Collisional excitation of the formyl radical (HCO) by molecular hydrogen

ABSTRACT This paper addresses the need for accurate rate coefficients for transitions between fine- and hyperfine-structure resolved rotational transitions in the formyl (HCO) radical induced by collisions with the two nuclear spin modifications of H2, the dominant molecule in the interstellar medium (ISM). These rate coefficients, as well as radiative transition rate coefficients, are required for accurate determination of the abundance of HCO in the ISM. Time-independent close-coupling quantum scattering calculations have been used to compute rate coefficients for (de-)excitation of HCO in collisions with para- and ortho-H2. These calculations utilized a potential energy surface for the interaction of HCO with H2 recently computed by the explicitly correlated RCCSD(T)-F12a coupled-cluster method. Rate coefficients for temperatures ranging from 5 to 400 K were calculated for all transitions among the fine and hyperfine levels associated with the first 22 rotational levels of HCO, whose energies are less than or equal to 144 K.

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Collisional excitation of H2S by molecular hydrogen

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1091 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5239-5243

Author(s):

Paul J Dagdigian

Keyword(s):

Energy Surface ◽

Rate Coefficients ◽

Cluster Method ◽

Quantum Scattering ◽

Collisional Excitation ◽

Close Coupling ◽

Accurate Knowledge ◽

Explicitly Correlated ◽

Collisional Rate Coefficients ◽

Collisional Rate

ABSTRACT Accurate estimates of the abundance of H2S, and inferences about the unmeasured H2 density, require accurate knowledge of radiative and collisional rate coefficients. Time-independent close-coupling quantum scattering calculations have been employed to compute rate coefficients for (de-)excitation of para- and ortho-H2S in collisions with para- and ortho-H2. These calculations utilized a potential energy surface for the interaction of H2S with H2 recently computed by the explicitly correlated CCSD(T)-F12a coupled-cluster method. Rate coefficients for temperatures ranging from 5 to 500 K were calculated for all transitions among the first 19 rotational levels of H2S, whose energies are less than or equal to 405 K. These rate coefficients are compared with previous estimates of these quantities.

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Hyperfine excitation of SH+ in collisions with para- and ortho-H2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1562 ◽

2019 ◽

Vol 487 (3) ◽

pp. 3427-3431 ◽

Cited By ~ 3

Author(s):

Paul J Dagdigian

Keyword(s):

Energy Surface ◽

Energy Levels ◽

Rate Coefficients ◽

Cluster Method ◽

Coupled Cluster ◽

Quantum Scattering ◽

Coupled Cluster Method ◽

Close Coupling ◽

Angular Momenta ◽

Explicitly Correlated

ABSTRACT Time-independent close-coupling quantum scattering calculations are employed to compute hyperfine-resolved rate coefficients for (de-)excitation of SH+ in collisions with para- and ortho-H2. These calculations utilized a potential energy surface for the interaction of SH+(X3Σ−) with H2 recently computed by the explicitly correlated RCCSD(T)-F12a coupled-cluster method. Rate coefficients for temperatures ranging from 10 to 500 K were calculated for all transitions among the first 37 hyperfine energy levels of SH+, with rotational angular momenta n ≤ 6, in collisions with para- and ortho-H2. As a first application of these data, the rate coefficients were employed in simple radiative transfer calculations to simulate the excitation of SH+ in typical molecular clouds.

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Hyperfine excitation of NS+ due to para-H2(j = 0) impact

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1700 ◽

2019 ◽

Vol 487 (4) ◽

pp. 5685-5691 ◽

Cited By ~ 1

Author(s):

Cheikh T Bop

Keyword(s):

