Metastable Oxygen Atoms Research Articles

Pentagon rules on media access to the Persian Gulf War

A high dispersion spectroscopic observation of Comet 116P/Wild 4 was performed on June 10, 2003, using the High Dispersion Spectrograph (HDS) on Subaru Telescope, when the comet was at 2.4 AU from the Sun. Three forbidden oxygen emission lines in optical region, the green line at 557.7330 nm (from 1S to 1D meta-stable state) and the red doublet lines at 630.0304 and 636.3776 nm (from 1D meta-stable state to 3P state) were observed. The oxygen atoms in meta-stable state are considered to be generated by the photo-dissociation of parent molecules such as H2O, CO, CO2, etc. H2O molecule is usually thought as the most dominant source of these oxygens in meta-stable state when a comet is at around 1 AU from the Sun. However, since the Comet 116P/Wild 4 was located at 2.4 AU far from the Sun at the observation, CO and/or CO2 could be a possible main source(s) of meta-stable oxygen atoms rather than H2O. The ratio between red doublet lines (630.0304 nm relative to 636.3776 nm) derived from our result is 2.94 ± 0.07, and the ratio of green line to the red doublet lines is 0.155 ± 0.007. The ratio of green to red doublet lines, which indicates the ratio of O(1S) to O(1D), give us a clue to distinguish the source of meta-stable oxygen atoms from different parent molecules. Considering the abundance of CO is comparable to or smaller than CO2, CO2 could be thought as the parent molecules of the meta-stable oxygen atoms as well as H2O. The number ratio of CO2/H2O within our observational aperture is discussed in this paper.

The yield of metastable atoms through dissociative recombination of O+2 ions with electrons

The yield of metastable oxygen atoms through dissociative recombination of O+2 ions with electrons has been studied using a plasma flow tube experiment. For O+2 with high vibrational excitation (around v=9) it was found that half of the oxygen atoms are formed on the O(1D) state and that the branching ratio toward O(1S) is large (∼0.4). Using Xe+ instead of Ar+ as precursor ions, it was shown that the O(1S) yield is much less for ions with low vibrational excitation. However, the present experimental results are not compatible with the extremely low theoretical value of this yield which was reported recently for O+2 (v=0).

Production d'atomes métastables O ( 5S) dans un plasma d'oxygène induit par microondes

The production of O ( 5 S) metastable oxygen atoms in a microwave induced plasma is studied. The density of metaslable atoms is measured by atomic absorption in the pressure range of 0.2 to 15 torr. Oxygen dilution by noble gases (He, Ar, and Kr) produces a variation of the steady-state concentration of the metastable atoms providing a monitoring technique to control O ( 5 S) concentration at constant flow, pressure and microwave power. The maximum O ( 5 S) concentration measured amounts to 1.8 × 10 11 cm −3 when helium is used as diluant at 4 torr and for a 10% O 2-90% He mixture whereas a typical concentration in pure oxygen at the same pressure is lower than 2 × 10 10 cm −3. A qualitative analysis of the results shows that the electron temperature seems to play a more important role in the O ( 5 S) formation rate than the electron density does.

GJfactor of metastableS25atomic oxygen using a time-of-flight, atomic-beam magnetic-resonance method

A time-of-flight, atomic-beam magnetic-resonance method was used to compare the ${g}_{J}$ factor of $2{p}^{3}3s^{5}S_{2}$ atomic oxygen with the ${g}_{J}$ factor of metastable $2^{3}S_{1}$ atomic helium in magnetic fields of 3209 and 4228 G. The metastable oxygen and helium atoms were produced in a pulsed radio-frequency discharge source and after traversing the apparatus were detected by electron emission from a tungsten surface. By collecting data only in a given interval of the time-of-flight distribution the $\mathrm{O}(^{5}S)$ and $\mathrm{He}(^{3}S)$ states were isolated from other discharge products. From 158 pairs of resonances taken with four relative field and hairpin orientations the atomic magnetic $g$ factor is ${g}_{J}(^{5}S_{2}, ^{16}\mathrm{O})=\frac{{\ensuremath{\mu}}_{J}}{J}=\ensuremath{-}2.0020910(10)$.

Kinetics of ozone photochemistry

The photolysis of ozone in the u.v. Hartley Band produces metastable oxygen atoms and molecules. At wavelengths shorter than 3100 A the primary quantum yield is probably unity but greater uncertainty exists about its value at longer wavelengths. At 2500 A, O2(1Δg) is produced with near unit efficiency and there is some evidence that singlet O2 is also a primary prduct at the short wavelenght end of the Huggins band. O2(1Σg+) is not a primary photolytic product at 2500 A but is produced as a secondary product from the rapid reaction of O(1D) with ground state O2. O(1D) reacts rapidly with O3 although the nature of the products of this reaction has not been unequivocally established and there is now strong evidence against the occurrence of energy chains in dry ozone. The reaction of O(3P) atoms with O3 has been found to have an activation energy of 4.4 kcal mole−1.

