Evidence for direct molecular oxygen production in CO
            <sub>2</sub>
            photodissociation

Lü, Zhou; Chang, Yih Chung; Yin, Qing‐Zhu; Ng, C. Y.; Jackson, William M.

doi:10.1126/science.1257156

Cited by 117 publications

(91 citation statements)

References 34 publications

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“…2.7 Ga) surface environment, supporting oxidative elemental cycling (Anbar et al, 2007; Kendall et al, 2010; Stolper et al, 2010; Crowe et al, 2013; Lalonde and Konhauser, 2015; Frei et al, 2016). These oxygen traces or the consequences of these oxidative processes could have resulted from abiotic reactions such as CO 2 photodissociation (Lu et al, 2014) and H 2 O 2 disproportionation (Haqq-Misra et al, 2011), but also from biological processes like benthic oxygenic photosynthesis (Lalonde and Konhauser, 2015). Atmospheric oxygen accumulation, however, did not occur at a global scale before the Great Oxidation Event around 2.33 Ga ago (Bekker et al, 2004; Kaufman et al, 2008; Konhauser et al, 2009; Lyons et al, 2014; Luo et al, 2016).…”

Section: Evolution Of the Biogeochemical Conditions In Ancient Oceansmentioning

confidence: 99%

Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments

et al. 2017

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Photoferrotrophy, the process by which inorganic carbon is fixed into organic matter using light as an energy source and reduced iron [Fe(II)] as an electron donor, has been proposed as one of the oldest photoautotrophic metabolisms on Earth. Under the iron-rich (ferruginous) but sulfide poor conditions dominating the Archean ocean, this type of metabolism could have accounted for most of the primary production in the photic zone. Here we review the current knowledge of biogeochemical, microbial and phylogenetic aspects of photoferrotrophy, and evaluate the ecological significance of this process in ancient and modern environments. From the ferruginous conditions that prevailed during most of the Archean, the ancient ocean evolved toward euxinic (anoxic and sulfide rich) conditions and, finally, much after the advent of oxygenic photosynthesis, to a predominantly oxic environment. Under these new conditions photoferrotrophs lost importance as primary producers, and now photoferrotrophy remains as a vestige of a formerly relevant photosynthetic process. Apart from the geological record and other biogeochemical markers, modern environments resembling the redox conditions of these ancient oceans can offer insights into the past significance of photoferrotrophy and help to explain how this metabolism operated as an important source of organic carbon for the early biosphere. Iron-rich meromictic (permanently stratified) lakes can be considered as modern analogs of the ancient Archean ocean, as they present anoxic ferruginous water columns where light can still be available at the chemocline, thus offering suitable niches for photoferrotrophs. A few bacterial strains of purple bacteria as well as of green sulfur bacteria have been shown to possess photoferrotrophic capacities, and hence, could thrive in these modern Archean ocean analogs. Studies addressing the occurrence and the biogeochemical significance of photoferrotrophy in ferruginous environments have been conducted so far in lakes Matano, Pavin, La Cruz, and the Kabuno Bay of Lake Kivu. To date, only in the latter two lakes a biogeochemical role of photoferrotrophs has been confirmed. In this review we critically summarize the current knowledge on iron-driven photosynthesis, as a remains of ancient Earth biogeochemistry.

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Section: Evolution Of the Biogeochemical Conditions In Ancient Oceansmentioning

confidence: 99%

Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments

et al. 2017

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“…However, theoretical simulations suggested the possibility of generating O 2 through the dissociation of a CO 2 molecule [4]. A recent experiment showed the evidence of O 2 formation from CO 2 molecules after UV excitation through the detection of C + [5]. So far, O 2 formation from CO 2 has not been directly observed.…”

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confidence: 99%

Molecular oxygen observed by direct photoproduction from carbon dioxide

et al. 2017

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Oxygen (O2 ) is one of the most important elements required to sustain life. The concentration of O2 on Earth has been accumulated over millions of years and has a direct connection with that of CO2 . Further, CO2 plays an important role in many other planetary atmospheres. Therefore, molecular reactions involving CO2 are critical for studying the atmospheres of such planets. Existing studies on the dissociation of CO2 are exclusively focused on the C-O bond breakage. Here we report first experiments on the direct observation of molecular Oxygen formation from CO2 in strong laser fields with a reaction microscope. Our accompanying simulations suggest that CO2 molecules may undergo bending motion during and after strong-field ionization which supports the molecular Oxygen formation process. The observation of the molecular Oxygen formation from CO2 may trigger further experimental and theoretical studies on such processes with laser pulses, and provide hints in studies of the O2 and O + 2 abundance in CO2 -dominated planetary atmospheres.PACS numbers: 33.80. Gj, 42.50.Hz, O 2 production is one of the most important processes for the biosphere of the Earth.Oxygen molecules are mainly generated via the photosynthesis by green plants and algae from carbon dioxide and water:. CO 2 is not only important for the atmosphere on Earth, it is also the dominant compound of the atmosphere on other planets, such as Mars and Venus. One of the most crucial tasks for the quest to establish a human settlement on Mars is the production of O 2 [2]. Because more than 95% of the atmosphere on Mars is CO 2 , it will be extremely helpful if O 2 can be produced directly from CO 2 . In the past, it was observed that dissociation of CO 2 via absorption of photons leads to carbon monoxide (CO) and oxygen atoms (O) [3]. However, theoretical simulations suggested the possibility of generating O 2 through the dissociation of a CO 2 molecule [4]. A recent experiment showed the evidence of O 2 formation from CO 2 molecules after UV excitation through the detection of C + [5]. So far, O 2 formation from CO 2 has not been directly observed.In the past decade, intense ultrashort laser pulses have been successfully applied to trigger and control molecular reactions such as dissociation and isomerization [6][7][8][9][10][11][12][13][14][15]. When a molecule interacts with a strong laser field, electrons from outer molecular orbitals can be excited or removed through tunneling or over-the-barrier ionization which may prepare the molecule in an excited state or a state with a certain charge. As a consequence, the excited or ionized molecule may undergo severe geometrical reconfiguration and may also break into several fragments or form new chemical bonds. Because of the importance of CO 2 in many research disciplines, strongfield induced reactions of CO 2 have been experimentally studied with ultrashort lasers by several research groups.However, these studies mainly focused on the topic of ionization and dissociation [16]. In this paper, for the first...

