Collisional Deexcitation Rate Research Articles

Vertical profiles of Mars 1.27 µm O2 dayglow from MRO CRISM limb spectra: Seasonal/global behaviors, comparisons to LMDGCM simulations, and a global definition for Mars water vapor profiles

Since July of 2009, The Compact Reconnaissance Imaging Spectral Mapper (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) has periodically obtained pole-to-pole observations (i.e., full MRO orbits) of limb scanned visible/near IR spectra (λ=0.4−4.0 µ m, △λ ∼ 10 nm- Murchie et al., 2007). These CRISM limb observations support the first seasonally and spatially extensive set of Mars 1.27 µm O2(1△g) dayglow profile retrievals (∼ 1100) over ≥ 8–80 km altitudes. Their comparison to Laboratoire de Météorologie Dynamique (LMD) global climate model (GCM) simulated O2(1△g) volume emission rate (VER) profiles, as a function of altitude, latitude, and season (solar longitude, Ls), supports several key conclusions regarding Mars atmospheric water vapor (which is derived from O2(1△g) emission rates), Mars O3, and the collisional de-excitation of O2(1△g) in the Mars CO2 atmosphere. Current (Navarro et al., 2014) LMDGCM simulations of Mars atmospheric water vapor fall 2–3 times below CRISM derived water vapor abundances at 20–40 km altitudes over low-to-mid latitudes in northern spring (Ls = 30-60°), and northern mid-to-high latitudes over northern summer (Ls = 60–140°). In contrast, LMDGCM simulated water vapor is 2–5 times greater than CRISM derived values at all latitudes and seasons above 40 km, within the aphelion cloud belt (ACB), and over high-southern to mid-southern latitudes in southern summer (Ls = 190-340°) at 15–35 km altitudes. Overall, the solstitial summer-to-winter hemisphere gradients in water vapor are reversed between the LMDGCM modeled versus the CRISM derived water vapor abundances above 10–30 km altitudes. LMDGCM-CRISM differences in water vapor profiles correlate with LMDGCM-CRISM differences in cloud mixing profiles; and likely reflect limitations in simulating cloud microphysics and radiative forcing, both of which restrict meridional transport of water from summer-to-winter hemispheres on Mars (Clancy et al., 1996; Montmessin et al., 2004; Steele et al., 2014; Navarro et al., 2014) and depend on uncertain cloud microphysical properties (Navarro et al., 2014). The derived low-to-mid latitude changes in Mars water vapor vertical distributions should reduce current model-data disagreements in column O3 and H2O2 abundances over low-to-mid latitudes (e.g., within the ACB; Lefèvre et al., 2008; Encrenaz et al., 2015; Clancy et al., 2016). Lastly, the global/seasonal average comparison of CRISM and LMDGCM O2(1△g) VER below 20 km altitudes indicates a factor of ∼3 times lower value (0.25×10−20 cm3sec−1) for the CO2 collisional de-excitation rate coefficient of O2(1△g) than derived recently by Guslyakova et al. (2016).

Broadening effects on opacity calculation of CH plasmas

Opacity is a function of the temperature and electron density of plasma. The plasma density can be determined by measurements of Stark-broadened K-shell spectral lines. The purpose of this work is to obtain a more detailed structure of opacity with regard to broadening effects. For this aim, the opacity frequency dependency and mean opacity of mixed plasmas are calculated under local thermodynamic equilibrium (LTE) conditions. The LTE state in inertial confinement fusion occurs when the collisional deexcitation rate from the upper level to the lower level greatly exceeds the spontaneous decay rate. Since the thermal radiation can be absorbed by the CH-ablator, by studying the behavior of the CH Polystyrene opacity, one can obtain the temperature and density of the plasma in investigations of matter found in stellar interiors, inertial fusion implosions, and Z pinches as a diagnostic technique. The main aspect of diagnostic application is spectrum broadening. The final results show that the Stark-broadened line shape is dependent on the density. Also, it is shown that the resonance peak and spectrum broadening of the opacity spectrum of a mixed plasma such as the CH-plasma is larger than a single atom plasma such as Carbon.

Collisional excitation of doubly deuterated ammonia ND2H by para-H2

Collisional de-excitation rates of partially deuterated molecules are different from the fully hydrogenated species because of lowering of symmetry. We compute the collisional (de)excitation rates of ND2H by ground state para-H2, extending the previous results for He- lium. We describe the changes in the potential energy surface of NH3- H2 involved by the pres- ence of two deuterium nuclei. Cross sections are calculated within the full close-coupling ap- proach and augmented with coupled-state calculations. Collisional rate coefficients are given between 5 and 35 K, a range of temperatures which is relevant to cold interstellar conditions. We find that the collisional rates of ND2H by H2 are about one order of magnitude higher than those obtained with Helium as perturber. These results are essential to radiative transfer modelling and will allow to interpret the millimeter and submillimeter detections of ND2H with better constraints than previously.

