Determination of photodissociation and radiative association cross sections from the same time-dependent calculation

Vranckx, Stéphane; Loreau, Jérôme; Desouter-Lecomte, Michèle; Vaeck, Nathalie

doi:10.1088/0953-4075/46/15/155201

Cited by 11 publications

(10 citation statements)

References 37 publications

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“…The observed beam brightness of the pure rotational transition j = 1 → 0 was about 4× higher than the value based on the rate constants for the RA (1.4 × 10 −16 cm 3 /s) and the DR (3.0 × 10 −10 cm 3 /s) processes at kinetic temperature of 10 4 K. This appears to indicate that either the currently known RA rate [2] underestimates the production of HeH + cations or else the measured DR rate [3] overestimates their destruction rate. Initial state-specific DR rate coefficients have recently been measured at the Cryogenic Storage Ring (CSR) [4].…”

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confidence: 57%

Dissociative Recombination of Cold HeH+ Ions

2020

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The HeH + cation is the simplest molecular prototype of the indirect dissociative recombination (DR) process that proceeds through electron capture into Rydberg states of the corresponding neutral molecule. This Letter develops the first application of our recently developed energy-dependent frame transformation theory to the indirect DR processes. The theoretical model is based on the multichannel quantum-defect theory with the vibrational basis states computed using exterior complex scaling (ECS) of the nuclear Hamiltonian. The ab initio electronic R-matrix theory is adopted to compute quantum defects as functions of the collision energy and of the internuclear distance. The resulting DR rates are convolved over the beam energy distributions relevant to a recent experiment at the Cryogenic Storage Ring, giving good agreement between the experiment and the theory.

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confidence: 57%

Dissociative Recombination of Cold HeH+ Ions

2020

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“…Numerical rate coefficients are presented in Table 1. Recently, Vranckx et al (2013) studied the reverse process of photodissociation,…”

Section: Resultsmentioning

confidence: 99%

“…( 5). Hence, the approximation proposed in Vranckx et al (2013) is not very reliable and, in fact, unnecessary. (8) They adopted updated rates for the latter two processes, but found that use of the radiative association rate coefficient from Vranckx et al (2013) resulted in a predicted abundance of a factor of ∼4 too small.…”

Section: Resultsmentioning

confidence: 99%

“…Hence, the approximation proposed in Vranckx et al (2013) is not very reliable and, in fact, unnecessary. (8) They adopted updated rates for the latter two processes, but found that use of the radiative association rate coefficient from Vranckx et al (2013) resulted in a predicted abundance of a factor of ∼4 too small. It should be noted that they also performed a non-local thermodynamic equilibrium (NLTE) spectral model of the HeH + rotational emission assuming excitation by electron collisions.…”

Section: Resultsmentioning

confidence: 99%

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Revisiting the Formation of HeH$^+$ in the Planetary Nebula NGC 7027

Forrey,

Babb,

Courtney

et al. 2020

Preprint

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From four independent calculations using three different theoretical approaches, rate coefficients for the formation of HeH + via the radiative association of He + and H were computed. Good agreement is found between our new calculations and prior results obtained two decades ago for kinetic temperatures between ∼800 and 20,000 K. This finding is inconsistent with a recent claim in the literature of a wide variation in published values and establishes the robustness of our knowledge of this process for the formation of HeH + . The implications of the current results to the first detection of HeH + and its modeled abundance in the planetary nebula NGC 7027 are discussed.

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“…a Except where noted, the parameters adopted are those given by Zijlstra et al (2008) b Geometric mean of the semi-major and semi-minor axes of the photoionized region c Adjusted to match the outer angular radius a Only the four reactions in boldface type are found to make a significant contribution b Based on the cross-section presented by Vranckx et al (2013). The published cross-sections are for collisions in which He + (1s) and H (1s) are in the singlet state with total spin 0 (Loreau 2019, private communication), but as only one-quarter of collisions will have spin 0, the rate has been reduced by a factor of four.…”

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confidence: 99%

Detection of vibrational emissions from the helium hydride ion (HeH$^+$) in the planetary nebula NGC 7027

Neufeld,

Goto,

Geballe

et al. 2020

Preprint

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We report the detection of emission in the v= 1 − 0 P (1) (3.51629 µm) and P (2) (3.60776 µm) rovibrational lines of the helium hydride cation (HeH + ) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. They confirm the discovery of HeH + reported recently by Güsten et al.(2019), who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J = 1 − 0 transition at 149.137 µm. The flux measured for the HeH + v= 1 − 0 P (1) line is in good agreement with our model for the formation, destruction and excitation of HeH + in NGC 7027. The measured strength of the J = 1 − 0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v= 1 − 0 P (2) line, by factors of 2.9 and 2.3 respectively. Possible causes of these discrepancies are discussed. Our observations of NGC 7027, covering the 3.26 -3.93 µm spectral region, have led to the detection of more than sixty spectral lines including nine rovibrational emissions from CH + . The latter are detected for the first time in an astronomical source.

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Determination of photodissociation and radiative association cross sections from the same time-dependent calculation

Cited by 11 publications

References 37 publications

Dissociative Recombination of Cold HeH+ Ions

Dissociative Recombination of Cold HeH+ Ions

Revisiting the Formation of HeH$^+$ in the Planetary Nebula NGC 7027

Detection of vibrational emissions from the helium hydride ion (HeH$^+$) in the planetary nebula NGC 7027

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