Observation Of Molecular Ions Research Articles

The Cosmic-Ray Ionization Rate in the Galactic Disk, as Determined from Observations of Molecular Ions

Abstract We have obtained estimates for the cosmic-ray ionization rate (CRIR) in the Galactic disk, using a detailed model for the physics and chemistry of diffuse interstellar gas clouds to interpret previously published measurements of the abundance of four molecular ions: ArH+, OH+, , and . For diffuse atomic clouds at Galactocentric distances in the range , observations of ArH+, OH+, and imply a mean primary CRIR of per hydrogen atom, where . Within diffuse molecular clouds observed toward stars in the solar neighborhood, measurements of and H2 imply a primary CRIR of per H atom, corresponding to a total ionization rate per H2 molecule of in good accord with previous estimates. These estimates are also in good agreement with a rederivation, presented here, of the CRIR implied by recent observations of carbon and hydrogen radio recombination lines along the sight line to Cas A. Here, our best-fit estimate for the primary CRIR is per H atom. Our results show marginal evidence that the CRIR in diffuse molecular clouds decreases with cloud extinction, , with a best-fit dependence for .

Observation of Molecular Ions and Analysis of Nonpolar Compounds with the Direct Analysis in Real Time Ion Source

Positive ions in the direct analysis in real time (DART) ion source are commonly formed by proton transfer. However, the DART source is similar to atmospheric pressure photoionization (APPI) in that it can produce molecular ions as well as protonated molecules, although the two sources differ in the initial ion formation process. This report discusses some of the factors that influence molecular ion formation in DART and shows how the DART source can be used to analyze "difficult" or nonpolar compounds such as alkanes and cholesterol. Trace reagent ions including NO(+) and O(2)(+)* formed from atmospheric gases are shown to play important roles in DART ionization. The use of the DART source as a gas chromatography/mass spectrometry (GC/MS) interface is demonstrated to show the difference between mass spectra obtained using conditions that favor proton transfer and those that favor molecular ion formation.

Polar cap optical observations of topside (>900 km) molecular nitrogen ions

The Ballistic Missile Defense Organization's (BMDO) Midcourse Space Experiment (MSX) has obtained the first optical observations of molecular ions at very high altitudes above the northern polar cap. Spectra over geomagnetic latitudes ∼ 80°N, at 1300 MLT of the N2+ 1st Negative Bands are identified with a total band intensity of 2.5 kR and an implied number density of 10³ ions cm−3 at 900 km. Additional N2+ transitions from the Meinel bands were also observed. No other permitted optical emissions were observed above 450 km indicating that the source must be solar resonance fluorescence of the N2+ ion. The presence of heavy molecular ions at high altitudes is an indication of the upward flow of ions from the ionosphere into the magnetosphere. These optical observations suggest a new technique for the study of the global structure and temporal variation of plasma energization and transport between the ionosphere and magnetosphere in the polar regions.

Electric currents in the subsolar region of the Venus lower ionosphere

The ion and electron momentum equations, along with Ampere's law, are solved for the ion and electron drift velocities and the electric field in the subsolar Venus ionosphere, assuming a partially ionized gas and a single ion species having the ion mean mass. All collision terms among the ions, electrons and neutral particles are retained in the equations. A general expression for the evolution of the magnetic field is derived and compared with earlier expressions (Luhmann et al., 1984; Cloutier, 1984; Cravens et al., 1984). Subsolar region data in the altitude range 150‐300 km from the Pioneer Venus Orbiter are used to calculate altitude profiles of the components of the current due to the electric field, gradients of pressure, and gravity. Altitude profiles of the ion and electron velocities as well as the electric field, electrodynamic heating, and the energy density are determined. Only orbits having a complete set of measured plasma temperatures and densities, neutral densities, and magnetic field were considered for analysis; the results are shown only for orbit 202. The vertical velocity at altitudes above 220 km is upgoing for orbit 202. This result is consistent with observations of molecular ions at high altitudes and of plasma flow to the nightside, both of which require upward velocity of ions from the dayside ionosphere. Above about 230 km the momentum equations are extremely sensitive to the altitude profiles of density, temperature, and magnetic field.

Observations of molecular ions in the Earth's magnetosphere

The retarding ion mass spectrometer on Dynamics Explorer 1 operating over the polar cap during a large magnetic storm has measured fluxes of up to 106 ions cm−2 s−1 of the molecular ions N2+, NO+, and O2+. These ions were measured beginning low in the satellite orbit (1.1 RE) and extending to about 3 RE geocentric altitude. Near perigee, the ions have a rammed distribution indicating a cold Maxwellian plasma (1000°–2000°K). The molecular ions gradually shift to a field‐aligned distribution at the higher altitudes. An upward flow of 5–10 km/s is found in these field‐aligned measurements. The density of the molecular ions is on the order of 2 cm−3 at all altitudes, and the energy of the ions generally increases as the satellite moves sunward across the southern polar cap. Kinetic energies of at least 20 eV were found at 2.5 RE geocentric distance.

Observation of molecular ions from large peptides using fast heavy ion induced desorption

Mass spectra from bovine insulin (51 aminoac. res., MW 5733) and a neurotoxin (71 aminoac. res., MW 7820) were studied by 252Cf-plasma desorption mass spectrometry ( 252Cf-PDMS). Molecular ions of insulin and the neurotoxin were observed. Fragment ions of insulin relating to the α and β chains and ions corresponding to the dimer and trimer were also detected. The yield of molecular ions from insulin were 0.5% and 0.05% for positive and negative ions respectively.

Ion chemistry in the cometary atmosphere

Dirty ice of a second kind (major components, H2O, CO, and N2; minor components less than several percents, NH3, CH4, and other organic substances such as HCN, CH3CN etc.) is assumed for the composition of volatiles in the cometary nucleus. The consistency with the observations of molecular ions and daughter molecules in the cometary atmosphere is argued by taking into account various ion-molecular reactions and dissociative recombinations. There is a satisfactory agreement for the second kind of dirty-ice model, but the presence of large amounts of CH4 and NH3 is found to be rather in contradiction with observational evidence. A velocity of 8 km s−1 for the hydrogen atoms, derived from analysis of the hydrogen Lyman-alpha corona around comets, is found from the dissociative recombination of H3O+, the dominant constituent of cometary ionosphere, in accordance with H3O++e−→OH+H+H.