Formation Of Molecular Species Research Articles

Developments at the CERN-ISOLDE Offline 2 mass separator

The Offline 2 mass separator laboratory is part of the CERN-ISOLDE Offline facilities - a suite of installations required to perform essential quality control on target and ion source units before irradiation at CERN-ISOLDE (Catherall et al., 2017) [1]. The facility is also used for extended preparatory offline studies as a prerequisite before conducting any beam development on-line, especially establishing systematic effects. The Offline 2 separator resembles the on-line CERN-ISOLDE Frontend and employs identical services such as beam instrumentation, gas delivery system, laser ionization and the equipment control system. The facility is able to generate dc as well as bunched non-radioactive beams up to an energy of 60keV. The mass resolving power of the existing 90° dipole mass separator magnet is R≈500 (Warren et al., 2020) [2]. The ion beams can be cooled and bunched in an unmodulated RFQ. In order to study effects of the RFQ buffer gas on the formation of molecular species, a dedicated identification setup is required. We intend to employ a Wien filter downstream the RFQ. This work presents initial beam dynamics simulations through the entire Offline 2 facility to prepare injection into the RFQ. The fields of the RFQ are also shown serving as a basis for field map PIC simulations. Furthermore, we present the status of the emittance meter preparations in front of the separator magnet allowing a comparison to the beam dynamics simulations.

The role of predissociation states in the UV photooxidation of acetylene

We study the photo-induced oxidation of acetylene in two different spectral areas, around 220 and 320 nm. In both spectral areas, the dominant reaction pathways involve the rupture of the acetylene C−H bond, thus primarily generating C2H and H fragments. The released fragments react in O2 presence resulting in glyoxal and other molecular species formation. We observe strong variations in the photooxidation rates, which point to the increased participation of excited, predissociation states, in the oxidation process. Such effects of increased excited state participation in photooxidation should be observed in a variety of photo-induced reactions, affecting the reaction spectral response and eventually the reaction cycles in terrestrial or planetary environments.

Insight into the formation of molecular species in laser-induced plasma of isotopically labeled organic samples.

Recently, the detection of molecular species in laser-induced breakdown spectroscopy (LIBS) has gained increasing interest, particularly for isotopic analysis. In LIBS of organic materials, it is predominantly CN and C2 species that are formed, and multiple mechanisms may contribute to their formation. To gain deeper insight into the formation of these species, laser-induced plasma of (13)C and (15)N labeled organic materials was investigated in a temporally and spatially resolved manner. LIBS on fumaric acid with a (13)C labeled double bond allowed the formation mechanism of C2 to be investigated by analyzing relative signal intensities of (12)C2, (12)C(13)C, and (13)C2 molecules. In the early plasma (<5 μs), the majority of C2 originates from association of completely atomized target molecules, whereas in the late plasma, the increased concentration of (13)C2 is due to incomplete dissociation of the carbon double bond. The degree of this fragmentation was found to be up to 80% and to depend on the type of the atmospheric gas. Spatial distributions of C2 revealed distinct differences for plasma generated in nitrogen and argon. A study of the interaction of ablated organics with ambient nitrogen showed that the ambient nitrogen contributed mainly to CN formation. The pronounced anisotropy of the C(15)N to C(14)N ratio across the diameter of the plasma was observed in the early plasma, indicating poor initial mixing of the plasma with the ambient gas. Overall, for accurate isotope analysis of organics, LIBS in argon with relatively short integration times (<10 μs) provides the most robust results. On the other hand, if information about the original molecular structure is of interest, then experiments in nitrogen (or air) with long integration times appear to be the most promising.

Optical and Electrical Diagnostics of the Effects of Conductivity on Liquid Phase Electrical Discharge

The influence of solution conductivity on liquid phase pulsed electrical discharge was investigated by optical emission spectroscopy in a reactor with point-to-plane electrode geometry. The emission intensities of hydroxyl (OH) radical, hydrogen (H) radical, and oxygen (O) radical were measured using an emission intensity calibration method which used argon gas as a chemical actinometer. Control experiments showed that the addition of argon (Ar) bubbles did not disturb the electrical discharge. It was also found that the Ar emission peak at 750 nm is linearly related to the peaks of the other major species of interest (OH, H, and O) and that the slopes of these lines depend upon the solution conductivities. Therefore, the calibration method allows comparison of the radical generation rates in solutions of different conductivity. Hydrogen (H2), oxygen (O2), and hydrogen peroxide (H2O2) were measured using gas chromatography and spectrophotometric methods. The results showed that OH radicals and H2O2 decreased with increasing solution conductivity consistently with previous results. The intensities of O and H radicals and the generation rates of H2 and O2 were found to have extrema values at a conductivity of 150 μS/cm, and these results in combination with the electrical diagnostics (current waveform and overall power input) and images of the discharge channels imply changes in discharge properties at this conductivity due partly to power input changes from the spark gap. This work clearly demonstrates the close coupling of radical and molecular species formation in liquid phase electrical discharge.

