Vibrational Relaxation of CO in Nonequilibrium Nozzle Flow, and the Effect of Hydrogen Atoms on CO Relaxation

Rosenberg, C. W. von; Taylor, R. L.; Teare, J.D.

doi:10.1063/1.1675128

Cited by 46 publications

(24 citation statements)

References 28 publications

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“…in deactivation) is the same as that measured in excitation in a shock wave (10,28,29). These experimental flows are very much more complicated than that described in this paper, being dominated by V-V transitions, Can and perhaps plagued by impurity effects (28).…”

Section: ( E ) the Vibrational Relaxation Tirnesupporting

confidence: 53%

“…However, using other ratios Ni/No, (rvib)ij rapidly diverges from the correct answer to something about lo3 too long, and then may become negative as described above. In the current terminology (28,29), 4 z which is considerably smaller than anything so far found experimentally. However, using Ni/Nj ratios where neither i nor j is zero, much faster relaxation times are also calculated, the fastest in our particular calculation being 4 z 20 which is similar to some of the controversial experimental values (29).…”

Section: ( E ) the Vibrational Relaxation Tirnementioning

confidence: 68%

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The Master Equation for the Dissociation of a Dilute Diatomic Gas. VII. Vibration–Dissociation Coupling in an Expansion Nozzle

Labib¹,

McElwain²,

Pritchard³

1972

Can. J. Chem.

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Nous rapportons un calcul de H + H + M + H, + M (sans couplage V-V) aboutissant a la temperature, la densite, la vitesse et les populations de chaque niveau vibrationnel individuel, de 3900-1500 O K , complete avec une precision acceptable le long de la ligne zero pendant un court temps d'ordinateur.Nous constatons qu'en I'absence de couplage V-V, que les populations sont toujours monotones avec le nombre quantique vibrationnel, quoique apparaissent certaines distortions dans les distributions des populations vibrationnelles; il est toutefois possible de susciter des surpopulations absolues d'un Ctat vibrationnel par rapport a un autre en simulant des effets de couplage vibrationnel.A partir de ce calcul, nous concluons principalement que sous ces conditions (i) la constante de vitesse de recombinaison est la constante de vitesse de recombinaison phenomenologique normale; (ii) le temps de relaxation vibrationnel T , , , semble varier sur plusieurs ordres de grandeur, dependant de l'approximation utilisee pour definir la quantite d'energie vibrationnelle, mais si on utilise une mesure approprite de l'energie vibrationnelle, rVi, peut &tre relit la deuxieme valeur quantifiee de la matrice de relaxation et par consequent est le m&me que celui qui aurait &ti: trouve au moyen d'une rnesure dans des tubes de choc.

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Section: ( E ) the Vibrational Relaxation Tirnesupporting

confidence: 53%

Section: ( E ) the Vibrational Relaxation Tirnementioning

confidence: 68%

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VII. Vibration–Dissociation Coupling in an Expansion Nozzle

Labib¹,

McElwain²,

Pritchard³

1972

Can. J. Chem.

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“…T-V energy transfer is enhanced due to the formation of the HCO intermediate complex. Vibrational relaxation probability for CO in collisions with H was first studied by von Rosenberg et al (1974), but here we use the results of the subsequent experiments by Glass & Kironde (1982), which were performed over a wider temperature interval (840-2680 K) (see also Ayres & Wiedemann 1989):…”

Section: Radiative Versus Collisional Excitationmentioning

confidence: 99%

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

González-Alfonso

Wright

Cernicharo³

et al. 2002

A&A

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Abstract. ISO/SWS observations of Orion Peak 1 and Peak 2 show strong emission in the ro-vibrational lines of CO v = 1−0 at 4.45-4.95 µm and of H2O ν2 = 1−0 at 6.3-7.0 µm. Toward Peak 1 the total flux in both bands is, assuming isotropic emission, ≈2.4 and ≈0.53 L , respectively. This corresponds to ≈14 and ≈3% of the total H2 luminosity in the same beam. Two temperature components are found to contribute to the CO emission from Peak 1/2: a warm component, with T k = 200-400 K, and a hot component with T k ∼ 3 × 10 3 K. At Peak 2 the CO flux from the warm component is similar to that observed at Peak 1, but the hot component is a factor of ≈2 weaker. The H2O band is ≈25% stronger toward Peak 2, and seems to arise only in the warm component. The P -branch emission of both bands from the warm component is significantly stronger than the R-branch, indicating that the line emission is optically thick. Neither thermal collisions with H2 nor with H I seem capable of explaining the strong emission from the warm component. Although the emission arises in the postshock gas, radiation from the most prominent mid-infrared sources in Orion BN/KL is most likely pumping the excited vibrational states of CO and H2O. CO column densities along the line of sight of N(CO) = 5-10×10 18 cm −2 are required to explain the band shape, the flux, and the P -R-asymmetry, and beam-filling is invoked to reconcile this high N(CO) with the upper limit inferred from the H2 emission. CO is more abundant than H2O by a factor of at least 2. The density of the warm component is estimated from the H2O emission to be ∼2 × 10 7 cm −3 . The CO emission from the hot component is neither satisfactorily explained in terms of non-thermal (streaming) collisions, nor by resonant scattering. Vibrational excitation through collisions with H2 for densities of ∼3 × 10 8 cm −3 or, alternatively, with atomic hydrogen, with a density of at least 10 7 cm −3 , are invoked to explain simultaneously the emission from the hot component and that from the high excitation H2 lines in the same beam. A jump shock is most probably responsible for this emission. The emission from the warm component could in principle be explained in terms of a C-shock. The underabundance of H2O relative to CO could be the consequence of H2O photodissociation, but may also indicate some contribution from a jump shock to the CO warm emission.

