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Observations of the temporal and spatial distribution of N2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N2O. The gas is removed in the atmosphere by photolysis and by reaction with O(1D), and there may be additional sinks in the ocean.
Rocket-ultraviolet spectra of comet West 1975n are reported which were obtained with scanning spectrophotometers in the wavelength range from 1200 to 1300 A. The principal emission features observed include lines of C, O, and C(+), as well as bands of OH, CO, CO(+). The estimated fluxes of the C, O, H, CO, and OH features are found to be consistent with a photodissociation source in which the CO evaporation rate is about one-third that of water. The presence of a large number of carbon atoms in the metastable 1D state is indicated and taken to suggest that dissociative recombination is important near the cometary nucleus, that CO must originate in the nucleus, and that CO is the primary carbon constituent of the comet.
The 3P to 1D electron-impact excitation cross section within the ground configuration of both neutral carbon and silicon is calculated in the distorted-wave approximation of the two-state Hartree-Fock coupled equations. An essential element of the present treatment is that orthogonality to core orbitals is not assumed in deriving equations for the scattering orbitals. A local adiabatic polarization potential is also added to the distorted-wave equations. Both elements are necessary in getting good agreement with close-coupling results for carbon to low impacting energies. The agreement is sufficiently good that predictions for silicon should be accurate to within a factor of 2.
Laboratory and solar data are presented which form the basis for identifying chromospheric Si I absorption lines in UV rocket spectra of the solar limb. Prints of the Si I laboratory spectrum between 1520 and 1570 A are matched with those of the chromospheric spectrum, and a striking line-to-line coincidence is observed. Individual absorption series of Si I covering the 3p(2), 3P, 1D, and 1S ground terms are tabulated in multiplet form over the wavelength range from 1517 to 3069 A. It is noted that many of the solar lines are blended with both other Si I lines and lines of other spectra.
The 3P - 1D electron-impact excitation cross section within the ground configuration of doubly ionized oxygen is calculated in the distorted-wave approximation. An essential element of the present treatment is that orthogonality is not assumed between core and scattering orbitals of the same angular symmetry. Resonance structures are included through the use of quantum-defect theory. Near threshold the effect of an isolated autoionization resonance in the dominant 2D(0) partial wave is found to be important, in agreement with previous close-coupling results.
Observational evidence suggests the presence of solar UV variability in the spectral range 0.175-0.310 micron during the 11-year solar cycle. The present paper reports the results of a study using a steady-state 1-D radiative-convective-photochemical model conducted to determine the response of stratospheric temperatures and O3, O(1D), O(3P), and N2O constituent distributions to UV variability. Results show that concentrations of constituents and the thermal structure may be altered significantly for the altitude interval between 20 and 55 km.
Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.
The rate constants for the deactivation of O(1D) by Xe, Kr, and Ar were measured over the range 110-330 K. Only Xe had a significant temperature dependence. Its Arrhenius expression is (8.5 + or - 1.7) times 10 to the -11th power exp(-103 + or - 52)/RT cu cm/molecule-sec. The rate constants for Kr and Ar are (6.4 + or - 1.3) times 10 to the -12th power and (5.0 + or - 1.5) times 10 to the -13th power cu cm/molecule-sec, respectively. The observed trend in deactivation efficiency, Xe (greatest), Kr, Ar (least), and the observed temperature effects support the results and the spin-orbit interaction mechanism for deactivation given by Husain and co-workers.
Absolute rate constants for the deactivation of O(1D) by CO have been measured at temperatures between 113 and 333 K. A very small temperature dependence is observed and is described by the Arrhenius expression (4.7 + or - 0.9) times 10 to the -11th power exp(126 + or 33)/RT cu cm/molecule-sec, where E is in cal/mol.
At present, there is an apparent conflict between one-dimensional stratospheric photochemistry models used in predicting ozone depletion and average data for stratospheric ozone. This conflict is in three particulars - column density of O3 and ozone density in the regions around 30 km and 50 km altitude. A study of the sensitivity of one such model to the values of reaction rates, boundary conditions, solar intensities, photolysis cross sections, and O(1D) yield parameters reveals that even at the 2-sigma uncertainty limit due to these input parameters, the model does not overlap the data for O3 density at 30 km and 50 km. The data is outside the 1-sigma model uncertainty limit for O3 column density. The study also shows the relative contribution of the various parameters studied to the imprecision in these model results.
Measurements of absolute continuum intensities in the wavelength range 1420-1960 A are presented for the SN subflare of 1973 August 9 and the 2B flare of 1973 September 7, observed from the NRL spectrograph aboard Skylab. Continuum measurements are also given for two active-region plages, which are used for background nonflaring levels. Major enhancement of the flare continuum intensity above the plage backgrounds occurs in the Si I 3P and 1D continua. The observed brightness-temperature minimum of the plages is approximately 310 K above the quiet-sun minimum, and occurs at longer wavelength. The earliest flare brightness-temperature minima are approximately 200 K above the plage minimum, and also at longer wavelength. The observed decay time of the flare brightness temperature, which is comparable to the Solrad 9 X-ray decay time, is much longer than the Ulmschneider radiative relaxation time for the 1973 September 7 flare and marginally longer for the 1973 August 9 flare, suggesting continuous excess heating of the plage temperature minimum region throughout the period of our flare observations.
