Formation Of Oxygen Research Articles

Oxygen Hole Formation Controls Stability in LiNiO2 Cathodes: DFT Studies of Oxygen Loss and Singlet Oxygen Formation in Li-Ion Batteries

Ni-rich cathode materials achieve both high voltages and capacities in Li-ion batteries but are prone to structural instabilities and oxygen loss via the formation of singlet oxygen. Using ab initio molecular dynamics simulations, we observe spontaneous O2 loss from the (012) surface of delithiated LiNiO2, singlet oxygen forming in the process. We find that the origin of the instability lies in the pronounced oxidation of O during delithiation, i.e., O plays a central role in Ni-O redox in LiNiO2. For LiNiO2, NiO2, and the prototype rock salt NiO, density-functional theory and dynamical mean-field theory calculations based on maximally localised Wannier functions yield a Ni charge state of ca. +2, with O varying between –2 (NiO), –1.5 (LiNiO2) and –1 (NiO2). Predicted XAS Ni K and O K-edge spectra are in excellent agreement with experimental XAS spectra, confirming the predicted charge states. The calculations also show that a high-voltage O K-edge feature at 531 eV previously assigned to lattice O-redox processes could alternatively arise from O-redox induced water intercalation and O–O dimer formation with lattice O at high states of charge. The O2 surface loss route observed here consists of 2 surface O•– radicals combining to form a peroxide ion, which is oxidised to O2, leaving behind 2 O vacancies and 2 O2– ions: effectively 4 O•– radicals disproportionate to O2 and 2 O2– ions. The reaction liberates ca. 3 eV per O2 molecule. Singlet oxygen formation is caused by the singlet ground state of the peroxide ion, with spin conservation dictating the preferential release of 1O2, the strongly exergonic reaction providing the free energy required for the formation of 1O2 in its excited state.

The Influence of Discharge Mediators on Singlet Oxygen Generation in Lithium-Air Batteries

Next-generation metal-air batteries are limited by factors such as high overpotential, and low energy efficiency. These factors lead to significant electrode and electrolyte decomposition, and consequently, limit the cell life. The primary cause of these parasitic reactions has been identified as the generation of singlet oxygen (1O2) 1 from the disproportionation of superoxide during both charge and discharge.2 Nonetheless, in addition to singlet oxygen generation, in a lithium air battery the insulating products such as lithium peroxide (Li2O2) tend to accumulate on the cathode overtime and passivate the active surface. This results in early cell death and significantly hinders the overall efficiency of the battery. 3, 4 Redox mediators (RMs) are one potential solution to these problems. For example, by mediating the charge and discharge pathway, they can shuttle electrons back-and-forth between the electrodes and the charge and discharge products. This prevents passivation of the porous cathode by facilitating both a greater distribution of the discharge products, as well as an easier means by which to re-oxidise these insulating materials. The literature shows several examples of redox couples, including quinones, that inhibit the formation of a passivating film to some extent and result in higher rates, higher capacities and longer cycle lives.5, 6 Previously, our group has shown that the choice of RM can either enhance or suppress 1O2 formation during charge.7 We have now expanded this investigation to discharge mediators. In this work, we explore the primary reason for singlet vs triplet oxygen formation and identify if it is possible to suppress 1O2 formation completely via RMs. We leverage mass spectrometry, pressure cell measurements, and spectro-electrochemistry in this work to gain insight into the reaction kinetics and 1O2 generation mechanism. These experimental results are further supported by density functional theory (DFT) to help elucidate the reaction pathway.

Structure–Property Relationships with Functionalized Subphthalocyanines: Toward Photovoltaic Devices More Stable to Photooxidative Degradation Mediated by Singlet Oxygen

AbstractIn this work, the overarching goal of improving the photooxidative stability of organic components used in photovoltaic devices is addressed, focusing on the common problem of degradation mediated by singlet molecular oxygen. Through a systematic exploration of boron subphthalocyanines (SubPcs), the influence of donor and acceptor substituents on the SubPc's redox properties has been examined, including the SubPc's ability to (1) act as a photosensitizer for singlet oxygen generation and (2) deactivate singlet oxygen are examined. How singlet oxygen formation and removal are influenced by linking together three SubPcs in a compact structure and by linking a SubPc to another molecular unit of relevance for organic photovoltaics (indenofluorene‐extended tetrathiafulvalene) is also examined. Synthetic protocols rooted in acetylenic scaffolding, experimental and computational structure–property relationships (optical and redox properties, singlet oxygen quantum yields, and removal kinetics), and characteristics of a functional photovoltaic device using a SubPc molecule are presented, demonstrating that cyano functionalization results in remarkably enhanced organic photovoltaic device stability.