Effects of non-LTE multiplet dynamics on lumped-state modelling in moderate to high atomic number plasmas

Two atomic models of the population dynamics of substates within the n = 4 and n = 3 multiplets of nickel-like tungsten and beryllium-like iron, respectively, are described in this paper. The flexible atomic code (FAC) is used to calculate the collisional and radiative couplings and energy levels of the excited states within these ionization stages. These atomic models are then placed within larger principal-quantum-number-based ionization dynamic models of both tungsten and iron plasmas. Collisional-radiative equilibrium calculations are then carried out using these models that demonstrate how the multiplet substates depart from local thermodynamic equilibrium (LTE) as a function of ion density. The effect of these deviations from LTE on the radiative and collisional deexcitation rates of lumped 3s, 3p, 3d, 4s, 4p, 4d and 4f states is then calculated and least-squares fits to the density dependence of these lumped-state rate coefficients are obtained. The calculations show that, with the use of lumped-state models (which are in common use), one can accurately model the L- and M-shell ionization dynamics occurring in present-day Z-pinch experiments only through the addition of these extra, non-LTE-induced, rate coefficient density dependences. However, the derivation and use of low-order polynomial fits to these density dependences makes lumped-state modelling both viable and of value for post-processing analyses.

Three-dimensional photoionization modelling of the hydrogen-deficient knots in the planetary nebula Abell 30

We have constructed a photoionization model, using the three-dimensional Monte Carlo code mocassin, for one of the hydrogen-deficient knots (J3) of the born-again planetary nebula Abell 30. The model consists of spherical knots, comprising a cold, dense, hydrogen-deficient core with very high metal abundances. The inner core, occupying 9.1 per cent of the total volume of the knot, is surrounded by a less dense hydrogen-deficient and metal-enriched gas envelope, with less extreme abundances. The envelope of the knot might have been formed by the mixing of the knot material with the surrounding nebular gas. This bi-chemistry, bi-density model did not produce enough heating to match the fluxes of the collisionally excited emission lines (CELs) and of the optical recombination lines (ORLs) observed in the spectrum of the knot. We therefore included heating by photoelectric emission from dust grains in the thermal equilibrium calculations, and found that dust-to-gas ratios of 0.077 and 0.107 by mass for the central core and the envelope of the knot, respectively, are sufficient to fit the spectrum. Surprisingly, photoelectric emission from grains is the dominant source of heating in the hot envelope of the knot, while heating by photoionization of helium and heavy elements dominates in the cold core. We obtain a good fit with the observations for most of the significant emission lines treated in our model. The two major discrepancies occurred for the [O ii] 3727,29- Å doublet and the [N ii] 6548,6584- Å lines, which are severely underestimated in our model. Recombination contributions could be significant and we included them for the O ii transitions. However, this was not sufficient to resolve the discrepancy, due to the high collisional de-excitation rates in the dense core, where most of the recombination lines would be produced. This possibly highlights a weakness in using a discontinuous density distribution like ours, where in reality one might expect an intermediate phase to exist. The chemical abundances inferred from our modelling of the central core region and of the envelope of the knot are, at least qualitatively, in agreement with the abundances derived by the empirical analysis of Wesson, Liu & Barlow, although the discrepancies between the core and the envelope abundances that we find are less dramatic than those implied by the ORL and CEL empirical analysis. Our models also indicate, in agreement with the empirical analysis of Wesson et al., that the C/O ratio in the two regions of the knot is less than unity, contrary to theoretical predictions for born-again nebulae.

On collisional vibrational deexcitation rate constantsk 1?0 of diatomic molecules

Collisional vibrational deexcitation rate constantsk 1→0 for diatomic molecules have been calculated and used by a number of authors. But sometimes scientists use some fit-formula instead of the actual expression. This may be caused by difficulties in understanding the actual formula. Here, I discuss the calculations of collisional deexcitation rate constants for diatomic molecules by using the actual expression.

