scholarly journals Recent Advances in Atomic Calculations and Experiments of Interest in the Study of Planetary Nebulae

1983 ◽  
Vol 103 ◽  
pp. 143-172 ◽  
Author(s):  
C. Mendoza
Keyword(s):  
Cross Sections ◽  
Transition Probabilities ◽  
Planetary Nebulae ◽  
Electron Excitation ◽  
Rate Coefficients ◽  
Excitation Rate ◽  
Recent Advances

Recent advances in the calculation and measurement of transition probabilities, electron excitation rate coefficients and photoionization cross sections relevant to the study of planetary nebulae are discussed. A compilation of these parameters is also presented.

scholarly journals Improved Neutron-Capture Element Abundances in Planetary Nebulae

2009 ◽  
Vol 26 (3) ◽  
pp. 339-344 ◽  
Author(s):  
N. C. Sterling ◽  
H. L. Dinerstein ◽  
S. Hwang ◽  
S. Redfield ◽  
A. Aguilar ◽  
...  
Keyword(s):  
Cross Sections ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Rate Coefficients ◽  
Atomic Data ◽  
Agb Stars ◽  
Iron Species ◽  
Element Abundances ◽  
Ionization Balance ◽  
Initial Results

AbstractSpectroscopy of planetary nebulae (PNe) provides the means to investigate s-process enrichments of neutron(n)-capture elements that cannot be detected in Asymptotic Giant Branch (AGB) stars. However, accurate abundance determinations of these elements present a challenge. Corrections for unobserved ions can be large and uncertain, since in many PNe only one ion of a given n-capture element has been detected. Furthermore, the atomic data governing the ionization balance of these species are not well-determined, inhibiting the derivation of accurate ionization corrections. We present initial results of a program that addresses these challenges. Deep high-resolution optical spectroscopy of ∼20 PNe has been performed to detect emission lines from trans-iron species including Se, Br, Kr, Rb and Xe. The optical spectral region provides access to multiple ions of these elements, which reduces the magnitude and importance of uncertainties in the ionization corrections. In addition, experimental and theoretical efforts are providing determinations of the photoionization cross sections and recombination rate coefficients of Se, Kr and Xe ions. These new atomic data will make it possible to derive robust ionization corrections for these elements. Together, our observational and atomic data results will enable n-capture element abundances to be determined with unprecedented accuracy in ionized nebulae.

scholarly journals Measurement of the A-Value of the Intersystem Transition in Al II at 2670 Å: Å Progress Report

1984 ◽  
Vol 86 ◽  
pp. 163-166
Author(s):  
B. Carol Johnson ◽  
H.S. Kwong
Keyword(s):  
Cross Sections ◽  
Radiative Decay ◽  
Transition Probabilities ◽  
Radiative Transition ◽  
Electron Excitation ◽  
Spectral Lines ◽  
Metastable Level ◽  
Astrophysical Plasmas ◽  
Atomic Ions ◽  
A Value

Ratios of intensities of spectral lines produced in the radiative decay of collisionally-excited levels of atomic ions are versatile indicators of electron density in astrophysical plasmas when one of the lines involves a metastable level (see the review by Feldman 1981 and references therein). Radiative transition probabilities (A-values) and electron excitation cross sections are necessary for accurate, quantitative analyses of these plasmas. The work reported here is part of a program of measurements of astrophysically interesting A-values and radiative lifetimes (see the review by Smith et al. 1984); until we began, such anaylyses of astrophysical plasmas depended upon unconfirmed calculated A-values.

scholarly journals Rotational relaxation of HCO+ and DCO+ by collision with H2

2020 ◽  
Vol 497 (4) ◽  
pp. 4276-4281 ◽  
Author(s):  
Otoniel Denis-Alpizar ◽  
Thierry Stoecklin ◽  
Anne Dutrey ◽  
Stéphane Guilloteau
Keyword(s):  
Cross Sections ◽  
Rate Coefficients ◽  
Local Thermal Equilibrium ◽  
Rotational Relaxation ◽  
Close Coupling ◽  
Excitation Rate ◽  
Rotational States ◽  
Non Local ◽  
The Difference ◽  
Isotopic Effects

ABSTRACT The HCO+ and DCO+ molecules are commonly used as tracers in the interstellar medium. Therefore, accurate rotational rate coefficients of these systems with He and H2 are crucial in non-local thermal equilibrium models. We determine in this work the rotational de-excitation rate coefficients of HCO+ in collision with both para- and ortho-H2, and also analyse the isotopic effects by studying the case of DCO+. A new four-dimensional potential energy surface from ab initio calculations was developed for the HCO+–H2 system, and adapted to the DCO+–H2 case. These surfaces are then employed in close-coupling calculations to determine the rotational de-excitation cross-sections and rate coefficients for the lower rotational states of HCO+ and DCO+. The new rate coefficients for HCO+ + para-H2 were compared with the available data, and a set of rate coefficients for HCO+ + ortho-H2 is also reported. The difference between the collision rates with ortho- and para-H2 is found to be small. These calculations confirm that the use of the rate coefficients for HCO+ + para-H2 for estimating those for HCO+ + ortho-H2 as well as for DCO+ + para-H2 is a good approximation.

scholarly journals Database NORAD-Atomic-Data for Atomic Processes in Plasma

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 68
Author(s):  
Sultana Nahar
Keyword(s):  
Cross Sections ◽  
Ground State ◽  
Recombination Rate ◽  
Bound States ◽  
Transition Probabilities ◽  
Rate Coefficients ◽  
Atomic Data ◽  
Atomic Processes ◽  
Ion Recombination ◽  
Atomic Species

