Real-time tracking of the entangled pathways in the multichannel photodissociation of acetaldehyde

Yang, Chung-Hsin; Bhattacharyya, Surjendu; Fang, Wei‐Hai; Liu, Kopin

doi:10.1039/d0sc00063a

Cited by 17 publications

(63 citation statements)

References 41 publications

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“…The evolving molecules couple to the S 0 PES with a range of geometries and nuclear momenta, which govern the subsequent athermal rearrangements of the S 0 # species. These vibrationally excited S 0 molecules are highly fluxional and can adopt at least three identified open-ring structures or re-form the parent thiophenone and have sufficient internal energy to dissociate (by loss of a CO moiety); the deduced ground state dynamics serve to bolster a recent prediction that isomerization of energized molecules prior to dissociation might well be the rule rather than the exception in many polyatomic unimolecular processes 33 . The distribution of vertical IPs computed from the AIMD trajectories on the S 0 PES reproduces the narrow spread of BEs observed experimentally and can be traced to the localized nature of the sulfur lone pair orbital that is the dominant contributor to the highest occupied molecular orbital in each species.…”

Section: Discussionmentioning

confidence: 85%

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

et al. 2020

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Photo-induced isomerization reactions lie at the heart of many chemical processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics occurring on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free-electron laser to trace the ultrafast ring opening of gas-phase thiophenone molecules following ultraviolet photoexcitation. When combined with ab initio electronic-structure and molecular-dynamics calculations of the excitedand ground-state molecules, the results provide insights into both the electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state is shown to be driven by ballistic S-C bond extension and to be complete within 350 femtoseconds. Theory and experiment also enable visualization of the rich ground-state dynamics -involving formation of, and interconversion between, ring-opened isomers and the cyclic structure, and fragmentation over much longer timescales.

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Section: Discussionmentioning

confidence: 85%

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

et al. 2020

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“…The dissociation of CH 3 CHO via R2 has been reported to occur via up to three different dynamical channels. Although the interpretation of each channel is still not agreed upon in the literature [15][16][17], the key factor for this work is that all hypothesised channels yield CH 4 and CO as photoproducts following dynamics on S 0 after initial photo-excitation to S 1 . The two different CO dynamical signatures from CF 3 CHO dissociation in Fig.…”

Section: Photodissociation Pathwaysmentioning

confidence: 96%

“…However, following absorption of an ultraviolet photon, CH 3 CHO can also access a rich photochemistry on the ground electronic state (S 0 ). These many ground state photodissociation pathways are discussed in the following section and, most importantly, include the exoergic formation of methane (CH 4 ) and carbon monoxide (CO) [15][16][17]. Fluoroform (CHF 3 or HFC-23) is the product analogue of CH 4 for CF 3 CHO.…”

Section: Main Textmentioning

confidence: 99%

Photodissociation of CF3CHO provides a new source of CHF3 (HFC-23) in the atmosphere: implications for new refrigerants.

Hansen

Campbell

Kable

2021

Preprint

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Throughout the last century, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) were the most widely used refrigerants. However, it was discovered that they released reactive chlorine in the upper atmosphere causing the hole in the ozone layer and they were phased out by the 1987 Montreal Protocol [1]. They were replaced by hydrofluorocarbons (HFCs), which contain no chlorine and do not damage the ozone layer. However, HFCs are potent greenhouse gases and they were phased out in a 2016 amendment to the Montreal Protocol [2]. The latest evolution of these refrigerants is the hydrofluoroolefins (HFOs). These molecules have no chlorine and incorporate a carbon-carbon double bond to greatly reduce their atmospheric lifetime, and hence their contribution as a greenhouse gas. In this work, we demonstrate that one of the most important HFOs in current use ultimately decomposes partially into HFC-23 (CHF3) in the atmosphere. HFC-23 is one of the most potent greenhouse gases known, and the most potent HFC. Despite its phaseout, the observed emissions of HFC-23 have been increasing recently and were the largest in history in 2018 with no conclusive explanation [3]. This work suggests that the production of HFOs might be partially responsible.

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“…In aldehydes, the formyl hydrogen is transferred to the main alkyl chain, forming CO and an alkane: R-(C=O)-H → CO + RH. Both roaming and TS decarbonylation mechanisms have been observed in gas-phase reactions of small aldehydes (Townsend et al, 2004;Houston and Kable, 2006;Heazlewood et al, 2008;Rubio-Lago et al, 2012;Yang et al, 2020). Figure 4 shows TS decarbonylation thresholds for the aldehydes in the dataset.…”

Section: Decarbonylation (Co-loss)mentioning

confidence: 99%

Photo-initiated ground state chemistry: How important is it in the atmosphere?

Rowell

Kable

Jordan

2021

Preprint

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Abstract. Carbonyls are among the most abundant volatile organic compounds in the atmosphere. They are central to atmospheric photochemistry as absorption of near-UV radiation by the C=O chromophore can lead to photolysis. If photolysis does not occur on electronic excited states, non-radiative relaxation to the ground state will form carbonyls with extremely high internal energy. These “hot” molecules can access a range of ground state reactions. Up to nine potential ground state reactions are investigated at the B2GP-PLYP-D3/def2-TZVP level of theory for a dataset of 20 representative carbonyls. Almost all are energetically accessible under tropospheric conditions. Comparison with experiment suggests the most significant ground state dissociation pathways will be concerted triple fragmentation in saturated aldehydes, Norrish type III dissociation to form another carbonyl, and H2-loss involving the formyl H atom in aldehydes. Tautomerisation, leading to more reactive unsaturated species, is also predicted to be energetically accessible and is likely to be important when there is no low-energy ground state dissociation pathway, for example in α,β-unsaturated carbonyls and some ketones. The concerted triple fragmentation and H2-loss pathways have immediate atmospheric implication to global H2 production and tautomerisaton has implication to the atmospheric production of organic acids.

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Real-time tracking of the entangled pathways in the multichannel photodissociation of acetaldehyde

Abstract:
Unraveling the entangled multi-channel dissociation pathways by a two-dimensional, time and product pair-correlation, measurement and ab initio calculations.

Cited by 17 publications

References 41 publications

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Photodissociation of CF3CHO provides a new source of CHF3 (HFC-23) in the atmosphere: implications for new refrigerants.

Photo-initiated ground state chemistry: How important is it in the atmosphere?

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Real-time tracking of the entangled pathways in the multichannel photodissociation of acetaldehyde

Abstract: Unraveling the entangled multi-channel dissociation pathways by a two-dimensional, time and product pair-correlation, measurement and ab initio calculations.

Cited by 17 publications

References 41 publications

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

Photodissociation of CF3CHO provides a new source of CHF3 (HFC-23) in the atmosphere: implications for new refrigerants.

Photo-initiated ground state chemistry: How important is it in the atmosphere?

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Abstract:
Unraveling the entangled multi-channel dissociation pathways by a two-dimensional, time and product pair-correlation, measurement and ab initio calculations.