Physical conditions in photodissociation regions: M17 northern bar

We present results of long-slit spectroscopy, from 2.0 to 2.5 μm, of the photodissociation region in the northern bar of the H II region M17. The emission from ionized material peaks to the south of that from molecular gas, in agreement with previous measurements. The diagnostic 1−0 S (1) to 2−1 S(1) line ratio is approximately 3, larger than the ratio for pure fluorescence, implying that the H 2 is slightly thermalized. The ratio does not change along the extent of the molecular emission which fills the slit (approximately 60 arcsec), suggesting that the collisional de-excitation rate is constant. We take this to mean that the physical conditions are constant across the region, implying that in the northern bar of M17 we are viewing the face of the molecular cloud

Laser-fluorescence measurements of nitric oxide in low-pressure H2/O2/No flames

The concentration profiles of NO in low-pressure (76 Torr) H 2 /O 2 /Ar flames to which nitric oxide was added (0.94% and 1.74% in argon), were measured by pulsed, laser-induced fluorescence. Laser excitation of NO in the (1,0) band of the A 2 Σ→X 2 Π transition at 214.34 nm was followed by detection, either time-integrated or temporally resolved, of the fluorescence in the (1,4) band at 252.2 nm. The temporally resolved fluorescence measurements were used to determine the collisional de-excitation rates needed to convert time-integrated fluorescence signal into nitric oxide concentration. Five flames were studied with H 2 /O 2 equivalence ratios of 0.88, 0.98, 1.22, 1.37, and 1.50. In these flames the collisional deexcitation rate decreases rapidly above the burner surface as the density decreases with increasing temperature. A 20% decrease was observed for the lean flames, and a 30% decrease for the rich flames. For the near stoichiometric flame, the measured de-excitation rate constant was used to determine a collision cross section of 38 2 at 1414 K for collisional deexcitation of the A 2 Σ ( v ′=1) state (including both electronic quenching and vibrational relaxation) by water. Within the precision of the measurement technique (±10%), no significant removal of nitric oxide was observed in these flames.

Measurements of Transition Probabilities for Intersystems Lines of Atomic Ions Used in Diagnosis of Astrophysical Plasmas

In many low-charge ions of astrophysically abundant light elements, the spins of the ground and first-excited terms are different. Because of spin-orbit interactions, the states of these terms are mixtures of LS basis states, and as a consequence, transitions with ∆S = 1, i.e., ‘intersystem transitions’, can occur. The_transition probabilities (A-values) for such lines in low-Z ions are about 104 sec -1 to 102 sec-1. These values are of the same order of magnitude as the collisional de-excitation rates in many low-density astronomical objects. Consequently, intersystem lines, which are not readily seen in the laboratory, are significant features in many astronomical spectra. IUE spectra that show such lines in novae, hot stars, cool stars, symbiotic stars, binary stars, variable stars, Herbig-Haro objects, H II regions, planetary nebulae, quasars, and galaxies are discussed in Kondo et al. (1982). Moreover, because of the commensurate radiative and collisional de-excitation rates for the upper levels, the ratios of intersystem-line intensities to allowed-line intensities are density sensitive in many objects.

Two- and three-body collision coefficients forXe(P13)andXe(P23)atoms and radiative lifetime of theXe2(1u)molecule

The time dependence of the vacuum-uv emissions from xenon was studied at pressures ranging from 4 to 1000 Torr. Excitation of the atoms was provided by a low-intensity electron beam. Measurements were made at the wavelengths of the $\mathrm{Xe}(^{3}P_{1})$ resonance line, the 1500-\AA{} (first) continuum, and the 1700-\AA{} (second) continuum. Two- and three-body collision coefficients for the destruction of $\mathrm{Xe}(^{3}P_{1})$ atoms and a three-body coefficient for $\mathrm{Xe}(^{3}P_{2})$ metastables were determined. A radiative lifetime of 99 nsec for the ${1}_{u}$ molecular state was measured at the wavelength of the second continuum. The pressure dependence of the decay constants at the three wavelengths leads to the following results: The collisional deexcitation rate for the transition $\mathrm{Xe}(^{3}P_{1})$ to $\mathrm{Xe}(^{3}P_{2})$ is ${9.1\ifmmode\times\else\texttimes\fi{}10}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$/Torr. The three-body coefficient for $\mathrm{Xe}(^{3}P_{1})$ atoms is 46 ${\mathrm{sec}}^{\ensuremath{-}1}$/${\mathrm{Torr}}^{2}$. The three-body destruction rate of $\mathrm{Xe}(^{3}P_{2})$ metastables is 40 ${\mathrm{sec}}^{\ensuremath{-}1}$/${\mathrm{Torr}}^{2}$. The estimated uncertainty in the results is \ifmmode\pm\else\textpm\fi{}10%.