The spatial distribution of O(1D) in comet Bennett on April 18 implies the existence of an average scale length of about 10,000 km for the source of one or several parents, and an average scale length also of about 10,000 km for their destruction. The spatial distribution of H2O(+) has also been studied sunward and tailward for the same comet and the same date. Two spectra taken 20 minutes apart show recognizable wave patterns moving tailward with a velocity of 17 km/sec. The interaction of the H2O(+) ions with the solar wind gives clues to the onset of the plasma tail. A characteristic time of 800 sec seems to be associated with the instabilities seen at the onset of the tail.
The rise of atmospheric O3 as a function of the evolution of O2 has been investigated using a one-dimensional steady-state photochemical model based on the chemistry and photochemistry of Ox(O3, O, O(1D)), N2O, NOx(NO, NO2, HNO3), H2O, and HOx(H, OH, HO2, H2O2) including the effect of vertical eddy transport on the species distribution. The total O3 column density was found to maximize for an O2 level of 0.1 present atmospheric level (PAL) and exceeded the present total O3 column by about 40%. For that level of O2, surface and tropospheric O3 densities exceeded those of the present atmosphere by about an order of magnitude. Surface and tropospheric OH densities of the paleoatmosphere exceeded those of the present atmosphere by orders of magnitude. It was also found that in the O2-deficient paleoatmosphere, N2O (even at present atmospheric levels) produces much less NOx than it does in the present atmosphere.
The paper presents an experimental technique which measures j/O3-O(1-D)/, the rate of solar photolysis of ozone to singlet oxygen atoms. It is shown that a flow actinometer carries dilute O3 in N2O into direct sunlight where the O(1D) formed reacts with N2O to form NO which chemiluminescence detects, with a time resolution of about one minute. Measurements indicate a photolysis rate of 1.2 (+ or - .2) x 10 to the -5/s for a cloudless sky, 45 deg zenith angle, 0.345 cm ozone column and zero albedo. Finally, ground level results compare with theoretical calculations based on the UV actinic flux as a function of ozone column and solar zenith angle.
Large amounts of long lived N2(A3Sigma) are created by the energy degradation of precipitating solar particles. Laboratory data suggest that in the stratosphere N2(A3Sigma) are efficiently converted into N2O. Through reactions with O(1D), N2O may gradually release NO and thereby influence the long term aspects of stratospheric chemical response. During the daytime, negative ions may transform an active NO(x) into an inactive HNO3. At night both negative and positive ion chemistry generate HO(x). Omission of ionic chemistry results in considerable underestimation of O3 depletion during the initial phases of solar particle events, and thereby introduces significant error in the estimation of the nature of the prompt response.
It is shown that the photodissociation of CO2(1Sigma/g/plus) into CO(X1Sigma/plus/) plus O(1D) with a quantum yield of unity is consistent with all known data on the CO2 ultraviolet absorption band between 1675 and 1400 A. Astrophysical data from the atmospheres of Mars and Venus are not inconsistent with this interpretation and cometary data seem to support it.
The dissociative recombination of vibrationally excited O2(+) ions is studied in light of the possible importance of this reaction in upper atmospheric chemistry. A plasma spectroscopy experiment was performed in a microwave cavity filled by an argon-oxygen mixture, with O(1S) production monitored by measurements of the 5577-A afterglow, the O2(+) density and the electron concentration. Plasma and optical data reveal the predominant afterglow ions to be Ar2(+) and O2(+), with an effective O(1S) dissociative recombination coefficient of 2.1 x 10 to the -8th cu cm/sec, corresponding to a quantum yield of 10%. Experiments with an argon-krypton-oxygen mixture reveal that vibrationally excited O2(+) ions are the chief source of the O(1S) atoms, with a specific recombination coefficient for the dissociation of O2(+)(2 pi g) into O(1S) and O(1D) of 4.2 x 10 to the -9th cu cm/sec. A comparison of the laboratory results with Atmospheric Explorer data on the 5577-A airglow implies that O2(+) ions in the sunlit ionosphere are vibrationally excited to the same degree as in the laboratory, with the vibrational relaxation of these ions much slower than dissociative recombination. Results also predict a dawn-twilight asymmetry in the effective O(1S) yield due to the normal variation of electron content.
The paper presents photolysis absorption spectroscopy experimental results which show rapid vibrational quenching of O2(1 Delta, v not less than 1) molecular oxygen fragments in an atmospheric environment. The reactions of this species were determined by flash photolysis of ozone in the Hartley band combined with absorption spectroscopic detection of O2(1 Delta v equals 0) fragments and resonance fluorescence detection of O(3P). It was shown that rapid vibrational deactivation occurs under atmospheric conditions; in addition, an upper limit was determined for the photolytic channel of the O(1D) + O3 yields O2(1 Sigma) reaction.