Pressure Of He Research Articles

Modeling and analysis of buffer gas effect on 52S1/2→52D5/2 and 52S1/2→72S1/2 broadened two-photon pumped Rb vapor lasers

The study introduces helium (He) as a buffer gas to theoretically investigate the characteristics of two-photon pumped Rb vapor laser (Rb-TPAL) in order to enhance the pumping absorption efficiency of Rb-TPAL and consequently achieve high-power laser output. The analysis is based on a three-dimensional computational model, incorporating the spectral distribution of pump and absorption, as well as the influence of He on the absorption spectrum. The theoretical calculation of the dependence of the 52S1/2 → 52D5/2 transition broadened as a function of the pressure of He has good agreement with experimental results. We also simulated the influence of the pump linewidth and pressure of He on the output characteristics when 52S1/2 → 52D5/2 and 52S1/2 → 72S1/2 transitions in Rb-TPAL. A comparative analysis revealed that opting for the 52S1/2 → 72S1/2 transition can achieve higher optical–optical efficiency. The results also substantiate that the addition of a small amount of He has a positive impact on the laser output, consistent with experimental findings. Our study is crucial for designing the high-power multi-wavelength output Rb-TPAL system.

Mechanisms of helium differential enrichment and helium‐nitrogen coupling: A case study from the Weiyuan and Anyue gas fields, Sichuan Basin, China

The helium (He) contents of the Weiyuan and Anyue gas fields in the Sichuan Basin (China) differ significantly despite their similar helium‐nitrogen (N2) coupling characteristics, that is, the positive correlation between the N2 and He contents, and the negative correlation between the nitrogen/helium (N2/He) ratio and depth. To determine the factors influencing the differential enrichment of He resources and He–N2 coupling in the Weiyuan and Anyue gas fields, this study analysed the compositions of natural gases within the study area and established a computational model for evaluating the dissolution and exsolution amount of He and N2 in the pore water. The results indicated that: the uplift of the basement granite was crucial for the exsolution and enrichment of dissolved helium, and it was also the main reason for He–N2 coupling. The differential uplift that occurred in the Leshan–Longnvsi palaeo‐uplift during the Himalayan period further promoted the differential enrichment of He resources, thus also impacting the N2/He ratio in the study area. The distinct quantities of N2 and He exsolution during the uplift directly affected the negative correlation between the N2/He ratio and the depth. Within the same depth range of the uplift, the average and variations of the N2/He ratio in the crust‐derived helium‐rich natural gas reservoir were inversely proportional to the in situ molar partial pressure of He. The uplift of the crystalline basement is an important mechanism that causes the enrichment of helium resources and the coupling of helium‐nitrogen in the crust‐derived helium‐rich natural gas reservoir, which is of great significance for understanding the variation of N2/He ratio and exploration of He resources.

H2, He, and CO2 Pressure-induced Parameters for the HITRAN Database. II. Line Lists of CO2, N2O, CO, SO2, OH, OCS, H2CO, HCN, PH3, H2S, and GeH4

In recent years, extended efforts have been made to increase the potential for modeling and interpreting the spectra of planetary atmospheres using the HITRAN database. A significant objective is to provide broadening parameters due to the ambient pressure of He, H2, and CO2 gases. Since hydrogen and helium are the main constituents in the atmospheres of gas giants, and carbon dioxide dominates the atmospheres of many rocky planets, these spectroscopic data are essential for radiative transfer models dedicated to planetary atmospheres. In HITRAN2016, the He-, H2- and CO2-broadening parameters and their temperature dependencies, and in some cases pressure-induced shifts, were added to the line lists of CO, SO2, NH3, HF, HCl, OCS, and C2H2. This work describes a further expansion introduced in the HITRAN2020 edition. In particular, relevant data for the line lists of CO2, N2O, OH, H2CO, HCN, PH3, H2S, and GeH4 were added, while those for CO, SO2, and OCS were revised. The new data are based on the semiempirical models constructed on available and validated experimental measurements and theoretical predictions. These models strongly depend on the extent and quality of the available data. The paper explains how to use the online interface or the HITRAN Application Programming Interface (HAPI) to retrieve these data from the database. Examples of calculating a molecule’s spectra in a mixture of buffer-gases using HAPI are also provided. We also provide a set of Python codes allowing one to populate any line list of corresponding molecules with relevant broadening parameters.

