A beam scattering study of non-dissociative charge transfer between Kr+ and CH4 at collision energies below 1 eV

Herman, Z.; Birkinshaw, K.; Pacak, V.

doi:10.1016/0168-1176(94)03978-x

Cited by 13 publications

(4 citation statements)

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“…The comparison with the Kr + charge transfer with CH 4 is also useful for this discussion because the N + ( 3 P) recombination energy, 14.53 eV, is between the two recombination energies, 14.0 and 14.66 eV, of the Kr + spin−orbit states, 2 P 3/2 and 2 P 1/2 , respectively. The Kr + + CH 4 reaction has been extensively studied for statistical mixtures of the spin−orbit states ,, or with selection of these states. , It was found that the charge transfer is near resonant and populates a range of CH 4 + internal energies of ±0.5 eV around the Kr + recombination energy producing CH 3 + and CH 4 + ions essentially in the backward hemisphere. At thermal energies, the Kr + ( 2 P 3/2 ) reaction leads to undissociated CH 4 + products ,and the Kr + ( 2 P 1/2 ) reaction leads to a 0.9:0.1 ratio of dissociated to undissociated products CH 3 + /CH 4 + .…”

Section: Discussionmentioning

confidence: 99%

¹⁵N⁺ + CD₄ and O⁺ + ¹³CO₂ State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

et al. 2004

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The dissociative photoionization of N2 and O2 by synchrotron radiation in coincidence with threshold photoelectrons is used to produce state-selected N+ and O+ atomic ions to study their reactivity. A pure selection of their ground state, N+(3P) and O+(4S), or excited states, N+(1D), O+(2D), and O+(2P), is obtained by the choice of the photon energy and by further discrimination of atomic ions produced with translational recoil energy. Both reactions studied, 15N+ + CD4 and O+ + 13CO2, are of major importance for the chemistry of Titan, Mars, and Venus' ionospheres and are strongly affected by excitation of the parent atomic ion. For the reaction of N+ with methane, DCN+ and DCND+ products coming from the decomposition of a long-lived complex are surprisingly not much sensitive to the N+ excitation, whereas the branching ratio between the dissociative charge-transfer channel, leading to CD3 +, which is the main product for the ground-state reaction, and the nondissociative charge-transfer channel, leading to CD4 +, is completely inverted in favor of the latter when N+ is excited into the 1D state. This unanticipated result can be well understood by the spin−orbit selection rule in the N+ recombination. For the reaction of O+ with carbon dioxide, the reactive channel producing O2 +, which dominates for the ground-state reaction for thermal collision energies, is completely displaced in favor of the endothermic charge-transfer channel leading to CO2 + if either collision energy or O+ internal energy is brought to the system. The O+(2P) metastable state has a larger reaction cross section than the lower 2D metastable state. Owing to the long lifetime of the N+ and O+ metastable states studied here and to their very specific reactivity, they should be individually considered in the models describing the planetary ionospheric chemistry.

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Section: Discussionmentioning

confidence: 99%

¹⁵N⁺ + CD₄ and O⁺ + ¹³CO₂ State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

et al. 2004

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“…The dissociative and non-dissociative charge transfer of rare gas cations on methane is well-documented and efficient near resonant charge transfers are observed. [66][67][68][69][70][71][72][73] For charge transfer processes involving reactions of atomic A + ions with molecule targets such as methane, two criteria are usually important for a good coupling between charge transfer states, the good overlap between CH 4 (v=0) and CH reaction at E CM = 0.2 eV, i.e. with the same total initial energy (about 5 eV), but with two very opposite repartitions between O + internal energy and collision energy, are very different (see last point in Figure 5 and first point in Figure 7).…”

Section: Discussionmentioning

confidence: 99%

“…The measured velocity distributions (see Figure ) have very strongly backward scattered components that are characteristic of either dissociative charge transfer or hydride transfer. The dissociative and nondissociative charge transfer of rare gas cations on methane is well-documented, and efficient near-resonant charge transfers are observed. − For charge transfer processes involving reactions of atomic A + ions with molecule targets such as methane, two criteria are usually important for a good coupling between charge transfer states, the good overlap between CH 4 ( v = 0) and CH 4 + ( v + ) vibrational wave functions, and the energy difference, Δ E , between the two states, A + * + CH 4 ( v = 0) and CH 4 + ( v + ) + A*. For the case of rare gas cations and methane, Δ E values of ±0.5 eV are generally observed.…”