Degradation of n-hexane by the high-throughput double dielectric barrier discharge: Influencing factors, degradation mechanism and pathways

The emission of volatile organic compounds (VOCs) is known to be a source of various environmental problems. N-hexane is a saturated aliphatic hydrocarbon that is a major precursor of ozone. For the decomposition of n-hexane, a novel double dielectric barrier discharge (DDBD) reactor design is developed and tested on a pilot scale. The factors influencing the plasma degradation of n-hexane have been thoroughly investigated. The degradation efficiency, carbon balance and nitrogen oxide concentration were measured and analysed. Through experiments, it was found that the maximum removal of n-hexane at an initial concentration of 2000 ppm and a flow rate of 5 L/min was 1544 ppm. The associated energy efficiency reached 67.71 ppm/J. The excited states of oxygen and nitrogen (O2+, O(3 s5S-3p5P), N2(C3Πu-B3Πg), N2+(B2Σu+-X2Σg+)) during n-hexane degradation were observed. Possible degradation pathways of n-hexane are proposed, and it is revealed that the active species play an important role in the formation of oxygen and nitrogen-containing volatile organic by-products. The results show that the pilot-scale design of the DDBD system provides a feasible way for the industrial treatment of n-hexane, and provides fundamental insights into the mechanism of plasma catalytic system operation.

Truxene-to-Fluorenone Energy Transfer in a Robust Mesoporous Zn-MOF.

A new metal-organic framework (MOF; [Zn4O(hett)4/3(fluo)1/2(bdc)1/2]n; TFT-MOF) constructed on chromophoric ligands 5,5',10,10',15,15'-hexaethyltruxene-2,7,12-triacetate (hett), 9-fluorenone-2,7-dicarboxylate (fluo), terephthalate (bdc), and the Zn4O node has been prepared and identified by powder X-ray diffraction. This luminescent MOF exhibits large mesoporous pores of 2.7 nm based on computer modeling using density functional theory (DFT) calculations. The steady-state and time-resolved fluorescence spectra and photophysical parameters of TFT-MOF have been investigated and compared with those of the free ligands and their basic chromophores. All in all, TFT-MOF exhibits particularly efficient singlet-singlet energy-transfer processes described as 1(hett)* → (fluo) and 1(bdc)* → (fluo), leading to fluorescence arising for the fluo lumophore operating only through Förster resonance energy transfer (FRET) with an efficiency of transfer of up to >95%. This experimental conclusion was corroborated by DFT and time-dependent DFT (TDDFT). For the 1(hett)* → (fluo) process, the approximated overall rate constant of energy transfer was evaluated to be at most 2.04 × 1010 s-1 (using a Stern-Volmer approach of solution data and the relationship between distance and concentration). This process was analyzed using the Förster theory, where two intrapore energy transfer paths of center-to-center distances of 13 and 25 Å have been identified. TFT-MOF photosensitizes the formation of singlet oxygen (1O2 (1Σg)) as detected by its phosphorescence signal at 1275 nm.

Enhancing non-radical peroxydisulfate activation by single-atom Fe-N-C catalyst through boron doping

Atomically dispersed transition metal-nitrogen-carbon (M-N-C) is regarded as one of the prospective materials to eliminate organic pollutants in water. However, manipulating the coordination sphere of the center metal to achieve the highest catalytic performance remains a challenge. Herein, a Fe-BNC catalyst with Fe atom decorated B,N-codoped hierarchical porous carbon was synthesized for peroxydisulfate (PDS) activation, which exhibits superb and highly selective degradation of model aqueous pollutants within a wide pH scope (2.63–10.36). The experiments and theoretical simulation indicate that the high activity of Fe-BNC origins from novel dual-pathway activation, involving PDS oxidation at the electron-poor B atoms for the formation of singlet oxygen (1O2) and PDS reduction over electron-rich Fe atoms for the generation of hydroxyl and sulfate radicals, where 1O2 was the primary active species. Moreover, the B atoms introduces point defects and optimizes the distribution of Fe 3d orbitals, which simultaneously facilitates PDS chemical adsorption and activation. We further loaded Fe-BNC on the widely used polyvinylidene fluoride (PVDF) microfiltration membrane and proved the stable performance for removing model pollutants when they pass through the filter, advancing the applications of M-N-C materials in actual practice.

