The 1s 2s states of negative hydrogen

Term values for the 1s 2s states of H^– are calculated with the use of simple eigenfunction approximations constructed on the basis of available Hartree-type functions for the 1s ² and 2s ² states of the ion. The results seem to support a tentative identification of the interstellar diffuse absorption bands at 4890 and 6180 as due to negative hydrogen.     

The abundance of negative hydrogen in small hot interstellar clouds

The observed intensities of the diffuse interstellar absorption band at 4430 have minimum values, for given stellar distances, that are equivalent to the reddening caused by the small Ambarzumian-type clouds studied by B Strömgren. This indicates that there is no negative hydrogen present between these clouds, which are then identified with the hot H I phase of interstellar matter.The equilibrium density of H^– inside such clouds is calculated from mean densities of neutral hydrogen atoms and free electrons, derived from radio observations for the local region outside the large Orion-arm clouds. The filling factor of the small clouds is taken to be the same as that preserved in the structure of the Gum Nebula from before its ionization. An electron temperature of 3375 K corresponding to the local degree of ionization of the small-cloud hydrogen then leads to a mean density of negative hydrogen equal to 2×10¹³ cm^–2 kpc^–1, in agreement with the observed diffuseband intensities.     

The first height measurements of the negative ion composition of the stratosphere

For the first time, height profiles of the stratospheric negative ion composition are presented. The results are from two nights of balloon borne mass spectrometers and cover an altitude range from 23.8 to 38.9 km. Below approx. 30km, NO^?₃ · mHNO₃ ions are dominant. These are replaced by HSO₄^? · nH₂SO₄ · oHNO₃ ions above this height. There are indications that the most abundant ions above 32 km have masses greater than 280 atomic mass units (amu), the instruments' mass range. The fractional ion count rates as a function of altitude are presented and their significance for neutral trace gas analysis and ion sampling is discussed.     

Ion-acoustic instability in a dusty negative ion plasma

The ion-acoustic instability in a dusty negative ion plasma is investigated, focusing on the parameter regime in which the negative ion density is much larger than the electron density. The dynamics of the massive dust grains are neglected, but collisions of electrons and ions with dust grains in addition to other collisional processes are taken into account. The presence of a population of charged dust can change the frequency of the fast wave, lead to additional damping due to ion–dust collisions, and change the conditions for wave growth. Applications to dusty negative ion plasmas in the laboratory and in space are discussed.     

First model of negative ion composition in the troposphere

A chemical model of negative ions in the troposhere (0–15 km) is presented. This model is an extension of the negative ion composition model in the lower stratosphere (Kawamoto and Ogawa, 1984, Planet. Space Sci. 32, 1223) with some modifications. The computed result shows that the predominant ions are NO₃⁻HNO₃H₂O below 10km and NO⁻₃(HNO₃)₂ above 10km, and that the fractional abundance of cluster ions having a HSO⁻₄ core increases with height below 12km and decreases with height above it. The ions having CO⁻₃ cores are at most 2% in fractional abundance. The other kinds of negative ions are far smaller in fractional abundance than the NO⁻₃, HSO⁻₄ and CO⁻₃ core ions. The result is compared with the two mass spectrometric observed results (Heitmann and Arnold, 1983, Nature, Lond. 306, 747; Perkins and Eisele, 1984, J. geophys. Res. 89, 9649). The problems on the tropospheric negative ions which arose are discussed.     

Ion acoustic solitons in negative ion plasmas with superthermal electrons

Korteweg-de Vries (KdV) equation for electrostatic wave in an unmagnetized negative ion plasma with superthermal electrons is derived using reductive perturbation technique. A generalized Lorentzian distribution (kappa distribution) is assumed for the electrons. The influence of spectral index (kappa) on the soliton is discussed in the presence of the negative ions. It is found that different plasma parameters such as (negative ion temperature, positive ion temperature, negative ion concentration, mass ratio of positive to negative ion) in the presence of superthermal electrons modify the ion acoustic solitary wave structure significantly.     

Synthesis of hydrogen peroxide in water ice by ion irradiation

We present infrared absorption studies on the effects of 50-100 keV Ar⁺ and 100 keV H⁺ ion irradiation of water ice films at 20-120 K. The results support the view that energetic ions can produce hydrogen peroxide on the surface of icy satellites and rings in the outer Solar System, and on ice mantles on interstellar grains. The ion energies are characteristic of magnetospheric ions at Jupiter, and therefore the results support the idea that radiolysis by ion impact is the source of the H₂O₂ detected on Europa by the Galileo infrared spectrometer. We found that Ar⁺ ions, used to mimic S⁺ impacts, are roughly as efficient as H⁺ ions in producing H₂O₂, and that 100 keV H⁺ ions can produce hydrogen peroxide at 120 K. The synthesized hydrogen peroxide remained stable while warming the ice film after irradiation; the column density of the formed H₂O₂ is constant until the ice film begins to desorb, but the concentration of H₂O₂ increases with time during desorption because the water sublimes at a faster rate. Comparing the shape of the 3.5-μm absorption feature of H₂O₂ to the one measured on Europa shows excellent agreement in both shape and position, further indicating that the H₂O₂ detected on Europa is likely caused by radiolysis of water ice.     

