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At least 217 records · Page 12

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NASA NTRS1972

Trace ferric ion in lunar and meteoritic titanaugites.

Evidence for presence of Fe(3+) in lunar rocks is furnished by heating them in air to 200-225 C for two hours. This causes a large decrease in the same charge transfer bands attributed to Fe(3+) that can be enhanced by heating the same rocks in air at 500 C. This is interpreted as evidence that the Fe(3+) was not in equilibrium in the melt but was produced by cosmic radiation subsequent to the rock formation. Possible tetrahedrally coordinated Fe(3+) is present in the meteoritic and lunar augites as suggested by comparison of their spectra to that of terrestrial augite high in Fe(3+). This would have been present in the original melt and is distinct from radiation produced Fe(3+) in the M-sites. The polarized absorption spectra of single crystal pigeonite and augite from rock 12021 before heating, and augite from 12018 after heating are compared to that of meteoritic titanaugite in the Angra dos Reis meteorite and terrestrial titanaugite from Maui, Hawaii. The absorption spectrum of meteoritic hypersthene (Tatahouine) is also included for comparison to the pigeonite.

Cohen, A. J.↗

NASA NTRS1971

Heavy ion plasma confinement in an RF quadrupole trap

The confinement of an electron free plasma in a pure quadrupole RF electric trap was considered. The ultimate goal was to produce a large density of mercury ions, in order to realize a trapped ion frequency standard using the hyperfine resonance of 199 Hg(+) at 40.7 GHz. An attempt was made to obtain an iodine plasma consisting of equal numbers of positive and negative ions of atomic iodine, the positive iodine ions, being susceptible to charge-exchange with mercury atoms, will produce the desired mercury ions. The experiment showed that the photoproduction of ions pairs in iodine using the necessary UV radiation occurs with a small cross-section, making it difficult to demonstrate the feasibility of space charge neutralization in a quadrupole trap. For this reason it was considered expedient to choose thallium iodide, which has a more favorable absorption spectrum (in the region of 2000 to 2100 A). The results indicate that, although the ionic recombination is a serious limiting factor, a considerable improvement can be obtained in practice for the density of trapped ions, with a considerable advantage in lifetimes for spectroscopic purposes. The ion pair formation by photoionization is briefly reviewed.

Schermann, J.↗

NASA NTRS1974

CO2 photodissociation and vibrational excitation in the planetary atmospheres

The principal subjects of investigation were the determination of the CO2 photodissociation quantum yields at the wavelengths from 1200 A to 1500 A, and the efficiency of electronic-to-vibrational energy transfer in the systems 0(1D) + CO, N2, CO2 yields 0(3P) + CO N2, CO2 vibrational energies. Measurements on the photodissociation quantum yield of CO2 in the 1200-1500 A region show that it is wavelength dependent, and for the six atomic line sources used, the quantum yield varied from 0.2 to 0.8. The data appear to fit the interpretation of stable CO2 bound states mixed with repulsive or predissociating states, since the low quantum yields coincide with the maximum structure in the CO2 absorption spectrum. The first reliable measurements were made on the efficiency of electronic-to-vibrational energy transfer in the systems 0(1D)-CO and 0(1D)-N2, using a uv resonance fluorescence technique. The 0(1D)-CO2 interaction was investigated by infrared techniques.

Slanger, T. G.↗

NASA NTRS1974

Optical spectra and the mass of SMC X-1

Photographic spectral data are presented for Sanduleak 160, an SMC B-type supergiant with which the strong binary X-ray source SMC X-1 is identified. These data show several important features: (1) Emission is conspicuously present at 4686 A at phases 0.1-0.3 and 0.7-0.85 (where phase 0.0 denotes X-ray eclipse) and undetectable near phase 0.5; (2) the emission has a large amplitude in velocity approximately out of phase with the expected motion of the primary star; (3) the absorption spectrum does not show any detectable change in spectral type throughout the orbit. The basic parameters of the system are studied on the basis of the new data, and a mass of near 2 solar masses is computed for the X-ray object. The data also furnish a number of constraints for models of the system.

