Intercombination oscillator strengths in the helium sequence.
Helium sequence ions spin forbidden transitions electric dipole oscillator strengths and transition probabilities evaluated by variational procedure
Dalgarno, A.↗
SEARCH · Search NASA
Results for “FORBIDDEN TRANSITION”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The perturbation spectrum of CO
Perturbation rotational levels in triplet states of CO emission spectra attributed to resonance fluorescence process involving optically forbidden transitions
Black, G.↗
The excitation of the forbidden coronal lines. II - Forbidden Ca XV lines at 5694 and 5446 A
Electron and proton excitation of forbidden transition lines in Ca XV ground configuration determined for coronal densities and temperature
Chevalier, R. A.↗
CO/a/3/pi/ - Its production, detection, deactivation, and radiative lifetime
Deactivation and radiative lifetime of CO Cameron forbidden transition spectral bands produced by photon absorption
Black, G.↗
Crystal field spectra of lunar pyroxenes.
Absorption spectra in the visible and near infrared regions have been obtained for pyroxene single crystals in rocks from the Apollo 11, 12, 14, and 15 missions. The polarized spectra are compared with those obtained from terrestrial calcic clinopyroxenes, subcalcic augites, pigeonites, and orthopyroxenes. The lunar pyroxenes contain several broad, intense absorption bands in the near infrared, the positions of which are related to bulk composition, Fe(2+) site occupancy and structure type of the pyroxene. The visible spectra contain several sharp, weak peaks mainly due to spin-forbidden transitions in Fe(2+). Additional weak bands in this region in Apollo 11 pyroxenes are attributed to Ti(3+) ions. Spectral features from Fe(3+), Mn(2+), Cr(3+), and Cr(2+) were not observed.
Burns, R. G.↗
Forbidden-line excitation data for certain coronal lines
Some new data pertinent to forbidden transitions for coronal lines of S XII, Ca XIII, K XI, Mn XIII, Fe XIV, Co XV, Ni XVI, N XV, Cr IX, Fe X, and Ni XII are presented. We include additional calculations of collision strengths for a number of ions and then set up and solve the equations of statistical equilibrium in the limiting approximations in which contributions to level population by cascade from higher levels are neglected. We then calculate volume emissivities per ion as a function of density and temperature.
Czyzak, S. J.↗
Spectroscopic studies of the solar corona at X-ray wavelengths
The spatial distribution of emission in several X-ray lines is discussed with emphasis on temperature dependence and association with active regions. Results are presented for the trio of helium-like O VII lines which demonstrate (1) a spatial variation in the density-dependent forbidden-to-intersystem line ratio, and (2) a strong spatial variation in the intensity of the O VII resonance line relative to the optically forbidden transitions. The second effect appears to be caused by resonance scattering by material in the line of sight.
Acton, L. W.↗
Long wavelength carbonyl sulfide photodissociation
The aeronomic implications of a preliminary observation of weak OCS photoabsorption above 270 nm are investigated. It is argued that the measured cross section is consistent with a forbidden transition in this wavelength region. Model calculations are made for the OCS photodissociation rates in daylight, the OCS and SO2 distributions in the upper atmosphere, and the budgets of sulfur in the stratosphere and OCS in the troposphere, assuming various extrapolations of the measured OCS absorption cross sections and quantum yields to longer wavelengths. It is shown that weak OCS absorption above 300 nm can have important consequences for all of these quantities. Laboratory and field experiments are identified which might lead to a better understanding of the atmospheric OCS cycle.
Turco, R. P.↗
The forbidden oxygen lines in comets
High spatial resolution observations of comet Bradfield (1979X) with the IUE spectrograph have made it possible to tentatively identify a feature at 2972 A as the 1S-3P forbidden transition of oxygen atoms. It is shown here that the most likely source of this emission is the photodissociation of water molecules, mainly by solar Lyman-alpha photons, but that a significant contribution of CO2 cannot be excluded.
Festou, M. C.↗
Reflectance spectroscopy of diogenite meteorite types from Antarctica and their relationship to asteroids
Measurements of the spectral reflectance (0.4-2.5 microns) of three diogenite meteorites found in Antarctica are examined. Comparisons are made with previous measurements of diogenites in order to correlate the mineralogy and petrography with the spectral characteristics that can also be measured on solar system objects of unknown composition. Even though the Antarctic diogenites have the same spectral characteristics as other diogenites, there are measurable differences between all diogenite spectra. Bands caused by spin-forbidden transitions of Fe(2+) ions in pyroxene, which are identified for the first time in reflectance spectra of powdered samples, are revealed in an analysis of the spectra into sums of Gaussian components. It is shown from these laboratory measurements that spectral reflectance measurements of asteroids and other solar system objects made with the visible CVF (circular variable filter) spectrometer used for laboratory measurements can provide useful information on their surface composition.
Mcfadden, L. A.↗
Collision strengths for 1199 and 1729 of S III
Collision strengths are calculated for the S III ground state from electron impact excitation in the Io torus. The study is based on data taken at 119.9 nm and 172.9 nm by the IUE spacecraft and with the rocket-borne Faint Object Telescope. The collision strengths of the 3p(2)3P3s3p(3)(5)S(4) and (3)P-3s3p(3)(3)D(0) UV lines are derived from a three-state close coupling aproximation. A Gailitis averaging scheme accounts for resonance effects in the forbidden transition. The calculated intensities of the two transitions at an electron temperature of 80,000 K are in agreement with observed intensities.
