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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Photodissociation of CO2 to produce CO /a super 3 pi/.

Carbon dioxide in a helium buffer at room temperature was irradiated with a photon beam. The wavelengths used in the investigation were in the range from 850 to 1090 A. Phosphorescence from CO Cameron bands was observed. The phosphorescent yield is zero at threshold and increases smoothly to a maximum of about 60% near 900 A. The smoothness of the percentage yield was an unexpected observation and is explained by postulating that the relevant potential surface crossings are outside the Franck-Condon region of carbon dioxide absorption.

Lawrence, G. M.↗
NASA NTRS1972

Production of O/1S/ from photodissociation of carbon dioxide.

The production efficiency was measured with the aid of a method based on the detection of the OI (5577 A) 'green' line. A sodium salicylate screen was used to monitor the intensity of the photons. Measurements at each of several individual wavelengths are conducted. The relative production efficiencies are shown in a graph. The absolute scale for the efficiency was determined in essentially the same way as in the Cameron band work reported by Lawrence (1972).

Lawrence, G. M.↗
NASA NTRS1975

Relative quantum yield for the production of O-atom and S-atom from the photodissociation of OCS in the vacuum UV

The relative efficiencies for two dissociative channels in the vacuum UV photolysis of carbonyl sulphide have been determined using the flash photolysis-resonance fluorescence technique to measure initial yields of atomic oxygen and atomic sulphur. At wavelengths above 105 nm, the dissociation of OCS to form atomic sulphur exceeded that for the formation of atomic oxygen to such an extent that only an upper limit could be placed on the minor process. In addition, the flash photo-excitation of carbonyl sulphide produced a long-lived spontaneous emission in the UV and vacuum UV that might be due to molecular fluorescence from OCS.

Klemm, R. B.↗
NASA NTRS1976

MCSCF potential energy surface for photodissociation of formaldehyde

The ground state potential energy surface for the dissociation of formaldehyde (H2CO to H2 and CO) is calculated with the ab initio MCSCF method with an extended (4-31G) basis set. The location, barrier height, and force constants of the transition state are determined, and the normal coordinate analysis is carried out. The calculated barrier height is 4.5 eV. Based on the calculated quantities, the detailed mechanism of the photochemical dissociation is discussed.

Jaffe, R. L.↗
NASA NTRS1977

Simplified methods for calculating photodissociation rates

Simplified methods for calculating the transmission of solar UV radiation and the dissociation coefficients of various molecules are compared. A significant difference sometimes appears in calculations of the individual band, but the total transmission and the total dissociation coefficients integrated over the entire SR (solar radiation) band region agree well between the methods. The ambiguities in the solar flux data affect the calculated dissociation coefficients more strongly than does the method. A simpler method is developed for the purpose of reducing the computation time and computer memory size necessary for storing coefficients of the equations. The new method can reduce the computation time by a factor of more than 3 and the memory size by a factor of more than 50 compared with the Hudson-Mahle method, and yet the result agrees within 10 percent (in most cases much less) with the original Hudson-Mahle results, except for H2O and CO2. A revised method is necessary for these two molecules, whose absorption cross sections change very rapidly over the SR band spectral range.

Shimazaki, T.↗
NASA NTRS1977

Dispersed fluorescence observations of the CO/A 1Pi to X 1Sigma+/ transitions from photodissociation of CO2

The spectra of vacuum ultraviolet (vuv) fluorescence resulting from the excitation of CO2 by photons from an intense line emission source at 15 wavelengths in the range 449-955 A were obtained. The vibrational population distributions for the v = 0, 1, and 2 levels of the CO(A 1Pi) fragments were obtained at several incident photon wavelengths from 700 to 923 A. At incident photon wavelengths of 901 and 923, the relative intensities of the CO(A to X) bands were determined, permitting examination of the variation of the electronic transition moment with the r centroid.

Phillips, E.↗
NASA NTRS1977

Determination of diurnal average photodissociation rates

The calculation of diurnal average photolysis rates in models of planetary atmospheres can be done efficiently and easily by utilizing the results of empirical numerical fitting procedures. Analytic expressions are given for the ratio of the diurnal average differential photolysis rate to that at noon, as a function of optical depth, latitude and solar declination. The accuracy is better than + or - 6% for all altitudes, all seasons of the year and latitudes up to 60 deg.

Rundel, R. D.↗
NASA NTRS1980

Neutral cometary atmospheres. I - An average random walk model for photodissociation in comets

A method for constructing physically realistic photochemical models, taking into account the isotropic ejection of dissociated molecular fragments as well as radiation pressure acceleration, has been developed using Monte Carlo techniques. The effect of the isotropic ejection, as opposed to the radial motion arbitrarily assumed in Haser's model, is adequately described by a simple average random walk model. It is shown that measured radial (Haser) scale lengths are in fact only lower limits to a range of possible true scale lengths for a given brightness profile, which explains the current discrepancies between observed scale lengths and those predicted by photochemistry.

Combi, M. R.↗
NASA NTRS1980

A simplified method for the calculation of diurnally averaged photodissociation rates

Expressions are given for the calculation of the diurnally averaged transmission of solar flux from a series summation involving relatively few terms and readily available mathematical functions. It is shown that these expressions can be scaled to remove much of the dependence on latitude and solar declination so that at large optical depth, they become asymptotic to a function which depends only on the optical depth at noon and displays an inverse-square-root variation. From this variation, a simple analytic form containing one adjustable parameter is proposed. The functional dependence of this parameter on latitude and solar declination is determined by numerical fitting procedures. The accuracy of the analytic approximation is better than 4.5% for all altitudes, latitudes and seasons of the year.

Boughner, R. E.↗
NASA NTRS1982

Fluorescence yields from photodissociation of SO2 at 1060-1330 A

The absorption and fluorescence cross sections of SO2 were measured in the 1060-1330 A region using synchrotron radiation as the light source. Several absorption bands were observed and assigned tentatively to the Rydberg states converging to the SO2(+) states. It is shown that the apparent quantum yields for excitation wavelengths longer than 1200 A are small, and are presumably emitted from the O(1S) and S(1S) metastable species. At shorter excitation wavelengths, the fluorescence cross sections increase at the threshold wavelengths of possible SO2 dissociation processes.

Suto, M.↗