Rate Coefficients for Electron Excitation of the First Resonance Transition in h, Li, Na, Ca, Ca', and Ba' Calculated from Experimental Data

view Abstract Citations (44) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rate Coefficients for Electron Excitation of the First Resonance Transition in h, Li, Na, Ca, Ca', and Ba' Calculated from Experimental Data Crandall, D. H. ; Dunn, G. H. ; Gallagher, A. ; Hummer, D. G. ; Kunasz, C. V. ; Leep, D. ; Taylor, P. O. Abstract By fitting cubic splines augmented with special functional forms for low and high energies to cross-section data determined experimentally at discrete values of the electron energy, we obtain an interpolation that can be visually inspected and adjusted to prevent the appearance of spurious features. The familiar integral expressing the rate coefficient in terms of the cross-sections can then be evaluated with no further approximation. This procedure is applied here to cross-section data for the first resonance transition of H, Li, Na, Ca, Ca +, and Ba +. The resulting collisional de-excitation rate coefficient, from which the excitation-rate coefficient can be determined by the detailed balance relation, is tabulated in each case for electron temperatures in the interval from 1O to 1O K and is expressed in terms of a Chebyshev expansion valid for this range of temperature. Subject heading: transition probabilities Publication: The Astrophysical Journal Pub Date: August 1974 DOI: 10.1086/153025 Bibcode: 1974ApJ...191..789C full text sources ADS |

Sound amplification from controlled excitation reactions

The possibility of acoustic amplification in a gas subjected to an external means of overpopulating internal energy levels has been explored theoretically. The basic concept that the temperature variation of the sound wave controls the flow of energy from the source to translation must take into account the internal structure of the gas. When the gas is pumped optically, the strong temperature dependence of the collisional de-excitation rate constants is included in addition to the temperature and pressure dependence of the optical absorption coefficient considered by others. The resulting attenuation or amplification of sound has been calculated both for a two-level and a multilevel gas. For illustrative purpose, a 90% CO-10% H2 numerical example has been developed. This example demonstrates that sound amplification should be experimentally observable.

Measurement of the Depopulation of the2P0,1,23Levels of Heliumlike Ions by Electron Collisions

The collisional depopulation rate of the $2^{3}P_{0,1,2}$ triplet levels of Cv, Nvi, Ovii, Fviii, and Ne ix was determined from measured $2^{3}S\ensuremath{-}2^{3}P$ line intensity ratios. The triplet lines were observed in a hot $\ensuremath{\theta}$-pinch deuterium plasma seeded with a few percent of the element to be examined. The plasma electron temperature and density were known from laser-light-scattering experiments. The total depopulation rate of the $2^{3}P_{0,1,2}$ levels is mainly due to the $2^{3}S\ensuremath{-}2^{3}P$ collisional deexcitation rate. The measured rate agrees well with calculations by Blaha based on the Coulomb---Born approximation. With these depopulation rates known, the electron density of the plasma can be determined just by measuring the triplet-line intensity ratios.

Spectroscopic Study of Electron Recombination with Monatomic Ions in a Helium Plasma

Recent work on electron-ion recombination has shown that a model including recombination into highly excited bound levels through electron-electron-ion collisions and transitions between the bound levels through electron-atom collisions, as well as the usual radiative transitions, is in good agreement with experiments in which processes involving molecular ions, etc., are unimportant. By making absolute intensity measurements of the lines of helium emitted from the decaying plasma of an arc jet in the visible and near ultraviolet, the number densities of the excited states of helium have been calculated. From these measurements electron temperatures between 0.15 and 0.30 eV and electron densities between 4\ifmmode\times\else\texttimes\fi{}${10}^{12}$ and 4\ifmmode\times\else\texttimes\fi{}${10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ are found, with a fractional ionization of the order of 1%. When interpreted by means of the collisional-radiative recombination model, these measurements also give values for ${K}_{n,n\ensuremath{-}1}$, the collisional de-excitation rate constant of an excited helium atom from level $n$ to $n\ensuremath{-}1$. The constancy of ${K}_{n,n\ensuremath{-}1}$ over a range of electron density from 4\ifmmode\times\else\texttimes\fi{}${10}^{12}$ to 4\ifmmode\times\else\texttimes\fi{}${10}^{14}$ per ${\mathrm{cm}}^{3}$ indicates the validity of the model, and the values of ${K}_{n,n\ensuremath{-}1}$ are in reasonable agreement with a recent theory of classical excitation cross sections. A square-root dependence of this cross section on the excess energy is indicated, since the values of ${K}_{n,n\ensuremath{-}1}$ appear to be independent of electron temperature. It is then found that ${Q}_{2,3}=9.3\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}E$, ${Q}_{3,4}=73\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}E$, and ${Q}_{4,5}=380\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}E$, where ${Q}_{n,n+1}$ is the averaged excitation cross section from the levels with principal quantum number $n$ to the levels with principal quantum number $n+1$ in units ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, and $E$ is the excess energy in eV. These cross sections have an estimated error of about 30% in the threshold energy range to about 0.3 eV.