Torr Of Helium Research Articles

Near-Thermal Reactions of Au+(1S,3D) and AuX+ with CH3X (X = Br, I): A Combined Experimental and Computational Analysis.

Reactions of Au+(1S,3D) and AuX+ with CH3X (X = I and Br) were performed in the gas phase by utilizing a selected-ion drift cell reactor. These experiments were done at room temperature as well as reduced temperature (∼200 K) at a total pressure of 3.5 Torr in helium. Rate coefficients, product sequencing, and branching fractions were obtained for all reactions to evaluate reaction efficiencies and higher-order processes. Reactions of both Au+ states proceed with moderate efficiencies as compared to the average dipole orientation model with these neutral substrates. Results from this work revealed that, dependent on the reacting partner, Au+(1S) exhibits, among others, halogen abstraction, HX elimination, and association. By comparison, Au+(3D) participates primarily in charge transfer and halogen abstraction. Dependent on the halogen ligand, AuX+ ions induce several processes, including association, charge transfer, halogen loss, and halogen substitution. AuI+ reacting with CH3Br resulted in association exclusively, whereas the AuI+/CH3I and AuBr+/CH3Br systems exhibited halogen loss as the dominant process. By contrast, all possible bimolecular pathways occurred in the reaction of AuBr+ with CH3I. Observed products indicate that displacement of bromine by iodine on gold is favored in ionic products, consistent with the thermochemical preference for formation of the Au+-I bond. All AuX+ reactions proceed at maximum efficiency. Potential energy surfaces calculated at the B3LYP/def2-TZVPP level of theory for the AuX+ reactions are in good agreement with the available thermochemistry for these species and with previously calculated structures and energetics. Experimental and computational results are consistent with a mechanism for the AuX+/CH3Y systems where bimolecular products occur either via direct loss of the halogen originally on Au or via a common intermediate resulting from methyl migration in which the Au center is three-coordinate.

Optical measurement of gas vibrational-translational relaxation time with high accuracy by the laser photo-acoustic set-up

This study aimed to measure the vibrational-translational (V-T) relaxation time of gases using photo-acoustic technique with high accuracy. For this purpose, a cylindrical resonator and its acoustic filters were simulated and then fabricated. The results showed that minimum detectable concentration of Ozone and Sulfur hexafluoride by this set-up was measured 7 and 33 ppb, respectively. So, this optical set-up can be used as a highly sensitive sensor to detect gases. Then, the signal and the resonant frequency changes in the presence of some noble gases in different pressures, at 0.42 W laser were studied. Finally, the V-T relaxation time of these gases at different pressures (100–800 Torr) of buffer gases was measured in the order of milliseconds. The V-T relaxation time of Ozone and Sulfur hexafluoride at 100 Torr Helium buffer gas was obtained 3.7 and 3.1 ms, respectively. Also, for both ozone and sulfur hexafluoride in the presence of helium buffer gas, the lowest V-T relaxation time and photo-acoustic signal and the highest frequency were obtained.

Hydrogen isotopic analysis of nuclear reactor materials using ultrafast laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy is a promising method for rapidly measuring hydrogen and its isotopes, critical to a wide range of disciplines (e.g. nuclear energy, hydrogen storage). However, line broadening can hinder the ability to detect finely spaced isotopic shifts. Here, the effects of varying plasma generation conditions (nanosecond versus femtosecond laser ablation) and ambient environments (argon versus helium gas) on spectral features generated from Zircaloy-4 targets with varying hydrogen isotopic compositions were studied. Time-resolved 2D spectral imaging was employed to detail the spatial distribution of species throughout plasma evolution. Results highlight that hydrogen and deuterium isotopic shifts can be measured with minimal spectral broadening in a ∼ 10 Torr helium gas environment using ultrafast laser-produced plasmas.

Experimental determination of the rate constants of the reactions of HO2 + DO2 and DO2 + DO2

