- ID:
- ivo://CDS.VizieR/J/A+A/625/A78
- Title:
- Carbon and nitrogen rate coefficients
- Short Name:
- J/A+A/625/A78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-energy inelastic collisions with neutral hydrogen atoms are important processes in stellar atmospheres, and a persistent source of uncertainty in non-LTE modelling of stellar spectra. We calculate and study excitation and charge transfer of CI and of NI due to such collisions. We use a previously presented method that is based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions for the adiabatic potential energies, combined with the multichannel Landau- Zener model for the collision dynamics. We find that charge transfer processes typically lead to much larger rate coefficients than excitation processes, consistent with studies of other atomic species. Two-electron processes were considered and lead to non-zero rate coefficients that can potentially impact statistical equilibrium calculations. However, they were included in the model in an approximate way, via an estimate for the two-electron coupling that was presented earlier in the literature: the validity of these data should be checked in a future work.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/620/A188
- Title:
- Carbon atom electron-impact double ionization
- Short Name:
- J/A+A/620/A188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Electron-impact single- and double-ionization cross sections and Maxwellian rate coefficients are presented for the carbon atom. Scaling factors are introduced for the electron-impact excitation and ionization cross sections obtained in the distorted wave (DW) approximation. It is shown that the scaled DW cross sections provide good agreement with measurements for the single ionization of the C atom and C1+ ion. The direct double-ionization (DDI) process is studied using a multi-step approach. Ionization-ionization, excitation-ionization-ionization, and ionization-excitation-ionization branches are analyzed. It is demonstrated that the three-step processes contribute 40% of the total DDI cross sections for the case where one of the electrons takes all of the excess energy after the first ionization process.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A24
- Title:
- Carbon isoelectronic sequence data
- Short Name:
- J/A+A/564/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extensive self-consistent multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations and subsequent relativistic configuration interaction (RCI) calculations are performed for 262 states belonging to the 15 configurations 2s22p2, 2s2p3, 2p4, 2s22p3l, 2s2p23l, 2p33l and 2s22p4l (l=0,1,2) in selected carbon-like ions from Ar XIII to Zn XXV. Electron correlation effects are accounted for through large configuration state function (CSF) expansions. Calculated energy levels are compared with existing theoretical calculations and data from the Chianti and NIST databases. In addition, Lande gJ-factors and radiative electric dipole transition rates are given for all ions. The accuracy of the calculations are high enough to facilitate the identification of observed spectral lines. Complete online tables of energy levels and transition rates are available.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A55
- Title:
- C3 by collision with H2
- Short Name:
- J/A+A/657/A55
- Date:
- 21 Mar 2022 09:24:59
- Publisher:
- CDS
- Description:
- An accurate analysis of the physical-chemical conditions in the regions of the interstellar medium in which C_3_ is observed requires knowing the collisional rate coefficients of this molecule with He, H_2_, electrons, and H. The main goals of this study are to present the first potential energy surface for the C_3_ +H_2_ complex, to study the dynamics of the system, and to report a set of rate coefficients at low temperature for the lower rotational states of C_3_ with para- and ortho-H_2_. Methods. A large grid of ab initio energies was computed at the explicitly correlated coupled-cluster with single-, double-, and perturbative triple-excitation level of theory, together with the augmented correlation-consistent quadruple zeta basis set (CCSD(T)-F12a/aug-cc-pVQZ). This grid of energies was fit to an analytical function. The potential energy surface was employed in close- coupling calculations at low collisional energies. We present a high-level four-dimensional potential energy surface (PES) for studying the collision of C_3_ with H_2_ . The global minimum of the surface is found in the linear HH-CCC configuration. Rotational deexcitation state-to-state cross sections of C_3_ by collision with para- and ortho-H_2_ are computed. Furthermore, a reduced two-dimensional surface is developed by averaging the surface over the orientation of H_2_. The cross sections for the collision with para-H_2_ using this approximation and those from the four-dimensional PES agree excellently. Finally, a set of rotational rate coefficients for the collision of C_3_ with para- and ortho-H_2_ at low temperatures are reported.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/102
- Title:
- ^12^C/^13^C ratio for 18 galactic R CrB stars
- Short Name:
- J/ApJ/747/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC) stars are analyzed by synthesizing the C_2_ Swan bands (1, 0), (0, 0), and (0, 1) using our detailed line list and the Uppsala model atmospheres. The (0, 1) and (0, 0) C_2_ bands are used to derive the ^12^C abundance, and the (1, 0) ^12^C^13^C band to determine the ^12^C/^13^C ratios. The carbon abundance derived from the C_2_ Swan bands is about the same for the adopted models constructed with different carbon abundances over the range 8.5 (C/He=0.1%) to 10.5 (C/He=10%). Carbon abundances derived from C I lines are about a factor of four lower than the carbon abundance of the adopted model atmosphere over the same C/He interval, as reported by Asplund et al., who dubbed the mismatch between adopted and derived C abundance as the "carbon problem." In principle, the carbon abundances obtained from C_2_ Swan bands and that assumed for the model atmosphere can be equated for a particular choice of C/He that varies from star to star. Then, the carbon problem for C_2_ bands is eliminated. However, such C/He ratios are in general less than those of the extreme helium stars, the seemingly natural relatives to the RCB and HdC stars. A more likely solution to the C_2_ carbon problem may lie in a modification of the model atmosphere's temperature structure. The derived carbon abundances and the ^12^C/^13^C ratios are discussed in light of the double degenerate and the final flash scenarios.
