Rotational state-changes in C5N− by collisions with He and H2

Biswas, Rajesh; Giri, Kousik; González-Sánchez, Lola; Gianturco, F. A.; Lourderaj, Upakarasamy; Sathyamurthy, N.; Veselinova, Anzhela; Yurtsever, E.; Wester, Roland

doi:10.1093/mnras/stad1261

Cited by 4 publications

(8 citation statements)

References 33 publications

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“…On the other hand, if we now consider the excitation processes shown by the data in Figure 5, we clearly see that the rate coefficients associated with the Δj = +1 value are much larger than the ones corresponding to the larger Δj reported in Figure 4. This is indeed to be expected from the changes in the relative energy gaps involved in the excitation processes, and as discussed in detail by us in our earlier work (Biswas et al 2023). It follows from these findings that the efficient collisional repopulations of the levels in the observational emission lines of Cernicharo et al (2020) would more easily occur from the contiguous levels that are active during those emission processes.…”

Section: Inelastic Rate Coefficientssupporting

confidence: 73%

“…The multipolar expansion was carried out to λ values up to λ = 93, to ensure numerical convergence, employing the procedure discussed more extensively earlier in this section, where we explain how a larger number of raw points were obtained by adding to the initial selection. The actual features of the multipolar coefficients for the C 5 N − partner with the He projectile are discussed in detail in our earlier work, reported by Biswas et al (2023), hence we shall not be repeating it in the present paper. We only report in Figure 2 a comparison between the lower six coefficients newly obtained for the longer molecular anion, C 7 N − , and those we had found earlier for the C 5 N − anion, to indicate the relative strength of the angular coupling that will be active for the various radial regions of their interactions with the neutral He atoms.…”

Section: The Ab Initio Computed Interaction Potentialmentioning

confidence: 82%

“…Figure 4 shows excitation processes that start from the j = 25 rotational state of this anion and end up in one of the higher rotational states involved in the emission lines experimentally detected in Cernicharo et al (2020). This example is meant to show how large the rates would be when considering excitation with fairly large Δj values beyond the more efficient cases with Δj = +/ − 1 discussed in our earlier work in (Biswas et al 2023).…”

Section: Inelastic Rate Coefficientsmentioning

confidence: 97%

“…In all the ab initio calculations, we used an angular grid of 5°intervals. The optimized bond distances in the C 5 N − partner were taken from our previous calculations, as described in our earlier publication (Biswas et al 2023), where all the details of this anion's interaction with both He and H 2 were reported. Hence, we shall not be repeating this information in this section, where instead we shall discuss the new calculations we have carried out for the longer anionic chain.…”

Section: The Ab Initio Computed Interaction Potentialmentioning

confidence: 99%

“…To ensure the smooth transition between the V FIT fitted PES (Equation ( 3)) and the V LR long-range term (Equation ( 4)) in the construction of the V f final PES, the switching procedure, which was already used for C 5 N − /He (Biswas et al 2023), has also been implemented for the longer chain anion:…”

Section: The Ab Initio Computed Interaction Potentialmentioning

confidence: 99%

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Computed Rotational Collision Rate Coefficients for Recently Detected Anionic Cyanopolyynes