Overall and state-to-state quenching of atomic oxygen O(2p33p 3PJ) by collisions with He and N2

Electronically excited atomic oxygen O(2p33p3PJ) was prepared by ultraviolet (225.6 nm) two-photon excitation from the ground state 2p43P2. The 2p33p3PJ state transfers to the 2p33s3S state via the infrared transition at 845 nm and/or by collisions with ambient gases. The vacuum ultraviolet (VUV) emission at 130 nm via the transition 2p33s3S → 2p43PJ was detected, and the time-resolved VUV emission at varying pressures of He and N2 was recorded. The kinetic analysis made by the integrated profiles method has given the rate coefficients not only for the overall quenching of the 2p33p3PJ state but also for the state-to-state quenching 2p33p3PJ → 2p33s3S by He and N2.

Study of He + 0.2% O2 plasma jet impinging on liquid surface from He(23S1) metastable atoms density measurements

This work presents spatial variations of the helium He(23S1) metastable atom absolute densities in a plasma jet at atmospheric pressure in He + 0.2% O2 gas mixture impinging on a liquid target. The plasma jet is ignited with 6 kV pulses of 2.5 μs duration and 8 ns rise and fall times at 20 kHz repetition rate. Streamers are created in both rising and falling fronts of the high voltage (HV). From Abel inversion of the line averaged absorbance of 1083 nm helium line, measured by laser absorption spectroscopy, the radial profiles of He(23S1) density along the plasma jet are deduced in two sources with different residence time of the gas within the discharge volume, having three different outlet tube diameters and with two gas flow rates. The metastable densities up to ∼3 × 1013 cm−3 have been measured. The radial profile remained always axially centered for the 1.5 mm outlet tube and with 0.5 slm for the larger diameter tubes. But in this later tubes and with 2 slm gas flow rate, the profile changed from a ring shape at the tube exit to axially centered when increasing the distance from the tube edge. In the rising front of the HV, the ring profile of He(23S1) density in the tube exit is attributed to the shape of the electric field, produced by the applied HV to the electrode wrapped around the dielectric tube. In the falling front of the HV, the electric field results from electrons deposited on the inner surface of the dielectric tube and positive ions accumulated on the surface of liquid during the 2.5 μs duration of the HV pulse. The influence of oxygen by-products formed in the plasma volume (O, O2(Δ), O3, positive and negative oxygen ions) on the dynamic of the plasma jet are analyzed.

Rate constant of the BrO + BrO reaction over the temperature range 220‐950 K

AbstractThe kinetics of the self‐reaction of BrO radicals has been studied over a wide temperature range (T = 220‐950 K) at 2 Torr total pressure of He using a low‐pressure flow reactor combined with a quadrupole mass spectrometer: BrO + BrO → 2Br + O2 (1a) and BrO + BrO → Br2 + O2 (1b). The overall rate constant for this reaction (defined by d[BrO]/dt = –2k1[BrO]2) was found to be k1 = k1a +k1b = (1.32 ± 0.09) × 10−12 exp(182 ± 22/T) cm3 molecule−1 s−1 at T = 220‐950 K (where the uncertainties represent precision at the 2σ level). The channel‐specific rate constant for the Br2 + O2 forming channel (1b) was determined at T = 220‐450 K: k1b = (2.83 ± 0.35) × 10−13 exp(34 ± 36/T) cm3 molecule−1 s−1 (with 2σ uncertainties). As a result of the comparative analysis of the present data and those from the previous studies, the following Arrhenius expressions are recommended from the present work: k1 = 1.4 × 10−12 exp(200/T) at T = 220‐950 K (independent of pressure at least for T ≥ 250 K) and k1b = 3.2 × 10−13 exp(34/T) cm3 molecule−1 s−1 at T = 220‐450 K and total pressure of 2 Torr, with a conservative estimate of uncertainty of 25%, independent of temperature.

Overall and state-specific electronic quenching of atomic sulfur S(3p34p 3PJ) by collisions with He

Atomic sulfur in the electronic ground state 3p43P2 was excited to the 3p34p 3P2 state by two-photon excitation at 308 nm and the vacuum ultraviolet (VUV) fluorescence via the 3p34s 3S → 3p43PJ transition at 180 nm was observed. The time-resolved VUV fluorescence was recorded at varying pressures of He. A kinetic analysis by the integrated profiles method gave the rate coefficient for overall quenching of the 3p34p 3PJ state by collisions with He. The He pressure dependence of the VUV fluorescence intensity averaged in time has derived the branching ratio of the state-specific quenching from the 3p34p 3PJ state to the 3p34s 3S state.

