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Microwave spectroscopy has long been the standard for sensitive and specific analysis of small organic molecules. Nearly every molecule identified in the interstellar medium was first studied on earth using microwave spectroscopy, and the technique has recently emerged as a powerful mixture analysis tool. Nearly all of this prior work was done in supersonic expansion experiments, which have cold rotational temperatures in the interaction region, but supersonic lab-frame molecule velocities, limiting total interaction time. Here, I present a variety of results using buffer gas cooled microwave spectroscopy, a different approach to achieving rotationally and translationally cold ensembles of neutral molecules. First, I demonstrate that microwave three-wave mixing, a previously demonstrated technique sensitive to molecular chirality, is also sensitive to molecules chiral only by virtue of isotope placement. Second, I discuss application of buffer-gas cooled microwave spectroscopy to the detection and characterization of gauche-isoprene, a species previously uncharacterizable in supersonic expansion techniques. The remaining chapters are dedicated to demonstration and discussion of third and fourth generation buffer gas cells for microwave spectroscopy. First, I make the most precise measurement of the energy differences between two chiral molecules ever conducted using a cryogenic tunable microwave Fabry-Perot resonator. Second, I demonstrate our ability to measure reaction rates between cold molecules, an essential piece of our understanding of interstellar chemistry. Third, I show that using the new BUGBITES technique, we can reach 880 Hz linewidths, a factor of 3 improvement over any other conventional rotational spectroscopy technique. Together, these experiments show the versatility and utility of buffer gas cells for microwave spectroscopy.

Ultra-small SiC nanoparticles with sizes smaller than 10 nm have wide prospects in optoelectronics and biomedical engineering, but challenges in their synthetic methods still limit their practical applications. In this paper, an AC multi-arc plasma device was designed for the continuous gas-phase synthesis of ultra-small SiC nanoparticles. SiC nanoparticles with an average size range of 7–10 nm, abundant surface functional groups, and obvious photoluminescence emission were fabricated by the decomposition of triethylsilane in AC multi-arc plasmas. The synthesized SiC nanoparticles had a typical core-shell structure, whose core was mainly β-SiC and whose shell was covered by a few carbon layers. It was also found that the buffer gas effectively adjusted the particle size, crystal texture, stoichiometric ratio of each element, functional group composition, and photoluminescence. These adjustments were meaningful for the controllable preparation and practical utilization of ultra-small SiC nanoparticles. According to the product characteristics, the formation path of SiC nanoparticles and the influence of buffer gases were proposed.

A novel combination of advanced gas-chromatography and detection systems coupled to a buffer-gas cell was characterized on-line to allow gas-phase chemical studies of accelerator-produced short-lived α -decaying mercury, francium, and astatine isotopes. These were produced in 40Ar- and 48Ca-induced nuclear fusion–evaporation reactions, subsequently isolated in the recoil separators MARS at Texas A&M University, USA, and TASCA at GSI Darmstadt, Germany, before being thermalized in a buffer-gas-stopping cell. From the latter, the nuclear reaction products were extracted into gas-phase chromatographic systems, suitable for registering α -decaying short-lived radionuclides, such as isotopes of superheavy elements. Efficiencies of 21(3)% for 204-209Fr were reached for the extraction into the optimized miniCOMPACT gas-chromatography setup, indicating that this technique enables the identification of isotopes of volatile as well as non-volatile elements. These studies guide the path towards chemical investigations of superheavy elements beyond flerovium, which are out of reach with currently used setups.

Potassium ion channels selectively permeate K+, as well as Rb+ and Cs+ to some degree, while excluding Na+ and Li+. Conformations of alkali metal complexes of Ac-Tyr-NHMe, a model peptide of the selectivity filter in a K+ channel, were previously found to correlate with the permeability of alkali metal ions to a K+ channel by cold ion trap infrared spectroscopy. With an additional temperature-controlled ion trap, we examined the conformations of the alkali metal complexes, allowing the ions to collide with a He buffer gas at different temperatures, prior to spectroscopic investigation. The conformational distribution of the K+-peptide complex shows the most significant variation with temperature, which suggests that this complex has more flexibility when complexed with K+ and suggests lower barrier heights than other metal-peptide complexes. The variability of the conformational distribution with temperature for the ions follows the same order of ion permeability of a K+ channel. This work demonstrates that the additional temperature-controlled ion trap is a powerful tool to explore the conformational landscape of flexible molecular systems.

