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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Autioionizing states in the photionization of the 3s(2)3p(4) (3)Pe ground state of sulfur

The partial and total photoionization cross sections for the S(3s/2/3p/4/ /3/Pe) ground state are calculated in both the dipole length and velocity forms. The prominent features in the cross sections are the autoionization Rydberg series converging to S+(3s/2/p/3/ /2/D/0/, /2/P/0/) excited-state thresholds. The results are pertinent to the study of sulfur in the plasma of Jupiter's satellite Io.

Tayal, S. S.↗
NASA NTRS1990

Medium resolution studies of extreme ultraviolet emission from N2 by electron impact - The effect of predissociation on the emission cross section of the b 1Pi(u) state

The electron impact induced fluorescence spectrum of N2 is measured in the 102-134 nm range at a 0.05 nm spectral resolution. The spectral measurements provide the emission cross sections of the transitions of the b 1Pi(u)-X 1Sigma(+)g Birge-Hopfield I-band system. The structure and vibrational population distribution of this system are strongly affected by a configuration interaction of the valence b 1Pi(u) and Rydberg c 1Pi(u) and o 1Pi(u) states. The excitation function (0-400 eV) for the b-X (1,2) transition is measured and a modified Born approximation analytic model is applied to calculate the oscillator strength for the b 1Pi(u)-X band system. With the exception of the v-prime = 1 level, vibrational levels of the b 1Pi(u) state predissociate with a branching ratio of between 0.95 and 1.00. Predissociation of the b 1Pi(u) state contributes approximately six percent of the total dissociation cross section of N2 by electron impact at 100 eV.

James, Geoffrey K.↗
NASA NTRS1975

Ultraviolet solar identifications based on extended absorption series observed in the laboratory spectrum of Si I

The absorption spectrum of Si I in the wavelength region between 1500 and 1900 A has been photographed at high resolution. The silicon vapor was produced in a 122-cm-long King furnace at 1800 to 2300 C. Forty-two Rydberg series have been observed from the ground state terms 3p(2)3P and 1D to terms associated with the 3pns and 3pnd configurations. All of the series from these configurations with J less than 4 have been extended with the 3pnd 3D(3) levels reaching n = 56. Numerous perturbations have been observed. This laboratory work has provided the basis for extending the identification of silicon lines in the solar spectrum. Nearly all lines found in the laboratory spectrum are also found in rocket spectrograms of the solar chromosphere. More than 300 lines have been attributed to Si I. The excellent correlation between laboratory and solar Si I lines is illustrated.

Moore, C. E.↗
NASA NTRS1978

H Lyman-alpha emission from photodissociation of H2O

Lyman-alpha fluorescence measurements were used to study the photodissociation of water vapor to produce H(n equals 2) atoms from threshold to 500 A. The experimental threshold of 813.0 A nearly coincides with the thermodynamic limit. Excitation cross sections rise slowly from threshold to a maximum value of (1.55 plus or minus 0.12) x 10 to the -18th sq cm at about 709 A and decrease to a negligible value below 550 A. Structure in the excitation function is attributed to predissociation of Rydberg series converging to the B(overbar)B2 state of H2O(plus).

Mentall, J. E.↗
NASA NTRS1959

Interactions Between Oxygen and Nitrogen: O[Single Bond]N, O[Single Bond]N (sub 2), and O (sub 2)[Single Bond]N (sub 2)

Potential energy curves for 0-N interactions corresponding to the X (sup 2) II (sub t/2), X (sup 2) II (sub 3/2), A (sup 2) Eta (sup plus), B (sup 2) II, C (sup 2) II, D (sup 2) Eta (sup plus), E (sup 2) Eta (sup plus), and B prime (sup 2 delta) states of nitric oxide have been calculated from spectroscopic data by the Rydberg- Klein-Rees method. Curves for the (sup 4) II, (sup 2) Eta, (sup 4) Eta, (sup 6) Eta, and (sup 6) II states have been obtained from limited spectroscopic results and from relations derived from approximate quantum-mechanical calculations. Two semi-independent calculations have been made, and are in good agreement with each other. The quantum-mechanical relations also lead to approximate curves for the O[Single Bond]N, and O[Single Bond]N (sub 2) interactions over a limited range. The O (sub 2)[Single Bond]N (sub 2) interaction is consistent with one valid at larger separation distances which has been derived from high-temperature gas viscosity data.