The online atomic database of NORAD-Atomic-Data, where NORAD stands for Nahar OSU Radiative, is part of the data sources of the two international collaborations of the Opacity Project (OP) and the Iron Project (IP). It contains large sets of parameters for the dominant atomic processes in astrophysical plasmas, such as, (i) photo-excitation, (ii) photoionization, (iii) electron–ion recombination, (iv) electron–impact excitations. The atomic parameters correspond to tables of energy levels, level-specific total photoionization cross-sections, partial photoionization cross-sections of all bound states for leaving the residual ion in the ground state, partial cross-sections of the ground state for leaving the ion in various excited states, total level-specific electron–ion recombination rate coefficients that include both the radiative and dielectronic recombination, total recombination rate coefficients summed from contributions of an infinite number of recombined states, total photo-recombination cross-sections and rates with respect to photoelectron energy, transition probabilities, lifetimes, collision strengths. The database was created after the first two atomic databases, TOPbase under the OP and TIPbase under the IP. Hence the contents of NORAD-Atomic-Data are either new or from repeated calculations using a much larger wave function expansion making the data more complete. The results have been obtained from the R-matrix method using the close-coupling approximation developed under the OP and IP, and from atomic structure calculations using the program SUPERSTRUCTURE. They have been compared with available published results which have been obtained theoretically and experimentally, and are expected to be of high accuracy in general. All computations were carried out using the computational facilities at the Ohio Supercomputer Center (OSC) starting in 1990. At present it contains atomic data for 154 atomic species, 98 of which are lighter atomic species with nuclear charge Z ≤ 28 and 56 are heavier ones with Z > 28. New data are added with publications.

scholarly journals The Measurement and Interpretation of NeV 2–2 Line Intensity Ratios

1988 ◽  
Vol 102 ◽  
pp. 59-62
Author(s):  
J. Lang
Keyword(s):  
Grazing Incidence ◽  
Electron Excitation ◽  
Spectral Lines ◽  
Rate Coefficients ◽  
Experimental Result ◽  
Measured Intensity ◽  
Laser Scattering ◽  
Excitation Rate ◽  
Theta Pinch ◽  
Intensity Ratios

AbstractA theta-pinch was used to produce NeV 2–2 spectral lines. The intensities of the lines were measured using a grazing incidence spectrometer which had been intensity calibrated by the branching ratios method. The electron temperature and density of the theta-pinch discharge were found by laser scattering. The measured intensity ratios are compared to theoretical predictions based on electron excitation rate coefficients calculated using the R-matrix close coupling method. For two of the measured ratios experiment and theory agree within the experimental uncertainty, For the other two ratios the theoretical prediction is greater than the experimental result.

The Relative Intensities of Lines From Bel-Like Ions in the Solar Spectrum

1971 ◽  
Vol 2 ◽  
pp. 519-526 ◽  
Author(s):  
Carole Jordan
Keyword(s):  
Cross Sections ◽  
Solar Spectrum ◽  
Rate Coefficients ◽  
Private Communication ◽  
Intensity Data ◽  
Excitation Rate ◽  
Excitation Cross Sections ◽  
Intensity Ratios ◽  
Intercombination Line

The permitted transitions 2s21S-2s2p1P and 2s2p3P-2p23P in the Bel-like ions CIII, NIV and OV have been observed for some years in the solar spectrum (Hall et al., 1963). Recently, intensity data have also been obtained for the intercombination line 2s21S-2s2p3P1 in these ions (Burton et al., 1970). A large number of excitation rate coefficients are needed before the intensity ratios of these transitions can be computed and compared with those observed. These excitation cross-sections are now becoming available (Osterbrock, 1970; Eissner, private communication), and the present paper gives the results of an analysis of the intensity data. Figure 1 shows a partial term scheme for the Bei-like ions and the observed transitions.

Dynamical constraints and nuclear spin caused restrictions in collision systems

2006 ◽  
Vol 364 (1848) ◽  
pp. 3007-3034 ◽  
Author(s):  
D Gerlich ◽  
F Windisch ◽  
P Hlavenka ◽  
R Plašil ◽  
J Glosik
Keyword(s):  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Transition Probabilities ◽  
Molecular Beams ◽  
Ion Traps ◽  
Specific Model ◽  
Rate Coefficients ◽  
Hydrogen Ions ◽  
Collision Dynamics ◽  
Model Calculations

This contribution summarizes a variety of results and ongoing activities, which contribute to our understanding of inelastic and reactive collisions involving hydrogen ions. In an overview of our present theoretical knowledge of various collision systems ( m + n ≤5), it is emphasized that although the required potential energy surfaces are well characterized, no detailed treatments of the collision dynamics are available to date, especially at the low energies required for astrochemistry. Instead of treating state-to-state dynamics with state of the art methods, predictions are still based on: (i) simple thermodynamical arguments, (ii) crude reaction models such as H atom exchange or proton jump, or (iii) statistical considerations used for describing processes proceeding via long-lived or strongly interacting collision complexes. A central problem is to properly account for the consequences of the fact that H and D are fermions and bosons, respectively. In the experimental and results sections, it is emphasized that although a variety of innovative techniques are available and have been used for measuring rate coefficients, cross-sections or state-to-state transition probabilities, the definitive experiments are still pending. In the centre of this contribution are our activities on various m + n =5 systems. We report a few selected additional results for collisions of hydrogen ions with p -H 2 , o -H 2 , HD, D 2 or well-defined mixtures of these neutrals. Most of the recent experiments are based on temperature variable multipole ion traps and their combination with pulsed gas inlets, molecular beams, laser probing or electron beams. Based on the state-specific model calculations, it is concluded that for completely understanding the gas phase formation and destruction of in a trap, an in situ characterization of all the experimental parameters is required with unprecedented accuracy. Finally, the need to understand the hydrogen chemistry relevant for dense pre-stellar cores is discussed.

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