Due to the greenhouse effect of SF6, the search for new environmentally friendly substitute gases has become an urgent task for the electrical industry. In this article, we have employed a 2-D fluid model to study the characteristic of streamer discharges in the C4F7N-N2 mixture. The discharge process and insulation performance of the C4F7N-N2 mixture with different C4F7N content are compared under the same conditions. In a5.07% C4F7N-N2 mixture, the streamer expands continuously and reaches the top boundary quickly. In 7% and 13.1% C4F7N-N2 mixture, the streamer is gradually stagnated in the simulation domain. The streamer radius shows a decreasing trend, and a low electron density area appears behind the streamer head as the streamer moves forward. The streamer discharge simulation in 50% SF6–50% N2 is also performed to compare its insulation performance to the C4F7N-N2 mixture. The results show that the discharge is suppressed more heavily in 13.1% C4F7N-N2 than in 50% SF6–50% N2. The influence of buffer gas is studied by comparing the discharge process in C4F7N-N2 and C4F7N-CO2 with 13.1% C4F7N content. It is found that the discharge is more easily to a breakdown in C4F7N-CO2 than that in C4F7N-N2 in our simulation configuration. The simulation provides a way to optimizing the buffer gas ratio of new environmentally friendly gases from a microscopic perspective.

This study explores the effect of O 2 as the second-component buffer gas on the power frequency breakdown characteristics and decomposition products of C5-PFK/CO 2 gas mixture. It is found that the breakdown voltage of C5-PFK/CO 2 gas mixture containing 7.5% C5-PFK is about 1.4 times that of CO 2 gas and about 2/3 of SF 6 gas at the same pressure. Although the average breakdown voltage of C5-PFK/CO 2 /O 2 gas mixture is slightly lowered, the addition of O 2 reduces the standard deviation of the breakdown voltage, improving the insulation stability of the C5-PFK/CO 2 gas mixture. The decomposition by products of C5-PFK/CO 2 gas mixture include CO, CO 2 , CF 4 , COF 2 , C 2 F 4 , C 2 F 6 , C 3 F 6 , C 3 F 6 0, C 3 F 8/ , C 4 F 10 , CHF 3 , C3HF7 and other fluorocarbon compounds. C5-PFK/CO 2 /O 2 gas mixture with 4% O 2 produces much CF 4 , C 2 F 6 and less CO after breakdown. It is recommended to add 4 to 6% O 2 in C5-PFK/CO 2 gas mixture to improve the power frequency breakdown characteristics for engineering application.

Electron ionization time-of-flight mass spectrometry (EI-TOF-MS) has been widely used in the fields of chemical, environmental, food, medical and pharmaceutical, etc. Coupling gas chromatography (GC) with EI-TOF-MS yields promising qualitative and quantitative results, and the performance is closely related to with the ion guide devices. A good ion guide device for EI ion source can generate a narrow beam of low-energy ions, resulting in high ion transition efficiency. In this study, an ion transition system for EI ion source with radio frequency quadrupole (RFQ) as the collisional focusing ion guide was developed. The ions in the RFQ could be cooled by collisions with buffer gas molecules and focused to near the axis by a RF field. To determine the parameters of the RFQ, including rod length, rod radius, field radius, RFQ exit orifice diameter, RF frequency, RF amplitude, and other transmission electrode voltages, vacuum design theory, RF quadrupole field theory and SIMION software simulations were applied. The performance of a GC-EI-TOFMS instrument was significantly improved using RFQ as collisional focusing ion guide, and the evaluation results showed that the mass resolution was up to 6500 FWHM (m/z 502), the limit of detection (LOD) was 1 pg of OFN (S/N > 30:1), the mass range was 15–968 amu, the mass accuracy was below 0.01 amu, and the relative standard deviation (RSD) was below 1.5% within one week. This study provided an example to build an ion transition system for mass spectrometry, which had important theoretical and practical significance in design and development of new mass spectrometric instrument.