AbstractThe rate constants of the reactions of DO2 + HO2 (R1) and DO2 + DO2 (R2) have been determined by the simultaneous, selective, and quantitative measurement of HO2 and DO2 by continuous wave cavity ring‐down spectroscopy (cw‐CRDS) in the near infrared, coupled to a radical generation by laser photolysis. HO2 was generated by photolyzing Cl2 in the presence of CH3OH and O2. Low concentrations of DO2 were generated simultaneously by adding low concentrations of D2O to the reaction mixture, leading through isotopic exchange on tubing and reactor walls to formation of low concentrations of CH3OD and thus formation of DO2. Excess DO2 was generated by photolyzing Cl2 in the presence of CD3OD and O2, small concentrations of HO2 were always generated simultaneously by isotopic exchange between CD3OD and residual H2O. The rate constant k1 at 295 K was found to be pressure independent in the range 25–200 Torr helium, but increased with increasing D2O concentration k1 = (1.67 ± 0.03) × 10−12 × (1 + (8.2 ± 1.6) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The rate constant for the DO2 self‐reaction k2 has been measured under excess DO2 concentration, and the DO2 concentration has been determined by fitting the HO2 decays, now governed by their reaction with DO2, to the rate constant k1. A rate constant with insignificant pressure dependence was found: k2 = (4.1 ± 0.6) × 10−13 (1 + (2 ± 2) × 10−20 cm3 × [He] cm−3) cm3 s−1 as well as an increase of k2 with increasing D2O concentration was observed: k2 = (4.14 ± 0.02) × 10−13 × (1 + (6.5 ± 1.3) × 10−18 cm3 × [D2O] cm−3) cm3 s−1. The result for k2 is in excellent agreement with literature values, whereas this is the first determination of k1.

Quantifying the Competition between Intersystem Crossing and Spin-Conserved Pathways in the Thermal Reaction of V+ + N2O.

The kinetics of V+ + N2O and VO+ + N2O are studied using a selected-ion flow tube from 300-600 K at pressures of 0.25-0.70 Torr helium. V+ + N2O yields VO+ (k = 4.9 ± 1.0 (T/300 K)-0.3±0.2 × 10-10 cm3 s-1) in both ground and excited states. The secondary reaction VO+ + N2O → VO2+ + N2 proceeds near the collision rate at >10-10 cm3 s-1, whereas thermalized VO+ + N2O studied as a primary reaction proceeds more than 100× more slowly (k = 4.2 ± 1.0 (T/300 K)-1.4±0.2 × 10-12 cm3 s-1). The results are best explained by contributions of competing pathways in V+ + N2O: a spin crossing to the lower energy 3VO+ in the exit well and a spin-conserved reaction yielding an electronically excited 5VO+. The intersystem crossing occurs in 35 ± 20% and 37 ± 15% of reactive interactions at 300 and 600 K, respectively. Statistical modeling of relevant reaction coordinates supports the lack of a temperature dependence, indicates an intersystem crossing rate constant of 1011 s-1, and yields derived bond and transition state energies.

Catalyst effect on the preparation of single-walled carbon nanotubes by a modified arc discharge

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharge furnace using 500 Torr helium as buffer gas at 600 °C. The effect of the catalyst type on the production of SWCNTs was studied by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The experimental results indicated that the catalyst composition plays an important role in the production rate and purity of the SWCNTs product. Fe-Ni-Mg and Co-Ni powder catalysts demonstrated excellent catalytic effect at a catalyst content of 3 wt%. The soot production rate was up to 15 g/hr and the mean diameter of SWCNTs was about 1.3 nm.

Experimental and theoretical investigation of the reaction of RO2 radicals with OH radicals: Dependence of the HO2 yield on the size of the alkyl group

AbstractThe HO2 yield in the reaction of peroxy radicals with OH radicals has been determined experimentally at 50 Torr helium by measuring simultaneously OH and HO2 concentration time profiles, following the photolysis of XeF2 in the presence of different hydrocarbons and O2. The following yields have been obtained: = (0.90 ± 0.1), = (0.75 ± 0.15), = (0.41 ± 0.08), and = (0.15 ± 0.03). The clear decrease in HO2 yield with increasing size of the alkyl moiety can be explained by an increased stabilization of the trioxide adduct, ROOOH. This has been confirmed by ab initio and Rice–Ramsperger–Kassel–Marcus master equation calculations. Extrapolation of the experimental results to atmospheric conditions shows that the stabilized adduct, ROOOH, is the nearly exclusive product of the reaction between OH radicals and peroxy radicals containing more than three C‐atoms. The fate and possible impact of these species is completely unexplored so far.

