Real-time quantitative analysis of H2, He,O2, and Ar by quadrupole ion trap mass spectrometry

The use of a quadrupole ion trap mass spectrometer (QITMS) for quantitative analysis of hydrogen and helium as well as of other permanent gases is demonstrated. Like commercial instruments, the customized QITMS uses mass selective instability; however, this instrument operates at a greater trapping frequency and without a buffer gas. Thus, a useable mass range from 2 to over 50 daltons (Da) is achieved. The performance of the ion trap is evaluated using part-per-million (ppm) concentrations of hydrogen, helium, oxygen, and argon mixed into a nitrogen gas stream, as outlined by the National Aeronautics and Space Administration (NASA), which is interested in monitoring for cryogenic fuel leaks within the Space Shuttle during launch preparations. When quantitating the four analytes, relative accuracy and precision were better than the NASA-required minimum of 10% error and 5% deviation, respectively. Limits of detection were below the NASA requirement of 25-ppm hydrogen and 100-ppm helium; those for oxygen and argon were within the same order of magnitude as the requirements. These results were achieved at a fast data recording rate, and demonstrate the utility of the QITMS as a real-time quantitative monitoring device for permanent gas analysis.     

Shock tube studies of the N2O/Ar and N2O/H2/Ar systems

N₂O decay has been monitored via infrared emission for a series of mixtures containing N₂O/Ar and N₂O/H₂/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950–3075°K with total concentrations ranging from 1.2 to 2.5 × 10¹⁸ molec/cm³. In all cases the N₂O decayed exponentially, and a rate constant k_obs was obtained. Runs without added H₂ could be described by the following Arrhenius parameters: log A = ?9.72 ± 0.08 (in units of cm³/molec · sec) and E_A = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H₂ was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H₂, where k_obs doubled. Mixtures with no added H₂ were analyzed by numerical integration of the following reactions: Quantitative agreement between calculations and observations were obtained with both high and low choices for k₂ and k₃. The additional reactions were included in the analysis of the mixtures containing H₂. Here agreement was obtained only when low values were assigned to k₂ and k₃. The combinations of k₁ ← k₃ which agreed with all the data were k₁ = 3.25 × 10^?10 exp (?215 kJ/RT) and k₂ = k₃ = 1.91 × 10^?11 exp (-105 kJ/RT).     

Alignment of H(2p) in H-He,Ne, Ar collisions

The integral alignmentA ₂₀ was investigated for H(2p) excitation in H-He, Ne, Ar collisions at incident energies of 1–25 keV. The experimental results are compared with theoretical calculations based on different theoretical models. Calculations which do not account for the quasi-molecular aspect of the collision process are at variance with the experimental data below incident energies of 10 keV. Above 15 keV, fair agreement is obtained with calculations which include simultaneous excitation of both projectile and target.     

Exchange interaction during electron capture in Ar2+, K-collisions

During electron capture of Ar²⁺ from alkali atoms prevailingly Ar⁺ 4p states are occupied. While decaying they give rise to a spectrum which consists almost exclusively of 4p ? 4s and 4p ? 3d lines. The intensity of the lines turns out to be dependent on the Ar²⁺ projectile energy. At energies as low as 1 keV lines which belong to the Ar⁺ 3p ⁴(¹ D)n, l-system are by far the strongest. When increasing the projectile energy to 6 keV and above this system fades away and lines of the 3p ⁴(³ P)n, l-system appear. Considering that the primary beam consists constantly of 65% Ar²⁺ 3p ⁴ (³ P) and 35% Ar²⁺ 3p ³(¹ D) the strength surprises at which the 3p ⁴(¹ D)n, l system evolves from the electron capture. It is suggested that exchange interaction of the valence electron and one 3p-electron changes the 3p ⁴-core. Relative matrix elements for direct and exchange interaction of the valence electron and the 3p ⁴-core are calculated and used in a multi channel Landau Zener calculation. With this concept the measured spectra could be fitted by adopting only two parameters, namely one line strength and the ratio of the reduced matrix elements of direct and exchange interaction.     

Ar+ laser-induced fluorescence in NO2

The assignment of the resonant fluorescence induced by the AR⁺ laser lines in ¹⁴N¹⁶O₂ is reported for the first time with the 4727 and 4765 Å laser lines and is further developed with the 4579 and 4965 Å laser lines.     