A theory is developed for the optical pumping of alkali atoms with allowance for Zeeman and hyperfine structures and atomic motion in the model of instantaneous mixing between the Zeeman and hyperfine sublevels in an excited state. The appearance of the angular momentum in the 87Rb and 133Cs atoms that is opposite to the momentum of the photons pumping these atoms is studied. This effect is found to be most pronounced in the D2 line. The influence of the buffer gas pressure and the optical pumping intensity on the features of this effect is analyzed. The influence of the counterpolarization effect on the parameters of high-sensitivity quantum magnetometers is discussed.

In this work, the TiO2@TixCyOz nanocomposite was obtained by adding a buffer gas to the initial mixture of reagents by the pulsed plasma-chemical method. Argon was used as a buffer gas. Pulsed plasma-chemical synthesis was realized using a TEA-500 electron accelerator. The physicochemical properties of the obtained TiO2@TixCyOz nanocomposites (morphology, average particle size, elemental, and phase composition) were studied. It was shown that by changing the buffer gas concentration, it was possible to control the phase composition, particle size, and shell thickness of TiO2@TixCyOz nanocomposites. The values of the band gap were calculated for the synthesized TiO2@TixCyOz nanocomposites. The photocatalytic and adsorption properties of TiO2@TixCyOz nanocomposites were studied.

The reaction kinetics of the isomers of the methylallyl radical with molecular oxygen has been studied in a flow tube reactor at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source storage ring. The radicals were generated by direct photodissociation of bromides or iodides at 213 nm. Experiments were conducted at room temperature and low pressures between 1 and 3 mbar using He as the buffer gas. Oxygen was employed in excess to maintain near pseudo-first-order reaction conditions. Concentration–time profiles of the radical were monitored by photoionisation. For the oxidation of 2-methylallyl (2-MA) and with k(2-MA + O2) = (5.1 ± 1.0) × 1011 cm3 mol−1 s−1, the rate constant was found to be in the high-pressure limit already at 1 mbar. In contrast, 1-methylallyl exists in two isomers, E- and Z-1-methylallyl. We selectively detected the E-conformer as well as a mixture of both isomers and observed almost identical rate constants within the uncertainty of the experiment. A small pressure dependence is observed with the rate constant increasing from k(1-MA + O2) = (3.5 ± 0.7) × 1011 cm3 mol−1 s−1 at 1 mbar to k(1-MA + O2) = (4.6 ± 0.9) × 1011 cm3 mol−1 s−1 at 3 mbar. While for 2-methylallyl + O2 no previous experimental data are available, the rate constants for 1-methylallyl are in agreement with previous work. A comparison is drawn for the trends of the high-pressure limiting rate constants and pressure dependences observed for the O2 recombination of allylic radicals with the corresponding reactions of alkyl radicals.

A recently introduced technique based on MALDI with laser-induced postionization (PI), also named MALDI-2, increases the ion yields for numerous classes of lipids, metabolites, and carbohydrates in MALDI-MS imaging experiments under certain experimental conditions. Here, we used a semiautomatic LabVIEW-based protocol to investigate and optimize the efficiency of the PI process dependent on four relevant input parameters and a dense parameter grid: pulse energies of the two lasers, delay between the laser pulses, and buffer gas pressure in the ion source. All experiments were conducted with a modified MALDI-2 Synapt G2-S mass spectrometer (Waters) and use of a focal spot size on the sample of 15-17 μm. A wavelength-tunable optical parametric oscillator (OPO) laser served for PI at 260 or 280 nm. The investigated MALDI matrices were: 2,5-dihydroxybenzoic acid (positive ion mode, +), 2,5-dihydroxyacetophenone (+), α-cyano-4-hydroxycinnamic acid (+), norharmane (negative-ion mode, -), and 1,5-diaminonapthalene (-). A porcine brain extract served as lipid standard. In the positive-ion mode, a maximum boost for the generated [M + H]+ species was found with a N2 buffer gas pressure of ∼2 mbar and a delay between the laser emissions of ∼10 μs. Higher optimal delay settings of several 10 μs were registered for the two studied matrices in negative-ion mode. With regard to the laser fluences, best PI efficiencies were reached using maximum available ablation and PI laser pulse energies of up to 25 and 160 μJ, respectively. For analytes not profiting from MALDI-2, best ion signal yields were recorded for ablation laser pulse energies of around 7 μJ, depending on the MALDI matrix. At higher laser pulse energies, sizable fragmentation is observed for these ions. The PI laser pulse energy did not have any influence on the ion signals of these species. For optimal ion yield of all analyte species, best results were obtained with an ablation laser pulse energy of ∼7 μJ and a PI laser pulse energy of ∼160 μJ. Our comprehensive data set provides valuable insight into the mechanisms underlying the MALDI-2 processes and could help to further optimize this emerging technique.

