Laboratory measurements of methanol photolysis branching ratios to guide astrochemical models

Weaver, Susanna Widicus; Powers, Carson Reed; McCabe, Morgan N.; Zinga, Samuel

doi:10.1017/s1743921317006408

Cited by 3 publications

(4 citation statements)

References 6 publications

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“…Although the photodissociation curves adopting the Paardekooper's BRs lead to better fits at the four temperatures, a few other cases also result in high fitness scores. For example, at 30 K, some models adopting the BRs from Weaver et al (2018) can also fit well the experiments. At 50 K and 70 K, models considering other BRs also provide a relatively good match with the experiments.…”

Section: Br Selectionmentioning

confidence: 86%

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Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

Rocha¹,

P.²,

S.³

et al. 2023

Preprint

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Context. Methanol is the most complex molecule securely identified in interstellar ices and is a key chemical species for understanding chemical complexity in astrophysical environments. Important aspects of the methanol ice photochemistry are still unclear such as the branching ratios and photo-dissociation cross-sections at different temperatures and irradiation fluxes. Aims. This work aims at a quantitative agreement between laboratory experiments and astrochemical modelling of the CH 3 OH ice UV photolysis. Ultimately, this work allows us to better understand which processes govern the methanol ice photochemistry present in laboratory experiments. Methods. We use the ProDiMo code to simulate the radiation fields, pressures and pumping efficiencies characteristic of laboratory measurements. The simulations start with simple chemistry consisting only of methanol ice and helium to mimic the residual gas in the experimental chamber. A surface chemical network enlarged by photo-dissociation reactions is used to study the chemical reactions within the ice. Additionally, different surface chemistry parameters such as surface competition, tunnelling, thermal diffusion and reactive desorption are adopted to check those that reproduce the experimental results.Results. The chemical models with the ProDiMo code including surface chemistry parameters can reproduce the methanol ice destruction via UV photodissociation at temperatures of 20, 30, 50 and 70 K as observed in the experiments. We also note that the results are sensitive to different branching ratios after photolysis and to the mechanisms of reactive desorption. In the simulations of a molecular cloud at 20 K, we observed an increase in the methanol gas abundance of one order of magnitude, with a similar decrease in the solid-phase abundance. Conclusions. Comprehensive astrochemical models provide new insights into laboratory experiments as the quantitative understanding of the processes that govern the reactions within the ice. Ultimately, those insights can help to better interpret astronomical observations.

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Section: Br Selectionmentioning

confidence: 86%

“…A different technique is used by Weaver et al (2018) to estimate the methanol photolysis BRs in the gas phase. In a vacuum chamber, methanol is photodissociated by a VUV laser in the throat of a supersonic expansion.…”

Section: Network and Branching Ratiosmentioning

confidence: 99%

Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

Rocha¹,

P.²,

S.³

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…Although the photodissociation curves adopting the Paardekooper BRs lead to better fits at the four temperatures, a few other cases also result in high fitness scores. For example, at 30 K, some models adopting the BRs from Weaver et al (2018) can also fit the experiments well. At 50 K and 70 K, models considering other BRs also provide a relatively good match with the experiments.…”

Section: Br Selectionmentioning

confidence: 95%

“…A different technique was used by Weaver et al (2018) to estimate the methanol photolysis BRs in the gas phase. In a vacuum chamber, methanol was photodissociated by a VUV laser in the throat of a supersonic expansion.…”

Section: Network and Branching Ratiosmentioning

confidence: 99%

Simulation of CH₃OH ice UV photolysis under laboratory conditions

Rocha¹,

P.²,

S.³

et al. 2023

A&A

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Context. Methanol is the most complex molecule that is securely identified in interstellar ices. It is a key chemical species for understanding chemical complexity in astrophysical environments. Important aspects of the methanol ice photochemistry are still unclear, such as the branching ratios and photodissociation cross sections at different temperatures and irradiation fluxes. Aims. This work aims at a quantitative agreement between laboratory experiments and astrochemical modelling of the CH 3 OH ice UV photolysis. Ultimately, this work allows us to better understand which processes govern the methanol ice photochemistry present in laboratory experiments. Methods. We used the code ProDiMo to simulate the radiation fields, pressures, and pumping efficiencies characteristic of laboratory measurements. The simulations started with simple chemistry consisting only of methanol ice and helium to mimic the residual gas in the experimental chamber. A surface chemical network enlarged by photodissociation reactions was used to study the chemical reactions within the ice. Additionally, different surface chemistry parameters such as surface competition, tunnelling, thermal diffusion, and reactive desorption were adopted to check those that reproduce the experimental results.Results. The chemical models with the code ProDiMo that include surface chemistry parameters can reproduce the methanol ice destruction via UV photodissociation at temperatures of 20, 30, 50, and 70 K as observed in the experiments. We also note that the results are sensitive to different branching ratios after photolysis and to the mechanisms of reactive desorption. In the simulations of a molecular cloud at 20 K, we observed an increase in the methanol gas abundance of one order of magnitude, with a similar decrease in the solid-phase abundance. Conclusions. Comprehensive astrochemical models provide new insights into laboratory experiments as the quantitative understanding of the processes that govern the reactions within the ice. Ultimately, these insights can help us to better interpret astronomical observations.

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Is There Any Linkage between Interstellar Aldehyde and Alcohol?

Mondal

Gorai

Sil

et al. 2021

ApJ

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It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA cycle 4 data of a hot molecular core, G10.47+0.03, are utilized for this study. Various aldehydes (acetaldehyde, propanal, and glycolaldehyde), alcohols (methanol and ethylene glycol), and a ketone (acetone) are identified in this source. The excitation temperatures and column densities of these species were derived via the rotation diagram method assuming local thermodynamic equilibrium conditions. An extensive investigation is carried out to understand the formation of these species. Six pairs of aldehyde–alcohol are considered for this study: (i) methanal and methanol, (ii) ethanal and ethanol, (iii) propanal and 1-propanol, (iv) propenal and allyl alcohol, (v) propynal and propargyl alcohol, and (vi) glycolaldehyde and ethylene glycol. One pair of ketone–alcohol (acetone and isopropanol) and ketene–alcohol (ethenone and vinyl alcohol) are also considered. Two successive hydrogenation reactions in the ice phase are examined to form these alcohols from aldehydes, ketone, and ketene, respectively. Quantum chemical methods are extensively executed to review the ice-phase formation route and the kinetics of these species. Based on the obtained kinetic data, astrochemical modeling is employed to derive the abundances of these aldehydes, alcohols, ketone, and ketene in this source. It is seen that our model could successfully explain the observed abundances of various species in this hot molecular core.

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Laboratory measurements of methanol photolysis branching ratios to guide astrochemical models

Cited by 3 publications

References 6 publications

Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

Simulation of CH₃OH ice UV photolysis under laboratory conditions

Is There Any Linkage between Interstellar Aldehyde and Alcohol?

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Laboratory measurements of methanol photolysis branching ratios to guide astrochemical models

Cited by 3 publications

References 6 publications

Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

Simulation of CH$_3$OH ice UV photolysis under laboratory conditions

Simulation of CH3OH ice UV photolysis under laboratory conditions

Is There Any Linkage between Interstellar Aldehyde and Alcohol?

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Simulation of CH₃OH ice UV photolysis under laboratory conditions