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At least 307 records · Page 17
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NASA NTRS1984

Fundamental Equations of the LIF Hydroxyl Measurements, Appendix a

The equation relating OH concentration to the observed detector count rate for a given laser flux is defined. That equation, which will be referred to henceforth as the central equation for absolute sensitivity, will be cast in terms of standard spectroscopic quantities such as oscillator strengths, Hoenl-London factors, rotational and vibrational quantum numbers, etc., such that it may be tested directly under laboratory conditions. The working expressions used by each of the OH laser induced fluorescence (LIF) groups will be related to this central equation, thereby establishing a common language for the comparison of experimental results and the definition of LIF system performance. The relevant structural details of the OH radical via a spectroscopic description of the energy levels and transitions employed in the LIF method are detailed. The central equation relating observed count rate to absolute concentration will be derived, and that equation will be related to the observed quantities cited by each of the experimental groups engaged in the measurement of OH in the Earth's atmosphere.

Source record↗
NASA NTRS1984

Possible form of vacuum deformation by heavy particles

The possibility is discussed that the lowest-energy state for certain quantum numbers involves a Higgs field polarized into a skyrmion-type configuration. In some models a new type of vacuum instability arises. Phenomenological consequences are indicated schematically.

Mackenzie, R.↗
NASA NTRS1985

Rotational-level-dependent quenching of A2Sigma(+) OH and OD

The role of rotation in the collisional quenching of the A2Sigma(+) v' = 0 states of OH and OD is investigated experimentally by laser-induced-fluorescence measurements in a two-chamber differentially pumped flow chamber similar to that of McDermid and Laudenslager (1982). The experimental apparatus is described in detail, and the results are presented in extensive tables and graphs. Collisional-quenching rate constants are determined for 21 different quenchers at various specific N' rotational levels and shown to decrease as the rotational quantum number increases, with no significant role for the internal levels of the colliding pairs and reasonable agreement with theoretical calculations incorporating attractive forces.

Copeland, R. A.↗
NASA NTRS1985

Submillimeter, millimeter, and microwave spectral line catalog

This report describes a computer accessible catalogue of submillimeter, millimeter, and microwave spectral lines in the frequency range between 0 and 10000 GHz (i.e., wavelengths longer than 30 micrometers). The catalogue can be used as a planning guide or as an aid in the identification and analysis of observed spectral lines. The information listed for each spectral line includes the frequency and its estimated error, the intensity, lower state energy, and quantum number assignment. The catalogue has been constructed using theoretical least squares fits of published spectral lines to accepted molecular models. The associated predictions and their estimated errors are based upon the resultant fitted parameters and their covariances. Future versions of this catalogue will add more atoms and molecules and update the present listings (151 species) as new data appear. The catalogue is available from the authors as a magnetic tape recorded in card images and as a set of microfiche records.

Poynter, R. L.↗
NASA NTRS1985

Report from the Transfer-Laser Working Group

Light absorbing molecules and lasing molecules were discussed with regard to satisfying the following criteria for blackbody transfer lasers: (1) Good absorbers of blackbody radiation at 1500-2000 K; (2) Near resonant energy transfer from the absorbing gas to the lasant, provided not too many quantum number changes are required; (3) Dipole-dipole interactions for most efficient energy transfer; (4) Exothermic forward transfer reaction; (5) Polyatomic lasant molecules with at least two fundamental vibrational modes to ensure one or more states between the upper laser level and the ground state; (6) Polyatomic lasant molecules should not be so large or so complex that fast V-V relaxation occurs; (7) Metastable upper laser level for maintaining inversion, at least with respect to radiative and V-V decay; (8) Fast V-V into the upper laser level and out of the lower laser level; and (9) Lasing wavelengths less than 10.6 microns. Possible combinations of absorbers and lasants satisfying these criteria were discussed.

Meador, W. E.↗
NASA NTRS1985

Radiative relaxation of molecular vibration of the nitric oxide molecule as a possible source of the infrared Shuttle glow

A model calculation to predict infrared Shuttle flow due to the radiative relaxation of vibration of the NO molecule is presented. Space Shuttles hit atmospheric NO molecules at a very high speed and excite vibrational and rotational motions up to the temperature of 54,000 K. With the electric dipole radiation of delta v = 1, 2, 3, and particularly 4 (v is the vibrational quantum number), the excited NO molecules emit infrared radiation before they collide with other molecules. The total radiation power is estimated to be 170 A micro-W, where A is the cross-section area of the Shuttle in sq m if no adsorption of the NO molecule takes place on the Shuttle surface. The intensity of each infrared line is calculated as a function of time, including all vibrational states up to v = 35.

