The vibrational temperature of molecular nitrogen in the thermosphere
Thermospheric molecular nitrogen vibrational temperature, studying various chemical reactions and collisions as energy sources
Nagy, A. F.↗
SEARCH · Search NASA
Results for “MOLECULAR COLLISION”
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.
Crossed-beam study of the reaction N/plus/ and O2 leading to NO/plus/ and O
Crossed beam model of nitrogen ion-molecular oxygen reactions in upper atmosphere as function of collision energy
Herman, Z.↗
Laboratory studies of irradiated nitrogen-methane mixtures - Applications to Triton
The characteristics of the near-IR spectrum of Triton is addressed in view of 0.8-2.5 micron laboratory transmission spectra obtained for methane dissolved in liquid nitrogen. It is found that, for methane concentrations greater than 3 percent of the saturation value, the collision-induced, 2.152-micron first-overtone band of molecular nitrogen is overshadowed by the methane band centered at 2.3 microns. While gamma-radiolysis of nitrogen-methane mixtures generates an unstable precipitate whose yellowish color is qualitatively similar to the yellow color of Triton, no specific absorption band in the precipitate can be unambiguously identified on Triton.
Piscitelli, J. R.↗
Statistical fluctuations in Monte Carlo calculations
The time counter and modified Nanbu simulation techniques are analyzed, with emphasis placed on the convergence of the calculations to a steady macroscopic state. Such variables as translational and rotational temperature, and flow velocity, sampled at several points in the flowfield, are considered. Both macroscopic averages and molecular distribution functions are analyzed. The calculation of inelastic collisions, in which transfer of energy between translational and internal energy modes is performed, is achieved through the use of the Larsen-Borgnakke phenomenological model. It is noted that, with reference to translational temperature, the time counter method shows less statistical scatter than that found with the modified Nanbu simulation technique.
Boyd, I. D.↗
First measurement of helium on Mars: Implications for the problem of radiogenic gases on the terrestrial planets
The 108 photons of the Martian He 584 A airglow detected by the Extreme Ultraviolet Explorer satellite during a two-day exposure (22-23 Jan. 1993) correspond to the effective disk average intensity of 43 (+/-) 10 Rayleigh. Radiative transfer calculations, using a model atmosphere appropriate to the conditions of the observation and having an exospheric temperature of 210 (+/-) 20 K, result in an He mixing ratio of 1.1 (+/-) 0.4 ppm in the lower atmosphere. Nonthermal escape of helium is due to the following: electron impact ionization and pickup of He(+) by the solar wind; collisions with hot oxygen atoms; and charge exchange with molecular species with corresponding column loss rates of 1.4 x 10(exp 5), 3 x 10(exp 4), and 7 x 10(exp 3) cm(exp -2)s(exp -1), respectively. The lifetime of helium on Mars is 5 x 10(exp 4) yr. The He outgassing rate, coupled with the Ar-40 atmospheric abundance and with the K:U:Th ratio measured in the surface rocks, is used as input to a simple two-reservoir degassing model which presumes the loss of all argon accumulated in the atmosphere during the first Byr by large-scale impacts. The model results in total planet mass ratios of 10(exp -5) g/g for K, 2.3 x 10(exp -9) g/g for U, 8.5 x 10(exp -9) g/g for Th, 4 x 10(exp -10) g/g for He, and 1.5 x 10(exp -9) g/g for Ar-40. The predicted radiogenic heat flux is 2 erg cm(exp -2)s(exp -1). Similar modeling for Venus results in total plant mass ratios of 4.7 x 10(exp -5) g/g for K, 6.7 x 10(exp -9) g/g for U, 2.2 x 10(exp -8) g/g for Th, 1.3 x 10(exp -9) for He, 6.7 x 10(exp -9) g/g for Ar-40, and a radiogenic heat flux of 15 erg cm(exp -2)s(exp -1). The implications of these results are discussed. The modeling shows that the radioactive elements were not distributed uniformly in the protoplanetary nebula, and their relative abundances differ very much in the terrestrial planets.
