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Parkinson, W. H.

Publications and source records attributed to Parkinson, W. H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Formation of ozone by irradiation of oxygen at 248 nanometers

While Slanger et al. (1988) have reported that the 248-nm KrF laser radiation generates ozone from oxygen, despite this wavelength's exceeding of the conventionally accepted photodissociation threshold of 242.4 for the ground electronic state, the initiating mechanism for this ozone formation remains obscure. It is presently suggested that the initiating step is the absorption of the 248-nm radiation by O2. In a reply to the present authors, Slanger et al. indicate that their original experiment should have been performed by introducing pure O2 into a baked cell, with the start time defined by the unblocking of the 248-nm laser.

Freeman, D. E.↗
NASA NTRS1989

Comment on predissociation of O2 in the B state

Theoretical models and experimental data on the predissociation of O2 in the B state are analyzed, with a focus on the results reported by Wodtke et al. (1988). Absorption cross sections in the (11,0) Schumann-Runge band of O2 at 79 K (Yoshino et al., 1987) are matched to curves synthesized from lower fine-structure components for 5Pi(u) and 3Pi(u) predissociative mechanisms. It is concluded that the 3Pi(u) predominance proposed by Wodtke et al. is not justified by the data. In a reply by Wodtke and Huwel, the need for further studies to clarify the apparent discrepancies between absorption and emission spectroscopy is indicated.

Freeman, D. E.↗
NASA NTRS1989

High resolution absorption cross-sections and band oscillator strengths of the Schumann-Runge absorption bands of isotopic oxygen, (0-16)(0-18), at 79 K

Cross-sections of (0-16)(0-18) at 79 K have been obtained from photoabsorption measurements on mixtures of (0-16)2, (0-18)2, and (0-16)(0-18) at various pressures throughout the wavelength region 180.5-195.3 nm with a 6.65 m photoelectric scanning spectrometer equipped with a 2400 lines/mm grating and having an instrumental width (FWHM) of 0.0013 nm. The measured absorption cross-sections of the (0-16)(0-18) Schumann-Runge bands (11.0)-(3.0) are independent of the instrumental width. The measured cross-sections are presented graphically.

Yoshino, K.↗
NASA NTRS1988

Improved absorption cross-sections of oxygen in the wavelength region 205-240 nm of the Herzberg continuum

The laboratory values of the Herzberg continuum absorption cross-section of oxygen at room temperature from Cheung et al. (1986) and Jenouvrier et al. (1986) are compared and analyzed. It is found that there is no discrepancy between the absolute values of these two sets of independent measurements. The values are combined in a linear least-squares fit to obtain improved values of the Herzberg continuum cross-section of oxygen at room temperature throughout the wavelength region 205-240 nm. The results are compared with in situ and other laboratory measurements.

Yoshino, K.↗
NASA NTRS1988

Determination of spectroscopic properties of atmospheric molecules from high resolution vacuum ultraviolet cross section and wavelength measurements

Progress is given on work on: cross section measurements in the transmission window regions of the Schumann-Runge bands of oxygen; the determinations of predissociation linewidths; the theoretical calculation of band oscillator strengths of the Schumann-Runge absorption bands of O-16O-18; the determination of molecular spectroscopic constants; and the combined Herzberg continuum cross sections. The experimental investigations relevant to the cross section measurements, predissociation linewidths, and molecular spectroscopic constants are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (FWHM = 0.0013 nm), suitable for cross section measurements of molecular bands with discrete rotational structure. Such measurements are needed for accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photo-predissociation of O-16O-18 by solar radiation penetrating between the absorption lines of O-16(sub 2).

Parkinson, W. H.↗
NASA NTRS1988

High resolution absorption cross-sections and band oscillator strengths of the Schumann-Runge absorption bands of isotopic oxygen, (O-18)2, at 79 K

Cross-sections of (O-18)2 at 79 K have been obtained from photoabsorption measurements at various pressures throughout the wavelength region 177.8-197.8 nm with a 6.65 m photoelectric scanning spectrometer equipped with a 2400 lines/mm grating and having an instrumental width (FWHM) of 0.0013 nm. The measured absorption cross-sections of the Schumann-Runge bands (14,0) through (2,0) are, with the exception of the (12,0) band, independent of the instrumental width. The measured cross-sections are presented graphically here and are available at wavenumber intervals of about 0.1/cm as numerical compilations stored on magnetic tape. Band oscillator strengths of those bands have been determined by direct numerical integration of the measured absolute cross-sections and are in excellent agreement with these theoretically calculated values.

