Fine and hyperfine excitation of NH and ND by He: On the importance of calculating rate coefficients of isotopologues

Dumouchel, F.; Kłos, Jacek; Toboła, Robert; Bacmann, A.; Maret, S.; Hily-Blant, Pierre; Fauré, Alexandre; Lique, François

doi:10.1063/1.4753423

Cited by 36 publications

(48 citation statements)

References 40 publications

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“…It is at higher temperatures and for heavier molecules/quenchers we expect that MQCT can successfully complement the existing methods. In its current form this theory can be applied to a number of important diatomic molecule + atom inelastic scattering processes, such as SO + He, 44 NH + He, 45 and CO + Ar. 46 Our recent MQCT calculations of rotational state-to-state transition cross sections for N 2 + Na system show excellent agreement with full quantum results for both excitation and quenching processes in a broad range of collision energies.…”

Section: Discussionmentioning

confidence: 99%

Mixed quantum/classical theory of rotationally and vibrationally inelastic scattering in space-fixed and body-fixed reference frames

Семенов

Babikov

2013

The Journal of Chemical Physics

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We formulated the mixed quantum/classical theory for rotationally and vibrationally inelastic scattering process in the diatomic molecule + atom system. Two versions of theory are presented, first in the space-fixed and second in the body-fixed reference frame. First version is easy to derive and the resultant equations of motion are transparent, but the state-to-state transition matrix is complexvalued and dense. Such calculations may be computationally demanding for heavier molecules and/or higher temperatures, when the number of accessible channels becomes large. In contrast, the second version of theory requires some tedious derivations and the final equations of motion are rather complicated (not particularly intuitive). However, the state-to-state transitions are driven by realvalued sparse matrixes of much smaller size. Thus, this formulation is the method of choice from the computational point of view, while the space-fixed formulation can serve as a test of the bodyfixed equations of motion, and the code. Rigorous numerical tests were carried out for a model system to ensure that all equations, matrixes, and computer codes in both formulations are correct.

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Section: Discussionmentioning

confidence: 99%

Mixed quantum/classical theory of rotationally and vibrationally inelastic scattering in space-fixed and body-fixed reference frames

Семенов

Babikov

2013

The Journal of Chemical Physics

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“…In the current case, the determination of the hyperfine propensity rules is more complex than for the case of only one nuclear spin, where the usual ∆j = ∆F propensity is observed (Ben Abdallah et al 2012;Kalugina et al 2012;Dumouchel et al 2012). In fact, as explained in Daniel et al (2004), because of the behaviour of the Wigner-6j coefficients in Eq.…”

Section: Hyperfine Rate Coefficientsmentioning

confidence: 99%

Hyperfine excitation of N2H+ by H2: towards a revision of N2H+ abundance in cold molecular clouds

Lique

Daniel

Pagani

et al. 2014

Monthly Notices of the Royal Astronomical Society

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The modelling of emission spectra of molecules seen in interstellar clouds requires the knowledge of collisional rate coefficients. Among the commonly observed species, N 2 H + is of particular interest since it was shown to be a good probe of the physical conditions of cold molecular clouds. Thus, we have calculated hyperfine-structure resolved excitation rate coefficients of N 2 H + (X 1 Σ + ) by H 2 (j = 0), the most abundant collisional partner in the cold interstellar medium. The calculations are based on a new potential energy surface, obtained from highly correlated ab initio calculations. State-to-state rate coefficients between the first hyperfine levels were calculated, for temperatures ranging from 5 K to 70 K. By comparison with previously published N 2 H + -He rate coefficients, we found significant differences which cannot be reproduced by a simple scaling relationship. As a first application, we also performed radiative transfer calculations, for physical conditions typical of cold molecular clouds. We found that the simulated line intensities significantly increase when using the new H 2 rate coefficients, by comparison with the predictions based on the He rate coefficients. In particular, we revisited the modelling of the N 2 H + emission in the LDN 183 core, using the new collisional data, and found that all three of the density, gas kinetic temperature and N 2 H + abundance had to be revised.

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“…Recent studies have shown, however, that isotopic effects in inelastic collisions can be important (Scribano et al 2010;Dumouchel et al 2012), even in the case of 14 N→ 15 N substitution (Flower & Lique 2015). We therefore decided to compute specific N 15 NH + -H 2 (J = 0) rate coefficients.…”

Section: N 2 H + and N 15 Nh + Collisional Rate Coefficientsmentioning

confidence: 99%

N₂H⁺and N¹⁵NH⁺toward the prestellar core 16293E in L1689N

Daniel

Fauré

Pagani

et al. 2016

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Context. Understanding the processes that could lead to an enrichment of molecules in 15 N atoms is of particular interest because this may shed light on the relatively strong variations observed in the 14 N/ 15 N ratio in various solar system environments. Aims. The sample of molecular clouds where 14 N/ 15 N ratios have been measured currently is small and has to be enlarged to allow statistically significant studies. In particular, the N 2 H + molecule currently shows the broadest spread of 14 N/ 15 N ratios in high-mass star-forming regions. However, the 14 N/ 15 N ratio in N 2 H + was obtained in only two low-mass star-forming regions (L1544 and B1b). We here extend this sample to a third dark cloud. Methods. We targeted the 16293E prestellar core, where the N 15 NH + J = 1−0 line was detected. Using a model previously developed for the physical structure of the source, we solved the molecular excitation with a nonlocal radiative transfer code. For this purpose, we computed specific collisional rate coefficients for the N 15 NH + -H 2 collisional system. As a first step of the analysis, the N 2 H + abundance profile was constrained by reproducing the N 2 H + J = 1−0 and 3−2 maps. A scaling factor was then applied to this profile to match the N 15 NH + J = 1−0 spectrum. Results. We derive a column density ratio N 2 H + /N 15 NH + = 330 +170 −100 . Conclusions. We performed a detailed analysis of the excitation of N 2 H + and N 15 NH + in the direction of the 16293E core with modern models that solve the radiative transfer and with the most accurate collisional rate coefficients available to date. We obtained the third estimate of the N 2 H + /N 15 NH + column density ratio in the direction of a cold prestellar core. The current estimate ∼330 agrees with the typical value of the elemental isotopic ratio in the local interstellar medium. It is lower than in some other cores, however, where values as high as 1300 have been reported.

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Fine and hyperfine excitation of NH and ND by He: On the importance of calculating rate coefficients of isotopologues

Cited by 36 publications

References 40 publications

Mixed quantum/classical theory of rotationally and vibrationally inelastic scattering in space-fixed and body-fixed reference frames

Mixed quantum/classical theory of rotationally and vibrationally inelastic scattering in space-fixed and body-fixed reference frames

Hyperfine excitation of N2H+ by H2: towards a revision of N2H+ abundance in cold molecular clouds

N₂H⁺and N¹⁵NH⁺toward the prestellar core 16293E in L1689N

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Fine and hyperfine excitation of NH and ND by He: On the importance of calculating rate coefficients of isotopologues

Cited by 36 publications

References 40 publications

Mixed quantum/classical theory of rotationally and vibrationally inelastic scattering in space-fixed and body-fixed reference frames

Mixed quantum/classical theory of rotationally and vibrationally inelastic scattering in space-fixed and body-fixed reference frames

Hyperfine excitation of N2H+ by H2: towards a revision of N2H+ abundance in cold molecular clouds

N2H+and N15NH+toward the prestellar core 16293E in L1689N

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N₂H⁺and N¹⁵NH⁺toward the prestellar core 16293E in L1689N