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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 37 records · Page 2
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NASA NTRS1982

Airborne observations of the Orion molecular hydrogen emission spectrum

The Orion near-infrared H2 emission spectrum was observed from an altitude of 12.5 km in order to measure line intensities free from interference by terrestrial H2O. For the peak source, the observations indicate that the differential extinction between 4126 and 4712 per cm is 0.59 + or -0.06 mag, and the relative line intensities are consistent with those expected from a homogeneous source in approximate LTE at 1540 + or -100 K. An anomalous ortho/para H2 abundance ratio of 3.5(+ or - 0.2):1 is found, and the estimated total luminosity in vibrationally excited H2 lines is 300 + or - 100 solar luminosities. Rough molecular abundance limits, based on the missing H2 Q(6) line and the good agreement between other line intensities and the LTE model, place the H2 region no deeper within OMC-1 than the IR cluster and no shallower than 50 percent of the depth to the cluster.

Davis, D. S.↗
NASA NTRS1995

A Coupled-Cluster Study of the Molecular Structure, Vibrational Spectrum, and Heats of Formation of XONO2 (X=H, F, Cl)

The equilibrium structures, harmonic vibrational frequencies, dipole moments, and IR intensities of nitric acid, fluorine nitrate, and chlorine nitrate have been investigated by using the singles and doubles coupled cluster method that also includes a perturbational estimate of the effects of connected triple excitations, CCSD(T). A standard triple-zeta double-polarized basis set was utilized. The equilibrium geometries and vibrational spectra of HONO2 and ClONO2 are shown to be in excellent agreement with the available experimental data. The ab initio vibrational spectrum of FONO2 is also shown to be in excellent agreement with experiment. Unlike the FOOF and FON molecules, but similar to the cis- and trans-FONO molecules, FONO2 is shown to possess normal bond distances. The bonding in FONO2 is shown to be more similar to that in ClONO2 than that in HONO2, although there are still significant differences, especially in the partial atomic charges as deduced from Mulliken populations. This causes FONO2 to possess almost no dipole moment, which is very different to both HONO2 and ClONO2. By using large atomic natural orbital basis sets, CCSD(T) energies are computed for four isodesmic reactions in order to determine an accurate heat of formation for FONO2. Our best estimate for DELTA H(raised circle) (sub f,298) is 3.1 plus or minus 2.0 kcal/mol, indicating that the F-ONO2 bond energy is 31.3 kcal/mol.

Lee, Timothy J.↗
NASA NTRS1994

A Coupled-Cluster Study of the Molecular Structure, Vibrational Spectrum, and Relative Energies of the XCN and XNC (X=F, Cl) Isomers

The XCN and XNC (X=F, Cl) isomers have been investigated using the CCSD and CCSD(T) methods in conjunction with a TZ2P basis set. Equilibrium geometries, dipole moments, harmonic frequencies, IR intensities and relative energies have been evaluated. The CCSD(T) geometries and vibrational frequencies for the XCN isomers are in good agreement with the available experimental data. The CCSD(T) results for FCN and FNC are in good agreement with the CEPA calculations of Botshwina et al., with the exception of the energy difference, which the CEPA method underestimates by about 1.2 kcal/mol. FCN and CICN are shown to be lower in energy than the FNC and ClNC isomers by 69.511.0 and 42.711.0 kcal/mol (0 K), respectively.

Lee, Timothy J.↗
NASA NTRS1972

The interstellar molecular hydrogen observed in the ultraviolet spectrum of delta Scorpii

Molecular hydrogen bands of the Lyman and Werner systems were observed in the ultraviolet, interstellar spectrum of delta Sco. The average molecular column density is given, and the average temperature of the gas of which the molecules are part is 47 K. Minimum and maximum gas temperatures are 25 and 98 K respectively. The ratio of the number of hydrogen atoms in molecular form to the total number of hydrogen atoms in either atomic or molecular form is 0.044 (+0.070, -0.018).

Smith, A. M.↗
NASA NTRS1972

Interpretation of the Minkowski bands in Grw + 70 deg 8247.

Demonstration on the basis of the spectral structure of circular polarization in Grw + 70 deg 8247, that the absorption bands are at least in part molecular in origin. The spectrum of molecular helium has strong bands coincident with several of the Minkowski bands and, in particular, at high temperature shows a strong band head at about 4125 A. Helium molecules could be formed in sufficient density to give the absorption features in the star if it has a pure helium atmosphere. The Zeeman effect in molecular helium can explain in general the observed spectral features in the polarization and also may be responsible for the continuum polarization.

Angel, J. R. P.↗
NASA NTRS1982

Measurement of the dispersive and refractive indices of germanium using diode lasers

Germanium Fabry-Perot etalons are commonly used in diode laser spectroscopy to establish relative frequency calibration scales for molecular absorption spectra. Typically the channel spectrum of the etalon is recorded simultaneously with the molecular spectrum as the laser injection current is tuned linearly, and the etalon free spectral range (fringe spacing) is used to measure the frequency separations among lines in the molecular spectrum. For this purpose, the etalon free spectral range must be known for the measurement wavelength, and this in turn relies on knowledge of the etalon length and the dispersive index at this wavelength. It is pointed out that the most satisfactory approach is to measure directly the free spectral range or dispersive index of the etalon at the wavelength of interest. A description is presented of measurements of this type, performed near 7.9 and 10.1 micrometers for a 7.7-cm long germanium etalon.

Jennings, D. E.↗
NASA NTRS1992

Ab initio study of the molecular structure and vibrational spectrum of nitric acid and its protonated forms

The equilibrium structures, harmonic vibrational frequencies, IR intensities, and relative energetics of HNO3 and its protonated form H2NO3+ were investigated using double-zeta plus polarization and triple-zeta plus polarization basis sets in conjunction with high-level ab initio methods. The latter include second-order Moller-Plesset perturbation theory, the single and double excitation coupled cluster (CCSD) methods, a perturbational estimate of the effects of connected triple excitations (CCSD(T)), and the self-consistent field. To determine accurate energy differences CCSD(T) energies were computed using large atomic natural orbital basis sets. Four different isomers of H2NO3+ were considered. The lowest energy form of protonated nitric acid was found to correspond to a complex between H2O and NO2+, which is consistent with earlier theoretical and experimental studies.

Lee, Timothy J.↗
NASA NTRS1967

Dipole properties of molecular nitrogen.

Optical absorption, refractivity and electron scattering used to construct model dipole spectrum of molecular nitrogen and calculate dipole properties

MOLECULAR GAS↗