On the calculation of electron-impact rotational excitation cross sections for molecular ions

Rabadán, I.; Sarpal, B K; Tennyson, Jonathan

doi:10.1088/0953-4075/31/9/020

Cited by 21 publications

(30 citation statements)

References 26 publications

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“…(12). The required value of the cross section constant σ 0 (amounting to ∼10 4Å2 ) is not unrealistic [55] and slightly smaller values may in fact be sufficient if transitions other than ∆J = ±1 [54] are considered in addition. Fig.…”

Section: Rotational Excitation and Coolingmentioning

confidence: 98%

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

et al. 2005

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The dissociative recombination (DR) of 3 He 4 He + has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions in a merged beams configuration at relative energies from near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and electron cooling for 35 s, an effective DR rate coefficient at nearzero energy of 3 × 10 −9 cm 3 s −1 is found. The temporal evolution of the neutral product rates and fragment imaging spectra reveals that the populations of vibrational levels in the stored ion beam are non-thermal with fractions of ∼0.1-1% in excited levels up to at least v = 4, having a significant effect on the observed DR signals. With a pump-probe-type technique using DR fragment imaging while switching the properties of the electron beam, the vibrational excitation of the ions is found to originate mostly from ion collisions with the residual gas. Also, the temporal evolution of the DR signals suggests that a strong electron induced rotational cooling occurs in the vibrational ground state, reaching a rotational temperature near or below 300 K. From the absolute rate coefficient and the shape of the fragment imaging spectrum observed under stationary conditions, the DR rate coefficient from the vibrational ground state is determined; converted to a thermal electron gas at 300 K it amounts to (3.3 ± 0.9) × 10 −10 cm 3 s −1 . The corresponding branching ratios from v = 0 to the atomic final states are found to be (3.7 ± 1.2)% for 1s2s 3 S, (37.4 ± 4.0)% for 1s2s 1 S, (58.6 ± 5.2)% for 1s2p 3 P , and (2.9 ± 3.0)% for 1s2p 1 P . A DR rate coefficient in the range of 2 × 10 −7 cm 3 s −1 or above is inferred for vibrational levels v = 3 and higher. As a function of the collision energy, the measured DR rate coefficient displays a structure around 0.2 eV. At higher energies, it has one smooth peak around 7.3 eV and a highly structured appearance at 15-40 eV. The small size of the observed effective DR rate coefficient at near-zero energy indicates that the electron induced rotational cooling is due to inelastic electron-ion collisions and not due to selective depletion of rotational levels by DR.

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Section: Rotational Excitation and Coolingmentioning

confidence: 98%

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

et al. 2005

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“…If one considers the integral over the resonance region, however, these resonances do not change the probability significantly. Thus, as previously observed by Rabadán et al (1998) for diatomic ions, a detailed treatment of vibrational motion is unnecessary to obtain reliable thermally-averaged rotational excitation rate coefficients of the type normally needed in astrophysical applications. On the other hand, in the region between the (2, 1) and (3, 1) channels, Rydberg resonances are found to increase the rotational probability by about a factor of 2 on average, i.e., the value of 0.15 just above the (3, 1) channel increases discontinuously to an averaged value of 0.29.…”

Section: Mqdt-rft Methodsmentioning

confidence: 95%

“…The CB theory thus predicts that transitions with ∆J=1 and 2 only are allowed for dipole and quadrupole interactions, respectively. Recent ab initio R-matrix studies on several astronomically important molecular ions have shown, however, that this prediction is incorrect and that the inclusion of short-range interactions is crucial, particularly for ions with small (or zero) dipole or transitions with ∆J > 1 (see Rabadán et al (1998), Faure and Tennyson (2002b) and references therein).…”