Oxido Pincer Ligands – Exploring the Coordination Chemistry of Bis(hydroxymethyl)pyridine Ligands for the Late Transition Metals

AbstractCoordination of the 2,6‐bis(hydroxymethyl)pyridine‐based oxido pincer ligands RR′pydimH2 [R = R′ = H (pydimH2); R = R′ = Me (pydipH2); R = 2‐tolyl, R′ = Me (pydotH2)] towards late transition metals CoII, NiII, CuII, ZnII, PdII and PtII allows the formation of molecular species (complexes), which exhibit three main structural motifs in the solid state. The two main species are pentacoordinate [(RR′pydimH2)MCl2] and hexacoordinate [(RR′pydimH2)2M]X2, both of which are stable in solution and can be interconverted by changing the solvent polarity. The disproportionation equilibrium [(RR′pydimH2)MCl2] [rlhar2] [(RR′pydimH2)2M]2+ + [MCl4]2– was studied by optical spectroscopy. The chiral ligand pydotH2 allows the formation of chiral complexes. In the square‐planar complexes [(pydimH2)2MCl2] (M = PdII or PtII) the oxido donor functions of the ligands do not take part in the coordination.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

Primary chemical reactions in pulsed electrical discharge channels in water

A mathematical model for the primary chemical processes occurring in 1 J/pulse electrical discharges in water has been developed. The discharge channel is divided into two zones: the core and the recombination region. The core is a very narrow (ca 10 µm) part of the channel where high temperature initiation reactions take place and where the majority of molecular hydrogen and 47% of the molecular oxygen are formed. The recombination region is a 200 µm radius zone where additional reactions such as hydrogen peroxide formation take place. The temperature in the core ranged from 5000 K at the centre to 2000 K at the boundary and the pressure, the only adjustable parameter in the system, was found to be 14 atm. The model describes for the first time how molecular oxygen is formed in an underwater discharge and it is also able to describe the experimentally observed stoichiometry of H2, O2 and H2O2 formation. The concentration and temperature profiles inside the discharge channel as well as a general scheme for the water dissociation and molecular species formation are also reported.

Ion irradiation of asphaltite as an analogue of solid hydrocarbons in the interstellar medium

We present the results of experiments of low temperature ion irradiation of pure asphaltite samples and those covered with water ice layers. Asphaltite (a natural bitumen) was used as an analogue of carbonaceous interstellar grains on which water- rich icy mantles can be formed in the dense and cold phases of the interstellar medium. We simulated irradiation by cosmic ions in the laboratory to study, by in situ infrared spectroscopy, the formation of molecular species in the asphaltite samples and at the interface between the refractory solid (asphaltite) and the water ice mantle. New molecular species were formed at the expense of water molecules and atoms (mainly carbon and hydrogen) from the asphaltite substrate. The vibration modes we detected at low temperature (16 K) include: C-H stretch (carbynoids), C-H asymmetric stretch (acetylene), C-H aromatic stretch, C=O stretch in CO2 ,C ≡O stretch in CO, and C≡C stretch (carbynoids). Some of these species remain stable after warming of the irradiated samples to room temperature.

Ion irradiation of CH 4-containing icy mixtures

We have studied by infrared absorption spectroscopy the effects of ion irradiation with 60 keV Ar 2+ ions on pure methane (CH 4) ice at 12 K and mixtures with water (H 2O) and nitrogen (N 2). Ion irradiation, among other effects, causes the rupture of original molecular bonds and the formation of molecular species not present in the initial ice. Here we present the experimental results and discuss their astrophysical relevance.

Synthesis of Silylborazines and Their Utilization as Precursors to Silicon-Containing Boron Nitride

The reactions of LiSi(SiMe3)3 with Cl(Me)2B3N3(Me)3, Cl2(Me)B3N3(Me)3, (ClBNMe)3, and (ClBNH)3 result in the formation of molecular species (Me3Si)3Si(Me)2B3N3(Me)3, [(Me3Si)3Si]2(Me)B3N3(Me)3, [(Me3Si)3SiBNMe]3, and [(Me3-Si)3SiBNH]3. The new compounds have been characterized by spectroscopic techniques, and a single-crystal X-ray diffraction analysis for [(Me3Si)3SiBNMe]3 has been completed. The monomer (Me3Si)3Si(Cl)2B3N3H3 was also prepared and combined with (Me3Si)2NH in hexane to form an organic solvent soluble oligomer. Pyrolysis of this oligomer provides composites containing BN and an SiXNYCZ phase that suppresses the crystallization of BN.

