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.

Relaxation of NO+ by collision with para-H2 (j = 0)

2020 ◽  
Vol 494 (1) ◽  
pp. 129-134
Author(s):  
L D Cabrera-González ◽  
D Páez-Hernández ◽  
O Denis-Alpizar
Keyword(s):  
Cross Sections ◽  
Reproducing Kernel ◽  
Reproducing Kernel Hilbert Space ◽  
Rate Coefficients ◽  
Local Thermal Equilibrium ◽  
Large Set ◽  
Close Coupling ◽  
Rotational States ◽  
Scaling Procedure ◽  
Collisional Rate Coefficients

ABSTRACT The first tentative detection of the nitrosylium ion (NO+) in the interstellar medium (ISM) was reported just a few years ago. The application of non-local thermal equilibrium models requires the knowledge of the collisional rate coefficients with the most common colliders in the ISM (e.g. He, H, H2, and e). The main goals of this paper are to study the collision of the NO+ molecule with para-H2 (j = 0) and report the rate coefficients for the lower rotational states of NO+. A large set of ab initio energies was computed at the CCSD(T)/aug-cc-pV5Z level of theory. A new potential energy surface averaged over the H2 orientations was then fitted using a reproducing kernel Hilbert space procedure. The state-to-state cross-sections of NO++para-H2 (j = 0) for the first 18 rotational levels were computed using the close-coupling method. The rotational rate coefficients of this system were compared with those for NO++He, and a different propensity rule was found. Furthermore, the hyperfine rate coefficients were also calculated using the infinite-order-sudden scaling procedure.

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.

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.

scholarly journals Dissociative Recombination of CH+ Molecular Ion Induced by Very Low Energy Electrons

Atoms ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 82 ◽  
Author(s):  
Zsolt J. Mezei ◽  
Michel D. Epée Epée ◽  
Ousmanou Motapon ◽  
Ioan F. Schneider
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Incident Energy ◽  
Dissociative Recombination ◽  
Boltzmann Distribution ◽  
Rate Coefficients ◽  
Rotational States ◽  
Low Energy Electrons ◽  
Quantum Defect Theory ◽  
Π State

We used the multichannel quantum defect theory to compute cross sections and rate coefficients for the dissociative recombination of CH + initially in its lowest vibrational level v i + = 0 with electrons of incident energy below 0.2 eV. We have focused on the contribution of the 2 2 Π state which is the main dissociative recombination route at low collision energies. The final cross section is obtained by averaging the relevant initial rotational states ( N i + = 0 , ⋯ , 10 ) with a 300 K Boltzmann distribution. The Maxwell isotropic rate coefficients for dissociative recombination are also calculated for different initial rotational states and for electronic temperatures up to a few hundred Kelvins. Our results are compared to storage-ring measurements.

scholarly journals Effect of uniform magnetic field on laser-produced Cu plasma and the deposited particles on the target surface

2017 ◽  
Vol 35 (2) ◽  
pp. 352-361 ◽  
Author(s):  
K.S. Singh ◽  
A. Khare ◽  
A.K. Sharma
Keyword(s):  
Magnetic Field ◽  
Target Surface ◽  
Peripheral Region ◽  
Impact Excitation ◽  
Rate Coefficients ◽  
Electron Impact Excitation ◽  
Photoluminescence Intensity ◽  
Excitation Rate ◽  
Intensity Enhancement ◽  
The Difference

