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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]

Collisional excitation of C5H+ by He was performed by mean of state-of-the-art methods. A high level of theory quantum chemical calculations were made to determine the interaction potential energy surface of C5H+ with helium. The new two-dimensional potential energy surface obtained from the RCCSD(T)-F12 ab initio approach associated with aug-cc-pVTZ basis sets, presents two minima below its dissociation limit with well depths of |$-101.8$| and |$-100.2\, \mathrm{cm}^{-1}$|. In order to derive accurate physical conditions from rotational transitions of the recently discovered C5H+ molecule in Taurus molecular cloud (TMC-1), rate coefficients calculations are performed. The C5H+(X1Σ+)–He de-excitation rates are obtained after averaging cross-sections for thermal temperature below 100 K. The integral cross-sections are computed with the close-coupling quantum time-independent formalism for |$E\le 520 \, \mathrm{cm}^{-1}$| and J ≤ 15. The new collisional data will allow accurate determination of the C5H+ abundance and will help to understand the chemistry of carbon chain ions in the interstellar gas. [ABSTRACT FROM AUTHOR]

Tricarbon and pentacarbon monoxides have been detected towards the Taurus Molecular Cloud (TMC-1) with relatively important abundances. Understanding the chemical formation of these molecules requires interpreting their observational spectra by mean of non-local thermodynamical equilibrium modelling. For this purpose, we report rate coefficients of  C3O and  C5O induced by collision with He for temperatures up to 100 K. These data are obtained by calculating inelastic cross sections for the 31 low-lying rotational levels of  C3O and  C5O using the close-coupling approach. The comparison of the new rate coefficients with those of HC3N and HC5N, previously used to interpret the observational spectra of  C3O and  C5O, reveals differences of up to an order of magnitude. The effect of the new collisional rate coefficients in radiative transfer calculations is checked by computing the excitation temperatures for some transitions and simulating the  C3O and  C5O column densities observed towards TMC-1. Our findings suggest that the use of HC n N as template for C n O may lead to local thermodynamic equilibrium conditions for gas densities as low as ∼103  cm−3. Regarding the interpretation of the observational spectra, using radiative transfer modelling based on the actual C n O collisional rate coefficients instead of rotational diagram analysis leads to underestimate the column densities reported in the literature by up to 25 per cent and accordingly the  C3O/ C5O abundance ratio by up to 50 per cent. We expect that the new rate coefficients and the radiative transfer calculations presented in this work will encourage further modellings of the C n O abundance and accordingly constrain the chemistry. [ABSTRACT FROM AUTHOR]

The CCN radical has been recently detected in the interstellar medium. Accurate modeling of its abundance in such media requires one to model its excitation by both radiation and collisions. Here, we report the first quantum mechanical close-coupling study of CCN—He collisions. Calculations of fine-structure resolved excitation cross sections of CCN(X2Π) induced by collision with He are performed for kinetic energies below 500 cm−1. The calculations are based on new two-dimensional potential energy surfaces obtained from coupled cluster approaches. We found that the inelastic cross sections for spin-orbit conserving transitions are larger than those for spin-orbit changing transitions. The new collisional data should significantly help the interpretation of interstellar CCN emission lines observed with current and future telescopes and we expect that they will allow accurate determination of the CCN abundance in the interstellar medium, which is crucial to understand the chemistry of carbon chain species in the interstellar gas. [ABSTRACT FROM AUTHOR]

In order to derive accurate physical conditions of the interstellar clouds (such as TMC-1) from the rotational transitions of C2O, collisional rates are needed. Based on a new two-dimensional potential energy surface (PES), we report a new rate coefficients calculation of C2O(X 3Σ−) induced by collision with He. This PES was obtained from the explicitly correlated restricted open-shell coupled cluster with single, double, and perturbative triple excitation (rccsd(t)-f12) ab initio approach associated with aug-cc-pVTZ basis sets. The C2O–He PES presents one minimum below its dissociation limit with a well depth of 42.376 cm−1. The close-coupling quantum time-independent formalism was used to derive cross sections for E ≤ 370 cm−1 and N ≤ 10. De-excitation rate coefficients are obtained for thermal temperature below 80 K. [ABSTRACT FROM AUTHOR]