Synthesis of Silylborazines and Their Utilization as Precursors to Silicon-Containing Boron Nitride⋆

The reactions of LiSi(SiMe3)3 with Cl(Me)2B3N3(Me)3, Cl2(Me)B3N3(Me)3, (ClBNMe)3, and (ClBNH)3 result in the formation of molecular species (Me3Si)3Si(Me)2B3N3(Me)3, [(Me3Si)3Si]2(Me)B3N3(Me)3, [(Me3Si)3SiBNMe]3, and [(Me3-Si)3SiBNH]3. The new compounds have been characterized by spectroscopic techniques, and a single-crystal X-ray diffraction analysis for [(Me3Si)3SiBNMe]3 has been completed. The monomer (Me3Si)3Si(Cl)2B3N3H3 was also prepared and combined with (Me3Si)2NH in hexane to form an organic solvent soluble oligomer. Pyrolysis of this oligomer provides composites containing BN and an SiXNYCZ phase that suppresses the crystallization of BN.

Testing the Limits of ICP‐MS: Determination of Trace Elements in Ground Water at the Part‐Per‐Trillion Level

AbstractAn ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.

Field Study of a Long and Very Narrow Contaminant Plume

AbstractA contaminant plume more than 7,700 meters long and a few hundred meters wide has been delineated using a network of bundle piezometers. The location, concentration, and starting time of the source are well‐defined. The plume occurs in a stratified, highly permeable, sand and gravel aquifer in which the ground‐water flow is unusually steady in direction and magnitude. A ground‐water velocity of 380 meters per annum and a longitudinal dispersivity of 60 to 120 meters are obtained by simulating chloride breakthrough data at 7,700 meters from the source. Simulation of the cross‐sectional distribution of chloride concentrations at 5,500 meters shows the horizontal transverse dispersivity to be at most 0.10 meters. This very small maximum value for horizontal transverse dispersivity is two to four orders of magnitude smaller than values reported in the literature for plumes of similar lengths. It is postulated that the very weak lateral dispersion is due primarily to the steadiness of the ground‐water flow.An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.

Use of Tension Infiltrometer Data with Unsaturated Hydraulic Conductivity Models

AbstractA new method is presented to estimate the relationship between unsaturated hydraulic conductivity and soil‐water pressure using tension infiltrometer data. In this method, both the early transient and the subsequent quasi‐steady stages of the infiltration process underneath a tension infiltrometer disc are analyzed. Our investigation indicates that the infiltration rate at early times closely follows the aquare‐root‐of‐time relationship (Philip, 1969). This behavior permits the evaluation of the sorptivity, which is an integrated measure of soil diffusivity. At later times, three‐dimensional quasi‐steady flow beneath the infiltrometer disc develops, and the Wooding equation for flow from a circular pond is used to evaluate the sorptive number and the saturated hydraulic conductivity. Simple algebraic expressions are introduced to relate the sorptivity and sorptive number to the parameters of the Brooks and Corey model of unsaturated hydraulic conductivity. The method described here extends the utility of tension infiltrometer data to a large class of hydraulic conductivity models and provides an in situ technique to determine suitable parameters values for these models.An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.

A Refraction Statics Method for Mapping Bedrock

AbstractThe bedrock surface beneath unconsolidated eolian sand and garbage at the active Casper, Wyoming landfill was successfully imaged using a refraction statics method. The method employed the summation of common‐detector refraction seismic traces in a manner analogous to common midpoint (CMP) reflection seismic methods. The method produces a seismic time section that is interpreted in much the same way as reflection seismic time sections. The method was very robust in imaging the bedrock surface, even when the refractions were poorly defined on both unprocessed and filtered shot records. Processing of a refraction statics data set is less expensive than CMP high‐resultion reflection processing and does not rely on the detailed graphical constructs of the more commonly used refraction seismic analysis methods. This alternative to more commonly used refraction and reflection seismic methods should be applicable in noisy and otherwise difficult data acquisition areas where the resolution of first breaks and/or reflections is difficult. The summation of data traces enhances the signal to noise ratio allowing direct observation of the bedrock image on the time section. A depth section can be calculated from the final time section. In poor data quality settings, the enhancement of the refraction signal by summation of multiple, common‐detector data traces is the significant advantage of the refraction statics method over other refraction seismic interpretation methods which are dependent on accurately picking refracted arrivals on individual data traces.An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.

Formation of molecular species in X-irradiated bromide and mixed iodide crystals

Abstract The formation of complex ions and molecules created in alkali bromides after X-irradiation at room temperature are studied by means of Resonant Raman Scattering. In NaBr, RbBr and CsBr, Br3 − -type defects are formed. In NaBr only, Clusters of bromine, (Br2)n are also observed. The process of halogen clustering is related to the formation of vacancies during the irradiation in the cationic sublattice. For comparison purpose, it is shown that similar results are obtained in mixed iodide crystal, K x Rb1−x , I, in which iodine aggregates are not observed whereas they are in Ki irradited in similar conditions.

Phase diagram calculations in glass-forming systems—I: Theory

The theory of regular associated solutions is assumed to deal with the formation of molecular species or chemical complexes of general formula A p B q , in a liquid phase. Two approximate treatments are developed, depending on the association strength, in order to treat binary and ternary systems. The solid-liquid equilibrium equations for a ternary system containing A p B q and A r C s complexes are calculated. The success of these treatments for glass-forming liquids is discussed.