Vacuum ultraviolet photodissociation of OCS via the 21Σ+ state: the S(1D2) elimination channel

Li, Zheng; Liao, Hong; Yang, Wenshao; Yang, Xueming; Yu, Shengrui

doi:10.1039/d2cp02044k

Cited by 6 publications

(5 citation statements)

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“…The vibronic origin of the absorption is associated with bending excitations in the 2 1 A′ and 1 1 A″ states (the 1 Δ u state splits into Renner–Teller pairs of A′ and A″ symmetry in the bent C s geometry). Based on previous studies, , the comparison between the absorption spectrum and the photofragment excitation (PHOFEX) spectrum reveals subtle differences. Therefore, in this work, the PHOFEX spectrum was obtained by measuring the total O( 1 D 2 ) atomic photofragment yield while scanning the VUV photolysis laser from 143.00 to 155.00 nm in this work.…”

Section: Results and Discussionmentioning

confidence: 97%

“…The experiment employed the time-sliced velocity-mapped ion imaging apparatus combined with two independent laser sources (a tunable VUV source for photolysis and a fixed UV source for (2 + 1) REMPI detection) for CO 2 molecular photodissociation. The detailed configuration of the experimental setup has been introduced in our previous studies, − and thus only a brief description is presented here. The CO 2 molecular beam (the rotational temperature was ∼10 K) was formed in a pulsed supersonic expansion of 10% CO 2 in Ar at a 1 bar backing pressure.…”

Section: Methodsmentioning

confidence: 99%

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Wavelength-Dependent Dynamics of the O(¹D₂) Channel in the ¹Δ_u State Photodissociation of CO₂

Liu,

Tan,

Zou

et al. 2024

J. Phys. Chem. A

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The wavelength-dependent dynamics of the O( 1 D 2 ) channel, formed by photoexcitation of CO 2 to the 1 Δ u state at 143.53−153.03 nm, is investigated by using the time-sliced velocity-mapped ion imaging method. The measured ionic peaks of the O( 1 D 2 ) images are analyzed to determine the total kinetic energy release (TKER) spectra and image anisotropy parameters. The structures observed in the TKER spectra can be directly assigned to the ro-vibrational state distributions of the counter CO photofragments. Compared to those observed at 157 and 155 nm, the highly rotationally excited CO photofragments still obviously appear in v = 0 and 1, but the fraction of rotational excitations is significantly reduced. Conversely, the CO photofragments exhibit substantially higher vibrational excitations, implying that the nearly linear 2 1 A′ state also contributes to dissociation in addition to the bend configuration. The image anisotropy parameters display an extremely slow decreasing trend with an increase of the CO ro-vibrational state besides those for the highest ro-vibrationally excited CO photofragments. Nevertheless, the nonaxial recoil effect, suggested in previous photodissociation studies of CO 2 and other triatomic molecular systems, is still appropriate to explain the observations of internal energy dependences of image anisotropy parameters.

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Section: Results and Discussionmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 99%

Wavelength-Dependent Dynamics of the O(¹D₂) Channel in the ¹Δ_u State Photodissociation of CO₂

Liu,

Tan,

Zou

et al. 2024

J. Phys. Chem. A

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“…Carbonyl sulfide (OCS) is the most abundant, long-lived S-containing gas in Earth's atmosphere and a major supplier of sulfur to the stratospheric sulfate aerosol layer. OCS has been observed in the deep atmosphere of Venus, in dense molecular clouds and in Jupiter's atmosphere following the impact of comets [ 75 ]. Carbon disulfide (CS 2 ) is also ubiquitous in the ISM and has been proposed as a likely precursor for CS and S 2 radicals observed in cometary coma [ 76 ].…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The photodissociation of OCS at near UV wavelengths λ >200 nm is dominated by the spin-allowed channel yielding S( 1 D) + CO(X) products; the latter are formed vibrationally ‘cold’ but rotationally ‘hot’, in at least qualitative accord with that expected given the forces introduced by a bent ← linear excitation process [ 84 ]. The same product channel has been investigated using TSVMI methods following excitation in the range 142.98 ≤ λ ≤ 154.37 nm [ 75 ] and other single-bond fission channels yielding S( 1 S) + CO(X) [ 85 ] and S( 3 P) + CO(A) [ 86 ] products have also been reported when exciting at similar VUV wavelengths.…”

Section: Experimental Methodsmentioning

confidence: 99%

Exploring the vacuum ultraviolet photochemistry of astrochemically important triatomic molecules

Chang

Ashfold

Yuan

et al. 2023

National Science Review

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The recently constructed vacuum ultraviolet (VUV) free electron laser (FEL) at the Dalian Coherent Light Source (DCLS) is yielding a wealth of new and exquisitely detailed information about the photofragmentation dynamics of many small gas phase molecules. This Review focuses particular attention on five triatomic molecules – H2O, H2S, CO2, OCS and CS2. Each shows excitation wavelength dependent dissociation dynamics, yielding photofragments that populate a range of electronic and (in the case of diatomic fragments) vibrational and rotational quantum states, which can be characterized by different translational spectroscopy methods. The photodissociation of an isolated molecule from a well-defined initial quantum state provides a lens through which one can investigate how and why chemical reactions occur, and provides numerous opportunities for fruitful, synergistic collaborations with high level ab initio quantum chemists. The chosen molecules, their photofragments, and the subsequent chemical reaction networks to which they can contribute, are all crucial in planetary atmospheres and in interstellar and circumstellar environments. The aims of this Review are three-fold: to highlight new photochemistry enabled by the VUV-FEL at the DCLS, notably the recently recognized central atom elimination process that is shown to contribute in all of these triatomic molecules; to highlight some of the potential implications of this rich photochemistry to our understanding of interstellar chemistry and molecular evolution within the universe; and to highlight other and future research directions in areas related to chemical reaction dynamics and astrochemistry that will be enabled by increased access to VUV-FEL sources.