Energy Spectra of Metastable Oxygen Atoms Produced by Electron Impact Dissociation ofO2

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Time-of-Flight Spectroscopy of CO2 Photodissociation in the Vacuum Ultraviolet. Electron Emission from Cesium Surface by Metastable Singlet Oxygen Atoms

Time-of-flight spectroscopy has been employed in conjunction with metastable photofragment detection by electron emission from metal surfaces to study the photodissociation of CO2 in the vacuum ultraviolet at wavelengths longer than 1050 Å. Irradiation was performed by unfiltered light. However, some wave-length selection was provided by the CO2 absorption itself and by choice of window material, LiF and CaF2. The metastable detector was coated with cesium. The photodissociation, CO2 + hυ→CO(X 1Σ)+O*, has been observed where O* can be O(1S) and/or O(1D) only. The result implies that the deactivation of metastable singlet oxygen atoms at a cesium surface produces electron emission. The analysis of the flight time distribution of O* shows that in the wavelength range from about 1160–1050 Å more than 50% of the dissociation leads to internally excited CO(X 1Σ) with considerable amounts of vibration-rotation energy.

Dissociation by Electron Impact of Oxygen into Metastable Quintet and Long-Lived High-Rydberg Atoms

Excitation of O2 by low energy electrons leads to its dissociation with the formation of metastable oxygen atoms. The metastable atoms which have been detected are in the 3s5S0 state at 9.14 eV and in long-lived high-Rydberg states. A molecular beam time-of-flight method is used to measure their translational energy. Electron impact excitation functions are given for the formation of metastable atoms. High-Rydberg atoms result from dissociation of initially formed high-Rydberg molecules. Because a high-Rydberg molecular orbital is nonbonding, dissociation is determined by states of the core O2+ ion. This mechanism is supported by general agreement between the observed kinetic energy distribution of high-Rydberg atoms and the kinetic energy distribution of O+ from dissociative ionization of O2. The fragment kinetic energy distributions are discussed in terms of known and predicted states of O2 and O2+.

A cross-spectral method for determining the mean lifetime of metastable oxygen atoms from photometric observations of quiet aurorae

Brightness fluctuations of the [OI] 32 and N 2 +( B 2∑ u + — X 2∑ g +; 0-0) emissions occur “almost always” in quiet auroral forms. A cross-spectral method of analyzing the photometric data is described by which the mean lifetime of the 1 S 0 level of OI is determined. The results obtained from data recorded at Saskatoon are comparable to those obtained from active forms with other methods by previous workers. Fluctuations of the brightness of these two auroral emissions are presented which indicate the spectral characteristics of the fluctuations in quiet-form aurorae. There are some indications that the mean life of the 1 S 0 level is related to the frequency of the brightness fluctuations in the N 2 +( B 2∑ u + — X 2∑ g +; 0-0) emission. If a direct relationship between the mean lifetime and auroral height can be established, the crossspectral method provides an excellent means for auroral height determinations.

Excitation of the auroral green line in nitrogen afterglow

Production of the auroral green line of OI ( 1D −1S , 5577 Å) is observed during long (30 sec) afterglows in a static system containing nitrogen and small amounts of oxygen. Relative to the intensities of the N 2 1st positive bands, the measured intensities of 5577 Å and the NO β bands increase with time. The long period of observation definitely eliminates the initial discharge as a possible source of the metastable oxygen atoms, and their chemical excitation in the afterglow volume is established. A probable process consistent with observations is that involving collision of N atoms with vibrationally excited NO molecules. This mechanism is discussed as a possible source of 5577 Å in the airglow.

Excitation of the Auroral Green Line in Nitrogen Afterglows

Production of the auroral green line of OI (1D—1S, 5577 A) is observed during long (30-sec) afterglows in a static system containing nitrogen and small amounts of oxygen. Relative to the intensities of the N2 1st positive bands, the measured intensities of 5577-A and the NOβ bands increase with time. The long period of observation definitely eliminates the initial discharge as a possible source of the metastable oxygen atoms, and their chemical excitation in the afterglow volume is established. A probable process consistent with observations is that involving collision of N atoms with vibrationally excited NO molecules. This mechanism is discussed as a possible source of 5577 A in the airglow.

Excitation of the green auroral line of oxygen

The excitation of the green auroral line of oxygen has been studied in a number of discharge tubes containing mixtures of argon and oxygen, and the early results obtained by McLennan for the optimum conditions for obtaining the line have been confirmed. It has been shown that, with discharge tubes passing heavy currents, the line is emitted mainly from an aureole surrounding the central, heavily ionized part of the gas, and the bearing of this result on the production of other forbidden lines is pointed out. The collision processes involved in the production of metastable oxygen atoms and in the quenching of the auroral line by certain impurities have been considered, and the probable importance of resonant collisions with metastable argon atoms established.

Excitation of the Green Auroral Line

THIS note will be of special interest when compared with my paper on the light of the night sky, published in a recent number of the Physical Review, and with my report before the Pasadena meeting of the American Physical Society, in which I reported the first effectively complete reproduction of the aurora spectrum. On many of the spectra which were photographed during the progress of the above-mentioned experiments, it was thought that there were definite, though weak, indications of the presence of the green auroral line. The failure of the green line to appear with considerable intensity in these experiments was never considered to be serious, since there was ample evidence for the occurrence of collisions between excited nitrogen molecules and metastable oxygen atoms in the states which are involved in the emission of the green line. Since the state on which the green line originates is metastable, it is not at all surprising that the line was either absent or missing in these experiments.