Bowyer, S.↗
Internal energy of reaction products by velocity analysis. i - scattered kbr' from the crossed molecular beam reaction k plus hbr.
Velocity distribution measurement of excited potassium bromide formed in reactive collision between crossed beams of K and HBr as function of scattering angle for selected K velocity
VELOCITY DISTRIBUTION↗
Effect of laser frequency on a collision-induced radiative process
A review is presented of the principles of collision induced radiative processes, followed by an examination of the effects of laser frequencies on these processes. A one-dimensional problem involving two electron states is considered, and it is found that the Hamiltonian of the radiation field is dominated by electric-dipole interaction which couples states of different parity. Transitions are noted to be dependent on collisions, and the complexities of three-dimensional systems are expressed as considerations of the angular momentum of the photon, the necessity of treating different states simultaneously, and the fact that a radiation field destroys rotational invariance. Changing the radiation frequency alters the crossing point and offers opportunities to study the interplay of potential surfaces with molecular dynamics. Experiments on Na+A systems are outlined for several collision energies and various laser frequencies. Multiple crossings were obtained, although the total cross-section, at all energies, decreased at 18,350/cm.
Devries, P. L.↗
Microwave evidence for interstellar molecules.
The present state of microwave observations of interstellar molecules is reviewed, with emphasis on the need for accurate theoretical understanding of their rates and modes of production. Typical abundances of molecular species in dark interstellar clouds are tabulated, and it is shown that in addition to abundance information observations of molecular lines can yield data on the isotope contents, velocities, and temperatures of the clouds in which they exist. Collisions, spontaneous emission, the isotropic radiation, radiation trapping, and higher-frequency radiation are evaluated as factors contributing to molecular excitation processes.
Townes, C. H.↗
Thin Film Mediated Phase Change Phenomena: Crystallization, Evaporation and Wetting
We focus on two distinct materials science problems that arise in two distinct microgravity environments: In space and within the space of a polymeric network. In the former environment, we consider a near eutectic alloy film in contact with its vapor which, when evaporating on earth, will experience compositionally induced buoyancy driven convection. The latter will significantly influence the morphology of the crystallized end member. In the absence of gravity, the morphology will be dominated by molecular diffusion and Marangoni driven viscous flow, and we study these phenomena theoretically and experimentally. The second microgravity environment exists in liquids, gels, and other soft materials where the small mass of individual molecules makes the effect of gravity negligible next to the relatively strong forces of intermolecular collisions. In such materials, an essential question concerns how to relate the molecular dynamics to the bulk rheological behavior. Here, we observe experimentally the diffusive motion of a single molecule in a single polymer filament, embedded within a polymer network and find anomalous diffusive behavior.
Wettlaufer, John S.↗
Some fluid dynamic problems in the studies of planetary collisions with cometary comas
The flow field in a cometary coma varies from free molecular flow to transition flow and finally to continuum flow. General discussions of these flow regimes with two-phase effects are given. Some numerical results of similarity solution of a strong shock propagation in a two-phase flow are presented.
Pai, S. I.↗
Molecular spectroscopy and collisional excitation
The paper examines the basic principles underlying the molecular transitions responsible for interstellar molecular spectra. The energy levels of molecules are discussed in detail with special attention given to the Born-Oppenheimer approximation, the electronic Hamiltonian, and the parameters of vibrational and rotational energy. The probabilities for radiative and collisional transitions are calculated. A brief review of techniques for molecular spectroscopy is presented along with methods used to determine collision cross sections on both an experimental and a theoretical basis.