Helium broadened propane absorption cross sections in the far-IR

Infrared absorption spectra for pure and He broadened propane have been recorded in the far-IR region (650-1300cm−1) at the Canadian Light Source (CLS) facility using either the synchrotron or internal glowbar source depending on the required resolution. The measurements were made for 4 temperatures in the range 202–292K and for 3 pressures of He broadening gas up to 100Torr. Infrared absorption cross sections are derived from the spectra and the integrated cross sections are within 10% of the corresponding values from the Pacific Northwest National Laboratory (PNNL) for all temperatures and pressures.

Silicon oxide film deposited at room temperatures using high-working-pressure plasma-enhanced chemical vapor deposition: Effect of O2 flow rate

Abstract Silicon oxide films were deposited by high-working-pressure plasma-enhanced chemical vapor deposition using hexamethyldisiloxane and O 2 /He plasma as the precursor and the reactant, respectively. As the O 2 flow rate increased during the process, the plasma density of O 2 and He decreased due to reduction in the partial pressure of He, which affected the composition of O/Si in the silicon oxide films. Consequently, we found out that the compositional ratio of SiO 2 /SiO could be modulated by O 2 flow conditions during the high-working-pressure plasma-enhanced chemical vapor deposition process. Additionally, it was observed that the water vapor transmission rate reduced with an increase in the O 2 flow rate because of a compositional change in the silicon oxide films.

A Portable and Autonomous Mass Spectrometric System for On-Site Environmental Gas Analysis.

We developed a portable mass spectrometric system ("miniRuedi") for quantificaton of the partial pressures of He, Ne (in dry gas), Ar, Kr, N2, O2, CO2, and CH4 in gaseous and aqueous matrices in environmental systems with an analytical uncertainty of 1-3%. The miniRuedi does not require any purification or other preparation of the sampled gases and therefore allows maintenance-free and autonomous operation. The apparatus is most suitable for on-site gas analysis during field work and at remote locations due to its small size (60 cm × 40 cm × 14 cm), low weight (13 kg), and low power consumption (50 W). The gases are continuously sampled and transferred through a capillary pressure reduction system into a vacuum chamber, where they are analyzed using a quadrupole mass spectrometer with a time resolution of ≲1 min. The low gas consumption rate (<0.1 mL/min) minimizes interference with the natural mass balance of gases in environmental systems, and allows the unbiased quantification of dissolved-gas concentrations in water by gas/water equilibration using membrane contractors (gas-equilibrium membrane-inlet mass spectrometry, GE-MIMS). The performance of the miniRuedi is demonstrated in laboratory and field tests, and its utility is illustrated in field applications related to soil-gas formation, lake/atmosphere gas exchange, and seafloor gas emanations.

Remote-sensing gas measurements with coherent Rayleigh-Brillouin scattering

We measure the coherent Rayleigh-Brillouin scattering (CRBS) signal integral as a function of the recorded gas pressure in He, Co2, SF6, and air, and we confirm the already established quadratic dependence of the signal on the gas density. We propose the use of CRBS as an effective diagnostic for the remote measurement of gas' density (pressure) and temperature, as well as polarizability, for gases of known composition.

Vibrational relaxation of S2(a1Δg, υ = 1–9) by collisions with He

Vibrationally excited S2(a1Δg, υ=1–10) was generated by the S(1D)+OCS reaction and detected with dispersed laser-induced fluorescence (LIF) via the f1Δu–a1Δg transition. The time profiles of the vibrational levels of interest were recorded at varying pressures of He. A kinetic analysis made by the integrated profiles method has given the rate coefficients for vibrational relaxation of S2(a1Δg,υ=1–9) by collisions with He. The energy gap law nicely correlates the probabilities of vibrational energy transfer per collision from S2(a1Δg), O2(X3Σg-), NO(X2Π), and CO(X1Σ+) to He.

Leak Rates and Residual Gas Pressure in Cavities Sealed by Metal Thermo-Compression Bonding and Silicon Direct Bonding