Cross Sections ◽

Basis Set ◽

Rate Coefficients ◽

Cluster Method ◽

Close Coupling ◽

Nitrogenous Compounds ◽

Deep Well ◽

Explicitly Correlated ◽

Correlation Consistent ◽

Triple Excitation

ABSTRACT Sulphur bearing nitrogenous compounds have been observed in space over this last decade. Modelling their abundances has been done using rate coefficients of isoelectronic molecules. In order to satisfy the astrophysical precision required, we report the actual rate coefficients of NS+ induced by collision with the most abundant interstellar species (para-H2). Considering the 23 low-lying rotational levels of NS+, we were able to compute the (hyperfine) rate coefficients up to 100 K. These latter were carried out by averaging cross-sections over the Maxwell–Boltzmann velocity distribution. The state-to-state inelastic cross-sections were determined in the quantum mechanical close coupling approach for total energies ranging up to 1400 cm−1. These dynamic data result from a four dimensional potential energy surface (4D-PES) which was spherically averaged over the H2 orientations. The 4D-PES was calculated using the explicitly correlated coupled cluster method with simple, double, and non-iterative triple excitation (CCSD(T)–F12) connected to the augmented–correlation consistent–polarized valence triple zeta Gaussian basis set (aug–cc–pVTZ). The so-averaged PES presents a very deep well of 596.72 cm−1 at R = 5.94 a0 and θ1 = 123.20°. Discussions on the propensity rules for the (hyperfine) rate coefficients were made and they are in favour of (Δj = ΔF) Δj = 1 transitions. The results presented here may be crucially needed in order to accurately model the NS+ abundance in space. In addition, we expect that this paper will encourage investigations on the sulphur bearing nitrogenous compounds.

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Inelastic scattering of interstellar silyl cyanide (SiH3CN) by helium atoms : cross-sections and rate coefficients for A- and E-SiH3CN

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2451 ◽

2021 ◽

Vol 507 (4) ◽

pp. 5264-5271

Author(s):

Manel Naouai ◽

Abdelhak Jrad ◽

Ayda Badri ◽

Faouzi Najar

Keyword(s):

Inelastic Scattering ◽

Total Energy ◽

Cross Sections ◽

Three Dimensional ◽

Basis Set ◽

Rate Coefficients ◽

Close Coupling ◽

Explicitly Correlated ◽

Correlation Consistent ◽

Triple Excitation

ABSTRACT Rotational inelastic scattering of silyl cyanide (SiH3CN) molecule with helium (He) atoms is investigated. Three-dimensional potential energy surface (3D-PES) for the SiH3CN–He interacting system is carried out. The ab initio 3D-PES is computed using explicitly correlated coupled cluster approach with single, double, and perturbative triple excitation CCSD(T)-F12a connected to augmented-correlation consistent-polarized valence triple zeta Gaussian basis set. A global minimum at (R = 6.35 bohr; θ = 90○; ϕ = 60○) with a well depth of 52.99 cm−1 is pointed out. Inelastic rotational cross-sections are emphasized for the 22 first rotational levels for total energy up to 500 cm−1 via close coupling (CC) approach in the case of A-SiH3CN and for the 24 first rotational levels for total energy up to 100 cm−1 via CC and from 100 to 500 cm−1 via coupled states (CS) in the case of E-SiH3CN. Rate coefficients are derived for temperature until 80 K for both A- and E-SiH3CN–He systems. Propensity rules are obtained for |ΔJ| = 2 processes with broken parity for A-SiH3CN and for |ΔJ| = 2 processes with |ΔK| = 0 and unbroken parity for E-SiH3CN.

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Inelastic rate coefficients for collisions of C4H− with H2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2563 ◽

2021 ◽

Author(s):

Christian Balança ◽

Ernesto Quintas-Sánchez ◽

Richard Dawes ◽

Fabien Dumouchel ◽

François Lique ◽

...

Keyword(s):

Cross Sections ◽

Rotational Level ◽

Carbon Chain ◽

Rate Coefficients ◽

Thermodynamical Equilibrium ◽

Close Coupling ◽

State Approximation ◽

Explicitly Correlated ◽

State Rate ◽

Chemical Conditions

Abstract Carbon-chain anions were recently detected in the interstellar medium. These very reactive species are used as tracers of the physical and chemical conditions in a variety of astrophysical environments. However, the Local Thermodynamical Equilibrium conditions are generally not fulfilled in these environments. Therefore, collisional as well as radiative rates are needed to accurately model the observed emission lines. We determine in this work the state-to-state rate coefficients of C4H− in collision with both ortho- and para-H2. A new ab initio 4D potential energy surface was computed using explicitly-correlated coupled cluster procedures. This surface was then employed to determine rotational excitation and de-excitation cross sections and rate coefficients for the first 21 rotational levels (up to rotational level j1 = 20) using the close-coupling method, while the coupled-state approximation was used to extend the calculations up to j1 = 30. State-to-state rate coefficients were obtained for the temperature range 2–100 K. The differences between the ortho- and para-H2 rate coefficients are found to be small.