Yoshino, K.↗
NASA NTRS1988

Absolute absorption cross-section measurements of ozone in the wavelength region 238-335 nm and the temperature dependence

The absolute absorption cross-section of ozone has been experimentally determined at the temperatures 195, 228, and 295 K at several discrete wavelengths in the 238-335-nm region. The present results for ozone at 295 K are found to be in agreement with those of Hearn (1961). Absolute cross-section measurements of ozone at 195 K have confirmed previous (Freeman et al., 1984) relative cross-section measurements throughout the 240-335-nm region.

Yoshino, K.↗
NASA NTRS1988

High-resolution spectra and photoabsorption coefficients for carbon monoxide absorption bands between 94.0 nm and 100.4 nm

Photoabsorption coefficients have been measured for the CO in interstellar clouds at a resolving power more than 20 times greater than previously obtainable. In order to facilitate comparisons, these data have been integrated over the same wavelength ranges as used in Letzelter et al. (1987). It is found that most of the results obtained for bands between 94.0 and 100.4 nm are larger than those of Letzelter; the discrepancy may be attributable to the difference between the resolving powers of the spectrometers used, because the saturation effects associated with low resolution can underestimate absorption coefficient values.

Yoshino, K.↗
NASA NTRS1988

Absolute, Extreme-Ultraviolet, Solar Spectral Irradiance Monitor (AESSIM)

AESSIM, the Absolute, Extreme-Ultraviolet, Solar Spectral Irradiance Monitor, is designed to measure the absolute solar spectral irradiance at extreme-ultraviolet (EUV) wavelengths. The data are required for studies of the processes that occur in the earth's upper atmosphere and for predictions of atmospheric drag on space vehicles. AESSIM is comprised of sun-pointed spectrometers and newly-developed, secondary standards of spectral irradiance for the EUV. Use of the in-orbit standard sources will eliminate the uncertainties caused by changes in spectrometer efficiency that have plagued all previous measurements of the solar spectral EUV flux.

Huber, Martin C. E.↗
NASA NTRS1987

High resolution absorption cross-sections and band oscillator strengths of the Schumann-Runge bands of oxygen at 79 K

Cross sections of O2 at 79 K have been obtained from photoabsorption measurements at various pressures throughout the wavelength region 179.3-198.0 nm with a 6.65-m photoelectric scanning spectrometer equipped with a 2400-lines/mm grating and having an instrumental width (FWHM) of 0.0013 nm. The measured absorption cross sections of the Schumann-Runge bands (12,0) through (2,0) are independent of the instrumental width. The measured cross-sections are presented graphically here and are available at wavenumber intervals of about 0.1/cm as numerical compilations stored on magnetic tape from the National Space Science Data Center, NASA/Goddard. Band oscillator strengths of these bands have been determined by direct numerical integration of the measured cross sections.

Yoshino, K.↗
NASA NTRS1986

Absorption cross section measurements of oxygen in the wavelength region 195-241 nm of the Herzberg continuum

The continuous absorption cross section of oxygen in the region 205-241 nm is studied as a function of path length and oxygen pressure. The technique used to study the continuous absorption cross section is described. Cross section measurements of oxygen in the wavelength region 193-205 nm obtained by Cheung et al. (1984) are applied in this experiment. The measured cross section is analyzed in terms of a Herzberg continuum and a pressure-dependent continuum. The total measured continuum cross section, the cross section involving two molecules of O2, and the Herzberg continuum absorption cross section values are calculated. It is observed that the Herzberg continuum cross section of oxygen values measured at 1 nm intervals in the region 195-241 nm, increase from 6.3 x 10 to the -24th sq cm at 195 nm to a maximum of 6.6 x 10 to the -24th sq cm at 201 nm and then decrease to 0.85 x 10 to the -24th sq cm at 241 nm. The Herzberg values are compared with data from previous investigations and the values correlate well.

Cheung, A. S.-C.↗
NASA NTRS1986

Transition probability of the Al II 2669 intersystem line

Time-resolved observations of the spin-changing, or 'intersystem' emission at 2669.157 A obtained by the ion storage technique are used to measure the transition probability of the 3s2 1S0 - 3s3p 3P1 exp 0 line in Al II. A laser-generated plasma was used as the source of the metastable Al(+) ions. The A-value result obtained for the intersystem transition is 3.33 + or - 0.23 x 10 to the 3rd/sec at the 90-percent confidence level; this value is used to derive two line-intensity ratios which involve the intersystem line as a function of electron density and temperature.

