Collisional excitation of H2S by molecular hydrogen

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.

Collisional excitation of methylene by molecular hydrogen

2021 ◽  
Vol 508 (1) ◽  
pp. 118-124
Author(s):  
Paul J Dagdigian
Keyword(s):  
Energy Surface ◽  
Energy Levels ◽  
Rate Coefficients ◽  
Coupled Cluster ◽  
Collisional Excitation ◽  
Work Time ◽  
Close Coupling ◽  
Collisional Rate Coefficients ◽  
Collisional Rate ◽  
Cluster Level

ABSTRACT Accurate estimates of the abundance of methylene (CH2) in the interstellar medium require knowledge of both the radiative and collisional rate coefficients for the transfer of population between rotational levels. In this work, time-independent quantum close coupling calculations have been carried out to compute rate coefficients for the (de-)excitation of ortho- and para-CH2 in collisions with ortho- and para-H2. These scattering calculations have employed a recently computed, high-quality potential energy surface, based on the coupled cluster level of theory [RCCSD(T)-F12a], for the interaction of CH2 in its ground $\tilde{X} ^3B_1$ electronic state with H2. The collisional rate coefficients were obtained for all fine-structure transitions among the first 22 and 24 energy levels of ortho- and para-CH2, respectively, having energies less than 277 cm−1. These rate coefficients are compared with previous calculated values, obtained by scaling data for CH2–He. In the case of ortho-CH2, whose levels display hyperfine structure, rate coefficients for transitions between hyperfine levels were also computed, by the MJ randomization approximation. Finally, some simple radiative transfer calculations are presented.

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

2019 ◽  
Vol 487 (3) ◽  
pp. 3427-3431 ◽  
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.

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

2020 ◽  
Vol 498 (4) ◽  
pp. 5361-5366
Author(s):  
Paul J Dagdigian
Keyword(s):  
Accurate Determination ◽  
Radiative Transition ◽  
Rate Coefficients ◽  
Cluster Method ◽  
Quantum Scattering ◽  
Close Coupling ◽  
Explicitly Correlated ◽  
Radiative Transition Rate ◽  
Fine And Hyperfine Structure

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.

Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

2020 ◽  
Vol 494 (4) ◽  
pp. 5675-5681 ◽  
Author(s):  
Sanchit Chhabra ◽  
T J Dhilip Kumar
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Cross Sections ◽  
Energy Surface ◽  
Molecular Ions ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Collisional Rate Coefficients

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

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

2019 ◽  
Vol 487 (4) ◽  
pp. 5685-5691 ◽  
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.

scholarly journals Rotational relaxation of H2S by collision with He

2020 ◽  
Vol 638 ◽  
pp. A31
Author(s):  
Otoniel Denis-Alpizar ◽  
Thierry Stoecklin
Keyword(s):  
Basis Set ◽  
Rate Coefficients ◽  
Coupled Cluster ◽  
Rotational Relaxation ◽  
Close Coupling ◽  
Bond Functions ◽  
Correlation Consistent ◽  
Collisional Rate Coefficients ◽  
Collisional Rate ◽  
Cluster Level

Context. The H2S molecule has been detected in several regions of the interstellar medium (ISM). The use of non-LTE models requires knowledge of accurate collisional rate coefficients of the molecules detected with the most common collider in the ISM. Aims. The main goal of this work is to study the collision of H2S with He. Methods. A grid of ab initio energies was computed at the coupled cluster level of theory including single, double, and perturbative triple excitations (CCSD(T)) and using the augmented correlation consistent polarized quadruple zeta (aug-cc-pVQZ) basis set supplemented by a set of mid-bond functions. These energies were fitted to an analytical function, which was employed to study the dynamics of the system. Close coupling calculations were performed to study the collision of H2S with He. Results. The rate coefficients determined from the close coupling calculation were compared with those of the collision with H2O+He, and large differences were found. Finally, the rate coefficients for the lower rotational de-excitation of H2S by collision with He are reported.

scholarly journals Collisional excitation of complex organic molecules

2008 ◽  
Vol 4 (S251) ◽  
pp. 137-138 ◽  
Author(s):  
Alexandre Faure ◽  
Eric Josselin ◽  
Laurent Wiesenfeld ◽  
Cecilia Ceccarelli
Keyword(s):  
Gas Phase ◽  
Degrees Of Freedom ◽  
Organic Molecules ◽  
Low Frequency ◽  
Rate Coefficients ◽  
Collisional Excitation ◽  
Phase Complex ◽  
Collisional Rate Coefficients ◽  
Complex Organic ◽  
Collisional Rate

AbstractA major difficulty in modelling the infrared and (sub)millimeter spectra of gas-phase complex organic molecules is the lack of state-to-state collisional rate coefficients. Accurate quantum or classical scattering calculations for large polyatomic species are indeed computationally highly challenging, particularly when both rotation and low frequency vibrations such as bending and torsional modes are involved. We briefly present here an approximate approach to estimate and/or extrapolate rotational and rovibrational rates for polyatomic molecules with many degrees of freedom.

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

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.

Inelastic rate coefficients for collisions of C4H− with H2

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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