Field Distortion Three Electrode Gaps

Schaêfer, G.

doi:10.1007/978-1-4899-2130-7_5

Cited by 18 publications

(22 citation statements)

References 35 publications

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“…Although earlier investigations indicated that scaling via the ratio of the square root of reduced masses gave reasonable estimates for collisional rate coefficients, the current study, shows that this agreement was fortuitous (see also Schaefer 1990 for similar findings for HD). The constant factor of ∼1.4 frequently used to predict the rate coefficients of para-H 2 from that of He generally lead to inaccurate results due to the fact that the underlying assumptions are not valid.…”

Section: Resultssupporting

confidence: 56%

On the Validity of Collider-Mass Scaling for Molecular Rotational Excitation

Walker

Yang

Stancil

et al. 2014

ApJ

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Rate coefficients for collisional processes such as rotational and vibrational excitation are essential inputs in many astrophysical models. When rate coefficients are unknown, they are often estimated using known values from other systems. The most common example is to use He-collider rate coefficients to estimate values for other colliders, typically H 2 , using scaling arguments based on the reduced mass of the collision system. This procedure is often justified by the assumption that the inelastic cross section is independent of the collider. Here we explore the validity of this approach focusing on rotational inelastic transitions for collisions of H, para-H 2 , 3 He, and 4 He with CO in its vibrational ground state. We compare rate coefficients obtained via explicit calculations to those deduced by standard reduced-mass scaling. Not surprisingly, inelastic cross sections and rate coefficients are found to depend sensitively on both the reduced mass and the interaction potential energy surface. We demonstrate that standard reduced-mass scaling is not valid on physical and mathematical grounds, and as a consequence, the common approach of multiplying a rate coefficient for a molecule-He collision system by the constant factor of ∼1.4 to estimate the rate coefficient for para-H 2 collisions is deemed unreliable. Furthermore, we test an alternative analytic scaling approach based on the strength of the interaction potential and the reduced mass of the collision systems. Any scaling approach, however, may be problematic when low-energy resonances are present; explicit calculations or measurements of rate coefficients are to be preferred.

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Section: Resultssupporting

confidence: 56%

On the Validity of Collider-Mass Scaling for Molecular Rotational Excitation

Walker

Yang

Stancil

et al. 2014

ApJ

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“…While we are unaware of any existing experimental data for He-HD inelastic collisions, the current results can be assessed by comparing to the previous calculations. Rotational transitions for v = 0 have been computed by Schaefer (1990) and Roueff & Zeippen (1999) which were found to be in good agreement. Our rotational transitions are also found to agree with the previous work.…”

Section: Resultsmentioning

confidence: 81%

“…Here, we have focused on collisions due to He, but H and H 2 are also important impactors. In fact, most modeling studies of primordial gas collapse have adopted the H-HD cooling function of Galli & Palla (1998), which was actually obtained by mass-scaling the He-HD {v = 0, j = 0} → {v = 0, j = 1} rotational excitation rate coefficients of Schaefer (1990). More elaborate cooling functions have been constructed by Flower et al (2000) and Lipovka et al (2005) with the former considering H, He, and H 2 colliders, but the latter limited to H (see the summary in Glover & Abel 2008).…”

Section: Astrophysical Implicationsmentioning

confidence: 99%

ROVIBRATIONAL QUENCHING RATE COEFFICIENTS OF HD IN COLLISIONS WITH He

Nolte

Stancil

Lee

et al. 2011

ApJ

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Along with H 2 , HD has been found to play an important role in the cooling of the primordial gas for the formation of the first stars and galaxies. It has also been observed in a variety of cool molecular astrophysical environments. The rate of cooling by HD molecules requires knowledge of collisional rate coefficients with the primary impactors, H, He, and H 2. To improve knowledge of the collisional properties of HD, we present rate coefficients for the He-HD collision system over a range of collision energies from 10 −5 to 5 × 10 3 cm −1. Fully quantum mechanical scattering calculations were performed for initial HD rovibrational states of j = 0 and 1 for v = 0-17 which utilized accurate diatom rovibrational wave functions. Rate coefficients of all Δv = 0, −1, and −2 transitions are reported. Significant discrepancies with previous calculations, which adopted a small basis and harmonic HD wave functions for excited vibrational levels, were found for the highest previously considered vibrational state of v = 3. Applications of the He-HD rate coefficients in various astrophysical environments are briefly discussed.

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“…Since the energy spacing of the rotational levels of HD is quite large, E 1 /k = 128 K, E 2 /k = 383 K, E 3 /k = 764 K, etc., GP computed the HD cooling function with a simple four-level system (J = 0-3) adopting the collisional coefficients of Schaefer (1990). Flower et al (2000) updated the calculations of GP adopting the collisional rate coefficients of Flower & Roueff (1999) and Roueff & Zeippen (1999).…”

Section: Heating and Coolingmentioning

confidence: 99%

“…The coefficients for inelastic scattering of He-HD were computed by Green (1974) and Schaefer (1990) at temperatures T ≤ 600 K, for 0 ≤ J ≤ 3 and ∆J = +1, +2. Collisional coefficients for rotational excitation of the system H-HD were usually derived by scaling the He-HD values with the square root of the ratio of the reduced masses of the two systems, γ H−HD = (µ He−HD /µ H−HD ) 1/2 γ He−HD , where (µ He−HD /µ H−HD ) 1/2 = 1.51 (see e.g.…”

Section: Heating and Coolingmentioning

confidence: 99%

Deuterium chemistry in the primordial gas

Galli

Palla

2002

Planetary and Space Science

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We review and update some aspects of deuterium chemistry in the postrecombination Universe with particular emphasis on the formation and destruction of HD. We examine in detail the available theoretical and experimental data for the leading reactions of deuterium chemistry and we highlight the areas where improvements in the determination of rate coefficients are necessary to reduce the remaining uncertainties. We discuss the cooling properties of HD and the modifications to the standard cooling function introduced by the presence of the cosmological radiation field. Finally, we consider the effects of deuterium chemistry on the dynamical collapse of primordial clouds in a simple "top-hat" scenario, and we speculate on the minimum mass a cloud must have in order to be able to cool in a Hubble time.

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Field Distortion Three Electrode Gaps

Cited by 18 publications

References 35 publications

On the Validity of Collider-Mass Scaling for Molecular Rotational Excitation

On the Validity of Collider-Mass Scaling for Molecular Rotational Excitation

ROVIBRATIONAL QUENCHING RATE COEFFICIENTS OF HD IN COLLISIONS WITH He

Deuterium chemistry in the primordial gas

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