An appropriate estimation of the abundance of the observed C5 radical in the interstellar medium requires accurate radiative and collisional rate coefficients. We present the first two-dimensional potential energy surface (2D-PES) for the ground electronic state of the C5(X1Σ+)–He(X1S) van der Waals system, obtained using an explicitly correlated coupled-cluster method with single, double, and perturbative triple excitations (RCCSD(T)-F12). This PES is subsequently used in quantum close-coupling (CC) scattering calculations. Collisional excitation cross-sections of the rotational levels of C5 by He were calculated for energies up to 1500 cm−1 using the standard (CC) method. The thermal dependence of the corresponding rate coefficients is given for the low and moderate temperature T ≤ 300 K regime of interstellar molecular clouds. This is the first study on the collisional rate coefficients for this system and may have important implications for the astrophysical detection of C5(X1Σ+) and modeling of carbon-rich media. [ABSTRACT FROM AUTHOR]

Despite 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( Σ + 1 ) downward rate coefficients, induced by collision with He, are performed by averaging the integral cross sections at low temperature (below 25 K ). Calculations of the cross sections in the close-coupling quantum time independent formalism for E c ≤ 110 cm − 1 and 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 cm − 1 located at R = 6.25 bohr and θ = 94 ∘ , and a second minimum of − 36.95 cm − 1 at R = 9.35 bohr and 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 Δ J > 2 . We expect that the new collisional data will allow for accurate determination of the C3S abundance in several interstellar regions. [ABSTRACT FROM AUTHOR]

The C5S molecule is the largest member of the series of sulphur-containing carbon chains C n S observed in space. Given the lack of data concerning this molecule, we computed rate coefficients of C5S(1Σ+) induced by collision with He. These rates are obtained for thermal temperature below 100 K by mean of a new two-dimensional potential energy surface (PES) calculated with the explicit correlated coupled cluster with single, double, and pertubative triple excitation (ccsd(t)-f12) ab initio approach and the aug-cc-pVTZ basis sets. The C5S–He PES presents three minimums of −59.726, −55.355, and −36.506 cm−1 below its dissociation limit. Using this PES, the integral cross-sections are performed in the close-coupling (CC) and coupled-state (CS) quantum time independent formalisms for |$E_\mathrm{ c}\le 500 \, \mathrm{ cm}^{-1}$| and J ≤ 13 (for CC) and J ≤ 50 (for CS). By averaging these cross-sections we obtained the downward rate coefficients. The new collisional data are used to simulate the excitation of C5S in the circumstellar gas. We obtain the excitation and brightness temperatures of the four lines observed towards the IRC+10216 which confirms the necessity of using radiative transfer calculations to accurately determine C5S abundance since the local thermodynamic equilibrium conditions are not fulfilled. The new collisional data should help to estimate the abundance of C5S in several interstellar regions. [ABSTRACT FROM AUTHOR]

Among the closed-shell hydrocarbons, the carbenes c- and l-C3H2 are the lightest ones to display a permanent electric dipole moment and be detectable by rotational spectroscopy. The cyclic form, cyclopropenylidene, is ubiquitous in the InterStellar Matter (ISM) of the Milky Way and external galaxies. As such, it serves as a marker to help in characterizing the physical conditions of the ISM. The linear form, propadienylidene, is less abundant. In order to get access to their absolute and relative abundances, it is essential to understand their collisional excitation/quenching schemes. We compute here a precise ab initio potential energy surface for the interaction of c- and l-C3H2 with helium, by means of a CCSD(T)-F12a formalism and a fit onto relevant spherical harmonics functions. We conduct quantum dynamical scattering in order to get precise cross sections using a coupled-channel approach for solving the nuclear motion. We average sections to have rates for rotational quenching from 5 to 150 K. We show that these new rates are vastly different, up to more than an order of magnitude, from the older rates presented in the literature, computed with angular momentum algebra only. We expect large differences in the astrophysical analyses of C3H2, including the chemical history of those ubiquitous carbenes. [ABSTRACT FROM AUTHOR]