Green, S.↗
Infrared line widths at planetary atmospheric temperatures
Recent theoretical models and measurements of the variation of collision-broadened line width with temperature in the infrared are discussed for temperatures relevant to planetary atmospheres. The present review is restricted to lines broadened by H2, N2, O2, CO2, and He, the lines formed in the atmospheres of Jupiter, Saturn, Uranus, and Neptune. The design for a low-temperature absorption cell consisting of a nickel-coated copper tube is described. The lack of an adequate theoretical model for variation of the collision-broadened line width with temperature in terms of the molecular constants of the colliding partners is pointed out.
Varanasi, Prasad↗
Collisional excitation of interstellar molecules - Deuterated water, HDO
Using an accurate theoretical interacting potential and coupled-channel molecular scattering calculations, excitation rates for deuterated water (HDO) in collisions with He atoms were computed. Data are presented for rates among the 34 rotational levels with energy below 400/cm for temperatures between 50 and 500 K. Excitation rate constants were determined using data from fixed energy cross sections averaged over thermal (Boltzmann) distributions of collision energies. Based on the agreement (for H2O) of rates from two different theoretical potentials and on agreement with the limited experimental data, the larger rates for HDO were estimated to be generally accurate to better than 50 percent.
Green, Sheldon↗
Chemistry of the outer planets
Various aspects were studied of past or present chemistry in the atmospheres of the outer planets and their satellites using lab simulations. Three areas were studied: (1) organic chemistry induced by kinetically hot hydrogen atoms in the region of Jupiter's atmosphere containing the ammonia cirrus clouds; (2) the conversion of NH3 into N2 by plasmas associated with entry of meteors and other objects into the atmosphere of early Titan; and (3) the synthesis of simple hydrocarbons and HCN by lightning in mixtures containing N2, CH4, and NH3 representing the atmospheres of Titan and the outer planets. The results showed that: (1) hot H2 atoms formed from the photodissociation of NH3 in Jupiter's atmosphere could account for some of the atmospheric chemistry in the ammonia cirrus cloud region; (2) the thermalization of hot H2 atoms in atmospheres predominated by molecular H is not as rapid as predicted by elastic collision theory; (3) the net quantum loss of NH3 in the presence of a 200 fold excess of H2 is 0.02, much higher than was expected from the amount of H2 present; (4) the conversion of NH3 into N2 in plasmas associated with infalling meteors is very efficient and rapid, and could account for most of the N2 present on Titan; (5) the yields of C2H2 and HCN from lightning induced chemistry in mixtures of CH4 and N2 is consistent with quenched thermodynamic models of the discharge core; and (6) photolysis induced by the UV light emitted by the gases in the hot plasmas may account for some, if not most, of the excess production of C2H6 and the more complex hydrocarbons.
Scattergood, Thomas W.↗
First measurement of helium on Mars: Implications for the problem of radiogenic gases on the terrestrial planets
108 +/- 11 photons of the martian He 584-A airglow detected by the Extreme Ultraviolet Explorer (EUVE) satellite during a 2-day exposure (January 22-23, 1993) correspond to the effective disk average intensity of 43 +/- 10 Rayleigh (Ra). Radiative transfer calculations, using a model atmosphere appropriate to the conditions of the observation and having an exospheric temperature of 210 +/- 20 K, result in a He mixing ratio of 1.1 +/- 0.4 ppm in the lower atmosphere. Nonthermal escape of helium is due to electron impact ionization and pickup of He(+) by the solar wind, to collisions with hot oxygen atoms, and to charge exchange with molecular species with corresponding column loss rates of 1.4 x 10(exp 5), 3 x 10(exp 4), and 7 x 10(exp 3)/sq cm/s, respectively. The lifetime of helium on Mars is 5 x 10(exp 4) years. the He outgassing rate, coupled with the Ar-40 atmospheric abundance and with the K:U:Th ratio measured in the surface rocks, is used as input to a single two-reservoir degassing model which is applied to Mars and then to Venus. A similar model with known abundances if K, U, and Th is applied to Earth. The models for Earth and Mars presume loss of all argon accumulated in the atmospheres during the first billion years by large-scale meteorite and planetesimal impacts. The models show that the degassing coefficients for all three planets may be approximated by function delta = delta(sub 0) x (t(sub 0)/t)(exp 1/2) with delta(sub 0) = 0.1, 0.04, and 0.0125 Byr for Earth, Venus, and Mars, respectively. After a R(exp 2) correction this means that outgassing processes on Venus and Mars are weaker than on Earth by factors of 3 and 30, respectively. Mass ratios of U and Th are almost the same for all three planets, while potassiumis depleted by a factor of 2 in Venus and Mars. Mass ratio of helium and argon are close to 5 x 10(exp -9) and 2 x 10(exp -8) g/g in the interiors of all three planets. The implications of these results are discussed.