Mizushima, M.↗
NASA NTRS1985

Improved excitation rate coefficients for the n = 2 and n = 3 levels of Ca XIX and Fe XXV including fine structure

Reently calculated collision strengths, including relativistic and resonance effects, are employed to compute Maxwellian averaged collision strengths for 78 transitions involving states of principal quantum numbers 2-1 and 3-1 in Ca XIX and Fe XXV. These rate parameters are tabulated at temperatures of interest in astrophysical and labortory plasmas with radiation in the hard X-ray wavelength range. For some transitions, significant differences are found with the earlier calculations of Pradhan, Norcross, and Hummer (1981).

Pradhan, A. K.↗
NASA NTRS1985

Shuttle glow emissions due to radiative relaxation of highly vibrationally excited NO molecules produced by surface reflection

A new mechanism is proposed for the Space Shuttle glow, which is due to the radiative relaxation of ambient nitric-oxide molecules that are excited to very high vibrational levels by collisions with the Shuttle surface. Many of the particles colliding with the Shuttle surface at a very high speed (about 8 km/sec) would bounce off, exciting vibrational and rotational motions of molecules up to the level of vibrational quantum number v not greater than 35. Radiative transfer from these high levels should cause emissions in the spectrum range from infrared (IR) to visible red depending upon the transition paths. A perturbation method is used to calculate the transition probability and the emission intensity for the transitions of Delta-v not greater than 4. The result indicates that the Delta-v not greater than 4 transitions from high vibrational levels dominates the other transitions; the Delta-v = 4 transitions generally occur at the IR range.

Shimazaki, T.↗
NASA NTRS1986

One-photon pair annihilation in magnetized relativistic plasmas

In supersonic magnetic fields, electron-positron pairs may annihilate into single photons producing spectral features above 1 MeV. The paper calculates the exact one-photon annihilation rate in the general case where pairs may annihilate from excited Landau states, extending the previous studies which were restricted to pairs in the ground state. Asymptotic expressions for annihilation spectra and rates in the limit of large pair quantum numbers are also derived. It is found that the rate of annihilation from excited states can exceed the rate from the ground state by orders of magnitude in fields less than about 2 x 10 to the 12th G. This allows one-photon annihilation to be competitive with the two-photon process at typical neutron star field strengths. Annihilation spectra from a Maxwellian pair plasma at transrelativistic temperatures show fine structure near threshold on a scale (h/2pi)omega sub B as the result of contributions from individual pair states, which blend into a smooth continuum at higher energies.

Harding, A. K.↗
NASA NTRS1985

HCl vibrational fundamental band - Line intensities and temperature dependence of self-broadening coefficients

Self-broadening in the vibrational fundamental of HCl is inversely proportional to the temperature for transitions which lie near the Boltzmann rotational maximum and becomes monotonically less temperature-dependent as the rotational quantum number increases. The rotationless transition moment was found to have the value of 5.57 + or - 0.13 x 10 to the -3rd (Debye)-squared and the first Herman-Wallis factor, C = -2.543 + or - 0.019 x 10 to the -2nd.

Chackerian, C., Jr.↗
NASA NTRS1987

Recombination-line intensities for hydrogenic ions. I - Case B calculations for H I and He II

Assuming Case B of Baker and Menzel (1938), the relative intensities of H I and He II recombination lines are determined for a larger range of temperature and density than previously considered and with the upper principle quantum number up to 50 and the lower number up to 29. Full collisional effects are included, and new collision strengths for the n = 1, 2, and 3 states of He(+) are presented. Case B theory is found to be invalidated for collisional excitation of the n = 3 levels from both n = 1 and n = 2 states under certain conditions which depend upon electron density and the Lyman-alpha escape probability, and the regimes of temperature and density for which Case B is valid are also considered.

Hummer, D. G.↗
NASA NTRS1987

Electron impact excitation cross section studies of methane and acetylene

The 40-200-nm emission features of electron-impact-excited CH4 and C2H2 are investigated experimentally using the crossed-beam apparatus and VUV calibration techniques described by Ajello et al. (1982 and 1985). The results are presented in extensive tables and graphs and characterized in detail. All of the features are attributed to the atomic dissociation fragments C I, C II, and H, and the long lifetimes and high kinetic energies of the excited H fragments are shown to truncate the H Lyman series near principal quantum number n = 10.