Reactions of OH radicals with 2-methyl-1-butyl, neopentyl and 1-hexyl nitrates. Structure-activity relationship for gas-phase reactions of OH with alkyl nitrates: An update

The kinetics of the reactions 2-methyl-1-butyl (2M1BNT), neopentyl (NPTNT) and 1-hexyl nitrates (1HXNT) with OH radicals has been studied using a low pressure flow tube reactor combined with a quadrupole mass spectrometer. The rate constants of the title reactions were determined under pseudo-first order conditions from kinetics of OH consumption in excess of nitrates. The overall rate coefficients, k2M1BNT = 1.54 × 10−14 (T/298)4.85 exp (1463/T) (T = 278–538 K), kNPTNT = 1.39 × 10−14 (T/298)4.89 exp (1189/T) (T = 278–500 K) and k1HXNT = 2.23 × 10−13 (T/298)2.83 exp (853/T) cm3molecule−1s−1 (T = 306–538 K) (with conservative 15% uncertainty), were determined at a total pressure of 1 Torr of helium. The yield of trimethylacetaldehyde ((CH3)3CCHO), resulting from the abstraction by OH of an α-hydrogen atom in neopentyl nitrate, followed by α-substituted alkyl radical decomposition, was determined as 0.31 ± 0.06 at T = 298 K. The calculated tropospheric lifetimes of 2M1BNT, NPTNT and 1HXNT indicate that reaction of these nitrates with OH represents an important sink of these compounds in the atmosphere. Based on the available kinetic data, we have updated the structure-activity relationship (SAR) for reactions of alkyl nitrates with OH at T = 298 K. Good agreement (within 20%) is obtained between experimentally measured rate constants (total and that for H-atom abstraction from α carbon) and those calculated from SAR using new substituents factors for almost all the experimental data available.

Picosecond Breakdown in High-Voltage Open Pulse Discharge With Enhanced Secondary Electron Emission

A 300-ps breakdown was registered in the experiments in the high-voltage open discharge with counter-propagating electron-beams with applying voltage pulses with rise times in 10–20 ns range. Discharge operates between two cathodes and grid-anode in the midplane at 10–35 Torr in helium at voltage 5–13 kV. It is shown in Particle-in-cell Monte Carlo collision (PIC MCC) simulations that the contributions of electrons, ions and energetic atoms in ionization and excitation processes are important for current development. The influence of different emissive cathode materials (titanium, silicon carbide, and CuAlMg-alloy) on evolution of discharge current is studied in the experiment and in kinetic PIC MCC simulations. The secondary electron emission from the cathodes is found to be a dominant process at the final stage of the breakdown. The current growth rate is larger (up to 700 A/cm2ns) for the cathode with a higher secondary electron emission yield. By choosing the cathode material, applied voltage amplitude and gas pressure, the characteristic time of the gas breakdown can be reduced.

Measurement of line strengths in the à 2A’ ← [formula omitted]2A” transition of HO2 and DO2

The absorption spectrum of the à 2A’ ← X˜2A” 000–000 band of HO2 and DO2 radicals has been measured in the range 6941–7077 cm−1 with a resolution of around 0.005 cm−1. HO2 and DO2 radicals were generated from the reaction of Cl-atoms with CH3OH and CD3OD, respectively, whereby Cl-atoms were generated by pulsed photolysis of (COCl)2 at 248 nm. One time-resolved absorption curve was measured by cw-Cavity Ring Down Spectroscopy (cw-CRDS) for each wavelength. The relative absorption coefficient for each wavelength was then obtained from the ring down time τ, extrapolated to t = 0 s with respect to the photolysis pulse, and the ring down time τ0 before the photolysis pulse. Absolute absorption coefficients were quantified for several selected lines relative to a well characterized absorption line of HO2 at 6638.21 cm−1 by a second cw-CRDS absorption path. The maximum absorption cross section at 50 Torr Helium was for HO2 the transition N Ka Kc J = 11 0 11 11.5 ← 11 1 11 11.5 with σ7000.28 cm−1 = 2.12 × 10−19 cm2 and for DO2 the doublet transition N Ka Kc J = 18 1 18 18.5 ← 18 0 18 18.5 and 18 1 18 17.5 ← 18 0 18 17.5 with σ7019.83 cm−1 = 2.97 × 10−19 cm2. The full spectrum has been very well reproduced by employing spectroscopic data from earlier works.

