Molecular Oxygen Ions Research Articles

Effects of Nitrogen and Oxygen Radicals on Low-Temperature Bio-Molecule Processing

The mechanism by which microwave plasma is able to modify the structure and function of proteinaceous molecules is investigated. The biomolecule cystine, a dimer aminoacid, was exposed to microwave surface wave plasma produced in reactive gases, such as oxygen and nitrogen, in different conditions. Except for the physical interactions of the charged particles with the samples and the photophysical reactions induced mostly by ultraviolet radiation, these plasmas contain reactive species which promote chemical interactions. In this study we focus on the changes of biomolecules due to neutral particles inside reactive plasmas. The results proved that the effects of neutrals and charged species are not cumulative. Moreover, it seems that the charged species inside the nitrogen plasma promote nitrogen addition while the outcome of neutral exposure is cleavage. Strong oxidation occurs for oxygen treatments, most reactive species which cause oxygen addition being the oxygen molecular ions O2+.

Luminescence of oxygen molecular ion in neodymium-doped yttria

Pulsed cathodoluminescence spectra of Nd3+:Y2O3 compacts registered after their annealing in air at a temperature above 950°C exhibit a structured band in the range 610–660 nm with four well-resolved components located at wavelengths of 620.6, 630.6, 645.3, and 655.6 nm. At the same time, the lattice parameter of the cubic yttria increases, and the color of samples changes from light blue to yellowish. In addition, the nearly complete absorption of the intrinsic luminescence band of yttria is observed in the range of 380–600 nm with a center at λ = 485 nm. We assume that these effects are caused by oxygen molecular ions O2−, which are formed in cubic yttria due to the penetration of oxygen into natural anion vacancies. The frequencies of vibrations of the ground and excited states of the oxygen molecular ion has been determined.

Electrocatalytic oxygen reduction and hydrogen evolution reactions on phthalocyanine modified electrodes: Electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric monitoring

This study describes electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric monitoring of the electrocatalytic reduction of molecular oxygen and hydronium ion on the phthalocyanine-modified electrodes. For this purpose, electrochemical and in situ spectroelectrochemical characterizations of the metallophthalocyanines (MPc) bearing tetrakis-[4-((4′-trifluoromethyl)phenoxy)phenoxy] groups were performed. While CoPc gives both metal-based and ring-based redox processes, H 2Pc, ZnPc and CuPc show only ring-based electron transfer processes. In situ electrocolorimetric method was applied to investigate the color of the electrogenerated anionic and cationic forms of the complexes. The presence of O 2 in the electrolyte system influences both oxygen reduction reaction and the electrochemical and spectral behaviors of the complexes, which indicate electrocatalytic activity of the complexes for the oxygen reduction reaction. Perchloric acid titrations monitored by voltammetry represent possible electrocatalytic activities of the complexes for hydrogen evolution reaction. CoPc and CuPc coated on a glassy carbon electrode decrease the overpotential of the working electrode for H + reduction. The nature of the metal center changes the electrocatalytic activities for hydrogen evolution reaction in aqueous solution. Although CuPc has an inactive metal center, its electrocatalytic activity is recorded more than CoPc for H + reduction in aqueous solution.

Latitudinal distribution of anomalous ion density as a precursor of a large earthquake

[1] Data obtained by the U.S. satellite DE‐2 are used to investigate possible precursor features in the ionosphere associated with a large earthquake (latitude �33.13°, longitude 73.07°, M = 7.5), which occurred during a moderate geomagnetic disturbance. Atomic oxygen ion and molecular ion distributions show characteristic latitudinal features similar to the well‐known equatorial ionization anomaly (EIA) feature but centered around the earthquake epicenter. We name this the precursor ionization anomaly (PIA). The density minima of both the atomic oxygen and molecular ions are in two latitude zones, depending on the distance from the epicenter. One of the PIA minima aligns with the geomagnetic latitude crossing the epicenter. Another minimum is found along the geographic latitude of the epicenter. These minima are located in an area spanning about 40° in latitude and about 140° in longitude. It is noted that the molecular ion minimum is more clearly defined even when the atomic ion density minimum is not indicated clearly. The ion density reduction seems to be caused by a superposition of natural/quiet time ionospheric eastward electric field and an electric field associated with the earthquake. Although we studied one single event, our careful examination of results suggests that the location and day of occurrence of the PIA can be predicted for some large earthquakes even during moderate geomagnetic disturbance if the satellite orbit is properly chosen.