- ID:
- ivo://CDS.VizieR/J/A+A/417/375
- Title:
- Cd III Stark broadening parameters
- Short Name:
- J/A+A/417/375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stark broadening parameters, widths and shifts, for 84 spectral lines of doubly-ionized cadmium (Cd III) have been calculated using the modified semi-empirical approach (MSE). Calculated spectral lines belong to the transitions 4d^9^5s-4d^9^5p and 4d^9^5p-4d^9^5d. Widths and shifts of the spectral lines are given for temperature range of 5000K-60000K and an electron density of 10^23^m^-3^. The influence of collisions with charged particles on Cd III UV stellar lines along the HR diagram is discussed. Compared to the Doppler broadening, the influence of the Stark broadening mechanism is more important for deeper atmospheric layers and for larger values of logg. Stark broadening does not depend on turbulent velocity for the considered stellar model of a standard main sequence hot star of A0 spectral type. The influence of the Stark widths for standard models of DA and DB white dwarfs is also discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/605/A95
- Title:
- CH4 and hot methane continuum hybrid line list
- Short Name:
- J/A+A/605/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A line list for methane (CH_4_) is constructed as a combination of 17 million strong absorption lines relative to the reference absorption spectra and a background methane continuum in two temperature-dependent forms of cross sections and super-lines. This approach significantly eases the use of large high temperature line lists as the computationally expensive calculation of pressure-dependent profiles (e.g. Voigt) only need to be performed for a relatively small number of lines. Both the line list and cross sections were generated using a new 34 billion methane line list (known as 34to10), which extends the 10to10 line list to higher temperatures (up to 2000K). The new hybrid scheme can be applied to any large line lists containing billions of transitions. We recommend using super-lines generated on a high resolution grid based on a resolving power of R=1000000 to model the molecular continuum as a more flexible alternative to the temperature-dependent cross sections.
- ID:
- ivo://CDS.VizieR/J/A+AS/142/113
- Title:
- C3H2 and SiC2 collisional rates
- Short Name:
- J/A+AS/142/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Collisional rate coefficients for rotational transitions in C3H2 and SiC2 due to collisions with H2 molecules are calculated. The C3H2 has two distinct species, ortho and para, whereas the SiC2 has only ortho specie due to spin statistics for the identical carbon nuclei. For ortho- and para-C3H2 we accounted for 47 and 48 energy levels, respectively. The calculations are done for the kinetic temperatures 30, 60, 90, and 120 K. For ortho-SiC2, we accounted for 40 energy levels and the calculations are done for the kinetic temperatures 25, 50, 75, 100, and 125 K. The results are reported here for the transitions in the upward direction. The values for the downward direction can easily be calculated with the help of the detailed equilibrium equation.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/L7
- Title:
- CH_3_CH_2_SH detection in Orion KL
- Short Name:
- J/ApJ/784/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New laboratory data of ethyl mercaptan, CH_3_CH_2_SH, in the millimeter- and submillimeter-wave domains (up to 880GHz) provided very precise values of the spectroscopic constants that allowed the detection of gauche-CH_3_CH_2_ SH toward Orion KL. This identification is supported by 77 unblended or slightly blended lines plus no missing transitions in the range 80-280GHz. A detection of methyl mercaptan, CH_3_SH, in the spectral survey of Orion KL is reported as well. Our column density results indicate that methyl mercaptan is {=~}5 times more abundant than ethyl mercaptan in the hot core of Orion KL.
- ID:
- ivo://CDS.VizieR/J/A+A/646/L7
- Title:
- CH3CO+ discovery in space and in laboratory
- Short Name:
- J/A+A/646/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Yebes 40m and IRAM 30m radiotelescopes, we detected two series of harmonically related lines in space that can be fitted to a symmetric rotor. The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and L1544. High level of theory ab initio calculations indicate that the best possible candidate is the acetyl cation, CH_3_CO^+^, which is the most stable product resulting from the protonation of ketene. We have produced this species in the laboratory and observed its rotational transitions Ju=10 up to Ju=27. Hence, we report the discovery of CH_3_CO^+^ in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH_3_CO^+^ with high accuracy up to 500GHz. We derive an abundance ratio N(H_2_CCO)/N(CH_3_CO^+^)~44. The high abundance of the protonated form of H2CCO is due to the high proton affinity of the neutral species. The other isomer, H_2_CCOH^+^, is found to be 178.9kJ/mol above CH_3_CO^+^. The observed intensity ratio between the K=0 and K=1 lines, ~2.2, strongly suggests that the A and E symmetry states have suffered interconversion processes due to collisions with H and/or H_2_, or during their formation through the reaction of H_3_^+^ with H_2_CCO.