Kinetic and Mechanistic Study of the Thermal Decomposition of Ethyl Nitrate

Thermal decomposition of ethyl nitrate (ENT; CH3CH2ONO2) has been studied in a low-pressure flow reactor combined with a quadrupole mass spectrometer. The rate constant of the nitrate decomposition was measured as a function of pressure (1–12.5 Torr of helium) and temperature in the range 464–673 K using two different approaches: from kinetics of ENT loss and those of the formation of the reaction product (CH3 radical). The fit of the observed falloff curves with two-parameter expression provided the following low- and high-pressure limits for the rate constant of ENT decomposition: k0 = 1.0 × 10−4 exp(−16,400/T) cm3 molecule−1 s−1 and k∞ = 1.08 × 1016 exp(−19,860/T) s−1, respectively, which allow to reproduce (via above expression and with 20% uncertainty) all the experimental data obtained for k1 in the temperature and pressure range of the study. It was observed that the initial step of the thermal decomposition of ethyl nitrate is O–NO2 bond cleavage leading to formation of NO2 and CH3CH2O radical, which rapidly decomposes to form CH3 and formaldehyde as final products. The yields of NO2, CH3, and formaldehyde upon decomposition of ethyl nitrate were measured to be near unity. In addition, the kinetic data were used to determine the O–NO2 bond dissociation energy in ENT: 38.3 ± 2.0 kcal mol−1.

Kinetics of the reactions of OH radicals with n-butyl, isobutyl, n-pentyl and 3-methyl-1-butyl nitrates

The kinetics of the reactions of n-butyl (BTN), isobutyl (IBN), n-pentyl (PTN) and 3-methyl-1-butyl (3M1BN) nitrates with OH radicals has been studied using a low pressure flow tube reactor combined with a quadrupole mass spectrometer. The rate constants of the title reactions were determined under pseudo-first order conditions from kinetics of OH consumption in high excess of the nitrates. The overall rate coefficients, kBTN = 1.0 × 10−13 (T/298)3.36 exp(838/T) (T = 288–500 K), kIBN = 2.8 × 10−14 (T/298)4.09 exp(1127/T) (T = 283–500 K), kPTN = 1.26 × 10−12 (T/298)4.56 exp(45/T) (T = 298–496 K) and k3M1BN = 8.47×10−14 (T/298)3.52 exp(1069/T) cm3molecule−1s−1 (T = 288–538 K) (with conservative 15% uncertainty), were determined at a total pressure of 1 Torr of helium. The yields of the carbonyl compounds, n-butanal (n-C3H7CHO) and isobutanal ((CH3)2CHCHO), resulting from the abstraction by OH of an α-hydrogen atom in n-butyl and isobutyl nitrates, followed by α-substituted alkyl radical decomposition, were determined at T = 300 K to be 0.10 ± 0.02 and 0.15 ± 0.03, respectively. The calculated tropospheric lifetimes of BTN, IBN, PTN and 3M1BN indicate that reaction of these nitrates with OH represents an important sink of these compounds in the atmosphere.

Thermal decomposition of n-propyl and n-butyl nitrates: Kinetics and products

Thermal decomposition of n-propyl (C3H7ONO2, PPN) and n-butyl (C4H9ONO2, BTN) nitrates has been studied in a low pressure flow reactor combined with a quadrupole mass spectrometer. The rate constants of the nitrates decomposition were measured as a function of pressure (0.95–12.8Torr of helium) and temperature in the range 473–659K using two different approaches: from kinetics of nitrate loss and those of the formation of the reaction products. The fit of the observed falloff curves with two parameter expression k=k0k∞[M]k0[M]+k∞×0.6(1+(log(k0[M]k∞))2)−1 provided the following low and high pressure limits for the rate constants of the nitrates decomposition: k0(PPN)=0.68×10−4 exp(−15002/T)cm3molecule−1s−1, k∞ (PPN)=7.34×1015 exp(−19676/T)s−1, k0(BTN)=2.80×10−4 exp(−15382/T)cm3molecule−1s−1 and k∞(BTN)=7.49×1015 exp(−19602/T)s−1, which allow to reproduce (via above expression and with 20% uncertainty) all the experimental data obtained for the rate constants of PPN and BTN decomposition in the temperature and pressure range of the study. It was observed that the initial step of the thermal decomposition of the nitrates is ONO2 bond cleavage leading to formation of NO2 and alkoxy radical, which rapidly decomposes or isomerizes to form C2H5 and formaldehyde and C3H7, CH2O and hydroxybutyl radical as final products of PPN and BTN decomposition, respectively. In addition, the kinetic data were used to determine the ONO2 bond dissociation energy of 38.0±1.2 and 37.8±1.0kcalmol−1 in PPN and BTN, respectively.