Silicon negative ion chemistry in the atmosphere-in situ and laboratory measurements

The results of a rocket-borne mass spectrometer measurement indicate that large concentrations of negative ions exist above the bottom of the atmospheric atomic oxygen layer. A large majority of these ions have a mass greater than 100 amu. In addition, an ion at mass 76 was observed with concentrations too large to be CO₄^?. In order to explain these features, a number of reactions involving silicon oxide negative ions have been measured in a flowing afterglow system. The ion SiO₃^? is produced by reaction of O₃^?, and CO₃^?, with SiO. The SiO₃^? ion is extremely stable and does not react measurably with NO, NO₂, CO, CO₂, O₃ or O. Since meteoroid ablation produces a large silicon input into the atmosphere, it appears possible that the ions observed at mass 76 may be SiO₃^?. Possible production mechanisms for this ion as well as the heavy ions are discussed.     

Upper stratosphere negative ion composition measurements and inferred trace gas abundances

In situ composition measurements of atmospheric negative ions were made at 40.8 km altitude using a balloon-borne mass spectrometer with large mass range and improved mass resolution. The data obtained show marked differences compared to previous data obtained mostly around or below 33 km.It appears that these differences are mostly due to a higher atmospheric temperature, a lower nitric acid vapour abundance and a larger HSO₃-vapour abundance prevailing at the higher altitude.A particularly striking feature is the relatively large fractional abundance of HSO₃-containing cluster ions.Another interesting result is that nitric acid vapour abundances can be inferred from the negative ion composition data with better accuracy than is possible for lower altitudes. The reason being that collisional ion dissociation occurring during ion sampling is less disturbing.The inferred nitric acid vapour abundance for 40.8 km altitude is consistent with current 2-dimensional model calculations.     

Search for neutral hydrogen with high negative velocities ejected from the galactic center

A search for neutral hydrogen in the velocity range –300>V>–1000 km s^–1 has been made in the zone around the galactic nucleus. Observations of 100 points reveal no neutral hydrogen at such high velocities, with brightness temperatures exceeding 0.25 K in the latitude range |b|<1°, and 0.20 K for |b|1°.     

K-dV and mK-dV equations for solitary waves in negative ion plasmas with non-Maxwellian electrons

Ion-acoustic (IA) solitons in a collisionless plasma consisting of positive and negative ions and superthermal electrons are studied by using the reductive perturbation method. The basic set of fluid equations is reduced to Korteweg-de Vries (K-dV) and modified Korteweg-de Vries (mK-dV) equations. It is found that both compressive and rarefactive solitons can be propagated in this system. Also it is shown that at critical concentration of positive ions mK-dV solitons coexist. The effects of spectral index kappa, positive to negative ion density ratio and mass ratio of positive to negative ions on IA solitons structure are also discussed.     

Implications for atmospheric negative ion composition measurements of laboratory ECA studies of sulfuric acid cluster ions

Laboratory studies of electric field-induced collisional activation (ECA) of HSO₄⁻(H₂SO₄)_n cluster ions were made revealing fragmentation via two channels: HSO₄⁻ + H₂SO₄ and HSO₄⁻SO₃ + H₂O. This result suggests that mixed cluster ions of the type HSO₄⁻(H₂SO₄)₁ X with X having a mass of 81±1 amu which were recently detected in the stratosphere may not represent true ambient ions but are fragments formed by ECA of ambient HSO₄⁻(H₂SO₄)_n clusters during ion sampling into the mass spectrometer. Implications for stratospheric negative ion composition measurements are discussed.     

The effect of particle precipitation events on the neutral and ion chemistry of the middle atmosphere: II. Odd hydrogen

A one dimensional time-dependent model of the neutral and ion chemistry of the middle atmosphere has been used to examine the production of odd hydrogen (H, OH, and HO₂) during charged particle precipitation. At altitudes above about 65 km, odd hydrogen production depends on the ionization rate, and the atomic oxygen and water vapor densities. Odd hydrogen production is shown to exhibit diurnal and other time dependent variations during such an event at these altitudes, and the assumption that two odd hydrogen particles are always produced per ionization is reexamined.     

Korteweg-de Vries equation for ion acoustic soliton with negative ions in the presence of nonextensive electrons

Korteweg-de Vries (KdV) equation for electrostatic ion acoustic wave in a three component plasma containing positive and negative ions along with the nonextensive electrons is derived. Fast and slow ion acoustic modes which propagate with different velocities are excited. The effects of variation of quantities like q (nonextensive parameter), Q (mass ratio of positive to negative ion), μ (electron to positive ion number density ratio), θ _i (positive ion to electron temperature ratio) and θ _n (negative ion to electron temperature ratio) have been presented for fast and slow ion acoustic modes. Both compressive and rarefactive solitons are observed. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as on nonextensive electron parameter.     

