Ion-molecule reactions of O+ with CH4

Ottinger, Ch.; Zimmermann, Steffen; Muschlitz, E. E.

doi:10.1016/0301-0104(83)85315-4

Cited by 2 publications

(44 citation statements)

References 9 publications

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“…In the case of ion-molecule reactions of O þ with CH 4 , other product ions are generated, such as OH À and CH 4 þ (ref. 49). Therefore, the above-mentioned reactions for CH 4 removal by oxidation with hydroxyl radicals and ion-molecule reactions provide feedback to the system.…”

Section: Articlementioning

confidence: 99%

Subterranean atmospheres may act as daily methane sinks

et al. 2015

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In recent years, methane (CH 4 ) has received increasing scientific attention because it is the most abundant non-CO 2 atmospheric greenhouse gas (GHG) and controls numerous chemical reactions in the troposphere and stratosphere. However, there is much that is unknown about CH 4 sources and sinks and their evolution over time. Here we show that near-surface cavities in the uppermost vadose zone are now actively removing atmospheric CH 4 . Through seasonal geochemical tracing of air in the atmosphere, soil and underground at diverse geographic and climatic locations in Spain, our results show that complete consumption of CH 4 is favoured in the subsurface atmosphere under near vapour-saturation conditions and without significant intervention of methanotrophic bacteria. Overall, our results indicate that subterranean atmospheres may be acting as sinks for atmospheric CH 4 on a daily scale. However, this terrestrial sink has not yet been considered in CH 4 budget balances. M ethane (CH 4 ) is currently the most abundant non-CO 2 greenhouse gas (GHG) in the atmosphere, reaching a global average concentration of B1,800 p.p.b. at midnorthern latitudes 1 . Despite significant research progress in recent years, large uncertainties remain about the CH 4 budget and its evolution over time because there is a lack of knowledge about CH 4 sinks and sources [2][3][4][5] . Superimposed on the long-term trend of increasing atmospheric CH 4 , there is significant interannual variability 1,6,7 , and the sources of variation remain controversial 8 .Current CH 4 estimates account for B22% of the total forcing potential of all long-lived GHGs 9 . By weight, CH 4 is 28 times more effective at trapping heat in the atmosphere than CO 2 over a 100-year period 10 . Sensible mitigation strategies also require a quantitative understanding of the CH 4 budget regarding emissions and sinks 11 . The total global emissions of CH 4 are constrained reasonably well by atmospheric observations and estimates of its lifetime, based on multiple atmospheric CH 4 inversion models (top-down studies). However, the uncertainties concerning emissions/consumption from individual sources/ sinks 12 are greater, and they are poorly constrained by the current atmospheric observation network 6 . Some unaccounted sinks (or sources) could contribute the global CH 4 budget and its long-term variations.The Earth's surface exerts its influence on the free atmosphere through the atmospheric boundary layer. This lowest portion of the atmosphere ranges from a few tens of metres to 1-2-km deep 13 . The subsurface atmosphere is usually overlooked as an important part of this boundary layer. At the top of the subsurface layer in the vadose zone (below the subsoil and above the groundwater table) highly specific biogeochemical processes occur, which may act as regulators of gas exchanges between the surface and the free atmosphere.The uppermost part of the vadose zone may contain large amounts of underground air, that is, a CO 2 -rich air reservoir permeating the unsaturated...