Kinetics and Products of the Reactions of Ethyl and n -Propyl Nitrates with OH Radicals

The kinetics of the reactions of ethyl (1) and n-propyl (2) nitrates with OH radicals has been studied using a low-pressure flow tube reactor combined with a quadrupole mass spectrometer. The rate constants of the title reactions were determined under pseudo–first-order conditions from kinetics of OH consumption in high excess of nitrates. The overall rate constants, k1 = 1.14 × 10−13 (T/298)2.45 exp(193/T) and k2 = 3.00 × 10−13 (T/298)2.50 exp(205/T) cm3 molecule−1 s−1 (with conservative 15% uncertainty), were determined at a total pressure of 1 Torr of helium over the temperature range (248–500) and (263–500) K, respectively. The yields of the carbonyl compounds, acetaldehyde and propanal, resulting from the abstraction by OH of an α-hydrogen atom in ethyl and n-propyl nitrates, followed by α-substituted alkyl radical decomposition, were determined at T = 300 K to be 0.77 ± 0.12 and 0.22 ± 0.04, respectively.

Thermal Decomposition of Isopropyl Nitrate: Kinetics and Products.

Kinetics and products of the thermal decomposition of isopropyl nitrate (IPN, C3H7NO3) have been studied using a low pressure flow reactor combined with a quadrupole mass spectrometer. The rate constant of IPN decomposition was measured as a function of pressure (1-12.5 Torr of helium) and temperature in the range 473-658 K using two methods: from kinetics of nitrate loss and those of reaction product (CH3 radical) formation. The fit of the observed falloff curves with two parameter expression [Formula: see text] provided the following low and high pressure limits for the rate constant of IPN decomposition: k0 = 6.60 × 10-5exp(-15190/T) cm3 molecule-1 s-1 and k∞ = 1.05 × 1016 exp(-19850/T) s-1, respectively, which allows one to determine (via the above expression) the values of k1 (with 20% uncertainty) in the temperature and pressure range of the study. It was observed that thermal decomposition of IPN proceeds through initial breaking of the O-NO2 bond, leading to formation of NO2 and isopropoxy radical (CH3)2CHO, which rapidly decomposes forming CH3 and acetaldehyde as final products. The yields of NO2, CH3, and acetaldehyde upon decomposition of isopropyl nitrate were measured to be (0.98 ± 0.15), (0.96 ± 0.14), and (0.99 ± 0.15), respectively. In addition, the kinetic data were used to determine the O-NO2 bond dissociation energy in isopropyl nitrate, 38.2 ± 4.0 kcal mol-1.

Cross Section of OH Radical Overtone Transition near 7028 cm(-1) and Measurement of the Rate Constant of the Reaction of OH with HO2 Radicals.

The absorption cross section of an overtone transition of OH radicals at 7028.831 cm(-1) has been measured using an improved experimental setup coupling laser photolysis to three individual time-resolved detection techniques. Time-resolved relative OH radical profiles were measured by laser-induced fluorescence (LIF), and their absolute profiles have been obtained by cw-cavity ring-down spectroscopy (cw-CRDS). HO2 radicals were quantified simultaneously at the well-characterized absorption line at 6638.21 cm(-1) by a second cw-CRDS absorption path. Initial OH concentrations and thus their absorption cross sections have been deduced from experiments of 248 nm photolysis of H2O2: OH and HO2 profiles have been fitted to a simple kinetic model using well-known rate constants. The rate constant of the reaction between OH and HO2 radicals turned out to be sensitive to the deduction of the initial OH concentration and has been revisited in this work: OH decays have been observed in the presence of varying excess HO2 concentrations. A rate constant of (1.02 ± 0.06) × 10(-10) cm(3) s(-1) has been obtained, in good agreement with previous measurements and recent recommendations. An absorption cross section of σOH = (1.54 ± 0.1) × 10(-19) cm(2) at a total pressure of 50 Torr helium has been obtained from consistent fitting of OH and HO2 profiles in a large range of concentrations.

Experimental and Theoretical Studies of the Reactivity and Thermochemistry of Dicyanamide: N(CN)(2)(-).