Section: Discussionmentioning

confidence: 99%

Reactions of State-Selected Atomic Oxygen Ions O⁺(⁴S, ²D, ²P) with Methane

et al. 2015

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An experimental study has been carried out on the reactions of state selected O(+)((4)S, (2)D, (2)P) ions with methane with the aims of characterizing the effects of both the parent ion internal energy and collision energy on the reaction dynamics and determining the fate of oxygen species in complex media, in particular the Titan ionosphere. Absolute cross sections and product velocity distributions have been determined for the reactions of (16)O(+) or (18)O(+) ions with CH4 or CD4 from thermal to 5 eV collision energies by using the guided ion beam (GIB) technique. Dissociative photoionization of O2 with vacuum ultraviolet (VUV) synchrotron radiation delivered by the DESIRS beamline at the SOLEIL storage ring and the threshold photoion photoelectron coincidence (TPEPICO) technique are used for the preparation of purely state-selected O(+)((4)S, (2)D, (2)P) ions. A complete inversion of the product branching ratio between CH4(+) and CH3(+) ions in favor of the latter is observed for excitation of O(+) ions from the (4)S ground state to either the (2)D or the (2)P metastable state. CH4(+) and CH3(+) ions, which are by far the major products for the reaction of ground state and excited states, are strongly backward scattered in the center of mass frame relative to O(+) parent ions. For the reaction of O(+)((4)S), CH3(+) production also rises with increasing collision energy but with much less efficiency than with O(+) excitation. We found that a mechanism of dissociative charge transfer, mediated by an initial charge transfer step, can account very well for all the observations, indicating that CH3(+) production is associated with the formation of H and O atoms (CH3(+) + H + O) rather than with OH formation by an hydride transfer process (CH3(+) + OH). Therefore, as the CH4(+) production by charge transfer is also associated with O atoms, the fate of oxygen species in these reactions is essentially the O production, except for the reaction of O(+)((4)S), which also produces appreciable amounts of H2O(+) ions but only at very low collision energy. The production of O atoms and the nature of the states in which they are formed are discussed for the reactions of O(+) ions with CH4 and N2.

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“…The internal energy of CH 4 •+ generated by charge exchange, ignoring the thermal energy, is well approximated by [39][40][41] Here, RE is the recombination energy of X •+ and IE is the ionization energy of CH 4 , which is 12.61 eV. In case of charge exchange with Kr •+ , or Kr/CE, Kr •+ both in the 2 P 3/2 and 2 P 1/2 states with REs of 14.0 and 14.7 eV, respectively, will contribute to formation of CH 4 •+ .…”

Section: Validity Of This Interpretation Will Become Clearer Belowmentioning

confidence: 99%

Excitation Mechanism in the Collision-Induced Dissociation of Methane Molecular Ion at Kiloelectronvolt Translational Energy

Lee

Kim

1996

J. Phys. Chem.

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Collision-induced hydrogen loss from methane molecular ion has been studied at kiloelectronvolt laboratory translational energy by using mass-analyzed ion kinetic energy spectrometry (MIKES). The kinetic energy release (KER) distribution evaluated from the MIKE profile is bimodal: a small KER component arising from vibrational excitation and a large KER component from electronic excitation. CH4 •+ has been generated by electron ionization and by charge exchange ionization to vary its internal energy content. It has been found that the collision-induced dissociation (CID) via electronic excitation becomes more efficient at higher incident energy, while the efficiency of the vibrational excitation is hardly affected by the incident energy. Most importantly, it has been found that the electronic excitation is the main mechanism in CID at kiloelectronvolt incident energy. Vibrational excitation also occurs but supplies only a few vibrational quanta and hence is important for the least endoergic process only.

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A beam scattering study of non-dissociative charge transfer between Kr+ and CH4 at collision energies below 1 eV

Cited by 13 publications

References 11 publications

¹⁵N⁺ + CD₄ and O⁺ + ¹³CO₂ State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

¹⁵N⁺ + CD₄ and O⁺ + ¹³CO₂ State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

Reactions of State-Selected Atomic Oxygen Ions O⁺(⁴S, ²D, ²P) with Methane

Excitation Mechanism in the Collision-Induced Dissociation of Methane Molecular Ion at Kiloelectronvolt Translational Energy

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A beam scattering study of non-dissociative charge transfer between Kr+ and CH4 at collision energies below 1 eV

Cited by 13 publications

References 11 publications

15N+ + CD4 and O+ + 13CO2 State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

15N+ + CD4 and O+ + 13CO2 State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

Reactions of State-Selected Atomic Oxygen Ions O+(4S, 2D, 2P) with Methane

Excitation Mechanism in the Collision-Induced Dissociation of Methane Molecular Ion at Kiloelectronvolt Translational Energy

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¹⁵N⁺ + CD₄ and O⁺ + ¹³CO₂ State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

¹⁵N⁺ + CD₄ and O⁺ + ¹³CO₂ State-Selected Ion−Molecule Reactions Relevant to the Chemistry of Planetary Ionospheres

Reactions of State-Selected Atomic Oxygen Ions O⁺(⁴S, ²D, ²P) with Methane