On the doubly ionized states of Ar2 and their intra- and interatomic decay to Ar2 3+

Potential energy curves of the Auger state Ar+(2p(-1))-Ar, the different one- and two-site dicationic states Ar2 ++ (with energies in the range of 32-77 eV), and the lowest two-site tricationic states Ar++ - Ar+ (with energies in the range of 64-76 eV) computed using elaborated ab initio methods are reported. The accessible relaxation channels of the electronic states of Ar++ - Ar populated by Auger decay are studied. In particular, we study in detail the interatomic Coulombic decay following the population of one-site satellite states of Ar++(3s(-1)3p(-1))-Ar recently observed experimentally. Other relaxation pathways of Ar++ - Ar, including radiative charge transfer, nuclear dynamics through curve crossing, and intra-atomic decay processes are also investigated.     

Carbon monoxide molecules in an argon matrix: empirical evaluation of the Ar·Ar,C·Ar and O·Ar potential parameters

A potential force field has been evaluated for the calculation of the properties of the solid CO-Ar system. The CO·Ar potential energy has been expressed as a sum of the C·Ar and O·Ar interatomic interactions. The (6-exp) Buckingham form of the atom—atom potential, ? = ?Ar^?6 + B exp (?αr), has been used (r is the interatomic distance). The values of the A, B and α numerical parameters for the C·Ar and O·Ar potential have been obtained from those for the C·C, O·O, and Ar·Ar potentials using known combining rules. These values are the following: A_C·Ar = 3379 kJ/mol A⁶, B_C·Ar = 3.12 × 10⁵ kJ/mol, α_C·Ar = 3.493 A^?1, A_O·Ar = 2737 kJ/mol A⁶, B_O·Ar = 3.28 × 10⁵ kJ/mol, α_O·Ar = 3.706 A^?1. The three parameters of the Ar·Ar potential function (A_Ar·Ar = 6554 kJ/mol A⁶, B_Ar·Ar = 3.27 × 10⁵ kJ/mol, α_Ar·Ar = 3.305 A^?1) have been fitted to a set of experimental data for the Ar crystal (zero-temperature lattice spacing and energy, and the value of the isothermal compressibility). The CO·Ar potential surface has been calculated showing the most favourable position of an Ar atom near the CO molecule and the orientational dependence of the CO·Ar interactions. The CO·Ar separation distance at the potential minimum and the depth of the potential well are equal to 3.63 A and ?1.321 kJ/mol, respectively. Comparison has been made of the derived Ar·Ar and Co·Ar potential functions with other such functions available in the literature.     

PAHs Formation in the Depositions in a Methyl tert-Butyl Ether/Ar,a Methyl tert-Butyl Ether/O2/Ar and a Methyl tert-Butyl Ether/H2/Ar RF Plasma Environment

Contents and distributions of polycyclic aromatic hydrocarbons (PAHs) in the depositions were investigated and discussed in a MTBE/Ar, a MTBE/O₂/Ar and a MTBE/H₂/Ar plasma systems. A radio-frequency (RF) plasma system was used to produce the depositions under the designed operational condition. The identification and quantification of PAHs was accomplished by using a GC with a mass selectivity detector (GC/MS). Results indicated that when the input power controlled at high wattage (70 W) in the three systems, the contents of total-PAH in the MTBE/Ar system are higher than those of total-PAH in other system with adding O₂ or H₂. The comparison of three systems indicated the formation and accumulation of PAHs in the MTBE/Ar system is easier than other systems. At high input power wattage, when the MTBE/Ar mixture added O₂ or H₂, the domain pattern was shifted from both 3- and 4-ring PAH to 2-ring PAH. As far as the total-PAH content is concerned, the MTBE/Ar system at 70 W was found to have the highest mean total-PAH content (1540 g/g), while the MTBE/O₂/Ar system at 20 W had the lowest mean total-PAH content (44.4 g/g).     