Osmer, P. S.↗

NASA NTRS1974

Photodissociation quantum yields of CO2 between 1200 and 1500 A

Measurements of the photodissociation quantum yields of CO2 have been carried out using various atomic line sources between 1200 and 1500 A. The production of CO was monitored by resonance fluorescence, and the results indicate that where the CO2 absorption spectrum is continuous, the CO quantum yield is high, but where there is structure, the yield is low.

Slanger, T. G.↗

NASA NTRS1975

Water vapor absorption spectra of the upper atmosphere /45-185 per cm/

The far IR nighttime absorption spectrum of the earth's atmosphere above 14 km is determined from observations of the bright moon. The spectra were obtained using a Michelson interferometer attached to a 30-cm telescope aboard a high-altitude jet aircraft. Comparison with a single-layer model atmosphere implies a vertical column of 3.4 plus or minus 0.4 microns of precipitable water on 30 August 1971 and 2.4 plus or minus 0.3 microns of precipitable water on 6 January 1972.-

Augason, G. C.↗

NASA NTRS1975

Infrared upconversion for astronomical applications

The performance of an upconversion system is examined for observation of astronomical sources in the low to middle infrared spectral range. Theoretical values for the performance parameters of an upconversion system for astronomical observations are evaluated in view of the conversion efficiencies, spectral resolution, field of view, minimum detectable source brightness and source flux. Experimental results of blackbody measurements and molecular absorption spectrum measurements using a lithium niobate upconverter with an argon-ion laser as the pump are presented. Estimates of the expected optimum sensitivity of an upconversion device which may be built with the presently available components are given.

Abbas, M. M.↗

NASA NTRS1976

Review of cometary spectra

The spectra of comet Kohoutek, comet Bradfield, and comet Mrkos are reviewed and compared in relation to stellar spectroscopy and evolution. The possibility of observing the absorption spectrum of a comet and direct measurement of Doppler shifts due to expansion or streaming motions in comets are considered along with the spectra of giant comets, such as, comet Minkowski, comet Baade, and comet Lovas. A speculative explanation for possible intrinsic abundance differences between comets is given.

Herbig, G. H.↗

NASA NTRS1976

Fundamental studies of black chrome for solar collector use

The thicknesses of black chrome plated for various times have been measured from electron photomicrographs and correlated with the solar spectrum absorptance and infrared emittance as calculated from spectral reflectance measurements. The maximum absorptance is reached at an average thickness of 0.5 micrometer. The emittance increases only slightly up to 1.0 micrometer but increases rapidly at thickness above 1.0 micrometer.

Mcdonald, G.↗

NASA NTRS1976

Infrared upconversion for astronomical applications

The performance of an upconversion system is examined for observation of astronomical sources in the low to middle IR spectral range. Theoretical values for the performance parameters of an upconversion system for astronomical observations are evaluated in terms of the conversion efficiencies, spectral resolution, field of view minimum detectable source brightness, and source flux. Experimental results of blackbody measurements and molecular absorption-spectrum measurements using a lithium niobate upconverter with an argon-ion laser as the pump are presented. Estimates are given of the expected optimum sensitivity of an upconversion device that may be built with presently available components.

Abbas, M. M.↗

NASA NTRS1976

Optical constants of sulphuric acid in the far infrared

The IR absorption spectrum of a 75% sulphuric acid solution is obtained experimentally in the 20-50 micron wavelength region. The complex refractive index is determined from these measurements by integration of the Kramers-Kronig dispersion relation. The application of this data to radiative transfer processes in the atmosphere of Venus is briefly discussed.

Jones, A. D.↗

NASA NTRS1976

Temperature dependence of the absorption edge of vitreous silica

During an investigation of the optical properties of high-purity vitreous silica (fused quartz), which is being developed by NASA as a reflective and ablative heat shield, some interesting properties of theoretical and experimental nature have become apparent which otherwise may have remained unnoticed. Of particular interest for the NASA application is the shift of the absorption edge toward longer wavelengths with increasing temperature. The results of studies of this shift and of the spectral dependence of the absorption edge are summarized in the present paper. Plots of the absorption edge and the absorption spectrum of fused quartz vs temperature are given and discussed.

