Mbar Total Pressure Research Articles

The reaction of fluorine atoms with formyl fluoride and the CFO self‐reaction at 293 K

AbstractA fast‐flow apparatus with mass spectrometric detection was used to study the system F + CHFO between 2 and 3.5 mbar total pressure. The rate constant of the primary reaction was evaluated directly to yield at 298 K k(1) = (8.8 ± 1.4) * 10−13 cm3 * molecule−1 * s−1. Numerical modelling was used to determine the rate constant at 298 K of the subsequent reaction CFO + CFO → CF2O + CO: k(2) = (4.9 ± 2.0) * 10−11 cm3 * molecule−1 * s−1. The possible occurrences of secondary reactions, CFO + F + M → CF2O + M, and CFO + F2 → CF2O + F, can be excluded under the present conditions. © 1993 John Wiley & Sons, Inc.

Copper Film Growth by Chemical Vapor Deposition: Electrical and Optical Measurements in Real Time, and Studies of Morphology

The deposition of copper by low pressure chemical vapor deposition (CVD) from copper bis‐hexafluoroacetylacetonate is monitored in real time and in situ by the measurement of the optical reflectivity and electrical resistance of the growing metal film. Changes of the deposit morphology during growth were analyzed by interrupting the CVD process at different stages and observing the samples by transmission electron microscopy. Pure copper is deposited at a temperature of 400°C and 1 mbar total reactor pressure of helium, precursor, and water vapor. Two successive regimes are distinguished in the deposition: island formation and continuous film growth. The transition between these two regimes is visible in the real time specular reflectance measurement. The copper deposition rate is twice higher during the island growth than during the continuous film growth at the applied conditions. The influence of a metal seeding layer (from 0.001 monolayer to 1 monolayer) on the copper deposition is shown both in the real time measurements and in the ex situ analysis of films.

Gas Phase Studies on Chloryl Chloride, ClClO2

AbstractClClO2 has been generated by reacting FClO2 with BCl3 or HCl in the gas phase at room temperature. It is also formed in the reaction of photolytically generated Cl‐atoms with ClO2. One weak and three strong fundamentals as well as two weak combination bands were observed in the mid infrared region. In the UV‐region ClClO2 strongly absorbs, exhibiting maxima at 231 and 296 nm with σ = 1.3 and 1.5 · 10−17 cm2 molecule−1. Decomposition of ClClO2 follows second order with a halflife of 60s at 1.0 mbar partial and 4 mbar total pressure, resulting in ClO2 and Cl2.

Reactions of peroxyacetyl radicals with reduced sulfur compounds

The reaction of peroxyacetyl radicals with reduced sulfur compounds was studied at 55°C in N2 at 1 000 mbar total pressure. The radicals were generated in equilibrium with peroxyacetyl nitrate and NO2 in large excess. The pseudo first order decay ofPAN was measured in the absence and presence of several 100 ppm CH3SH, C2H5SH,n-C4H9SH, (CH3)2S, and (CH3S)2. Computer simulations yielded the following rate constants of peroxyacetyl radicals with the above mentioned sulfur compounds: 3.7, 2.8, 13.0, 0.9, and 1.8·10−16 cm3/s, respectively. An electron capturing compound of the thiols with NO2 was observed.

Relative-rate study of the gas-phase reaction of hydroxy radicals with difunctional organic nitrates at 298 K and atmospheric pressure

Rate coefficients for the reactions of difunctional nitrates with atmospherically important OH radicals are not currently available in the literature. This study represents the first determination of rate coefficients for a number of C(3) and C(4) carbonyl nitrates and dinitrates with OH radicals in a 38 l glass reaction chamber at 1000 mbar total pressure of synthetic air by 298±2 K using a relative kinetic technique. The following rate coefficients (in units of 10-12 cm3 molecule-1 s-1) were obtained: 1,2-propandiol dinitrate, <0.31; 1,2-butandiol dinitrate, 1.70±0.32; 2,3-butandiol dinitrate, 1.07±0.26; α-nitrooxyacetone, <0.43; 1-nitrooxy-2-butanone, 0.91±0.16; 3-nitrooxy-2-butanone, 1.27±0.14; 1,4-dinitrooxy-2-butene, 15.10±1.45; 3,4-dinitrooxy-1-butene, 10.10±0.50. The possible importance of reaction of OH as an atmospheric sink for the compounds compared to other loss processes is considered.