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“…An example of a small but important sulfur-bearing species is carbonyl sulfide (OCS). , For example, OCS is the most abundant sulfur-containing molecule in Earth’s atmosphere, with a mixing ratio of ∼500 ppt . Moreover, OCS contributes to stratospheric sulfate aerosol formation, due to the long tropospheric lifetime of OCS (τ > 2 years) allowing transportation to the stratosphere. − In the Venusian atmosphere, a rapid reduction in the OCS mixing ratio from 10 to 20 ppm at an altitude of 30 km, to 0.35 ppm at 38 km, is observed, with reasons for this decline still unknown. , Furthermore, OCS was found to exist in several Jupiter family comets and, more recently, in the L1455-IRS1 and L1551-IRS5 class I protostars …”

Section: Introductionmentioning

confidence: 99%

Ab Initio and Statistical Rate Theory Exploration of the CH (X²Π) + OCS Gas-Phase Reaction

Lucas,

Kavaliauskas,

Blitz

et al. 2023

J. Phys. Chem. A

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The first theoretical results regarding the gas-phase reaction mechanism and kinetics of the CH (X2Π) + OCS reaction are presented here. This reaction has a proposed importance in the removal of OCS in regions of the interstellar medium (ISM) and has the potential to form the recently observed HCS/HSC isomers, with both constitutional isomers having recently been observed in the L483 molecular cloud in a 40:1 ratio. Statistical rate theory simulations were performed on stationary points along the reaction potential energy surface (PES) obtained from ab initio calculations at the RO-CCSD(T)/aug-cc-pV(Q+d)Z//M06-2X-D3/aug-cc-pV(Q+d)Z level of theory over the temperature and total density range of 150–3000 K and 1011–1024 cm–3, respectively, using a Master Equation analysis. Exploration of the reaction potential energy surface revealed that all three pathways identified to create CS + HCO products required surmounting barriers of 16.5 kJ mol–1 or larger when CH approached the oxygen side of OCS, rendering this product formation negligible below 1000 K, and certainly under low-temperature ISM conditions. In contrast, when CH approaches the sulfur side of OCS, only submerged barriers are found along the reaction potential energy surface to create HCCO + S or CO + HCS, both of which are formed via a strongly bound OCC(H)S intermediate (−358.9 kJ mol–1). Conversion from HCS to HSC is possible via a barrier of 77.8 kJ mol–1, which is still −34.1 kJ mol–1 below the CH + OCS entrance channel. No direct route from CH + OCS to H + CO + CS was found from our ab initio calculations. Rate theory simulations suggest that the reaction has a strong negative temperature dependence, in accordance with the barrierless addition of CH to the sulfur side of OCS. Product branching fractions were also determined from MESMER simulations over the same temperature and total density range. The product branching fraction of CO + HCS reduces from 79% at 150 K to 0.0% at 800 K, while that of HCS dissociation to H + CS + CO increases from 22% at 150 K to 100% at 800 K. The finding of CO + HCS as the major product at the low temperatures relevant to the ISM, instead of H + CS + CO, is in opposition to the current supposition used in the KIDA database and should be adapted in astrochemical models as another source of the HCS isomer.

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Vacuum ultraviolet photodissociation of OCS via the 2¹Σ⁺ state: the S(¹D₂) elimination channel

Abstract: The photodissociation of OCS is necessary to model the primary photochemical processes of OCS in the global cycling of sulfur and interstellar photochemistry. Here, by combining the time-sliced velocity-map ion...

Cited by 6 publications

References 54 publications

Wavelength-Dependent Dynamics of the O(¹D₂) Channel in the ¹Δ_u State Photodissociation of CO₂

Wavelength-Dependent Dynamics of the O(¹D₂) Channel in the ¹Δ_u State Photodissociation of CO₂

Exploring the vacuum ultraviolet photochemistry of astrochemically important triatomic molecules

Ab Initio and Statistical Rate Theory Exploration of the CH (X²Π) + OCS Gas-Phase Reaction

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Vacuum ultraviolet photodissociation of OCS via the 21Σ+ state: the S(1D2) elimination channel

Abstract: The photodissociation of OCS is necessary to model the primary photochemical processes of OCS in the global cycling of sulfur and interstellar photochemistry. Here, by combining the time-sliced velocity-map ion...

Cited by 6 publications

References 54 publications

Wavelength-Dependent Dynamics of the O(1D2) Channel in the 1Δu State Photodissociation of CO2

Wavelength-Dependent Dynamics of the O(1D2) Channel in the 1Δu State Photodissociation of CO2

Exploring the vacuum ultraviolet photochemistry of astrochemically important triatomic molecules

Ab Initio and Statistical Rate Theory Exploration of the CH (X2Π) + OCS Gas-Phase Reaction

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Vacuum ultraviolet photodissociation of OCS via the 2¹Σ⁺ state: the S(¹D₂) elimination channel

Wavelength-Dependent Dynamics of the O(¹D₂) Channel in the ¹Δ_u State Photodissociation of CO₂

Wavelength-Dependent Dynamics of the O(¹D₂) Channel in the ¹Δ_u State Photodissociation of CO₂

Ab Initio and Statistical Rate Theory Exploration of the CH (X²Π) + OCS Gas-Phase Reaction