucial role in controlling not only the adsorption geometry but also the extent of dechlorination and the resulting adspecies upon RT adsorption on Si(1 1 1).