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“…Subsequent works include the shock-tube experiments by von Rosenberg et al (1971), Glass & Kironde (1982), and more recently Kozlov et al (2000) (between 2000 and 3000 K). Shock-tube experimental measurements are deexcitation timescales,which can be fitted in terms of the LandauTeller rate coefficients in cm 3 s −1 (Ayres & Wiedemann 1989):…”

Section: Co-h Collision Ratesmentioning

confidence: 99%

Radiation thermo-chemical models of protoplanetary discs

Thi

Kamp²,

Woitke

et al. 2013

A&A

110

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Context. The carbon monoxide (CO) ro-vibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X 1 Σ + to the electronic A 1 Π state of CO should be taken into account in disc models. Aims. We wish to understand the excitation mechanism of CO ro-vibrational emission seen in Herbig Ae discs, in particular in transitions involving highly excited rotational and vibrational levels. Methods. We implemented a CO model molecule that includes up to 50 rotational levels within nine vibrational levels for the ground and A-excited states in the radiative-photochemical code ProDiMo. We took CO collisions with hydrogen molecules (H 2 ), hydrogen atoms (H), helium (He), and electrons into account. We estimated the missing collision rates using standard scaling laws and discussed their limitations. We tested the effectiveness of ultraviolet (UV) fluorescence pumping for the population of high-vibrational levels (v = 1-9, J = 1-50) for four Herbig Ae disc models (disc mass M disc = 10 −2 , 10 −4 and inner radius R disc = 1, 20 AU). We tested the effect of infrared (IR) pumping on the CO vibrational temperature and the rotational population in the ground vibrational level. Results. UV fluorescence and IR pumping impact on the population of ro-vibrational v > 1 levels. The v = 1 rotational levels are populated at rotational temperatures between the radiation temperature around 4.6 μm and the gas kinetic temperature. The UV pumping efficiency increases with decreasing disc mass. The consequence is that the vibrational temperatures T vib , which measure the relative populations between the vibrational levels, are higher than the disc gas kinetic temperatures (suprathermal population of the vibrational levels). The effect is more important for low-density gases because of lower collisional de-excitations.The UV pumping is more efficient for low-mass (M disc < 10 −3 M ) than high-mass (M disc > 10 −3 M ) discs. Rotational temperatures from fundamental transitions derived using optically thick 12 CO v = 1−0 lines do not reflect the gas kinetic temperature. Uncertainties in the rate coefficients within an order of magnitude result in variations in the CO line fluxes up to 20%. CO pure rotational levels with energies lower than 1000 K are populated in local thermodynamic equilibrium but are sensitive to a number of vibrational levels included in the model. The 12 CO pure rotational lines are highly optically thick for transition from levels up to E upper = 2000 K. The model line fluxes are comparable with the observed line fluxes from typical Herbig Ae low-and high-mass discs.

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Vibrational Relaxation of CO in Nonequilibrium Nozzle Flow, and the Effect of Hydrogen Atoms on CO Relaxation

Cited by 46 publications

References 28 publications

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VII. Vibration–Dissociation Coupling in an Expansion Nozzle

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VII. Vibration–Dissociation Coupling in an Expansion Nozzle

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2

Radiation thermo-chemical models of protoplanetary discs

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Vibrational Relaxation of CO in Nonequilibrium Nozzle Flow, and the Effect of Hydrogen Atoms on CO Relaxation

Cited by 46 publications

References 28 publications

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VII. Vibration–Dissociation Coupling in an Expansion Nozzle

The Master Equation for the Dissociation of a Dilute Diatomic Gas. VII. Vibration–Dissociation Coupling in an Expansion Nozzle

CO and H2O vibrational emission toward Orion Peak 1 and Peak 2

Radiation thermo-chemical models of protoplanetary discs

Contact Info

Product

Resources

About

CO and H₂O vibrational emission toward Orion Peak 1 and Peak 2