Bates, C. W., Jr.↗

NASA NTRS1976

Fundamental studies of black chrome for solar collector use

Mcdonald, G.↗

NASA NTRS1978

A shock-tube determination of the SiO /A 1 Pi - X 1 Sigma +/ transition moment

The sum of the squares of the electronic transition moments for the A 1 Pi - X 1 Sigma + band system of SiO has been determined from absorption measurements conducted in the reflected-shock region of a shock tube. The test gas was produced by shock-heating a mixture of N2O, SiCl4, and Ar, and the spectra were recorded photographically in the 260-290-nm wavelength range. The values of the sum as a function of internuclear distance between 2.8 and 3.3 Bohr were determined by comparing the measured absorption spectrum with that produced by a line-by-line synthetic-spectrum calculation which accounted for instrumental broadening. The value of the sum so deduced at an internuclear distance of 3.0 Bohr was 1.0 + or - 0.3 atomic units.

Park, C.↗

NASA NTRS1978

IUE observations of extragalactic objects

During the commissioning phase of IUE several extragalactic objects were observed spectrally at low dispersion in the UV range lambda lambda 1150-3200: the Seyfert galaxies NGC4151 and NGC1068, the QSO 3C273, the BL Lacertae object B2 1101+38, the giant elliptical galaxy M87 and the spiral galaxy M81. The results obtained are presented and a preliminary analysis given for all six objects, discussing the continuous spectrum, extinction, emission line spectrum and absorption line spectrum, where possible for each case. Several new or confirmatory astrophysical results are obtained.

Boksenberg, A.↗

NASA NTRS1979

Tunable single-longitudinal-mode operation of an injection-locked TEA CO2 laser

The tunable single-longitudinal-mode operation of a TEA CO2 laser by an injection technique using a CW waveguide laser as the master oscillator is reported. With the experimental arrangement described, in which the waveguide laser frequency is tuned to correspond to one of the oscillating longitudinal modes of the TEA laser, single-longitudinal-mode operation was achieved with no apparent reduction in the TEA output energy, on various CO2 lines with frequency offsets from the line center as large as 300 MHz. The capability of this technique for high-resolution spectroscopy or atmospheric lidar studies is demonstrated by the recording of the absorption spectrum of a strong ozone line.

Megie, G.↗

NASA NTRS1980

Production of OH from photolysis of HOCl at 307-309 nm

Laser-induced fluorescence has been used to measure the amount of OH produced in the laser photolysis of HOCl at 310 nm. The HOCl was generated by the Cl2O + H2O and by the HCl + Cl2O reactions. The laser technique samples OH on a microsecond time scale so that secondary radical reactions cannot contribute significantly to the observed signals. The fluorescence signals were calibrated with O3-H2O mixtures, the reactions O3 + h(nu) yields O(1D) + O2 and O(1D) + H2O yields 2OH yielding known amounts of OH. The value for the absorption cross section of HOCl at 310 nm has been determined to be 6 x 10 to the -20th sq cm, assuming K(eq) = 0.082 for the Cl2O + H2O yields 2HOCl system and assuming unit quantum yield for the production of OH. The present investigation further supports earlier experimental work concluding that HOCl will photodissociate rapidly and will not be an important holding tank for chlorine in the stratosphere. These results are in disagreement with theoretical calculations of the UV absorption spectrum of HOCl in the 300-350-nm wavelength region.

Molina, M. J.↗

NASA NTRS1980

Ultraviolet downconverting phosphor for use with silicon CCD imagers

The properties and application of a UV downconverting phosphor (coronene) to silicon charge coupled devices are discussed. Measurements of the absorption spectrum have been extended to below 1000 A, and preliminary results indicate the existence of useful response to at least 584 A. The average conversion efficiency of coronene was measured to be approximately 20% at 2537 A. Imagery at 3650 A using a backside illuminated 800 x 800 CCD coated with coronene is presented.

Blouke, M. M.↗