Rate constants for rotational transitions of CO scattered by para-hydrogen

Schinke, Reinhard; Engel, Volker; Buck, U.; Meyer, H. O.; Diercksen, Geerd H. F.

doi:10.1086/163760

Cited by 63 publications

(48 citation statements)

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“…This preference is the same one we observed in He-CO scattering, 26 and also appears in calculations on the earlier H 2 -CO potential of Schinke et al at 75 and 200 meV. 44 …”

Section: State-to-state Cross Sectionssupporting

confidence: 87%

State-to-state rotational excitation of CO by H2 near 1000 cm−1 collision energy

Antonova

Tsakotellis

Lin

et al. 2000

The Journal of Chemical Physics

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Relative state-to-state rotationally inelastic cross sections for excitation of carbon monoxide by hydrogen were measured in a crossed molecular beam experiment at collision energies 795, 860, and 991 cm Ϫ1 . The results are compared to predictions of a recent ab initio potential energy surface ͓J. Chem. Phys. 108, 3554 ͑1998͔͒. The agreement is very good. A comparison with older data on thermally averaged total depopulation cross sections ͓Chem. Phys. 53, 165 ͑1980͔͒ indicates that the absolute magnitudes of the cross sections predicted by the surface are too high. The CO excitation is dominated by collisions that are elastic in H 2 rotation, and the collision dynamics are very similar for different rotational levels of hydrogen.

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“…This preference is the same one we observed in He-CO scattering, 26 and also appears in calculations on the earlier H 2 -CO potential of Schinke et al at 75 and 200 meV. 44 …”

Section: State-to-state Cross Sectionssupporting

confidence: 87%

State-to-state rotational excitation of CO by H2 near 1000 cm−1 collision energy

Antonova

Tsakotellis

Lin

et al. 2000

The Journal of Chemical Physics

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“…Comparison with full-scale radiative transfer codes, which solve the radiative transfer and level populations self-consistently throughout the cloud, show good agreement with the Sobolev approximation for the level populations as well as the total intensity of the cooling line, provided the optical depth to the surface is calculated from the actual column density in the relevant states rather than approximated from the local level populations . As a result, in semi-infinite slabs the PDR temperature structure can be calculated from the outside to the inside without the 9 Convenient fitting formulae for the collisional excitation rates have been published by Tielens and Hollenbach (1985a), Hollenbach and McKee (1989), and Spaans et al (1994) for the atomic fine structure and forbidden lines, by Hollenbach and McKee (1979), McKee et al (1982), Draine and Roberge (1984), and Schinke et al (1985) for rotational transitions of CO, and by Martin and Mandy (1995) and Martin et al (1996) for rovibrational transitions of H 2 .…”

Section: Heating and Coolingmentioning

confidence: 99%

Photodissociation regions in the interstellar medium of galaxies

Hollenbach

Tielens²

1999

Rev. Mod. Phys.

754

712

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The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eVϽh Ͻ13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed PhotoDissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C ϩ , and O; rovibrational lines of H 2 ; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H 2 and C ϩ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 m with the CO Jϭ1 -0 emission, the CO Jϭ1 -0 luminosity with the interstellar molecular mass, and the [CII] 158 m plus [OI] 63 m luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds. [S0034-6861(99)01001-6] CONTENTS

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“…The spontaneous transition probability for the transition is A 32 = 2.158 × 10 −6 s −1 , the transition temperature is T tr = 15.813 K and the statistical weight of the upper level is g u = 7. Using the collisional rate coefficients of Schinke et al (1985) for collisions with para-H 2 , yields critical densities, n crit ∼ A 32 /γ 32 (T k ), of about 2 × 10 5 to 3 × 10 4 cm −3 for T k = 10 K to 300 K, respectively (Table 3). Therefore, except perhaps for the very lowest temperatures, the condition of LTE should be fulfilled for the C 18 O (3−2) transition (cf.…”

Section: O and H 2 Column Densitiesmentioning

confidence: 99%

$O^{18}$O and $C^{18}$O observations ofρOphiuchi A

Liseau¹,

Larsson²,

Bergman³

et al. 2010

A&A

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Context. Contrary to theoretical expectation, surprisingly low concentrations of molecular oxygen, O 2 , have been found in the interstellar medium. Telluric absorption makes ground based O 2 observations essentially impossible and observations had to be done from space. Millimetre-wave telescopes on space platforms were necessarily small, which resulted in large, several arcminutes wide, beam patterns. Observations of the (N J = 1 1 −1 0 ) ground state transition of O 2 with the Odin satellite resulted in a 5σ detection toward the dense core ρ Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam width of 10 , larger than the size of the dense core.Aims. The precise nature of the emitting source and its exact location and extent are therefore unknown. The current investigation is intended to remedy this. Methods. Although the Earth's atmosphere is entirely opaque to low-lying O 2 transitions, it allows ground based observations of the much rarer 16 O 18 O in favourable conditions and at much higher angular resolution with larger telescopes. In addition, ρ Oph A exhibits both multiple radial velocity systems and considerable velocity gradients. Extensive mapping of the region in the proxy C 18 O (J = 3−2) line can be expected to help identify the O 2 source on the basis of its line shape and Doppler velocity. Line opacities were determined from observations of optically thin 13 C 18 O (J = 3−2). During several observing periods, two C 18 O intensity maxima in ρ Oph A were searched for O 18 O in the (2 1 −0 1 ) line at 234 GHz with the 12 m APEX telescope. These positions are associated also with peaks in the mm-continuum emission from dust.

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Rate constants for rotational transitions of CO scattered by para-hydrogen

Cited by 63 publications

References 0 publications

State-to-state rotational excitation of CO by H2 near 1000 cm−1 collision energy

State-to-state rotational excitation of CO by H2 near 1000 cm−1 collision energy

Photodissociation regions in the interstellar medium of galaxies

$O^{18}$O and $C^{18}$O observations ofρOphiuchi A

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