Pang, K. D.↗
NASA NTRS1987

On the bond distance in methane

The equilibrium bond distance in methane was optimized using coupled-pair functional and contracted CI wave functions, and a Gaussian basis that includes g-type functions on carbon and d-type functions on hydrogen. The resulting bond distance, when corrected for core-valence correlation effects, agrees with the experimental value of 2.052 a(0) to within the experimental uncertainty of 0.002 a(0). The main source of error in the best previous studies, which showed discrepancies with experiment of 0.007 a(0) is shown to be basis set incompleteness. In particular, it is important that the basis set be close to saturation, at least for the lower angular quantum numbers.

Bowen-Jenkins, Philippa↗
NASA NTRS1987

Vibration-rotational intensities for the X 1Sigma(+) state of A1H and A1D

In the present calculation of vibrational-rotational line strengths for the ground electronic state of A1H and A1D, the vibrational and rotational quantum numbers used are respectively in the Delta-v zero-5 range for v-prime between zero and 15, and J-prime-J of + or - 1 for J-prime in the zero-50 range. The transition matrix elements were obtained on the basis of the Meyer and Rosmus (1975) ab initio dipole-moment function, together with the numerical vibrational-rotational energy function.

Tipping, R. H.↗
NASA NTRS1988

The laboratory millimeter- and submillimeter-wave spectrum of CH3OD

The millimeter-wave and submillimeter-wave spectrum of CH3OD, a deuterated isotope of methanol known to be present in the interstellar medium, has been studied in the laboratory. Like all isotopes of methanol, CH3OD possesses a complex dense spectrum because of the phenomenon of internal rotation, sometimes referred to as torsional motion. Approximately 300 lines in the frequency range 130-700 GHz have been assigned. These lines involve transitions between rotational states with rotational quantum number J of not greater than 9 in both the A and the E substates of the lowest torsional state (v sub t = 0). The present data and previous data at lower frequencies (longer wavelengths) have been combined and analyzed by a procedure called the 'internal axis method'. The analysis yields spectral constants for CH3OD which, in turn, have been used to predict the frequencies of a number of other transitions of this species not measured in the laboratory.

Anderson, Todd↗
NASA NTRS1988

On the bond distance in methane

The equilibrium bond distance in methane has been optimized using coupled-pair functional and contracted CI wave functions, and a Gaussian basis that includes g-type functions on carbon and d-type functions on hydrogen. The resulting bond distance, when corrected for core-valance correlation effects, agrees with the experimental value of 2.052 a(0) to within the experimental uncertainty of 0.002 a(0). The main source of error in the best previous studies, which showed discrepancies with experiment of 0.007 a(0) is shown to be basis set incompleteness. In particular, it is important that the basis set be close to saturation, at least for the lower angular quantum numbers.

Bowen-Jenkins, Philippa↗
NASA NTRS1988

Theoretical study of the nitrogen atom hyperfine coupling constant

The nitrogen-atom isotropic hyperfine coupling constant A(iso) is studied as a function of improvements in both the one-particle and n-particle basis sets. The study underscores the importance of diffuse basis functions. For example, the (9s 5p) primitive set of Huzinaga (1965) augmented with an even-tempered diffuse s function yields values for A(iso) that are virtually identical to an energy-optimized (23s 12p) even-tempered set. The A(iso) constant is found to converge relatively quickly with increasing l quantum numbers: d, f, and g functions are estimated to contribute 2.5 + or - 0.2, 0.4 + or - 0.1, and 0.05 + or - 0.05 MHz, respectively. Full CI calibration calculations indicate that very high levels of correlation treatment are required for quantitative results. In addition, a strong coupling is observed between the one-particle and n-particle requirements. The best result, 10.4 MHz, is in excellent agreement with the accurate experimental value of 10.4509 MHz.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1989

Solution of multi-center molecular integrals of Slater-type orbitals

The troublesome multi-center molecular integrals of Slater-type orbitals (STO) in molecular physics calculations can be evaluated by using the Fourier transform and proper coupling of the two center exchange integrals. A numerical integration procedure is then readily rendered to the final expression in which the integrand consists of well known special functions of arguments containing the geometrical arrangement of the nuclear centers and the exponents of the atomic orbitals. A practical procedure was devised for the calculation of a general multi-center molecular integrals coupling arbitrary Slater-type orbitals. Symmetry relations and asymptotic conditions are discussed. Explicit expressions of three-center one-electron nuclear-attraction integrals and four-center two-electron repulsion integrals for STO of principal quantum number n=2 are listed. A few numerical results are given for the purpose of comparison.

Tai, H.↗