Low, controlled, and stable gas pressures in sealed cavities are key features of wafer-level bonding processes used for hermetic sealing. The gas pressure is determined by e.g. the permeability of the seal and capping materials, gas produced during the bonding process, and device and material out-gassing. Both thermo-compression bonding with Au [1] and high-temperature silicon direct (fusion) bonding [2, 3] are used for hermetic sealing of commercial micro electro-mechanical (MEMS) devices today. Low-temperature silicon direct (plasma) bonding and thermo-compression bonding with Al are technologies with unverified hermeticity. This paper presents a comparison of the hermeticity of plasma and Al thermo-compression bonding and the hermeticity of fusion and Au thermo-compression bonding. Test cavities were realized by TMAH etching of 280 µm thick 6-inch silicon wafers with SiO2 mask. The cavities had a volume of 1.6 mm3and formed membranes with side edge 2.5 mm and 36 µm thickness. The cavities were bonded to silicon wafers by fusion bonding, plasma bonding, or thermo-compression bonding applying Al or Au. An overview of the bonded laminates and bonding parameters is found in Table 1. Wafers sealed by fusion and plasma bonding were laminated to blanket silicon wafers. Wafers sealed by Au thermo-compression bonding were laminated to silicon wafers with patterned Au bond frames of width 20 – 200 µm. Wafers sealed by Al thermo-compression bonding were laminated to silicon wafers with defined protruding silicon frames of width 20 – 200 µm that defined the bonding area. Figure 1 shows cross-sectional sketches of the four laminate types and the geometry of the cavities.After bonding, the wafers were stored for a time ranging from 2 – 5 months. The membrane deflection was measured during this period by white light interferometry on 3 – 481 membranes. A maximum estimate for the leak rate was calculated. Individual dies underwent a Helium (He) fine leak test. The dies were exposed to 3 bar absolute pressure of He for 4 hours. Then the He leak rate was measured on individual dies within 30 minutes using an industry standard He leak detector. The detection limit of the measurement system was found to be 7 – 8×10-10 mbar×l×s-1, measured by leak testing of the empty test chamber.The He leak rates measured on individual dies were not significantly different from the leak rate of the empty test chamber. This indicates that the measured He leak rate of all bonds were of the order of 10-10 mbar×l×s-1 or lower. The calculated maximum estimates for the leak rates based on deflection measurements are listed in Table 1. The average deflections are also listed. No significant change in membrane deflection was observed, giving a maximum leak rate for all die types of 2×10-11 mbar×l×s-1. The differences in estimated leak rates reflect the variations in laminate storage time only, and longer storage times may reveal that the maximum leak rates are even lower.The presented results indicate that the hermeticity of plasma bonded seals is similar to the hermeticity of fusion bonded seals, and that the hermeticity of thermo-compression bonded seals applying Au and Al is similar. However, for many devices, true leakage rates below 10-15 mbar×l×s-1are required [3], and knowledge of residual gas composition may also be desired. Such measurements are underway and are expected to be presented in the full paper.

HCl yield and chemical kinetics study of the reaction of Cl atoms with CH3I at the 298 K temperature using the infra-red tunable diode laser absorption spectroscopy

Pulsed ArF excimer laser (193nm) – CW infrared(IR) tunable diode laser Herriott type absorption spectroscopic technique has been made for the detection of product hydrochloric acid HCl. Absorption spectroscopic technique is used in the reaction chlorine atoms with methyl iodide (Cl+CH3I) to the study of kinetics on reaction Cl+CH3I and the yield of (HCl). The reaction of Cl+CH3I has been studied with the support of the reaction Cl+C4H10 (100% HCl) at temperature 298K. In the reaction Cl+CH3I, the total pressure of He between 20 and 125Torr at the constant concentration of [CH3I] 7.0×1014moleculecm−3. In the present work, we estimated adduct formation is very important in the reaction Cl+CH3I and reversible processes as well and CH3I molecule photo-dissociated in the methyl [CH3] radical. The secondary chemistry has been studied as CH3+CH3ICl=product, and CH3I+CH3ICl=product2. The system has been modeled theoretically for secondary chemistry in the present work. The calculated and experimentally HCl yield nearly 65% at the concentration 1.00×1014moleculecm−3 of [CH3I] and 24% at the concentration 4.0×1015moleculecm−3 of [CH3I], at constant concentration 4.85×1012moleculecm−3 of [CH3], and at 7.3×1012 moleculecm−3 of [Cl]. The pressure dependent also studied product of HCl at the constant [CH3], [Cl] and [CH3I]. The experimental results are also very good matching with the modelling work at the reaction CH3+CH3ICl=product (k=(2.75±0.35)×10−10s−1) and CH3I+CH3ICl=product2 (k=1.90±0.15)×10−12s−1. The rate coefficients of the reaction CH3+CH3ICl and CH3I+CH3ICl has been made in the present work. The experimental results has been studied by two method (1) phase locked and (2) burst mode.