AbstractLaser-produced copper plasma in the presence of variable transverse external magnetic field in air is investigated using optical emission spectroscopy. As the magnetic field increases from 0 to 0.5 T, the intensity of Cu I lines initially increases and then decreases slightly at a 0.5 T. The maximum intensity enhancement of all five Cu I lines occurs at a magnetic field of 0.3 T. The increase in intensity is attributed to an increase in the electron impact excitation of Cu. With increase in magnetic field, the electron density and temperature were found to increase due to increase in the confinement of plasma. The difference in intensity enhancement factor is due to the difference in excitation rate coefficients. The surface morphology of irradiated copper target is also analyzed at 0.3 T magnetic field at which the density is maximum and reveals the formation of Cu/Cu2O/CuO nanoparticles (NPs). More NPs are formed at the peripheral region than at the central region of the ablated crater and is due to the oxidation of Cu atom in the plasma–ambient interface. The larger grain size of nanostructures in the presence of magnetic field is due to an increase in the inverse pulsed laser deposition. The intensity of Raman peak of Cu2O decreases in the presence of magnetic field and that of CuO increases which is more likely due to conversion of Cu2O to CuO. The photoluminescence intensity of CuO increases in the presence of magnetic field due to the phase transformation of Cu2O to CuO in agreement with the result of Raman spectroscopy.

scholarly journals Rotational quenching of HD induced by collisions with H2 molecules

2019 ◽  
Vol 488 (1) ◽  
pp. 381-386
Author(s):  
Yier Wan ◽  
N Balakrishnan ◽  
B H Yang ◽  
R C Forrey ◽  
P C Stancil
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Cross Sections ◽  
Energy Surface ◽  
Rate Coefficients ◽  
Quantum Mechanical ◽  
Cooling Efficiency ◽  
Close Coupling ◽  
Rotational Transitions ◽  
Good Agreement

ABSTRACT Rate coefficients for rotational transitions in HD induced by H2 impact for rotational levels of HD j ≤ 8 and temperatures 10 K ≤ T ≤ 5000 K are reported. The quantum mechanical close-coupling (CC) method and the coupled-states (CS) decoupling approximation are used to obtain the cross-sections employing the most recent highly accurate H2–H2 potential energy surface (PES). Our results are in good agreement with previous calculations for low-lying rotational transitions The cooling efficiency of HD compared with H2 and astrophysical applications are briefly discussed.

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.

Collisional (de-)excitation of protonated cyanoacetylene (HC3NH+) by helium at low and moderate temperatures

2021 ◽  
Vol 503 (2) ◽  
pp. 2902-2912
Author(s):  
M Mogren Al Mogren ◽  
D Ben Abdallah ◽  
S Dhaif Allah Al Harbi ◽  
M S Al Salhi ◽  
M Hochlaf
Keyword(s):  
Cross Sections ◽  
Quantum Scattering ◽  
Thermodynamical Equilibrium ◽  
Close Coupling ◽  
Molecular Chemistry ◽  
Excitation Cross Sections ◽  
Non Local ◽  
Total Energies ◽  
Highly Correlated ◽  
Local Thermodynamical Equilibrium

ABSTRACT Protonated cyanoacetylene, HC3NH+, is detected in astrophysical media, where it plays a key role as an intermediate in the chemistries of HCN/HNC and of cyanopolyynes. We first generated a potential energy surface (PES) describing the intermonomer interaction between HC3NH+ and He in Jacobi coordinates using the highly correlated CCSD(T)-F12/aug-cc-pVTZ ab initio methodology. Then, scattering calculations based on an exact close-coupling quantum-scattering technique were done to obtain pure rotational cross-sections for the rotational (de-)excitation of HC3NH+ after collision with He for total energies up to 2500 cm−1. These cross-sections are used to deduce the collision rates in the 5–350 K temperature range for the low-lying rotational levels of HC3NH+ (up to $j\,\, = \,\,15$). In addition, we generated an average PES for the HC3NH+–H2 system. The preliminary results show that the H2($j_{\mathrm{H_2}} = 0$) and He state-to-state de-excitation cross-sections have similar magnitudes, even though the H2 cross-sections are larger by a factor of 2–2.5. This work should help with the accurate derivation of protonated cyanoacetylene abundances in non-local thermodynamical equilibrium astrophysical media. These will put more constraints on the chemical pathways involving the formation and destruction of HC3NH+ while going back to the cyanopolyyne family and more generally those parts of nitrogen-containing molecular chemistry.

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