Breakdown characteristics of air in the lower atmosphere

This study is devoted to an analysis of the ionization and loss of electrons at early stages of discharge development in air at an altitude of 0–12 km. Ionization in an external electric field and background ionization, electron attachment and detachment from atomic and molecular oxygen, charge exchange, and negative ion conversion are considered. The dependence of the process rate constants on pressure is taken into account. It is demonstrated that the electric field at which effective air ionization begins decreases with increasing altitude.

Electronic and vibrational states of oxygen and sulfur molecular ions inside implanted SiO 2 films

The paper presents the results of a low-temperature time-resolved photoluminescence (PL) investigation of thin SiO 2 films implanted with either oxygen or sulfur ions. Both PL and PLE spectra of the samples demonstrate vibronic oscillations which were attributed to the ground and excited states of sulfur- and oxygen-related molecular species. Vibrational frequencies and anharmonicity parameters calculated from the experimental data agree well with known literature. The most intensive excitation is observed in the spectral region of silica matrix excitons. It is established that such high-energy irradiation leads to non-bridging oxygen hole center creation as well as to the luminescence of molecular species. The results obtained on silica film modification could be of interest for future planar waveguides and thin oxide structure design.

Tracking nuclear wave-packet dynamics in molecular oxygen ions with few-cycle infrared laser pulses

We have tracked nuclear wave-packet dynamics in doubly charged states of molecular oxygen using few-cycle infrared laser pulses. Bound and dissociating wave packets were launched and subsequently probed via a pair of 8-fs pulses of 790 nm radiation. Ionic fragments from the dissociating molecules were monitored by velocity-map imaging. Pronounced oscillations in the delay-dependent kinetic energy release spectra were observed. The occurrence of vibrational revivals permits us to identify the potential curves of the ${\mathrm{O}}_{2}$ dication which are most relevant to the molecular dynamics. These studies show the accessibility to the dynamics of such higher-charged molecules.

Autoionization dynamics and Feshbach resonances: Femtosecond EUV study of O2 excitation and dissociation

In this work, we present a time-domain study of the complex, multi-step, evolution of highly excited states of oxygen (O2) that result from EUV photoionization. By monitoring the dissociation of molecular oxygen ions, we show that autoionization cannot occur until the internuclear separation is 30 Å or greater. As the ion and excited neutral atom separate, we directly observe the transformation of electronically bound states of the molecular ion into Feshbach resonances of the neutral oxygen atom. We achieve this by using laser high-harmonics in a femtosecond EUV-IR pump-probe scheme, combined with a triple coincidence reaction microscope measurement. Finally, we show control of the dissociation pathway through IR pulse induced ionization.

First-principles study of cadmium vacancy in CdWO 4 crystal

The structural relaxation, electronic structures and optical properties of CdWO 4 crystal containing cadmium vacancy (CWO: V Cd) are studied by the CASTEP code. The cadmium vacancy ( V Cd) would trap two holes to maintain the local electrical neutrality. The calculated structural relaxation and electronic density of states reveals that the existent form of the hole in CWO: V Cd should be oxygen molecular ion (O 2 3−). Therefore an associated color center [O 2 3−– V Cd–O 2 3−] named as V F center would form in the crystal. The calculated optical absorption spectrum for CWO: V Cd indicates that this V F center would cause an absorption band peaking at about 650 nm with a shoulder at around 400 nm, which is in agreement with the experimental optical absorptions of the blue–grey colored CWO crystal.

A dose dependence study of O2 adsorbed on large Ar clusters

An investigation of the behavior of O(2) molecules in and on O(2)-doped large (N approximately 8000) Ar host clusters has been performed by means of core and valence photoelectron spectroscopy. Data from pure O(2) and Ar clusters, as well as from O(2)-doped Ar clusters, are presented. The experimental data together with calculations of the binding energy shifts of oxygen molecular ions in and on the surface of a large host Ar cluster show that the diffusion behavior has a strong dependence on the doping pressure. We conclude that the oxygen molecules in the doped Ar host do not partake in band formation, since there is clear vibrational resolution in the spectral features stemming from screened O(2) (+) ions. This implies that valence photoelectron spectroscopy can be used to determine the geometrical structure of this and certain, similar, cluster systems.