The study of the vibrational dependence of H2O polarizability α is based on the comparison of experimental and calculated line shifts induced by argon, nitrogen, and air pressure in different H2O vibrational bands. The dependence of α on the internal coordinate θ, which describes large-amplitude bending vibration in the molecule, is expressed by a power series. The coefficients of the power series were selected so as to ensure the best agreement between the calculated matrix elements 〈ψn|α(θ)|ψn〉 and the polarizability values α(n) derived from the analysis of experimental H2O absorption line shifts in nν2 vibrational bands by nitrogen, oxygen, air, and argon pressure. The rotational contributions in the effective H2O polarizability are calculated and discussed. The α(θ) representation found is compared with ab initio calculations.

C 3 F 7 CN/CO 2 and C 3 F 7 CN/N 2 gas mixtures are regarded as the most promising substitutes to replace SF 6 in high-voltage devices. In this study, a measurement system for steady state Townsend (SST) method was built and the effective ionization coefficient (α), density normalized critical electric field (E/N) and the coefficient of synergistic effect (C) of the two gas mixtures were obtained. The effective ionization coefficients were measured in the variety of E/N between 150 and 1050 Td (1 Td = 10−21 V-m2). The density normalized critical electric fields ((E/N) lim ) of gas mixtures shows nonlinear increase with the increase of C 3 F 7 CN concentration, from 0 to 100%. It was found that the (E/N) Um of C 3 F 7 CN/N 2 gas mixture is higher than that of C 3 F 7 CN/CO 2 at a C 3 F 7 CN mole ratio lower than 60.5%, and the difference between two gas mixtures becomes very small when the ratio of C 3 F 7 CN is higher than 60.5%. The synergistic effect rises sharply and then decreases slowly with increasing ratio of C 3 F 7 CN. When the mole ratio is 6.9% and 6.6%, the coefficients of synergistic effect in C 3 F 7 CN/CO 2 and C 3 F 7 CN/N 2 gas mixtures reach to the highest point respectively. In the range where the ratio is less than 20.5%, the synergistic effect of gas mixture using N 2 as the buffer gas is stronger. This paper will supply the basic data for C 3 F 7 CN/CO 2 and C 3 F 7 CN/N 2 gas mixtures measured by SST.

Strong environmental dependence is an intractable problem for vapor cell clocks, for which the high-temperature sensitivity of the physics package is considered one of the dominant reasons. In this paper, we report the design and realization of a low-temperature-sensitive physics package for vapor cell clocks. The physics package comprises three layers of magnetic shields, three layers of heating ovens, and the cavity-cell assembly. The cavity-cell assembly employs a compact magnetron-type cavity and a Rb vapor cell sealed with N2-Ar mixed buffer gas. The dependence of the clock frequency on temperature fluctuation is evaluated to be 2 × 10−11/°C. In pursuit of the stable temperature, a three-stage temperature regulator is implemented on the physics package. It adopts a combination of open and closed-loop control to address the problem of significant thermal coupling between the heating ovens. Under a laboratory environment, the measured Hadamard deviation of the temperature variation is 4 × 10−5 °C in 1 day of averaging.

