Collisional quenching of highly rotationally excited HF

Yang, Benhui; Walker, Kyle M.; Forrey, Robert C.; Stancil, P. C.; Balakrishnan, N.

doi:10.1051/0004-6361/201525799

Cited by 15 publications

(20 citation statements)

References 43 publications

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“…However, a subsequent reconsideration by Shepler et al (2007) of the interaction potential employed suggested that the results of Balakrishnan, Yan, & Dalgarno (2002) are erroneous 1 . This is confirmed by a very recent paper by Yang et al (2013), which finds results for H 0 -CO collisions very similar to those of Green & Thaddeus (1976).…”

Section: Collision Rate Coefficientssupporting

confidence: 83%

Diffuse Molecular Cloud Densities From Uv Measurements of Co Absorption

Goldsmith

2013

ApJ

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We use UV measurements of interstellar CO toward nearby stars to calculate the density in the diffuse molecular clouds containing the molecules responsible for the observed absorption. Chemical models and recent calculations of the excitation rate coefficients indicate that the regions in which CO is found have hydrogen predominantly in molecular form and that collisional excitation is by collisions with H 2 molecules. We carry out statistical equilibrium calculations using CO-H 2 collision rates to solve for the H 2 density in the observed sources without including effects of radiative trapping. We have assumed kinetic temperatures of 50 K and 100 K, finding this choice to make relatively little difference to the lowest transition. For the sources having T ex 10 only for which we could determine upper and lower density limits, we find n(H 2 ) = 49 cm −3 . While we can find a consistent density range for a good fraction of the sources having either two or three values of the excitation temperature, there is a suggestion that the higher-J transitions are sampling clouds or regions within diffuse molecular cloud material that have higher densities than the material sampled by the J = 1-0 transition. The assumed kinetic temperature and derived H 2 density are anticorrelated when the J = 2-1 transition data, the J = 3-2 transition data, or both are included. For sources with either two or three values of the excitation temperature, we find average values of the midpoint of the density range that is consistent with all of the observations equal to 68 cm −3 for T k = 100 K and 92 cm −3 for T k = 50 K. The data for this set of sources imply that diffuse molecular clouds are characterized by an average thermal pressure between 4600 and 6800 K cm −3 .

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Section: Collision Rate Coefficientssupporting

confidence: 83%

Diffuse Molecular Cloud Densities From Uv Measurements of Co Absorption

Goldsmith

2013

ApJ

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“…It is explained that as the rotational quantum number increases, the energy gap between adjacent levels becomes larger and the energy transfer thus is inefficient. These quasi-resonant features of state-to-state ro-vibrational relaxation were also found in other rare gas-hydrogen fluoride (Rg-HF) [35] and H 2 -HF energy transfer systems [36].…”

Section: B Ro-vibrational Relaxationsupporting

confidence: 56%

Theoretical study on quantum dynamics for Ar-HF inelastic collision

Yang

Liu

Zhao

et al. 2019

Chinese Journal of Chemical Physics

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The integral cross sections and rate constants of pure rotational and ro-vibrational energy transfer processes for the Ar-HF system are thoroughly studied by using the timeindependent close coupling method based on our newly constructed potential energy surface. Compared to previous theoretical results, pure rotational transitions in this work achieve better agreement with the experimental data. For ro-vibrational energy transfer, it is found that quasi-resonant transitions dominate the cross sections in all cases. Furthermore, the vibrational-resolved rate constant of transition v=1→v=0 increases very quickly with the temperature from 100 K to 1500 K and is also in good agreement with the available experimental results.

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“…We consider three collision partners for the RADEX models, namely atomic H, H 2 , and electrons. We use the new rate coefficients for the HF-H system by Desrousseaux & Lique (2018) which are provided between 10 and 500 K. Yang et al (2015) published rate coefficients for p-H 2 with HF for temperatures up to 3000 K. The previous coefficients for the HF-H 2 system provided by Guillon & Stoecklin (2012) are consistent with the more recent Yang et al (2015) results, and hence we use the coefficients of Guillon & Stoecklin (2012). Based on quantum mechanical calculations of collisional cross sections for the e-HF system by Thummel et al (1992) for T > 500 K, van der Tak et al (2012) estimated the excitation rate by electrons for HF ∆J = 1 at T < 500 K.…”

Section: Column Densitymentioning

confidence: 99%

Origin of hydrogen fluoride emission in the Orion Bar

Kavak

Tak

Shipman

et al. 2019

A&A

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Context. The hydrogen fluoride (HF) molecule is seen in absorption in the interstellar medium (ISM) along many lines of sight. Surprisingly, it is observed in emission toward the Orion Bar, which is an interface between the ionized region around the Orion Trapezium stars and the Orion molecular cloud. Aims. We aim to understand the origin of HF emission in the Orion Bar by comparing its spatial distribution with other tracers. We examine three mechanisms to explain the HF emission: thermal excitation, radiative dust pumping, and chemical pumping. Methods. We used a Herschel/HIFI strip map of the HF J = 1 → 0 line, covering 0.5′ by 1.5′ that is oriented perpendicular to the Orion Bar. We used the RADEX non-local thermodynamic equilibrium (non-LTE) code to construct the HF column density map. We use the Meudon PDR code to explain the morphology of HF. Results. The bulk of the HF emission at 10 km s−1 emerges from the CO-dark molecular gas that separates the ionization front from the molecular gas that is deeper in the Orion Bar. The excitation of HF is caused mainly by collisions with H2 at a density of 105 cm−3 together with a small contribution of electrons in the interclump gas of the Orion Bar. Infrared pumping and chemical pumping are not important. Conclusions. We conclude that the HF J = 1 → 0 line traces CO-dark molecular gas. Similarly, bright photodissociation regions associated with massive star formation may be responsible for the HF emission observed toward active galactic nuclei.

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Collisional quenching of highly rotationally excited HF

Cited by 15 publications

References 43 publications

Diffuse Molecular Cloud Densities From Uv Measurements of Co Absorption

Diffuse Molecular Cloud Densities From Uv Measurements of Co Absorption

Theoretical study on quantum dynamics for Ar-HF inelastic collision

Origin of hydrogen fluoride emission in the Orion Bar

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