The structure and time variability of the ring atmosphere and ionosphere

The saturnian system is subject to constant bombardment by interplanetary meteoroids and irradiation by solar UV photons. Both effects release neutral molecules from the icy ring particles either in the form of impact water vapor or gas emission in the form of H 2O, O 2 and H 2. The observations of the Cassini spacecraft during its orbit insertion have shown the existence of molecular and atomic oxygen ions. Subsequent modeling efforts have led to the picture that an exospheric population of neutral oxygen molecules is probably maintained in the vicinity of the rings via photolytic-decomposition of ice and surface reactions. At the same time, ionized products O + and O 2 + ions move along the magnetic field lines and, depending on the optical local thickness rings, can thread through the ring plane or impact a ring particle, the ion principal sink. In addition, collisional interactions between the ions and neutrals will change the scale height of the ions and produce a scattered component of O 2 molecules and O atoms which can be injected into Saturn’s upper atmosphere or the inner magnetosphere. The ring atmosphere, therefore, serves as a source of O 2 + ions throughout Saturn’s magnetosphere. If photolysis of ice is the dominant source of O 2, then the complex structure of the ring atmosphere/ionosphere and the injection rate of neutral O 2 will be subject to modulation by the seasonal variation of Saturn along its orbit. In this work, we show how the physical properties of the ring oxygen atmosphere, the scattered component, and the magnetospheric O 2 + ion source rate vary as the ring system goes through the cycle of solar insolation. In particular, it is shown that the magnetopheric O 2 + ions should be nearly depleted at Saturn’s equinox if O 2 is produced mainly by photolysis of the ring material.

Scattering of light molecules from thin Al 2O 3 films

Molecular oxygen and hydrogen ions were scattered at grazing incidence from various thin Al 2O 3 films. The energy of incident particles was varied from 390 to 1000 eV. For scattered positive oxygen ions, negative ion fractions of up to 17% were recorded. For scattered positive hydrogen ions, the negative ion fractions reached up to 2%. These findings qualify thin films of Al 2O 3 as possible candidates for use as charge state conversion surfaces in neutral particle sensing instruments, which will work in space.

Laser stimulation of low-temperature dissociative recombination of electrons and oxygen molecular ions

A theory of dissociative recombination of slow electrons and molecular ions in a strong monochromatic light field is developed. The theory takes into account interference between various reaction channels and is constructed in a rigid basis adiabatic with respect to rotation (the approximation of a fixed molecular axis). The mathematical apparatus of the theory is based on the stationary formalism of the matrix of radiation collisions, whose poles correspond to “quasi-energy” states of a composite system. Along with transitions into dissociative configurations, field-induced nonadiabatic transitions into bound intermediate states of valence (non-Rydberg) configurations are considered. As a particular application of the theory, the e− + O2+(2Πg) → \( O(^{2s_1 + 1} l_1 ) + O(^{2s_2 + 1} l_2 ) \) reaction is analyzed. A study of this reaction requires detailed information about the potential curves of the states participating in it with taking into account the external electromagnetic field (l and s are the electronic angular momenta and reaction product spins). For this purpose, the general problem is divided into three stages. At the first stage, the theoretical approach is formulated, and at the second stage, the corresponding potential curves are calculated and the main reaction mechanisms are determined. The third stage should include calculations of the total and differential cross sections. This work is concerned with the first two stages; that is, the adiabatic potential curves of the singlet and triplet dissociative states of the O2** oxygen molecule are calculated, a classification of all possible transition types is given, and reaction mechanisms in the presence of monochromatic laser radiation are determined. The frequency regions of external radiation in which these mechanisms are most effective are found.

Limit resolution in low-voltage FIB without correction of chromatic aberration

The resolution in a scanning focused-ion beam (FIB) microscope is determined by two factors: the size of the ion source image on the target and the particle dispersion in the target. A model of low-voltage micro FIB is proposed and calculated, in which the influence of these factors is reduced. It is shown that a resolution of 1.7 nm can be obtained in the analytical mode under target irradiation by helium ions, with detection of potential-emission secondary electrons, and a resolution of 1.3 nm is possible in the technological mode upon reactive etching of a diamond target by molecular oxygen ions.