González-Sánchez,

Veselinova,

Martín Santa Daría

et al. 2023

ApJ

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We report new results from quantum calculations of energy-transfer processes taking place in interstellar environments and involving two newly observed molecular species: C5N− and C7N− in collision with He atoms and p–H2 molecules. These species are part of the anionic molecular chains labeled as cyanopolyynes, which have been observed over the years in molecule-rich circumstellar envelopes and in molecular clouds. In the present work, we first carry out new ab initio calculations for the C7N− interaction potential with He atoms and then obtain state-to-state rotationally inelastic cross sections and rate coefficients involving the same transitions, which have been observed experimentally by emission in the interstellar medium (ISM) from both of these linear species. For the C5N−/He system, we extend the calculations already published in Biwas et al. to compare more directly the two molecular anions. We extend further the quantum calculations by also computing in this work collision rate coefficients for the hydrogen molecule interacting with C5N−, using our previously computed interaction potential. Additionally, we obtain the same rate coefficients for the C7N−/H2 system by using a scaling procedure that makes use of the new C7N−/He rate coefficients, as discussed in detail in the present paper. Their significance in affecting internal state populations in ISM environments where the anionic cyanopolyynes have been found is analyzed by using the concept of critical density indicators. Finally, similarities and differences between such species and the comparative efficiency of their collision rate coefficients are discussed. These new calculations suggest that, at least for the case of these longer chains, the rotational populations could reach local thermal equilibrium conditions within their observational environments.

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Section: Inelastic Rate Coefficientssupporting

confidence: 73%

Section: The Ab Initio Computed Interaction Potentialmentioning

confidence: 82%

Section: Inelastic Rate Coefficientsmentioning

confidence: 97%

Section: The Ab Initio Computed Interaction Potentialmentioning

confidence: 99%

Section: The Ab Initio Computed Interaction Potentialmentioning

confidence: 99%

See 3 more Smart Citations

Computed Rotational Collision Rate Coefficients for Recently Detected Anionic Cyanopolyynes

González-Sánchez,

Veselinova,

Martín Santa Daría

et al. 2023

ApJ

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An improved artificial neural network fit of the ab initio potential energy surface points for HeH+ + H2 and its ensuing rigid rotors quantum dynamics

Biswas,

Gianturco,

Giri

et al. 2023

Artificial Intelligence Chemistry

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Abundance and excitation of molecular anions in interstellar clouds

Agúndez¹,

Marcelino²,

Tercero³

et al. 2023

A&A

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We present new observations of molecular anions with the Yebes 40 m and IRAM 30 m telescopes toward the cold, dense clouds TMC-1 CP, Lupus-1A, L1527, L483, L1495B, and L1544. We report the first detections of C3N− and C5N− in Lupus-1A as well as C4H− and C6H− in L483. In addition, we detected new lines of C6H− toward the six targeted sources, of C4H− toward TMC-1 CP, Lupus-1A, and L1527, and of C8H− and C3N− in TMC-1 CP. Excitation calculations using recently computed collision rate coefficients indicate that the lines of anions accessible to radiotelescopes run from subthermally excited to thermalized as the size of the anion increases, with the degree of departure from thermalization depending on the H2 volume density and the line frequency. We noticed that the collision rate coefficients available for the radical C6H are not sufficient to explain various observational facts, thereby calling for the collision data for this species to be revisited. The observations presented here, together with observational data from the literature, have been used to model the excitation of interstellar anions and to constrain their abundances. In general, the anion-to-neutral ratios derived here agree with the literature values, when available, within 50% (by a factor of two at most), except for the C4H−/C4H ratio, which shows higher differences due to a revision of the dipole moment of C4H. From the set of anion-to-neutral abundance ratios derived two conclusions can be drawn. First, the C6H−/C6H ratio shows a tentative trend whereby it increases with increasing H2 density, as we would expect on the basis of theoretical grounds. Second, the assertion that the higher the molecular size, the higher the anion-to-neutral ratio is incontestable; furthermore, this supports a formation mechanism based on radiative electron attachment. Nonetheless, the calculated rate coefficients for electron attachment to the medium size species C4H and C3N are probably too high and too low, respectively, by more than one order of magnitude.

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Rotational state-changes in C5N− by collisions with He and H2

Cited by 4 publications

References 33 publications

Computed Rotational Collision Rate Coefficients for Recently Detected Anionic Cyanopolyynes

Computed Rotational Collision Rate Coefficients for Recently Detected Anionic Cyanopolyynes

An improved artificial neural network fit of the ab initio potential energy surface points for HeH+ + H2 and its ensuing rigid rotors quantum dynamics

Abundance and excitation of molecular anions in interstellar clouds

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