We have generated an ab initio three-dimensional potential energy surface (PES) for the [image omitted] state of LiSH. The spectroscopic data calculated from a full quartic force field are in very good agreement with the values obtained from microwave spectroscopic experiments. The PES has been used to solve variationally the nuclear motion problem and the vibrational energy levels are given up to about 3500 cm-1 for LiSH and 2400 cm-1 for LiSD. For LiSH, the anharmonic fundamental modes lie at 2571 (SH stretch), 578 (LiS stretch) and 372 (LiSH bending), and for LiSD the corresponding values are: 1866, 582 and 276 (all values are in cm-1), respectively. Anharmonic resonances between the bending and the LiS stretching modes are identified in both species. The calculated electric dipole moment μe = 7.03 debye mirrors the strong charge separation in the lithium hydrosulphide. The electronically excited states up to vertical transition energies of 36 000 cm-1 predissociate along the Li ... SH path. [ABSTRACT FROM AUTHOR]

Abstract: Reliable theoretical data on spectroscopy and spin–orbit matrix elements are computed for the lowest electronic states of SH+ and LiS+ ions. Accurate spectroscopic predictions for their excited electronic states are given. For SH+, polarization minima at large internuclear distances are located in addition to the strongly bound electronic states already known. For LiS+, our calculations confirm that the electronic ground state of this ion is of 3Σ− species and reveal the existence of a 1Δ state presenting a potential well as deep as the potential of the ground state. Moreover, the LiS+ electronic excited states potential energy curves possess shallow potential minima in the molecular region and at long-internuclear distances. Generally, these shallow minima may be populated during low energy collisions between the corresponding atomic fragments. Finally, spin–orbit calculations have allowed giving accurate determinations of the spin–orbit splittings for these cations and elucidation of the predissociation mechanisms of SH+ leading to the formation of the S+ and H species in their electronic ground states. Accordingly, long-lived SH+ ions can be found in the X 3Σ−, a1Δ and b1Σ+ electronic states and the rovibrational levels of LiS+ in its electronically excited and ground states should be weakly perturbed. [Copyright &y& Elsevier]

We present quantum coupled-state calculations for the rotational excitation of interstellar propargylimine due to collisions with helium. The calculations are based on new high-accurate three-dimensional potential energy surfaces (3D-PESs) adapted for rigid-rotor scattering computations. The two PESs ( Z / E -PGIM-He) were determined using the explicitly correlated coupled-cluster approach with single, double and perturbative triple excitation [CCSCD(T)-F12] and the standard aug-cc-pVTZ basis set. These PESs present many minima with a global minimum of -47.61 cm -1 for Z -PGIM-He and -54.16 cm -1 for E -PGIM-He. While the PESs for both complexes are qualitatively similar, that of E -PGIM-He is more anisotropic. The state-to-state collisional cross-section calculations are performed for all rotational levels J ≤ 12 with energies below E rot = 30 cm -1 and for total energies up to 500 cm -1 . The corresponding collisional rate coefficients are derived for kinetic temperatures up to 120 K. A propensity rule is seen, for rotational excitation cross sections and de-excitation rate coefficients, that favors even Δ J transitions but with different orders of magnitude. We expect that the retrieved results will contribute to improving atmospheric and astrophysics models.

The theoretical study of collisions between atoms and molecules provides a detailed description of the involved mechanisms and greatly contributes to improving atmospheric and astrophysics models. In the present paper, we focus on the new calculation of rate coefficients for the first 25 rotational levels of the CaNC molecule in collision with He. A new 2D potential energy surface (2D-PES), for the CaNC-He system, was determined using the single, double and perturbative triple excitation restricted coupled-cluster method [rccsd(t)] and the standard aug-cc-pVQZ basis sets. This PES presents a global minimum with a well depth of -21.93 cm -1 located at R = 8 a 0 and γ = 116°. State-to-state collisional excitation cross-sections of the fine-structure levels of CaNC( 2 Σ + )-He are calculated for energies up to 305 cm -1 , which yield, after thermal averaging, rate coefficients up to 70 K. A Δ J = Δ N propensity rule was observed. A comparison of the CaNC rates with those of valence isoelectronic MgNC has been investigated. These new data are necessary for the CaNC abundance determination and interpretation of its observed lines.

