Search

Given its abundance in the interstellar medium recently justified by astronomical observations, the chemistry and reactivity of the metal-bearing molecule MgS require special attention. The availability of up-to-date collision data between this MgS molecule and the most abundant perturbing species H |$_2$| and He in the interstellar medium is an essential resource to derive reliable values of its molecular abundance from astronomical observations. This work aims to provide improved scattering parameters for the MgS molecular system in collision with He. A new 2D potential energy surface (2D-PES) is derived by adopting the state-of-the-art level of theory of the explicitly correlated coupled cluster with single, double, and perturbative triple excitations (RCCSD(T)-F12) method in conjunction with the aug-cc-pVTZ basis sets. This PES was used to calculate inelastic cross-sections within the framework of the close-coupling (CC) theory for total energies |$\le 500$|  cm |$^{-1}$| and J |$\le 21$|⁠. Using the Maxwell–Boltzmann distribution of kinetic energies, these cross-sections were integrated to generate the collisional (de)-excitation rate coefficients for temperatures below 100 K. We expect that the new rate coefficients will help us to analyse present and future observations of this key molecule for the interstellar chemistry. [ABSTRACT FROM AUTHOR]

The cyclic form of magnesium dicarbide molecule (c-MgC |$_2$|⁠) has been detected in the carbon-rich circumstellar envelope of IRC+10216 and is considered as a valuable tracer for characterizing the physical conditions of the surrounding gas. In order to make the most of c-MgC |$_2$| observations and accurately derive the physical conditions of the media where c-MgC |$_2$| is detected, radiative transfer modelling, including collisional and radiative (de-)excitations, have to be performed. Here, we study the excitation of c-MgC |$_{2}$| induced by collisions with He (as a proxy for H |$_2$|⁠). A new 3D potential energy surface (PES) is constructed using highly correlated ab initio methods. This PES reveals a minimum with a well depth of 20.66 cm |$^{-1}$| below the c-MgC |$_2$| -He dissociation limit. Using this PES, we compute excitation cross sections for transitions between the low-lying rotational energy levels of c-MgC |$_2$| using the time-independent quantum mechanical close-coupling formalism. These cross sections are then thermally averaged over a Boltzmann energy distribution in order to derive excitation rate coefficients at low temperatures (⁠|$T \le 30$|  K). To evaluate the impact of these new rate coefficients on the interpretation of c-MgC |$_2$| observational spectra, we perform radiative transfer calculations. We find that a very high gas density (⁠|$n \gt 10^6$| cm |$^{-3}$|⁠) is needed in order for the collisional excitation to compete with the radiative de-excitation. We also find that the excitation temperatures of the observed lines predicted by our model differ by a factor two from the value derived from the observations in IRC+10216 circumstellar envelope, indicating that the excitation of c-MgC |$_{2}$| may also be driven by a strong radiative pumping in such media. Therefore, a more sophisticated non-LTE modelling, that takes into account the collisional and radiative excitations as well as the radiative pumping, is required to accurately interpret the observational spectra of c-MgC |$_2$|⁠. [ABSTRACT FROM AUTHOR]

For a better understanding of the physico-chemistry in the interstellar medium, collisional data are needed. In this work, we provide rate coefficients for the recently detected by Cabezas and collaborators in 2023 sodium cyanoacetylide molecule NaC |$_{3}$| N(⁠|$X^{1}\Sigma ^{+}$|⁠) induced by collisions with He. A new two-dimensional potential energy surface (2D-PES) is derived by adopting the high-level theory of the explicitly correlated coupled cluster with single, double, and perturbative triple excitations (CCSD(T)-F12) in conjunction with the aug-cc-pVTZ basis sets. Our 2D-PES presents two minima: the global one with a well depth of |$-86.58$|  cm |$^{-1}$| and the second well with a |$-47.01$|  cm |$^{-1}$| depth. This was expected by the Natural Bond Orbital analysis showing two electrophilic zones located on Na and N linked Carbon with respective atomic charges : |$+0.96575$| and |$+0.28910$|⁠. This PES was used to calculate inelastic cross-sections within the framework of the close-coupling theory for total energies |$\le 170$|  cm |$^{-1}$| and |$J\le 22$|⁠. Using the Maxwell–Boltzmann distribution of kinetic energies, these cross-sections were integrated to generate the collisional (de)-excitation rate coefficients for temperatures below 30 K. In order to estimate the impact of the computed collisional rates, a non-local thermodynamical equilibrium radiative transfer calculation was performed. The new collisional data can allow accurate NaC |$_{3}$| N abundance determination in the interstellar medium. [ABSTRACT FROM AUTHOR]