High performance and highly selective sensing of triethylamine sensors based on Cu-doped MoO3 nanobelts

Developing high-performance triethylamine (TEA) gas sensors are vital for human health. Defect engineering is a common method to enhance sensor performance. In this work, Cu-doped MoO3 nanobelts with different Cu/Mo molar ratios were synthesized by a low-cost solvothermal method. The 7.5CM sensor (molar ratio of Cu/Mo=7.5%) exhibited a response value of 135 to 10 ppm TEA at 240 °C. The sensor also showed excellent selectivity and sub-ppm detection limit (12.5 ppb). Based on X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS) analysis, the enhanced gas sensing performance and mechanism of Cu-doped MoO3 were discussed. PALS results indicated that higher V′MoVo··Vo·· vacancy defect clusters content on the surface of Cu-doped MoO3. The enhanced gas sensing performance was attributed to the increased concentration of vacancies/vacancy clusters on the surface of MoO3 nanobelts due to Cu doping, which facilitated the formation of surface chemisorbed oxygen and provided more active sites for the reaction of TEA. Additionally, CuMoO4 nanocrystals formed in MoO3 nanobelts can provide p-n heterojunctions on the surface, which generates potential barrier, enabling a wide variation range for the resistance of the sensor. This work provided a simple and effective method for the application of defect engineering in gas sensing materials.

Effect of ethylene glycol chelated on ultrathin TiO2(B) nanosheets on the photocatalytic selective benzyl alcohol oxidation

The two-dimensional (2D) photocatalysts have been paid intensive attention in catalysis due to their excellent activity, which was greatly improved by the higher exposure of active sites and a facile reaction platform, and the separation efficiency of charge carriers. Herein, TiO2(B) nanosheets, which were synthesized via solvothermal method in ethylene glycol, could photocatalytically oxidize benzyl alcohol to benzaldehyde with high selectivity. The study revealed that the material's photocatalytic performance is highly influenced by the surface-chelated ethylene glycol. The pristine TiO2(B) was effective in selectively photocatalytic oxidizing benzyl alcohol, achieving a 94.5 % conversion, while the conversion decreased to 55 % after the elimination of the surface ethylene glycol. The presence of ethylene glycol on the surface of TiO2(B) nanosheets benefits the transfer of photogenerated charge carriers and improves charge separation efficiency. It is favorable for the selective formation of singlet oxygen (1O2) species, which results in enhanced photocatalytic activity and selectivity. We believe that our findings can shed light on the importance of the surface species and properties of photocatalysts in photocatalysis, and pave an avenue for the design and preparation of high-efficiency photocatalysts with unique surface properties.

Primary processes in photophysics and photochemistry of a potential light-activated anti-cancer dirhodium complex.

Photophysics and photochemistry of a potential light-activated cytotoxic dirhodium complex [Rh2(µ-O2CCH3)2(bpy)(dppz)](O2CCH3)2, where bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine (Complex 1 or Rh2) in aqueous solutions was studied by means of stationary photolysis and time-resolved methods in time range from hundreds of femtoseconds to microseconds. According to the literature, Complex 1 demonstrates both oxygen-dependent (due to singlet oxygen formation) and oxygen-independent cytotoxicity. Photoexchange of an acetate ligand to a water molecule was the only observed photochemical reaction, which rate was increased by oxygen removal from solutions. Photoexcitation of Complex 1 results in the formation of the lowest triplet electronic excited state, which lifetime is less than 10ns. This time is too short for diffusion-controlled quenching of the triplet state by dissolved oxygen resulting in 1O2 formation. We proposed that singlet oxygen is produced by photoexcitation of weakly bound van der Waals complexes [Rh2…O2], which are formed in solutions. If this is true, no oxygen-independent light-induced cytotoxicity of Complex 1 exists. Residual cytotoxicity deaerated solutions are caused by the remaining [Rh2…O2] complexes.

Modified ESR-based photosafety test (ESR-PT) detecting singlet oxygen and free radical formation.

The electron spin resonance-based photosafety test (ESR-PT) was modified using a new parameter, photoreactivity index (PRI), to detect singlet oxygen and free radical photoproducts simultaneously. With this modification, the modified ESR-PT is expected to reduce the number of false negative results due to chemicals producing free radical photoproducts other than singlet oxygen. The assay performance of the modified ESR-PT was evaluated using 56 chemicals, including hydrophobic chemicals. When using the PRI cutoff value of 2.0 in the modified ESR-PT, the accuracy relative to photosafety reference data was 91.1%, and the applicability (100%) was better than the other non-animal photosafety test. Among the chemicals producing positive results, bithionol, fenticlor, and doxycycline HCl were considered positive based on the detection of free radical photoproducts, suggesting that these three chemicals may have phototoxic or photoallergic potential via radical reactions. Additionally, this finding demonstrated the fundamental advantage of the modified ESR-PT using ESR spectroscopy, which can detect radicals selectively and quantitatively. Accordingly, the new parameter PRI is effective for photosafety evaluations based on not only singlet oxygen but also free radical photoproducts generated from chemicals. Therefore, the modified ESR-PT has a great potential for a photosafety test method applicable to various chemicals.