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Section: Articlementioning

confidence: 99%

Subterranean atmospheres may act as daily methane sinks

et al. 2015

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“…35 The best values for the fraction of 2 D + 2 P metastable states, consistent with the two sets of data at U A = 40 and 90 V, was found to be 3 % and 30-35 % respectively, but no information on the relative proportions of 2 D / 2 P states for these two experimental conditions can be given. 35 With these assumed compositions, the cross sections for the O + ( 2 D + 2 P) + CH 4 reaction, shown in Figures 6-7, have been inferred from the cross sections measured in the two experiments at U A = 40 and 90 V. 35 As can be seen in Figure 6, at 5 eV collision energy, our CD 3 + /OD + cross section measurement for the reaction of O + ions, prepared in pure 2 D population, with CD 4 is in good agreement with the CH 3 + cross section reported by Ottinger et al for the reaction of O + ions in a mixed 2 D + 2 P composition with CH 4 , 35 whereas our measurement for the reaction of O + ions, prepared in pure 2 P population (see Figure 7) is a bit lower than their value. This could be an indication that a larger fraction of the 2 D state than the 2 P state are produced in their discharge at U A = 90 V. This seems reasonable according to former results they obtained for a close value of the ion-source voltage, U A = 80 V, 19 As will be discussed in the following section, dissociative charge transfer (O3) could be the main channel accounting for the very efficient production of CD 3 + ions ) cross sections from Equations ( 4) and ( 5), at all collision energies for which the "continuous" mode experiments were conducted.…”

Section: Measurement Overviewmentioning

confidence: 56%

“…Cross sections lower than 1 Å 2 are measured for the OH + ions production. 35 As visible in Figure 5, the values obtained for CH 4 + 19 was assumed here by making various hypotheses on the proportion of metastable states while analyzing the coherence of the inferred cross sections. 35 The best values for the fraction of 2 D + 2 P metastable states, consistent with the two sets of data at U A = 40 and 90 V, was found to be 3 % and 30-35 % respectively, but no information on the relative proportions of 2 D / 2 P states for these two experimental conditions can be given.…”

Section: Measurement Overviewmentioning

confidence: 99%

“…35 As visible in Figure 5, the values obtained for CH 4 + 19 was assumed here by making various hypotheses on the proportion of metastable states while analyzing the coherence of the inferred cross sections. 35 The best values for the fraction of 2 D + 2 P metastable states, consistent with the two sets of data at U A = 40 and 90 V, was found to be 3 % and 30-35 % respectively, but no information on the relative proportions of 2 D / 2 P states for these two experimental conditions can be given. 35 With these assumed compositions, the cross sections for the O + ( 2 D + 2 P) + CH 4 reaction, shown in Figures 6-7, have been inferred from the cross sections measured in the two experiments at U A = 40 and 90 V. 35 As can be seen in Figure 6, at 5 eV collision energy, our CD 3 + /OD + cross section measurement for the reaction of O + ions, prepared in pure 2 D population, with CD 4 is in good agreement with the CH 3 + cross section reported by Ottinger et al for the reaction of O + ions in a mixed 2 D + 2 P composition with CH 4 , 35 whereas our measurement for the reaction of O + ions, prepared in pure 2 P population (see Figure 7) is a bit lower than their value.…”

Section: Measurement Overviewmentioning

confidence: 99%

“…31 The importance to consider the reactions with methane stems from the multiple other possible oxygen bearing products, such as H x O (+) (with x = 1-3) or H y CO (+) (with y = 0-3), which could initiate a very different chemistry. Many product reaction channels among the (O1-O10) processes listed below have been identified and discussed in experimental [33][34][35][36][37][38] and theoretical [38][39][40] studies of the reaction of atomic oxygen ions with methane: The energetics in equation (O1-O10) are given for ground-state reactants and products and for the most abundant isotopes, 16 O and 12 CH 4 . These channels are displayed in Figure 1 together with channels, which will be discussed later, where reactants or products are in electronically excited states.…”

Section: Introductionmentioning

confidence: 99%

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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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Ion-molecule reactions of O+ with CH4

Cited by 2 publications

References 9 publications

Subterranean atmospheres may act as daily methane sinks

Subterranean atmospheres may act as daily methane sinks

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

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Ion-molecule reactions of O+ with CH4

Cited by 2 publications

References 9 publications

Subterranean atmospheres may act as daily methane sinks

Subterranean atmospheres may act as daily methane sinks

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

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