Ho, Y. K.↗
S V line ratios in the sun
In the present prediction of level populations and emission line intensity ratios for electron densities and temperatures appropriate to the sun, on the basis of new atomic data for S V, the electron impact collision rates for spin-forbidden transitions, and the intercombination transition spontaneous radiative rate, are noted to be substantially larger than previously ascertained. The S V intensity ratio is shown to be a useful electron density diagnostic for log N(e) greater than 11.5 ratios deduced from observations obtained with a slit spectrograph aboard Skylab generally agree with the theoretical values presented.
Dufton, P. L.↗
The production of NH(A 3Pi i) through photodissociative excitation of NH3
The NH(A-X) emission produced by photodissociation of NH3 is examined using a line emission source in the 600-1340 A region. It is observed that the production of the NH(A 3Pi i) photofragment involves a spin-forbidden transition. Fluorescence spectra of NH3 are derived and analyzed. The relationship between fluorescence cross sections and fluorescence count rates and gas pressure is studied. The fluorescence cross sections of NH(A-X) are calculated as 2.1 x 10 to the -22nd, 3.1 x 10 to the -22nd, 3.0 x 10 to the -21st, 1.5 x 10 to the -20th, and 3.4 x 10 to the -20th sq cm for the primary photon wavelength of 1239, 1184, 1065, 1037, and 976 A, respectively; and the corresponding fluorescence quantum yields are 0.00002, 0.00003, 0.0012, 0.0085, and 0.015.
Wu, C. Y. Robert↗
Accurate energy levels for singly ionized platinum (Pt II)
New observations of the spectrum of Pt II have been made with hollow-cathode lamps. The region from 1032 to 4101 A was observed photographically with a 10.7-m normal-incidence spectrograph. The region from 2245 to 5223 A was observed with a Fourier-transform spectrometer. Wavelength measurements were made for 558 lines. The uncertainties vary from 0.0005 to 0.004 A. From these measurements and three parity-forbidden transitions in the infrared, accurate values were determined for 28 even and 72 odd energy levels of Pt II.
Reader, Joseph↗
Forbidden lines of np(q) ions. II - Line intensities
Ground state forbidden transitions of np(q) ions of C, N, O, Ne, Mg, Si, S, and Fe can provide important information on the state of cosmic ionized gases. The line intensities of 95 transitions of these ions have been tabulated, including those used to calculate the line ratios as well as other strong lines of the ions in the ground state terms in the same temperature and density ranges treated previously. These data can be used for calculations of the absolute line intensities if the ionic abundances are known. These calculations are important for studies of the solar transition region, ionized nebulae, circumstellar nebulae such as found in symbiotic stars, supernova remnants, interstellar bubbles produced by stellar winds, and emission regions in active galactic nuclei.
Lynch, John P.↗
Ferric iron in primitive asteroids - A 0.43-micron absorption feature
A search of reflectance spectra of C- P-, D- and S-class asteroids to hunt for the Soret band near 0.4 micron that is indicative of porphyrins yielded an identification of an 0.43 micron absorption feature in 11 primitive asteroids of the C, P, and G classes and in one S-class asteroid. It is proposed that the feature is an Fe(3+) spin-forbidden transition in aqueously altered material, possibly located near 0.43 micron due to an enhancement effect similar to the mechanism operating in jarosite. The significance of the feature for the aqueous alteration history of these asteroids is addressed.
Vilas, Faith↗
Study of Luminescence Characteristics of Trivalent Terbium in Silicate Glass
An important use of silicate glasses doped with terbium oxide (Tb2O3) is their use as fiber optic sensors for high-resolution imaging applications requiring the detection of x-rays (e.g. tomography and radiography). The x-ray radiation is absorbed by the glass, producing electron-hole pairs (excitons). The excitons migrate through the glass matrix and then recombine, emitting characteristic Tb(3+) luminescence in the optical wavelength region. This emission is due to forbidden transitions of 4f electrons and therefore has a long decay time. Long decay time is undesirable when imaging transient events since it results in blurring in time of the images. It has been reported elsewhere that in crystals Tb(3+) ions can act both as luminescence centers and as fluorescence traps. These traps can capture excitons and delay their recombination. This delayed fluorescence is seen as a long lived, secondary component to the luminescence decay curve, or afterglow. Such a secondary decay component to the luminescence decay of Tb(3+) has been observed before in soda glass following pulsed optical excitation. In order to determine the conditions under which afterglow occurs, an understanding of the material's luminescent properties is required.
West, Mike S.↗
Extending the McDonald Observatory Serendipitous Survey of UV/Blue Asteroid Spectra
Moderate resolution asteroid spectra in the 350 - 650 nm spectral range acquired randomly over many years (Cochran and Vilas, Icarus v 127, 121, 1997) identified absorption features in spectra of some of the asteroids. A feature centered at 430 nm was identified in the spectra of some low-albedo asteroids (C class and subclass), similar to the feature identified by Vilas et al. (Icarus, v. 102, 225,1993) in other low-albedo asteroid spectra and attributed to a ferric iron spin-forbidden transition in iron alteration minerals such as jarosite. Features at 505 nm and 430 nm were identified in the spectrum of 4 Vesta. The 505-nm feature is highly diagnostic of the amount and form of calcium in pyroxenes. This suggested further research on the sharpness and spectral placement of this feature in the spectra of Vesta and Vestoids (e.g., Cochran and Vilas, Icarus v. 134, 207, 1998). In 1997 and 1998, additional UV/blue spectra were obtained at the 2.7-m Harlan J. Smith telescope with a facility cassegrain spectrograph. These included spectra of low-albedo asteroids, the R-class asteroid 349 Dembowska, and the M-class asteroid 135 Hertha. These spectra will be presented and identified features will be discussed.
Vilas, Faith↗