Vanderslice, Joseph T.↗
NASA NTRS1986

Double photon excitation of high-Rydberg atoms as a long-lived submillimeter detector

A method and apparatus for detecting submillimeter or IR radiation is disclosed. A rare gas, such as xenon, is supplied at its ground state via a pressurized cylinder and an adjustable leak valve into a cryogenically cooled detection area. The ground state of xenon is double photon excited to a particularized level of the Rydberg series by a resonance lamp and a laser. The doubly excited gas is then further excited by the radiation to be measured. A field ionization and an ion measurement indicative of the radiation intensity is achieved.

Chutjian, A. N.↗
NASA NTRS1987

Assignments of autoionization states of O2-asterisk

Attention is given to the uncertainties that remain concerning the autoionization states of O2 leading to the a 4Pi(u) and A 2Pi(u) states of O2(+), as well as some of the assignments of the autoionization states and the determinations of effective quantum numbers and quantum defects. The former problems of vibrational assignments are unambiguously established in view of a study of isotopic oxygen molecules. A systematic examination of the known Rydberg series is conducted, and new assignments and interpretations for several autoionization states leading to the various states of O2(+) are suggested.

Wu, C. Y. Robert↗
NASA NTRS1977

Dissociative excitation of H2, HD, and D2 by electron impact

Time-of-flight techniques have been used to investigate the electron-impact dissociation of H2, HD, and D2 in order to determine the effect of isotopic mass variation in the target molecule on the dissociative excitation process. At incident electron energies near 100 eV, the time-of-flight spectrum produced from each molecule consists of atoms in the metastable 2s state and in high-lying long-lived Rydberg levels. The individual time-of-flight distributions, kinetic-energy spectra, and relative differential cross sections for these two species resulting from each molecule have been measured. The kinetic-energy spectrum of the Rydberg atoms produced from dissociative excitation of H2 was notably dissimilar in shape from the corresponding distributions produced from HD and D2. Also the 2s and Rydberg production cross sections differed between the three molecules. In the dissociation of the heteronuclear HD molecule, the ratio of fast H(2s) atoms to D(2s) atoms was about 1 to 1, while the same ratio comparing the Rydberg atoms was nearly 2 to 1. These differences indicate the influence of the mass variation on the position of the Franck-Condon region in the production of 2s atoms and on the competition between autoionization and dissociation in the formation of Rydberg fragments.

Carnahan, B. L.↗
NASA NTRS1990

Positronium ions and molecules

Recent theoretical studies on positronium ions and molecules are discussed. A positronium ion is a three particle system consisting of two electrons in singlet spin state, and a positron. Recent studies include calculations of its binding energy, positron annihilation rate, and investigations of its doubly excited resonant states. A positronium molecule is a four body system consisting of two positrons and two electrons in an overall singlet spin state. The recent calculations of its binding energy against the dissociation into two positronium atoms, and studies of auto-detaching states in positronium molecules are discussed. These auto-dissociating states, which are believed to be part of the Rydberg series as a result of a positron attaching to a negatively charged positronium ion, Ps-, would appear as resonances in Ps-Ps scattering.

Ho, Y. K.↗
NASA NTRS1992

Schroedinger's radial equation - Solution by extrapolation

A high-accuracy numerical method for the solution of a 1D Schroedinger equation that is suitable for a diatomic molecule, obtained by combining a finite-difference method with iterative extrapolation to the limit, is presently shown to have several advantages over more conventional methods. Initial guesses for the term values are obviated, and implementation of the algorithm is straightforward. The method is both less sensitive to round-off error, and faster than conventional methods for equivalent accuracy. These advantages are illustrated through the solution of Schroedinger's equation for a Morse potential function suited for HCl and a numerically derived Rydberg-Klein-Rees potential function for the X 1Sigma(+) state of CO.

Goorvitch, D.↗
NASA NTRS1994

Electronic spectroscopy of diatomic molecules

This article provides an overview of the principal computational approaches and their accuracy for the study of electronic spectroscopy of diatomic molecules. We include a number of examples from our work that illustrate the range of application. We show how full configuration interaction benchmark calculations were instrumental in improving the understanding of the computational requirements for obtaining accurate results for diatomic spectroscopy. With this understanding it is now possible to compute radiative lifetimes accurate to within 10% for systems involving first- and second-row atoms. We consider the determination of the infrared vibrational transition probabilities for the ground states of SiO and NO, based on a globally accurate dipole moment function. We show how we were able to assign the a(sup "5)II state of CO as the upper state in the recently observed emission bands of CO in an Ar matrix. We next discuss the assignment of the photoelectron detachment spectra of NO and the alkali oxide negative ions. We then present several examples illustrating the state-of-the-art in determining radiative lifetimes for valence-valence and valence-Rydberg transitions. We next compare the molecular spectroscopy of the valence isoelectronic B2, Al2, and AlB molecules. The final examples consider systems involving transition metal atoms, which illustrate the difficulty in describing states with different numbers of d electrons.

