Photochemistry of glyoxylate embedded in sodium chloride clusters, a laboratory model for tropospheric sea-salt aerosols

Heller

et al. 2018

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Marine aerosols consist of a variety of compounds and play an important role in many atmospheric processes. In the present study, sodium iodide clusters with their simple isotope pattern serve as model systems for laboratory studies to investigate the role of iodide in the photochemical processing of sea‐salt aerosols. Salt clusters doped with camphor, formate and pyruvate are studied in a Fourier transform ion cyclotron resonance mass spectrometer (FT‐ICR MS) coupled to a tunable laser system in both UV and IR range. The analysis is supported by ab initio calculations of absorption spectra and energetics of dissociative channels. We provide quantitative analysis of IRMPD measurements by reconstructing one‐photon spectra and comparing them with the calculated ones. While neutral camphor is adsorbed on the cluster surface, the formate and pyruvate ions replace an iodide ion. The photodissociation spectra revealed several wavelength‐specific fragmentation pathways, including the carbon dioxide radical anion formed by photolysis of pyruvate. Camphor and pyruvate doped clusters absorb in the spectral region above 290 nm, which is relevant for tropospheric photochemistry, leading to internal conversion followed by intramolecular vibrational redistribution, which leads to decomposition of the cluster. Potential photodissociation products of pyruvate in the actinic region may be formed with a cross section of <2×10−20 cm2, determined by the experimental noise level.

true [Na_{6} I_{4} (CH_{3} COCOO)]^{+} \to [Na_{6 - x} I_{3 - x} (CH_{3} COCOO)]^{•}^{+} + [Na_{x} I_{x + 1}]^{•} x = 0 - 3

true [Na_{6} I_{4} (CH_{3} COCOO)]^{+} \to [Na_{6 - x} I_{4 - x} (COO)]^{•}^{+} + Na_{x} normalI_{x} CH_{3} CO^{•} x = 0 - 3

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Section: Resultssupporting

confidence: 75%

Section: Resultsmentioning

confidence: 52%

Section: Pyruvic Acidmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photodissociation of Sodium Iodide Clusters Doped with Small Hydrocarbons

Bersenkowitsch

Heller

et al. 2018

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Infrared Multiple Photon Dissociation Spectroscopy of Hydrated Cobalt Anions Doped with Carbon Dioxide CoCO₂(H₂O)_n⁻, n=1–10, in the C−O Stretch Region

Barwa

Pascher

et al. 2020

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We investigate anionic [Co,CO 2 ,nH 2 O] À clusters as model systems fort he electrochemical activation of CO 2 by infrared multiple photon dissociation (IRMPD) spectroscopy in the range of 1250-2234 cm À1 using an FT-ICR mass spectrometer.W es how that both CO 2 and H 2 Oa re activated in a significant fraction of the [Co,CO 2 ,H 2 O] À clusters since it dissociates by CO loss, and the IR spectrum exhibits the characteristic CÀOs tretching frequency.A bout 25 %o ft he ion population can be dissociated by pumping the CÀOs tretching mode.W ith the help of quantum chemical calculations, we assign the structure of this ion as Co(CO)(OH) 2 À .H owever,c alculations find Co(HCOO)(OH) À as the globalm inimum, which is stable against IRMPD under the conditions of our experiment. Weak features around1 590-1730 cm À1 are most likely due to higher lying isomerso ft he composition Co(HOCO)(OH) À .U pon additional hydration, all species [Co,CO 2 ,nH 2 O] À , n ! 2, undergo IRMPD through loss of H 2 O molecules as ar elatively weakly bound messenger.T he main spectralf eaturesa re the CÀOs tretching mode of the CO ligand around1 900 cm À1 ,t he water bending mode mixed with the antisymmetric CÀOs tretching mode of the HCOO À ligand around 1580-1730 cm À1 ,a nd the symmetric CÀO stretching mode of the HCOO À ligand around 1300 cm À1 .A weak feature above 2000 cm À1 is assigned to water combination bands.T he spectrala ssignment clearly indicates the presence of at least two distinct isomers for n ! 2.

UV/Vis Spectroscopy of Copper Formate Clusters: Insight into Metal‐Ligand Photochemistry

Pascher

Linde

et al. 2020

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The electronic structure and photochemistry of copper formate clusters, Cu I 2 (HCO 2 ) 3 − and Cu II n (HCO 2 ) 2 n +1 − , n ≤8, are investigated in the gas phase by using UV/Vis spectroscopy in combination with quantum chemical calculations. A clear difference in the spectra of clusters with Cu I and Cu II copper ions is observed. For the Cu I species, transitions between copper d and s/p orbitals are recorded. For stoichiometric Cu II formate clusters, the spectra are dominated by copper d–d transitions and charge‐transfer excitations from formate to the vacant copper d orbital. Calculations reveal the existence of several energetically low‐lying isomers, and the energetic position of the electronic transitions depends strongly on the specific isomer. The oxidation state of the copper centers governs the photochemistry. In Cu II (HCO 2 ) 3 − , fast internal conversion into the electronic ground state is observed, leading to statistical dissociation; for charge‐transfer excitations, specific excited‐state reaction channels are observed in addition, such as formyloxyl radical loss. In Cu I 2 (HCO 2 ) 3 − , the system relaxes to a local minimum on an excited‐state potential‐energy surface and might undergo fluorescence or reach a conical intersection to the ground state; in both cases, this provides substantial energy for statistical decomposition. Alternatively, a Cu II (HCO 2 ) 3 Cu 0− biradical structure is formed in the excited state, which gives rise to the photochemical loss of a neutral copper atom.