Dicyanamide [N(CN)2(-)] is a common anionic component of ionic liquids, several of which have shown hypergolic reactivity upon mixing with white-fuming nitric acid. In this study, we explore the thermochemistry of dicyanamide and its reactivity with nitric acid and other molecules to gain insight into the initial stages of the hypergolic phenomenon. We have developed and utilized an electrospray ion source for our selected ion flow tube (SIFT) to generate the dicyanamide anion. We have explored the general reactivity of this ion with several neutral molecules and atoms. Dicyanamide does not show reactivity with O2, H2SO4, H2O2, DBr, HCl, NH3, N2O, SO2, COS, CO2, CH3OH, H2O, CH4, N2, CF4, or SF6 (k < 1 × 10(-12) cm(3)/s); moreover, dicyanamide does not react with N atom, O atom, or electronically excited molecular oxygen (k < 5 × 10(-12) cm(3)/s), and our previous studies showed no reactivity with H atom. However, at 0.45 Torr helium, we observe the adduct of dicyanamide with nitric acid with an effective bimolecular rate constant of 2.7 × 10(-10) cm(3)/s. Intrinsically, dicyanamide is a very stable anion in the gas phase, as illustrated by its lack of reactivity, high electron-binding energy, and low proton affinity. The lack of reactivity of dicyanamide with H2SO4 gives an upper limit for the gas-phase deprotonation enthalpy of the parent compound (HNCNCN; <310 ± 3 kcal/mol). This limit is in agreement with theoretical calculations at the MP2/6-311++G(d,p) level of theory, finding that ΔH298 K(HNCNCN) = 308.5 kcal/mol. Dicyanamide has two different proton acceptor sites. Experimental and computational results indicate that it is lower in energy to protonate the terminal nitrile nitrogen than the central nitrogen. Although proton transfer to dicyanamide was not observed for any of the acidic molecules investigated here, the calculations on dicyanamide with one to three nitric acid molecules reveal that higher-order solvation can favor exothermic proton transfer. Furthermore, the formation of 1,5-dinitrobiuret, proposed to be the key intermediate during the hypergolic ignition of dicyanamide ionic liquids with nitric acid, is investigated by calculation of the reaction coordinate. Our results suggest that solvation dynamics of dicyanamide with nitric acid play an important role in hypergolic ignition and the interactions at the droplet/condensed-phase surface between the two hypergolic liquids are very important. Moreover, dicyanamide exists in the atmosphere of Saturn's moon, Titan; the intrinsic stability of dicyanamide strongly suggests that it may exist in molecular clouds of the interstellar medium, especially in regions where other stable carbon-nitrogen anions have been detected.

Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range.

The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene → products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k1b = (3.70 ± 0.42) × 10(-11) exp[-(772 ± 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k1 = (1.82 ± 0.48) × 10(-12) exp[(607 ± 70)/T] or, in a biexponential form, k1 = k1a + k1b = 3.7 × 10(-11) exp(-772/T) + 6.3 × 10(-13) exp(856/T), independent of the pressure between 1 and 5 Torr of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant.

Highly zone-dependent synthesis of different carbon nanostructures using plasma-enhanced arc discharge technique

Three kinds of carbon nanostructures, i.e., graphene nanoflakes (GNFs), multi walled carbon nanotubes (MWCNTs), and spherical carbon nanoparticles (SCNPs) were comparatively investigated in one run experiment. These carbon nanostructures are located at specific location inside the direct current plasma-assisted arc discharge chamber. These carbon nanomaterials have been successfully synthesized using graphite as arcing electrodes at 400 torr in helium (He) atmosphere. The SCNPs were found in the deposits formed on the cathode holder, in which highly curled graphitic structure are found in majority. The diameter varies from 20 to 60 nm and it also appears that these particles are self-assembled to each other. The MWCNTs with the diameter of 10–30 nm were obtained which were present inside the swelling portion of cathode deposited. These MWCNTs have 14–18 graphitic layers with 3.59 A interlayer spacing. The GNFs have average lateral sizes of 1–5 μm and few of them are stacked layers and shows crumpled like structure. The GNFs are more stable at low temperature (low mass loss) but SCNPs have low mass loss at high temperature.

Experimental Study of the Reaction of Isopropyl Nitrate with OH Radicals: Kinetics and Products

ABSTRACTThe kinetics of the reaction of isopropyl nitrate (IPN) with OH radicals has been studied using a low‐pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + (CH3)2CHONO2 → products (2). The rate constant of the title reaction was determined using both the absolute method, monitoring the kinetics of OH radicals consumption in excess of IPN, and the relative rate method using the reaction of OH with Br2 as reference one and following HOBr formation. As a result of the absolute and relative measurements, the overall rate coefficients, k2 = (6.6 ± 1.2) × 10−13 exp(–(233 ± 56)/) was determined at a pressure of 1 Torr of helium over the temperature range 268–355 K. Acetone, resulting from H‐atom abstraction from the tertiary C–H bond of IPN followed by 2‐nitroxy‐2‐propyl radical decomposition, was found to be a major reaction product with the yield of 0.82 ± 0.13, independent of temperature in the range 277–355 K.