Observations of molecular oxygen ions in Saturn's inner magnetosphere

We present an analysis of molecular oxygen ion (O2+) abundance in Saturn's inner magnetosphere based on observations made with the Cassini Plasma Spectrometer (CAPS). Using data summed over 23 orbits, we resolve and isolate O2+ counts from the tail of the water group ion mass distribution (W+ [O+, OH+, H2O+, H3O+]) and from background sources. O2+ was initially estimated at ∼1–2% of the total ion population in the inner magnetosphere based on CAPS data from the Saturn orbital insertion pass. Through refined analysis techniques, we have found O2+ to account for just above 0.3% of all W+ ions at L = 4.5, with only minor fluctuations in relative density out to L = 7.5 − 8.0. Beyond L = 7.5, the relative O2+/W+ abundance exhibits a statistically significant increase through L = 10.5, which may indicate a neutral O2 source in the vicinity of Rhea.

Calibration of charge state conversion surfaces for neutral particle detectors

Molecular oxygen and hydrogen ions were scattered off hydrogen terminated diamondlike carbon (DLC) charge state conversion surfaces at incident grazing angles. The energy range of the scattered particles was 390–1000 eV, and the surface roughness of the DLC surface was of the order of 1 Å rms. For all surfaces almost equal angular scattering and negative ion fractions were found within the uncertainties of the measurement. This result supports the fact that charge state conversion with DLC surfaces is a reliable technology for neutral particle sensing instruments. Furthermore, these instruments can work in the laboratory as well as in the harsh environment on board a satellite.The surfaces measured here are used in the IBEX-lo sensor, a neutral particle sensing instrument on the NASA IBEX mission, which is scheduled for launch into orbit around Earth in July 2008.

Emission Spectroscopy and Energy Transfer Process in Atmospheric Dielectric Barrier Discharge in Oxygen

To investigate physical chemical behaviors of dielectric barrier discharge at atmospheric pressure in oxygen, the chemical active species which might exist in plasma were analyzed with the diagnosis technique of optical emission spectroscopy (OES) in oxygen discharge system. From the oxygen atom emission spectra in 500-950 nm, the electronic temperature was calculated by some atomic lines to be (1.02±0.03) eV. The oxygen atmospheric band O2 (b1Σ+g-X3Σ-g) in 760 nm was analyzed, and the rotational temperature (gas temperature) was calculated by its rotational structure to be (650±20) K. The first negative system O+2(b4Σ-g-a4Πu) in 500-700 nm and the Hopfield system O+2(c4Σ+u-b4Σ-g) in 190-240 nm were observed. The research showed that there were various reactive species in plasma of dielectric barrier discharge at atmospheric pressure in oxygen, such as a series excited oxygen atoms, excited oxygen molecules, ground and excited states of oxygen molecular ions. The formation of reactive species concerned many procedures of excitation, dissociation and ionization of oxygen, many energy transfer steps were included in every procedure. The oxygen atoms produced from oxygen molecule dissociation were ruling factor leading to generate reactive species besides electron.

First‐principles study on electronic structures and absorption bands of CaWO4 crystals with interstitial oxygen atoms

AbstractThe electronic structures of CaWO4 crystals with interstitial oxygen atoms are studied within the framework of the fully relativistic self‐consistent Dirac–Slater theory, using a numerically discrete variation (DV‐Xα) method. It is concluded by the calculation that interstitial oxygen atoms combine with two formal lattice oxygen ions forming oxygen molecular ions, which exhibits donor energy level locating in the forbidden bands. The optical transition energy is 3.85 eV, which correspond to the 324 nm absorption bands. It is predicted that the 324 nm absorption bands originate from the interstitial oxygen in CaWO4 crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Computer simulation of PbMoO 4 crystal with interstitial oxygen atoms

The optimal position of the interstitial oxygen atom in PbMoO 4 (PMO) crystal is obtained using computer simulation. Based on the computed results, the total density of states and the partial densities of states for perfect PMO crystal and PMO crystal containing interstitial oxygen atoms are calculated using the DV-Xα program. By analyzing the calculated results it can be concluded that an interstitial oxygen atom could combine with two nearest formal lattice oxygen ions apart from it forming oxygen molecular ions O 3 4 - causing the 430 nm absorption band.

Chemical sputtering of carbon films by argon ions and molecular oxygen at cryogenic temperatures

The experiments demonstrate the existence of a synergistic interaction of molecular oxygen and energetic ions with amorphous carbon leading to enhanced erosion; although the samples, amorphous hydrogenated carbon films, are not gasified by O2 at room temperature, additional ion bombardment at the same temperature leads to erosion rates that drastically exceed those of physical sputtering. Investigation of the temperature dependence from 400 down to 113K shows that the erosion rate increases with decreasing temperature.