Structure and valence properties of ceria films synthesized by laser ablation under reducing atmosphere

Film thicknesses, the oxidation state of metal and structural behaviour have important impacts on CeO2 film properties. CeO2 films have been deposited on Si substrates using pulsed laser deposition under various pressures of He–H2 gas mixture. A systematic study has been made regarding the influence of various parameters both on the surface composition and on the structure of the deposited films. The effects of the background pressure, the composition of the gas, the target–substrate and the radial distance have been studied. The most important parameter for the control of the Ce3+ content is the target–substrate distance. A distance of under five centimetres led to the formation of a poorly crystalline film with high Ce3+ content. A greater distance led to the formation of well crystallized CeO2 films.

Influence of He Buffer Gas Pressure on Cs Atomic Polarizability

All optical cesium (Cs) atomic magnetometer with high sensitivity is an important technique to detect weak magnetic field. The Cs vapor cell is filled with He buffer gas to reduce spin relaxation rate. However the pressure of He also influences the Cs atomic polarizability due to pressure broadening effect. In this work, the principle of all optical Cs atomic magnetometer is analyzed. The rate equation is used to calculate Cs atomic polarizability as the pressure of He is about 100Torr and pure Cs vapor cell. The calculation shows that higher pressure of He buffer gas can decrease Cs atomic polarizability without considering spin-exchange collisions, as the pump beam frequency is locked to Cs D1 transition F=3F=4.

Atomistic study of the thermodynamic equilibrium of nano-sized helium cavities in βSiC

The estimation of the number of inert gas atoms contained at equilibrium in microscale bubbles in a solid usually relies on a well-known formula equilibrating the internal pressure of He to the surface energy of the bubble. This approach evidences a strong variation with temperature of He content for a given bubble. At the opposite, at the Angstrom scale, ab initio calculations for He contained in vacancy assemblies neglect temperature effects. In this work, empirical potential molecular dynamics simulations are used to study, in the case of helium inserted in cubic silicon carbide, the variation of the He content of sub-nanoscale cavities with temperature. To do so free energy for He atoms inserted in cavities made of a few vacancies (up to 29) are calculated. One then evidences the existence of a sub-surface segregation in interstitial sites close to the surface of the cavity. The variation of the He content with temperature is observed to be negligible at the nanoscale, thus validating the ab initio approach.

Fabrication and Characterization of Magnesium Nanoparticle by Gas Evaporation Method

We have fabricated the Mg nanoparticles by the gas evaporation method. The AFM observation shows Mg nanoparticles fabricated under the several gas pressures of He have the average diameter of 3.6 nm to 8.0 nm. We have studied the influence of the atmospheric oxidation for the chemical state of the Mg nanoparticles by the Mg K-edge NEXAFS technique. The NEXAFS measurement shows that the chemical state of MgCO3 exists on the most lateral surface of the Mg nanoparticles and the degree of atmospheric oxidation depends on the size of Mg nanoparticles. [DOI: 10.1380/ejssnt.2010.246]

Pd/Mg/Pd thin films prepared by pulsed laser deposition under different helium pressures: Structure and electrochemical hydriding properties

Abstract Three-layered Pd/Mg/Pd thin films were prepared by pulsed laser deposition in the presence of helium gas. For Pd layer deposition, the He pressure was fixed at 200 mTorr whereas different pressures of He were used for Mg layer deposition (50, 200 and 600 mTorr). The degree of crystallinity and of (001) texture in the Mg layer increase with increasing He pressure. In addition, the increase in He pressure upon Mg deposition greatly accentuates the roughness of the Mg layer, which induces an extension of the outer Pd/Mg interface region. In contrast, the inner Pd/Mg interface is sharp for all the Pd/Mg/Pd films. The electrochemical hydrogen sorption properties of the Pd/Mg/Pd films are improved by increasing the He pressure for Mg layer deposition. However, the maximum H-solubility in the Mg layer remains low (H/Mg ∼0.26) and is not significantly increased by the presence of the inner Pd layer, indicating that Mg hydride phase is confined in the outer Pd/Mg interface region.

Pressure of stable He–vacancy complex in bcc iron: Molecular dynamics simulations

Molecular dynamic simulation was employed to study the stable state of He–vacancy (He–V) complex in bcc iron. The pressure of He–V complex was calculated using the concept of atomic-level stress. In the case of no initial vacancies introduced in the simulation box, self-interstitial atoms (SIAs) are emitted by the small He cluster. As the number of the He cluster is above a critical value, interstitial-type dislocation loops (I-loop) will be generated. After the interstitial-type defects (SIA or I-loop) were created, it is found that the ratio of He atoms to athermal vacancies keeps nearly constant in the He–V complex.