An appropriate estimation of the abundance of the observed C 5 radical in the interstellar medium requires accurate radiative and collisional rate coefficients. We present the first two-dimensional potential energy surface (2D-PES) for the ground electronic state of the C 5 (X 1 Σ + )-He(X 1 S) van der Waals system, obtained using an explicitly correlated coupled-cluster method with single, double, and perturbative triple excitations (RCCSD(T)-F12). This PES is subsequently used in quantum close-coupling (CC) scattering calculations. Collisional excitation cross-sections of the rotational levels of C 5 by He were calculated for energies up to 1500 cm -1 using the standard (CC) method. The thermal dependence of the corresponding rate coefficients is given for the low and moderate temperature T ≤ 300 K regime of interstellar molecular clouds. This is the first study on the collisional rate coefficients for this system and may have important implications for the astrophysical detection of C 5 (X 1 Σ + ) and modeling of carbon-rich media.

Tricarbon monoxide (C3O) is an astrochemically important molecule. It is a probe element for determining the chemical composition of gases in molecular clouds, as C3O is a major intermediate of ion-molecule reactions in the gas phase. For C3O, no collision coefficients are available in the literature. To estimate the abundance of C3O in a solar cold dark cloud: Taurus Molecular Cloud 1 (TMC-1) and find the range of cloud parameters, some authors used the calculated values for the HC3N molecule, which is isoelectronic and has similar rotational constants. Indeed, the calculation of the rate coefficients of C3O(1Σ+) induced by collision with He is performed for thermal temperatures below 25 K. These calculations are based on a new two-dimensional potential energy surface obtained from the explicitly correlated coupled cluster with a single, double and perturbative triple excitation (ccsd(t)-f12) ab initio approach associated with aug-cc-pVTZ basis sets. The PES was found to have a global minimum at (R = 6.2 Bohr and θ = 73°) with a depth of -53.4 cm-1 below the C3O-He dissociation limit. Using this PES, the integral cross sections are performed in the close-coupling quantum time independant formalism for Ec ≤ 110 cm-1 and J ≤ 12. These cross sections were then averaged at low temperature to obtain the downward rate coefficients. The new collisional data should significantly help the interpretation of interstellar C3O emission lines observed with current and future telescopes. We expect that they will allow the accurate determination of the C3O abundance in the interstellar medium, which is crucial to understand the chemistry of carbon chain species in the interstellar gas.

Among the closed-shell hydrocarbons, the carbenes c- and l-C 3 H 2 are the lightest ones to display a permanent electric dipole moment and be detectable by rotational spectroscopy. The cyclic form, cyclopropenylidene, is ubiquitous in the InterStellar Matter (ISM) of the Milky Way and external galaxies. As such, it serves as a marker to help in characterizing the physical conditions of the ISM. The linear form, propadienylidene, is less abundant. In order to get access to their absolute and relative abundances, it is essential to understand their collisional excitation/quenching schemes. We compute here a precise ab initio potential energy surface for the interaction of c- and l-C 3 H 2 with helium, by means of a CCSD(T)-F12a formalism and a fit onto relevant spherical harmonics functions. We conduct quantum dynamical scattering in order to get precise cross sections using a coupled-channel approach for solving the nuclear motion. We average sections to have rates for rotational quenching from 5 to 150 K. We show that these new rates are vastly different, up to more than an order of magnitude, from the older rates presented in the literature, computed with angular momentum algebra only. We expect large differences in the astrophysical analyses of C 3 H 2 , including the chemical history of those ubiquitous carbenes.

The CCN radical has been recently detected in the interstellar medium. Accurate modeling of its abundance in such media requires one to model its excitation by both radiation and collisions. Here, we report the first quantum mechanical close-coupling study of CCN-He collisions. Calculations of fine-structure resolved excitation cross sections of CCN(X 2 Π) induced by collision with He are performed for kinetic energies below 500 cm -1 . The calculations are based on new two-dimensional potential energy surfaces obtained from coupled cluster approaches. We found that the inelastic cross sections for spin-orbit conserving transitions are larger than those for spin-orbit changing transitions. The new collisional data should significantly help the interpretation of interstellar CCN emission lines observed with current and future telescopes and we expect that they will allow accurate determination of the CCN abundance in the interstellar medium, which is crucial to understand the chemistry of carbon chain species in the interstellar gas.