Kinetic oscillations in the NO + CO reaction on Pt(100): Experiments and mathematical modeling

The reaction of NO and CO on Pt(100) exhibits two branches of steady state production of N2 and CO2 and the occurrence of kinetic oscillations. This system was studied under steady flow conditions in the 10−6 mbar total pressure range using low-energy electron diffraction-(LEED), work function measurement, and mass spectrometry for determination of the reaction rate. These studies revealed that kinetic oscillations can only be initiated from one of the two stable reaction branches. Two separate existence regions were detected in which the oscillations are always damped. Oscillations can be very reproducibly excited by slight decreases in temperature. The 1×1■hex phase transition of the surface structure was observed to take place only in one of the two regions of reaction rate oscillations. Its influence seems to be of minor relevance to the mechanism of oscillations as oscillations in one region occur on the surface that maintains a 1×1 structure. The experiments were modeled by a set of coupled differential equations based on knowledge about the elementary reaction steps. The model calculations reproduced the steady states of the reaction as well as the occurrence of kinetic oscillations in different ranges in excellent agreement with experimental observation. In the model, the phase transition also has no relevance for the oscillation mechanism. The occurrence of oscillations can be rationalized in terms of a periodic sequence of autocatalytic ‘‘surface explosions’’ and the restoration of an adsorbate-covered surface. The damping, experimentally observed, is attributed to insufficient spatial coupling between different regions of the surface.

CH 4 nonlocal thermodynamic equilibrium in the atmospheres of the giant planets

CH 4 vibrational relaxation in the upper stratospheres of the Giant Planets has been examined. A model was developed for the thermalization of solar energy absorbed under nonlocal thermodynamic equilibrium (non-LTE) conditions in the CH 4 band groups centered at λ ⋍ 1.7, 2.3, and 3.3 μ m . Assuming radiative equilibrium and employing a non-LTE radiative transfer algorithm from J. S. Hogan (1968, Ph.D. dissertation), a range of model atmospheres was produced, reflecting uncertainties in CH 4 collisional relaxation rates and their temperature dependences. Nominal models for the Giant Planets indicate that the ratios S/ B (source function/Planck function) at 1300 cm −1 (near the center of the CH 4 ν 4 fundamental) begin to depart significantly from unity at P − 0.1 mbar total pressure. In the formulation used here, this ratio drops to roughly 0.8 at P = 0.01 mbar. The results show large departures from LTE at lower pressures: for example, S/ B < 0.5 at 1 μbar in all models. Rough estimates of CH 4 7.7-μm non-LTE emission resulting from scattered sunlight suggest that it is a negligible component of the 7.7-μm flux emanating from all four planets, with the possible exception of Uranus. At 0.1 mbar, all of the non-LTE models are within 2°K of the LTE reference models. Differences between extreme non-LTE and reference LTE models increase steadily upward, however, reaching about ±20°K at 0.1 μbar (near the tops of the models). For Uranus, temperature profiles based on stellar occultation measurements are considerably more complex than the models: some of the data exhibit temperature variations having smaller vertical wavelengths and, at some levels, larger amplitudes. These comparisons, however, encompass many uncertainties, both in the non-LTE computations and in the contemplation of a data set that is of good quality but very complex. Requirements for improving the theoretical models are discussed.

Gas phase reactions of alkyl nitrates with hydroxyl radicals under tropospheric conditions in comparison with photolysis

Rate constants for the reaction of OH radicals with some branched alkyl nitrates have been measured applying a competitive technique. Methyl nitrite photolysis in synthetic air was used as OH radical source at 295±2 K and 1000 mbar total pressure. Using a rate constant of 2.53×10-12 cm3 s-1 for the reaction of OH radicals with n-butane as reference, the following rate constants were obtained (units: 10-12 cm3 s-1): isopropyl nitrate, 0.59±0.22; isobutyl nitrate, 1.63±0.20; 3-methyl-2-butyl nitrate, 1.95±0.15; 2-methyl-1-butyl nitrate, 2.50±0.15; 3-methyl-1-butyl nitrate, 2.55±0.35. These values have been combined with the literature data to recalculate the substituent factors F(X) for the different nitrate groups which can be used to predict OH rate constants for organic nitrates for which experimental data are not available.

Lasers pumped by ion beams

Eleven rare-gas laser lines in the near infrared and the 1.45-μm line in carbon have been pumped with an intense 3.6-MeV He+ dc beam from the Stuttgart Dynamitron accelerator. In one experimental run a 40 Ar beam was also successfully tested. Laser action was observed in gas mixtures up to several hundred mbar total pressure using a differentially pumped gas target. A maximum output power of 170 mW was observed from He-Ar laser lines. This shows that ion beam accelerators which are widely used in nuclear physics can also be used as a versatile pumping source for lasers. The maximum power which can presently be provided by the Stuttgart accelerator is about 1 kW (dc). The observed laser lines in the infrared region between 1.15 and 3.07 μm are known from low-pressure electrical discharge lasers. The excitation scheme at the relatively high pressures used had been investigated in connection with nuclear pumped lasers by other authors. Ion beam pumping is found to be an interesting pumping method in itself and at present a suitable way to optimize the conditions relevant for nuclear-pumped lasers as the measurements do not have to be performed in the vicinity of a high flux nuclear reactor.