Investigation of the properties of electrostatic IA solitary wave structures in negative ion magneto-plasmas with superthermal electrons

A rigorous theoretical investigation is carried out in analyzing the excitation of electrostatic ion acoustic (IA) solitary wave (SW) structures in two dimensional negative ion magneto-plasmas with superthermal electrons (following κ type distribution). The Zakharov-Kuznetsov (ZK) equation is derived by employing the well known reductive perturbation method, and the analytical solution of ZK equation assists to find out the SW profiles along with their properties. The consequences of different plasma parameters (regarding our considered plasma system) variation on SW structures has been studied. It is found that magnetic field intensity, superthermal parameter κ and temperature of positive and negative ions as well as their densities significantly modify the basic characteristics (amplitude, width, etc.) of the SW waves. A comparison of the SW structures is also presented when the electrons are Maxwellian to when they are superthermal. The relevance of the findings of this work with astrophysical plasmas is briefly pointed out.     

The light ion trough

A distinct feature of the ion composition results from the OGO-2, 4 and 6 satellites is the light ion trough, wherein the mid latitude concentrations of H⁺ and He⁺ decrease sharply with latitude, dropping to levels of 10³ ions/cm³ or less near 60° dipole latitude (L=4). In contrast to the ‘main trough’ in electron density, N_e, observed primarily as a nightside phenomenon, the light ion trough persists during both day and night. For daytime winter hemisphere conditions and for all seasons during night, the mid latitude light ion concentration decrease is a pronounced feature. In the dayside summer and equinox hemispheres, the rate of light ion decrease with latitude is comparatively gradual, and the trough boundary is less well defined, particularly for quiet magnetic conditions. In response to magnetic storms, the light ion trough minimum moves equatorward, and deepens, consistent with earlier evidence of the contraction of the plasmasphere in response to storm time enhancements in magnetospheric plasma convection. The fact that a pronounced light ion trough is observed under conditions for which the dominant ion O⁺ may exhibit little or no simultaneous decrease appears to explain why earlier studies of the ‘main trough’ in topside distributions of N_e and N_i may, at times, have been inconclusive in relating the total ionization minimum with the mechanism of the plasmapause. In particular, the topside distribution of N_i appears to be the complex resultant of several variables within the ion composition, being governed by the competing processes of chemical production and loss, loss through magnetospheric convection, and large-scale dynamic transport resulting from neutral winds and electric fields. The net result is that in general, the light ion trough, rather than N_i, provides a more fundamental parameter for examining the structure and behavior of the plasmapause.     

The terrestrial hydrogen problem

Current theoretical models do not satisfactorily explain observed variations of the global exospheric atomic hydrogen density distribution. Differences between the mesospheric upward flux and the Jeans escape mechanism indicate that other escape fluxes affect hydrogen density. Observations of latitudinal depletions and an early morning trough in the exosphere can be attributed to the influence of additional escape mechanisms. These variations of the exospheric hydrogen density distribution seem to be correlated with other observed variations in the atmosphere; however, no straightforward explanation has been proposed to date.     

First operation of bulk micromegas in low pressure negative ion drift gas mixtures for dark matter searches

A bulk micromegas micropattern charge readout device has, for the first time, been operated at room temperature in low pressure carbon disulphide vapour. This is a key step opening prospects for use of micromegas readout for large volume negative ion time projection chambers (TPCs) without magnets, such as proposed for directional dark matter detectors and other rare event applications. The dependence of the gain on the amplification field, pressure and drift field has been evaluated. For the available gap size of 75 μm a maximum gain of 1300 ± 120 was achieved in 40 torr vapour with an energy resolution of 22% for 5.9 keV ⁵⁵Fe X-rays. From a fit to the data, the Townsend coefficient gas parameters A and B have been derived. Operation has also been successfully achieved in xenon:carbon disulphide blends over a range of partial and total pressures. A gain of 890 ± 130 at an energy resolution of 35% has been recorded for a 1:1 blend at a total pressure of 80 torr. Possible improvements are discussed in the context of operation in directional dark matter TPCs as a replacement for multi-wire proportional counters.     

First operation of bulk micromegas in low pressure negative ion drift gas mixtures for dark matter searches

A bulk micromegas micropattern charge readout device has, for the first time, been operated at room temperature in low pressure carbon disulphide vapour. This is a key step opening prospects for use of micromegas readout for large volume negative ion time projection chambers (TPCs) without magnets, such as proposed for directional dark matter detectors and other rare event applications. The dependence of the gain on the amplification field, pressure and drift field has been evaluated. For the available gap size of 75 μm a maximum gain of 1300 ± 120 was achieved in 40 torr vapour with an energy resolution of 22% for 5.9 keV ⁵⁵Fe X-rays. From a fit to the data, the Townsend coefficient gas parameters A and B have been derived. Operation has also been successfully achieved in xenon:carbon disulphide blends over a range of partial and total pressures. A gain of 890 ± 130 at an energy resolution of 35% has been recorded for a 1:1 blend at a total pressure of 80 torr. Possible improvements are discussed in the context of operation in directional dark matter TPCs as a replacement for multi-wire proportional counters.