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“…The dynamics of these reactions is not mediated by a single conventional TS associated with an SP of index one. [7,[11][12][13][35][36][37][38][39][40] For this reason it is important to have a method that explores a region of a PES where an SP 2 emerges. The GAD method is a potential algorithm to be used for this aim.…”

Section: Search Of Sp's Of Higher Index By Gad Trajectoriesmentioning

confidence: 99%

“…Such non-RP dynamics may well be the rule rather than the exception for hot molecules. [7][8][9][10][11] Recently, theoretical work has suggested that a hint for many of these non-RP processes is a "secondindex saddle point" (SP 2 ) on the PES. The index is the number of unstable directions attached to the saddle.…”

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confidence: 99%

Embedding of the saddle point of index two on the PES of the ring opening of cyclobutene

Quapp

Bofill

2015

Int. J. Quantum Chem.

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The ring opening of cyclobutene is characterized by a competition of the two different pathways: a usual pathway over a saddle of index one (SP 1 ) along the conrotatory behavior of the end groups, as well as a "forbidden" pathway over a saddle point of index two (SP 2 ) along the disrotatory behavior of the end CH 2 groups. We use the system of ordinary differential equations for the method of the gentlest ascent dynamics (GAD) to determine saddle points of the potential energy surface (PES) of the ring opening of cyclobutene to cis-butadiene. We apply generalized GAD formulas for the search of a saddle point of index two. To understand the relation of the different regions of the PES (around minimums, around SPs of index one or two) we also calculate valley-ridge inflection (VRI) points on the PES using Newton trajectories (NT). VRIs and the corresponding singular NTs subdivide the regions of "attraction" of the different SPs. We calculate the connections of the SP 2 (in its different symmetry versions) with different SPs of index one of the PES by different "reaction pathways." We compare the possibilities of the tool of the GAD curves for the exploration of PESs with these of NT. The barrier of the disrotatory SP 2 is somewhat higher than the barrier of the conrotatory SP 1 , however, pathways across the slope to the SP 2 open additional reaction valleys. IntroductionMathematics has had a profound impact on science, providing a means to understand the world around us in unprecedented ways.[1] With the advantage of the computer age, the subject of modelization has hugely grown in importance. In particular, over the last decades significant advances in our understanding of the world of chemistry have culminated in the development of a very large set of concepts. Some of these concepts are the potential energy surface (PES) [2][3][4] and the chemical reaction path (RP) [5] being the basic concepts for the theories of chemical dynamics and chemical transformations. The PES is a continuous function of the coordinates of the nuclei over an IR N , thus it is an N-dimensional hypersurface. It should have continuous derivatives of at least second order for our treatments. If Cartesian coordinates are used, then N53 n, however, we may also use N53 n26 nonredundant, internal coordinates for an n-atomic molecule. The PES can be seen as formally divided in catchments associated with local minima.[2] For such a picture, one has in mind steepest descent (SD) curves. The first order saddle points or transition states (TSs) are located at the deepest points of the boundary of the basins. TSs and minima correspond to stationary points of the PES. Two adjacent minima of the PES can be connected through a TS via a continuous curve in the N-dimensional coordinate space, describing the coordinates of the nuclei. The curve characterizes a RP. The concept of the RP has found a widespread use in descriptions of reaction mechanisms, which are based on geometrical rearrangements of the atoms comprising a given chemical system. [6] Mor...

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Evidence for direct molecular oxygen production in CO ₂ photodissociation

Cited by 117 publications

References 34 publications

Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments

Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments

Molecular oxygen observed by direct photoproduction from carbon dioxide

Embedding of the saddle point of index two on the PES of the ring opening of cyclobutene

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Evidence for direct molecular oxygen production in CO 2 photodissociation

Cited by 117 publications

References 34 publications

Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments

Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments

Molecular oxygen observed by direct photoproduction from carbon dioxide

Embedding of the saddle point of index two on the PES of the ring opening of cyclobutene

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Evidence for direct molecular oxygen production in CO ₂ photodissociation