The element effect in nucleophilic aromatic photosubstitution (SN2Ar*)

Photoreactions of 4-nitroanisole and the 2-halo-4-nitroanisoles (halogen = F, Cl, Br, I) with NaCN have been investigated. 4-Nitroanisole gave a novel, stable nitronate ion adduct (74%) with cyanide. For the five compounds, we report product distributions, Stern-Volmer kinetic plots, triplet lifetimes, and triplet yields, which afford rate constants for attack by the cyanide ion. Cyanide attack on the fluoride is diffusion controlled; the relative rates for attack at F, Cl, Br, and I are 27:2:2:1, respectively.     

Infrared spectra of monomeric thioformaldehyde in Ar,N2 and Xe matrices

Pyrolysis products of 1,3-dithietane were trapped in low-temperature matrices and their infrared spectra were recorded. The vibrational bands of monomeric H₂CS, which was not perturbed by other decomposition products, were identified in Ar, N₂ and Xe matrices. These results will be useful to evaluate the frequency shifts of H₂CS induced by the interaction with other molecules.     

Reaction Mechanisms in Both a CCl2F2/O2/Ar and a CCl2F2/H2/Ar RF Plasma Environment

Decomposition of dichlorodifluoromethane (CCl₂F₂ or CFC-12) in aradiofrequency (RF) plasma system is demonstrated. The CCl₂F₂decomposition fractions _{CCl 2 F 2} and mole fractionsof detected products in the effluent gas stream of CCl₂F₂/O₂/Ar andCCl₂F₂/H₂/Ar plasma, respectively, have been determined. The experimentalparameters including input power wattage, O₂/CCl₂F₂ or H₂/CCl₂F₂ ratio,operational pressure, and CCl₂F₂ feeding concentration wereinvestigated. The main carbonaceous product in the CCl₂F₂/O₂/Arplasma system was CO₂, while that in the CCl₂F₂/H₂/Ar plasma systemwas CH₄ and C₂H₂. Furthermore, the possible reaction pathways werebuilt-up and elucidated in this study. The results of the experimentsshowed that the highly electronegative chlorine and fluorine wouldeasily separate from the CCl₂F₂ molecule and combine with the addedreaction gas. This led to the reactions terminated with the CO₂,CH₄, and C₂H₂ formation, because of their high bonding strength. Theaddition of hydrogen would form a preferential pathway for the HCland HF formations, which were thermodynamically stable diatomicspecies that would limit the production of CCl₃F, CClF₃, CF₄, andCCl₄. In addition, the HCl and HF could be removed by neutral orscrubber method. Hence, a hydrogen-based RF plasma system provideda better alternative to decompose CCl₂F₂.     

Etching Characteristics and Mechanisms of TiO2 Thin Films in HBr/Ar and Cl2/Ar Inductively-Coupled Plasmas

The TiO₂ etching characteristics and mechanisms in HBr/Ar and Cl₂/Ar inductively-coupled plasmas were investigated under fixed gas-mixing ratio and bias power conditions. It was found that in both systems, an increase in gas pressure from 4 to 10 mTorr results in a non-monotonic TiO₂ etching rate, while a variation of input power in the range 500–800 W causes a faster-than-linear acceleration of the etching process. Plasma diagnostics performed by Langmuir probes and zero-dimensional plasma modeling provided data on plasma parameters, steady-state densities, and fluxes of the active species on the etched surface. The model-based analysis of the etching mechanism showed that for the given set of processing parameters, the TiO₂ etch kinetics correspond to the transitional regime of ion-assisted chemical reaction in which a chemical-etch pathway dominates.     

Determination of Trace Impurities of H2, O2, Ar, N2, CO, CO2, and Hydrocarbons in High-Purity Monosilane by Gas Chromatography

Procedures were proposed for the determination of impurities of permanent gases (H₂, O₂, Ar, N₂, and CO), carbon dioxide, and hydrocarbons in high-purity monosilane by gas chromatography with detection limits of 1–3 ppm, 2 ppm, and 0.02–0.04 ppm, respectively, which are lower by 1–2 orders of magnitude than those published in the literature. The procedures make it possible to check the compliance of the purity of monosilane with present standards of microelectronics (TU 48-0513-057.0-91).     

Interaction of SiCl2 with CO2 in Ar matrices

1. Download : Download high-res image (70KB)
2. Download : Download full-size image