Partridge, Harry↗
NASA NTRS1991

Theoretical study of the NO beta system

A theoretical determination of the transition moment functions (TMFs) for the beta system of NO is presented. High levels of correlation treatment are required to show the changing degree of Rydberg character in the B2II with decreasing r values. The state-averaged complete-active-space self-consistent-field multireference configuration-interaction method is used for the determination. Previous lifetime measurements made with laser-induced fluorescence, varying between 2 and 0.85 microns, are discussed in terms of the calculated lifetimes for v-prime values 0-6, which vary from 2.12-1.17 microns. When larger r values are used for the transition moment function, the calculated lifetimes correlate with experimental lifetimes. The Einstein coefficients agree with experimental results, although limitations in the calibration of the spectrometer can account for systematic differences. The correlation with earlier experimental results suggests that radiative lifetimes are in the range of 1-2 microns.

Langhoff, Stephen R.↗
NASA NTRS1960

Potential Energy Curves of Hydrogen Fluoride

Potential energy curves for the X(sup 1)sigma+ and V(sup 1)sigma+ states of HF and DF have been calculated by the Rydberg-Klein-Rees method. The results calculated from the different sets of data for HF and DF are found to be in very good agreement. The theoretical results of Karo are compared to the experimental results obtained here.

Fallon, Robert J.↗
NASA NTRS1994

Effect of dispersion forces on squeezing with Rydberg atoms

We report exact results concerning the effect of dipole-dipole interaction (dispersion forces) on dynamic and steady-state characteristics of squeezing in the emitted fluorescent field from two identical coherently driven two-level atoms. The atomic system is subjected to three different damping baths in particular the normal vacuum, a broad band thermal field and a broad band squeezed vacuum. The atomic model is the Dicke model, hence possible experiments are most likely to agree with theory when performed on systems of Rydberg atoms making microwave transitions. The presence of dipole-dipole interaction can enhance squeezing for realizable values of the various parameters involved.

Ng, S. K.↗
NASA NTRS1983

Study of sulfur-containing molecules in the EUV region. III Photoexcitation of CS2

Using synchrotron radiation as a continuum background, the absorption cross section of CS2 has been measured using a double ionization chamber. The cross sections range from four to a maximum value of 65 Mb in the 175-760 A region. Two new Rydberg series X and XI have been identified and apparently converge to the D2Pi state of CS2(+) at 16.943 eV.

Wu, C. Y. R.↗
NASA NTRS1991

Vibrational relaxation and dissociation in nitrogen

Calculations of the vibrational and dissociation transition probabilities are made for N2-N2 and N2-N collisions by means of a semiclassical N-state approximation. The flaws in previous techniques are reviewed, with special attention given to the prediction of overtones. The method presented ignores the effects of molecular rotation and employs a revised extended Rydberg intermolecular potential to describe diatom-diatom and diatom-atom collisions. The collision velocities investigated exhibit probabilities of less than unity by means of the N-state method. The continuum is quantized to treat dissociation, and the collision results demonstrate probability enhancements for V-V-T transitions in both bound-bound and bound-free transitions. The technique is of particular interest for the theoretical modeling of reentry flows such as those encountered in aerobraking maneuvers.

Varghese, Philip L.↗
NASA NTRS1994

A photoionization study of OH and OD from 680A to 950A: An analysis of the Rydberg series

The photoionization spectra of OH(+) and OD(+) have been reported from 680 to 950 A (18.23 to 13.05 eV) at a wavelength resolution of 0.07 A. Through interpretation of both spectra, the Rydberg series and their higher vibrational members have been reported for three of the excited ionic states, a(sup 1)Delta, A(sup 3)Pi(i), and b(sup 1) Sigma(sup +). A vibrational progression has also been observed in both OH(+) and OD(+) which is apparently related to a fourth excited ionic state, c(sup 1)Pi. Finally, the dissociative ionization limits, corrected to 0 K,for H2O AND D2O have been measured to be 18.11+/-0.01 and 18.21+/-0.01 eV, respectively, and shown to be in good agreement with previously reported results.

Cutler, J. N.↗