The rate coefficient for the unimolecular decomposition of CH3OCH2, k 1, has been measured in time-resolved experiments by monitoring the HCHO product. CH3OCH2 was rapidly and cleanly generated by 248 nm excimer photolysis of oxalyl chloride, (ClCO)2, in an excess of CH3OCH3, and an excimer pumped dye laser tuned to 353.16 nm was used to probe HCHO via laser induced fluorescence. k 1(T,p) was measured over the ranges: 573–673 K and 0.1–4.3 × 1018 molecule cm−3 with a helium bath gas. In addition, some experiments were carried out with nitrogen as the bath gas. Ab initio calculations on CH3OCH2 decomposition were carried out and a transition-state for decomposition to CH3 and H2CO was identified. This information was used in a master equation rate calculation, using the MESMER code, where the zero-point-energy corrected barrier to reaction, ΔE 0,1, and the energy transfer parameters, ⟨ΔEdown⟩ × T n, were the adjusted parameters to best fit the experimental data, with helium as the buffer gas. The data were combined with earlier measurements by Loucks and Laidler (Can J. Chem. 1967, 45, 2767), with dimethyl ether as the third body, reinterpreted using current literature for the rate coefficient for recombination of CH3OCH2. This analysis returned ΔE 0,1 = (112.3 ± 0.6) kJ mol−1, and leads to k 1 ∞ ( T ) = 2.9 × 10 12 $k_{1}^{\infty}(T)=2.9\times{10^{12}}$ (T/300)2.5 exp(−106.8 kJ mol−1/RT). Using this model, limited experiments with nitrogen as the bath gas allowed N2 energy transfer parameters to be identified and then further MESMER simulations were carried out, where N2 was the buffer gas, to generate k 1(T,p) over a wide range of conditions: 300–1000 K and N2 = 1012–1025 molecule cm−3. The resulting k 1(T,p) has been parameterized using a Troe-expression, so that they can be readily be incorporated into combustion models. In addition, k 1(T,p) has been parametrized using PLOG for the buffer gases, He, CH3OCH3 and N2.

We describe a microwave (MW) magnetic-field detection technique based on the Rabi resonance of a Cs-buffer gas vapor cell. Inside the vapor cell, alkali atoms interact with MWs radiated from an antenna through an open-ended rectangular waveguide. We obtained the Rabi resonance line shape, which determines precisely the Rabi frequency of the MW magnetic field with a phase modulation frequency. For various vapor cells, a detailed characterization of several experimental parameters and a theoretical analysis were performed. The optimal laser intensity and the cell temperature that maximize the Rabi resonance amplitude are obtained. Moreover, the cell-temperature-based frequency shift of the Rabi resonance was investigated. These experimental results are important in developing future International System of Units-traceable MW magnetic field sensors and an MW power standard.

Funding Information: The part of the work related to the arc-discharge plasma-chemical synthesis, structural and electrochemical analysis was supported by the RSF grant 20-79-00085 . The part of the work related to the calculation and numerical simulation of the gas-dynamic processes was supported by the state contract with IT SBRAS. Publisher Copyright: © 2021 It was found that the variation of a buffer gas pressure in the reactor chamber can control the structure of the synthesized materials during electric arc sputtering of composite Sn–C electrodes. The gas dynamic model calculated by the direct simulation Monte Carlo method shows that the buffer gas pressure affects the local parameters of tin and carbon vapor condensation. As a result, Core-shell Sn–SnO2 nanoparticles packed in a carbon matrix with various structural properties have been synthesized. It has been found that an increase in the buffer gas pressure leads both to an increase in the average size of the synthesized nanoparticles and to the formation of a more disordered structure of carbon. In turn, the tin and carbon structure affects the electrochemical characteristics of the synthesized Sn–C composite as anode materials for lithium-ion batteries.

For a thermal dusty plasma with metal particles, the relations of the particle charge to the temperature of the system and the particle size have been obtained using a two-plasma model and the approximation of a rectangular potential well. The number densities of electrons and ions in the plasma have been determined for various temperatures and particle sizes of the system. It has been shown that in the case of metal particles, the ionization of the buffer gas leads to underestimation of the charge in comparison with the case when the ionization of the gas is negligible.