Johnson, B. C.↗
NASA NTRS1986

Determination of band oscillator strengths of atmospheric molecules from high resolution vacuum ultraviolet cross section measurements

An account is given of progress in work on (1) the determination of band oscillator strengths of the Schumann-Runge absorption bands of (16)O2 and (18)O2 from cross section measurements conducted at 79 K; (2) the determination of the absolute absorption cross section of the Schumann-Runge bands of (16)O(18)O from optical depth measurements performed on mixtures of (16)O2, (18)O2 and (16)O(18)O at 79K; and (3) the influence of Schumann-Runge linewing contributions on the determination of the Herzberg continuum absorption cross section of (16)O2 in the wavelength region 194 to 204 nm. The experimental investigations are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (EWHM = 0.0013 nm), uniquely suitable for cross section measurements of molecular bands with discrete rotational structure. Absolute cross sections, which are independent of the instrumental function and from which band oscillator strengths are directly determined, are measured for the absorption bands that are most predissociated. Such measurements are needed for (1) accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photopredissociation of (18)O(16)O by solar radiation penetrating between the absorption lines of (16)O2; (2) elucidation of the mechanism of predissociation of the upper state of the Schumann-Runge bands; and (3) determination of the true shape of the Herzberg continuum cross section.

Parkinson, W. H.↗
NASA NTRS1985

Determination of band oscillator strengths of atmospheric molecules from high resolution vacuum ultraviolet cross section measurements

An account is given of progress during the six month period 1/11/84 to 4/30/85 in work on: (1) rovibronic assignments of the Schumann-Runge bands of O2-18; and (2) optical depth measurements of the Schumann-Runge bands of O2-18. The work summarized above is part of a comprehensive spectroscopic investigation of the absorption wavelengths, rotational line assignments, cross sections, and band oscillator strengths of the Schumann-Runge bands of O2-18 and O-18 O-16 in the wavelength region 175-205 nm. The investigation is conducted at high resolution with a 6.65 m scanning spectrometer/spectrograph which is, by reason of its small instrumental width (FWHM = 0.0013 nm), uniquely suitable for cross section measurements of molecular bands with discrete rotational structure. Absolute cross sections, which are independent of the instrumental function and from which band oscillator strengths are directly determined, will be measured for the absorption bands that are most predissociated.

Parkinson, W. H.↗
NASA NTRS1985

Lyman alpha coronagraph research sounding rocket program

The ultraviolet light coronagraph was developed and successfully flown on three rocket flights on 13 April 1979, 16 February 1980 and 20 July 1982. During each of these flights, the Ultraviolet Light Coronagraph was flown jointly with the White Light Coronagraph provided by the High Altitude Observatory. Ultraviolet diagnostic techniques and instrumentation for determining the basic plasma parameters of solar wind acceleration regions in the extended corona were developed and verified and the understanding of the physics of the corona through the performance, analysis and interpretation of solar observations advanced. Valuable UV diagnostics can be performed in the absence of a natural solar eclipse.

Parkinson, W. H.↗
NASA NTRS1984

Absolute Transition Probabilities of Lines in the Spectra of Astrophysical Atoms, Molecules, and Ions

Progress in the investigation of absolute transition probabilities (A-values or F values) for ultraviolet lines is reported. A radio frequency ion trap was used for measurement of transition probabilities for intersystem lines seen in astronomical spectra. The intersystem line at 2670 A in Al II, which is seen in pre-main sequence stars and symbiotic stars, was studied.

Parkinson, W. H.↗
NASA NTRS1984

Measurements of transition probabilities for spin-changing lines of atomic ions used in diagnostics of astrophysical plasmas

The intensities of ultraviolet, spin-changing, 'intersystem' lines of low-Z atomic ions are frequently used in determinations of electron densities and temperatures in astrophysical plasmas as well as in measurements of element abundances in the interstellar gas. The transition probabilities (A-values) of these lines, which are about five orders of magnitude weaker than allowed lines, have not been measured heretofore and various calculations produce A-values for these lines that differ by as much as 50 percent A radio-frequency ion trap has been used for the first measurements of transition probabilities for intersystem lines seen in astronomical spectra. The measurement procedure is discussed and results for Si III, O III, N II, and C III are reviewed and compared to calculated values. Discrepancies exist; these indicate that some of the calculated A-values may be less reliable than has been beleived and that revisions to the electron densities determined for some astrophysical plasmas may be required.

Smith, P. L.↗