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Rotational de-excitation of tricarbon monosulfide (C3S) in collision with (He): potential energy surface and rates

Astrophysics and Space Science ◽

10.1007/s10509-020-03892-5 ◽

2020 ◽

Vol 365 (12) ◽

Author(s):

E. Sahnoun ◽

M. Ben Khalifa ◽

F. Khadri ◽

K. Hammami

Keyword(s):

Potential Energy ◽

Interstellar Medium ◽

Potential Energy Surface ◽

Cross Sections ◽

Energy Surface ◽

Accurate Determination ◽

Carbon Chain ◽

Basis Sets ◽

Rate Coefficients

AbstractDespite that the tricarbon monosulfide (C3S) is among the first sulfur-containing carbon-chain molecules to be detected in the interstellar medium, no studies focused on the determination of its collisional rates. These rate coefficients are essential to estimate the abundance of C3S in the interstellar medium. Computations of the C3S($^{1}\Sigma^{+}$ Σ + 1 ) downward rate coefficients, induced by collision with He, are performed by averaging the integral cross sections at low temperature (below $25~\text{K}$ 25 K ). Calculations of the cross sections in the close-coupling quantum time independent formalism for $E_{c}\leq110~\text{cm}^{-1}$ E c ≤ 110 cm − 1 and $J\leq10$ J ≤ 10 are based on a new 2-D potential energy surface. This PES is obtained from the explicit correlated coupled cluster with a single, double and perturbative triple excitation [ccsd(t)-f12] ab initio approach and the aug-cc-pVTZ basis sets. The PES have a global minimum of $-55.69~\text{cm}^{-1}$ − 55.69 cm − 1 located at $R=6.25$ R = 6.25 bohr and $\theta=94^{\circ}$ θ = 94 ∘ , and a second minimum of $-36.95~\text{cm}^{-1}$ − 36.95 cm − 1 at $R=9.35$ R = 9.35 bohr and $\theta=0^{\circ}$ θ = 0 ∘ . A comparison of C3S rates with those of the isoelectronic molecule C3O was made. The results indicate a great temperature dependence of the rates for transitions of $\Delta J>2$ Δ J > 2 . We expect that the new collisional data will allow for accurate determination of the C3S abundance in several interstellar regions.

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Detection of PLP Structure for Accurate Determination of Propagation Rate Coefficients over an Enhanced Range of PLP-SEC Conditions

Macromolecules ◽

10.1021/acs.macromol.8b01943 ◽

2018 ◽

Vol 52 (1) ◽

pp. 55-71 ◽

Cited By ~ 4

Author(s):

Anatoly N. Nikitin ◽

Igor Lacık ◽

Robin A. Hutchinson ◽

Michael Buback ◽

Gregory T. Russell

Keyword(s):

Accurate Determination ◽

Propagation Rate ◽

Rate Coefficients

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Advances in atomic data for neutron-capture elements

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312012148 ◽

2011 ◽

Vol 7 (S283) ◽

pp. 504-505

Author(s):

Nicholas C. Sterling ◽

Michael C. Witthoeft ◽

David A. Esteves ◽

Phillip C. Stancil ◽

A. L. David Kilcoyne ◽

...

Keyword(s):

Cross Sections ◽

Accurate Determination ◽

Photoionization Cross Section ◽

Dielectronic Recombination ◽

Rate Coefficients ◽

Atomic Data ◽

Ionization Equilibrium ◽

Elemental Abundances ◽

Progenitor Stars

AbstractNeutron(n)-capture elements (atomic number Z > 30), which can be produced in planetary nebula (PN) progenitor stars via s-process nucleosynthesis, have been detected in nearly 100 PNe. This demonstrates that nebular spectroscopy is a potentially powerful tool for studying the production and chemical evolution of trans-iron elements. However, significant challenges must be addressed before this goal can be achieved. One of the most substantial hurdles is the lack of atomic data for n-capture elements, particularly that needed to solve for their ionization equilibrium (and hence to convert ionic abundances to elemental abundances). To address this need, we have computed photoionization cross sections and radiative and dielectronic recombination rate coefficients for the first six ions of Se and Kr. The calculations were benchmarked against experimental photoionization cross section measurements. In addition, we computed charge transfer (CT) rate coefficients for ions of six n-capture elements. These efforts will enable the accurate determination of nebular Se and Kr abundances, allowing robust investigations of s-process enrichments in PNe.

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