Due to the core assumptions of kinetic theory and the drive toward realizing reproducible gas-phase measurements, ion mobility experiments are commonly conducted in the presence of an inert, neat buffer gas, usually nitrogen or helium. Mixing drift gases in defined, static ratios can provide useful information not only for optimizing the separation of analytes but also for defining the interaction between the ion and neutral particle. In a foundational effort, we seek to validate the role of the drift gas polarizability on the observed mobility of the ions by systematically mixing drift gases to discretely access a range of bulk gas polarizabilities not given by pure drift gases. Compared to historical efforts to probe the role of polarizability on the ion-neutral collisional cross section where a linear relationship was assumed, the data collected in the present effort clearly illustrate a quadratic dependency of the ion-neutral particle collision cross section and polarizability (R2 > 0.999). When translating these data into the mobility dimension, we illustrate that the gas-phase mobility of polyatomic ions conforms to Blanc's law. These observations combined with considerations related to Langevin's polarization limit provide an experimental mechanism to estimate to what degree an ion-neutral interaction conforms to either the hard-sphere or induced-dipole model. To support these observations, additional comparisons are made with the respective reduced masses, polarizabilities, and mobilities of ions in mixtures where different degrees of hard-sphere interactions are present.

Recent studies have demonstrated that fluoronitrile (FN) Novec™ 4710 and fluoroketone (FK) Novec™ 5110 show higher dielectric strength than SF 6 . These gases can be mixed with a buffer gas such as CO 2 and technical air to have suitable dielectric properties for high voltage insulation applications. With the rapid growth of HVDC networks, these gases may replace SF 6 in future HVDC apparatus such as GIS/GIL. This paper focuses on the study of the partial discharge (PD) characteristics of SF 6 and SF6 alternative gases with a protrusion defect on the high voltage conductor with DC voltage. The results show that, for calculated equivalent SF 6 dielectric strength under homogeneous electric field, a difference in terms of partial discharge inception voltage was noted for gas mixtures compared to SF 6 . This difference may be due to the influence of gas pressure under highly inhomogeneous electric field. FN-CO 2 and FK-Air mixtures showed the highest PD amplitude under positive polarity while it was higher under negative polarity for SF 6 . Moreover, PD repetition frequency is higher for SF 6 investigated alternative gases. The results can help for the design of SF 6 free HVDC GIS partial discharge monitoring system.

A low-energy branch is under development for the MARA vacuum-mode recoil separator at the Accelerator Laboratory of the University of Jyvaskyla. This development will allow for the study of proton-rich nuclei through laser ionisation spectroscopy and mass measurements. After stopping and extraction from a buffer gas cell, the ions of interest will be accelerated and transported to dedicated experimental setups by an ion transport system consisting of several focusing, accelerating and mass-separating elements. This article presents the current design and simulations for the ion transport.

Thermalization of fast ions in a buffer gas provides a method to transform the high-energy, exotic beams produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory (NSCL) into low-energy beams. The process includes slowing down the fast exotic beams in solid degraders combined with momentum compression and removal of the remaining kinetic energy by collisions with a buffer gas. The original beam thermalization area for mass measurements at the NSCL was reconfigured to accommodate a new momentum compression beam line, a large radio-frequency (RF) gas catcher constructed by Argonne National Lab and a low-energy beam transport system. A large variety of exotic isotopes produced by projectile fragmentation and selected by the A1900 fragment separator was thermalized in the 1.2 m long gas catcher filled with helium at approximately 100 mbar. The ions were guided to an extraction nozzle with a combination of electrostatic and RF potentials and ejected by the gas flow. A novel RF ion guide was used in a differential pumping system to remove the helium and transport the ions into ultrahigh vacuum. Finally, the ions were accelerated to 30 kV for transport to various experiments. The distribution of the thermalized ions among chemical adducts is one of the operational challenges. The important steps implemented to minimize the production of the chemical adducts in the gas catcher are discussed. The operational status of the facility and some example results from characterization of the gas catcher operation with 37 K and 47 K beams are presented.

The ability to use molecular hydrogen, H2, as a buffer gas in spin exchange optical pumping of noble gases enables the production of hydrogen gas containing a low percentile (5%) of hyperpolarized ...

Carbon nanotubes are obtained using chemical vapor deposition (CVD) equipment via the pyrolysis of natural gas in the presence of nanoscale iron. The influence of various parameters on the yield of nanomaterials synthesized is studied, and we find that the yield of nanocarbon increases with an increase in the pyrolysis temperature from 650 to 850°C. At the same time, the introduction of argon, which acts as a buffer gas, into the reactor significantly increases the yield of carbon nanotubes. The samples synthesized are studied by physical methods.