Krasnopolsky, V. A.↗
Computer Simulation of the far Infrared Collision Induced Absorption Spectra of Gaseous CO2
Far infrared collision induced absorption spectra of gaseous CO2 were computed using molecular dynamics simulations. The quadrupole and hexadecapole multipolar induction, through the trace, and the anisotropy of the molecular polarizability were found to be insufficient to represent properly the dipole induction mechanism. For a detailed analysis of the induction process the spectra obtained were decomposed into components resulting from different terms of the induced dipole. Based on this decomposition, all additional overlap contribution for each term was proposed. When spectra were recomputed including such overlap, good agreement between experiment and simulation was achieved over the temperature range at which measurements exist (233-400 K). The use of an anisotropic intermolecular potential was found to be of critical importance for obtaining the right shape of the far wings of the spectra.
Gruszka, Marcin↗
Electron-Molecule Col1isions: Quantitative Approaches, and the Legacy of Aaron Temkin
This article, on electron-molecule collisions, is dedicated to the legacy of my good friend and sometime collaborator, Aaron Temkin on his retirement from the NASA-Goddard Space Flight Center after many years of work at the highest intellectual level in the theoretical treatment of electron-atom and electron-molecule scattering. Aaron's contributions to the manner in which we think about electron-molecule collisions is clear to all of us who have worked in this field. I doubt that the great progress that has occurred in the computational treatment of such complex collision problems could have happened without these contributions. For a brief historical account, see the discussion of Temkin's contribution to electron-molecule scattering in the first article of this volume by Dr. A. K. Bhatia. In this article, I will concentrate on the application of the so called, non-adiabatic R-matrix theory, to vibrational excitation and dissociative attachment, although I will also present some results applying the Linear Algebraic and Kohn-Variational methods to vibrational excitation. As a starting point for almost all computationally effective approaches to electron-molecule collisions, is the fixed nuclei approximation. That is, one recognizes, just as one does with molecular bound states, that there is a separation of electronic(fast) and nuclear(s1ow) degrees of freedom. This separation makes it possible to "freeze" the nuclei in space, calculate the collision parameters for the frozen molecule and then, somehow to add back the vibrations and rotations. The manner in which this is done, depends on the details of the collision problem. It is the work of Aaron and a number of other researchers that has provided the guidance necessary to resolve these issues.
Schneider, B.I.↗
Far-infrared observations of the Cepheus OB3 molecular cloud
The molecular cloud accompanying the Cepheus OB3 association is observed in the infrared at wavelengths of 10-400 microns. Far-infrared emission at 55 microns and 125 microns from the two CO hot spots, Cep A and Cep B, is mapped with a resolution of approximately one arcmin. Cep A is also mapped at 400 microns with a resolution of approximately one arcmin, and both hot spots are searched for 20-micron sources. It is noted that the Cep A hot spot appears to be heated by energy sources internal to the molecular cloud. The dust temperatures are considered sufficient to explain the gas temperatures provided the dust heats the gas by collisions. In marked contrast, the Cep B region appears to be heated from outside the cloud, with the strongest far-infrared emission arising near the interface between the molecular cloud and the S155 H II region. It is thought that the gas heating rate through collisions with dust may be insufficient to achieve the gas temperature observed in Cep B.
Evans, N. J., II↗