Determining physical conditions in interstellar environments requires reliable estimation of collisional data for molecules detected in space. In this work, we report a rate coefficients calculation of MgC3N(X 2Σ+) induced by collision with He. This study is based on a new 2D potential energy surface (2D-PES), obtained from the explicitly correlated restricted open-shell coupled cluster approach with single, double, and perturbative triple excitation (rccsd(t)-f12) and the aug-cc-pVTZ basis sets. The MgC3N–He PES presents a global minimum with a well depth of −45.6 cm−1. Based on this interaction potential, we derived the excitation cross-sections using the close-coupling quantum time-independent formalism for total energies ≤500 cm−1 and N ≤ 40. These cross-sections were then integrated on a Maxwell–Boltzmann distribution of kinetic energies to obtain the collisional (de)-excitation rate coefficients for thermal temperature below 100 K. A non-LTE radiative transfer calculation was performed using the present collisional rates in order to estimate their impact on the abundance of MgC3N. These collisional data can help astronomers for the detection and an accurate determination of MgC3N abundance in the investigated interstellar clouds. [ABSTRACT FROM AUTHOR]

The potential energy surface is computed at the explicitly correlated coupled cluster with simple, second and perturbative triple excitation method (CCSD(T)–F12) in connection with the augmented–correlation consistent–polarized valence triple zeta (aug–cc–pVTZ) Gaussian basis set for the NeH+ −He system. The calculations were performed by first taking into account the vibration of the molecule and then averaging the so-obtained three-dimensional potential. From this average interaction potential, cross-sections among the 11 first rotational levels of NeH+ induced by collision with He are calculated for energies up to 4000 cm−1 using the quantum mechanical close coupling (CC) approach. Collisional rate coefficients are obtained by thermally averaging these cross-sections at low temperature (T ≤ 300 K). The propensity rules of the rotational transitions obtained in this paper are discussed and compared with those of HeH+ and ArH+ in collision with electron. This work may be helpful for the eventual investigations, both theoretical and experimental, focused to detect the key cationic noble gas hydride NeH+ in the interstellar and circumstellar media as well as in laboratory experiments. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the determination of the rotational excitation rate coefficients of the first observed molecule containing noble gas 36ArH+ isotope by He. Hence, we present the first potential energy surface (PES) of ArH+ --He van der Waals system. The interaction PES of the ArH+ (X¹ Σ)+-He(¹S) complex is calculated by the ab initio explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in connection with the augmented correlation consistent triple zeta Gaussian basis (aug-cc-pVTZ). The interaction potential presents two global minima of 708.00 and 172.98 cm-1 below the ArH+ (X¹ Σ +)-He(¹S) dissociation limit. Using the PES obtained, we have computed integral inelastic cross-sections in the close-coupling approach among the first 11 rotational levels of ArH+ for energies up to 2500 cm-1. Downward rate coefficients were determined at low temperature (T ≤ 300 K). It is expected that the data worked out in this study may be beneficial for further astrophysical investigations as well as laboratory experiments. [ABSTRACT FROM AUTHOR]

Aims. The present paper focuses on the calculation of the collision rate coefficients for rotational excitation of the 12CF+ and its isotopologue 13CF+ by He for temperature ranging from 10 to 300 K. Methods. A two-dimentional (2D) potential energy surface (PES) of the CF+(X1Σ+)-He(1S) system is calculated at the ab initio coupled cluster with single, double, and perturbative triple excitation level of theory with the aug-cc-pV5Z basis set. The basis set superposition errors were taken into account in our computation. Dynamical calculations of state-to-state rotational integral cross sections of the CF+ by collision with He were performed using the close-coupling method. Results. The PES presents a global minimum of ∼212 cm-1 below the CF+-He dissociation limit. Collisional cross sections among the first 11 rotational levels of CF+ were calculated for total energies up to 1500 cm-1. Downward rate coefficients between the rotational levels were calculated for temperature ranging from 10 to 300 K. A propensity toward an even parity of ΔJ is observed. [ABSTRACT FROM AUTHOR]