Section: Introductionmentioning

confidence: 99%

Near-threshold rotational excitation of molecular ions by electron impact

Fauré¹,

Kokoouline²,

Greene³

et al. 2006

J. Phys. B: At. Mol. Opt. Phys.

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Abstract.New cross sections for the rotational excitation of H + 3 by electrons are calculated ab initio at low impact energies. The validity of the adiabatic-nuclei-rotation (ANR) approximation, combined with R-matrix wavefunctions, is assessed by comparison with rovibrational quantum defect theory calculations based on the treatment of Kokoouline and Greene (Phys. Rev. A 68 012703 2003). Pure ANR excitation cross sections are shown to be accurate down to threshold, except in the presence of large oscillating Rydberg resonances. These resonances occur for transitions with ∆J = 1 and are caused by closed channel effects. A simple analytic formula is derived for averaging the rotational probabilities over such resonances in a 3-channel problem. In accord with the Wigner law for an attractive Coulomb field, rotational excitation cross sections are shown to be large and finite at threshold, with a significant but moderate contribution from closed channels.

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“…photo-electrons. Recent studies of rotational excitation include H2 (Danby et al 1996), HeH+ and N0+ (Rabadan et al 1998), CO (Randell et al 1996), 0 2 (Mukherjee & Ghosh 1996), H 2 0 (Gianturco et al 1998a), 0 3 (Gianturco et al 1998b), C 0 2 (Gianturco & Stoecklin 1997), and S 0 2 ). Vibrational excitation due to electron collisions has been investigated for H 2 (Lee et al 1996a;Kazanskii 1996;Mazevet et al 1998), HD (Kazanskii 1996), N 2 (Grimm-Bosbach et al 1996;Sweeney & Shyn 1997), OH (Chen & Morgan 1997), CO , and CH 4 (Bundschu et al 1997) while studies of electronic excitation of H 2 (Celiberto et al 1996), CO (Lee et al 1996b;Zubek et al 1997;Zetner et al 1998), CO, C0 2 , and S0 2 (Fomunung et al 1996), N 2 (Gillan et al 1996), NO (Mojarrabi et al 1996), 0 3 (Sweeney & Shyn 1996), H 2 0 (Morgan 1998), H 2 S (Michelin et al 1997), and CH4 and SiH4 (Bettega et al 1998) have been performed.…”

Section: Electron Impact Of Moleculesmentioning

confidence: 99%

Commission 14: Atomic and Molecular Data: (Donnees Atomiques et Moleculaires)

Rostas¹,

Smith²,

Berrington³

et al. 2000

Trans. Int. Astron. Union

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In recognition of its special interdisciplinary character, IAU Commission 14 is linked directly to the Executive Committee. The Commission’s role is to inform the astronomical community of new developments in the diverse fields of research which involve atoms and molecules. Conversely it endeavors to sensitize the research community active in those fields to the specific needs of astronomy, especially concerning basic data and modeling tools. More generally, Commission 14 tries to foster long term relations and collaborations between the two communities and, when necessary, to alert funding authorities to the specific needs of ground and space based astronomy for specific atomic and molecular data. This report is one of the main contributions of Commission 14 to the information of the astronomical community. Several meetings concerned, at least in part, with the need and availability of atomic and molecular data for astrophysics were also sponsored or co-sponsored. In the last triennium, Commission 14 cosponsored IAU Symposium 194 “Astrochemistry: From Molecular Cloud to Planetary Systems” held in Sogwipo (Korea) from Aug. 23 to 27, 1999 and organized by Commission 34. A Joint Discussion: JD1 on “Atomic and Molecular Data for Astrophysics, New Developments, Case Studies and Future Needs” has been planned for the XXIVth IAU General Assembly in Manchester (Aug. 7-19, 2000) and cosponsored by Commissions 15, 16, 29, 34, 36, 40 and 44. Several other Joint Discussions to be held at the Manchester General Assembly are co-sponsored by this commission.

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On the calculation of electron-impact rotational excitation cross sections for molecular ions

Cited by 21 publications

References 26 publications

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

Near-threshold rotational excitation of molecular ions by electron impact

Commission 14: Atomic and Molecular Data: (Donnees Atomiques et Moleculaires)

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