Generation of volatiles from heated enzymatic hydrolysates of perilla meal with coconut oil in Maillard reaction system

Perilla meal hydrolysates (PMHs) were prepared by proteases; volatile profiles from heated mixtures of PMH and coconut oil (CO) were evaluated for their application as odor providers. Amino acids composition and degree of hydrolysis, and antioxidant activity in O/W emulsion of PMHs were assessed. PMHs were heated with different concentration of CO or with CO, xylose, and cysteine, which were non-Maillard and Maillard system, respectively. Among PMHs, double enzyme treatment using Alcalase and Flavourzyme showed higher degree of hydrolysis and antioxidant activity compared to PMHs from one type of enzymes. The presence of CO significantly increased oxygen, sulfur, and nitrogen-containing volatiles from PMHs in non-Maillard system. In case of Maillard system, PMHs with 10 % (w/w) CO contributed the formation of oxygen and nitrogen-containing volatiles such as furan and 2-methylpyrazine. PMHs might serve as an odor generator in the presence of edible oils like CO.

The influence of Helicobacter pylori, proton pump inhibitor, and obesity on the gastric microbiome in relation to gastric cancer development

Helicobacter pylori infection is still the main risk factor for the development of gastric cancer (GC). We explore the scientific evidence for the role of the gastric microbiome beyond Helicobacter pylori (H. pylori) in gastric carcinogenesis. The composition of the gastric microbiome in healthy individuals, in presence and absence of H. pylori infection, in proton pump inhibitor (PPI)-users, obese individuals, and GC patients was investigated. Possible mechanisms for microbial involvement, limitations of available research and options for future studies are provided.A common finding amongst studies was increased levels of Streptococcus, Prevotella, Neisseria, and Actinomyces in healthy individuals or those with H. pylori-negative gastritis. In PPI-users the risk for GC increases with the treatment duration, and the gastric microbiome shifts, with the most consistent increase in the genus Streptococcus. Similarly, in obese individuals, Streptococcus was the most abundant genus, with an increased risk for cardia GC. The genera Streptococcus, Lactobacillus and Prevotella were found to be more prominent in GC patients in multiple studies. Potential mechanisms of non-H. pylori microbiota contributing to GC are linked to lipopolysaccharide production, contribution to inflammatory pathways, and the formation of N-nitroso compounds and reactive oxygen species.In conclusion, the knowledge of the gastric microbiome in GC is mainly descriptive and based on sequencing of gastric mucosal samples. For a better mechanistic understanding of microbes in GC development, longitudinal cohorts including precancerous lesions, different regions in the stomach, and subtypes of GC, and gastric organoid models for diffuse and intestinal type GC should be employed.

High-density accessible Ru[sbnd]O[sbnd]Co moieties with accelerated formation of activated oxygen species for freshwater and seawater electrolysis

Promoting the activated oxygen formation and the accessible site density is crucial for boosting the mass and price activity of Ru in water/seawater electrolysis. However, a rational catalyst architecture is lacking to satisfy the above requirements. Herein, Ru was intentionally embedded into few-layer Co3O4 (Ru-Co3O4) to construct high-density accessible RuOCo moieties for water/seawater splitting. The moiety structure accelerates the generation and dissociation of activated H2O during hydrogen evolution reaction (HER), and ensures the rapid evolution of key “activated oxygen” species in oxygen evolution reaction (OER), thus improving HER/OER intrinsic kinetics. Besides, these moieties embedded within few-layer structure effectively promote site formation and utilization. Consequently, compared with Ru/C and Pt/C, an order of magnitude increase in mass and price activity was achieved for bifunctional HER/OER. When applied in an anion-exchange-membrane (AEM) electrolyzer, this catalyst realizes industrial-level current densities for freshwater and seawater electrolysis, more than twice than Ru/C(+)||Pt/C(−), and robust durability.

Enhanced activation of PMS by a novel MnFe2O4@N-PC-GM composite for rapid 1-naphthol degradation: Formation and mechanism of singlet oxygen

A novel magnetic catalyst, MnFe2O4 functionalized N-doped porous carbon/geopolymer (MnFe2O4 @N-PC-GM) composite, was synthesized using pine cones and geopolymer as precursors for efficient and sustainable removal of 1-naphthol. Experimental results indicated that MnFe2O4 particles were distributed in in the structure of N-PC-GM carrier, greatly increasing the number of active sites. The removal ratio of 1-naphthol was up to 86.06% in MnFe2O4 @N-PC-GM/PMS system, and the degradation process followed pseudo-second-order kinetics (R2 = 0.996). Quenching experiments and EPR analysis validated that 1-naphthol was degraded in MnFe2O4 @N-PC-GM/PMS system mainly through a non-radical oxidation pathway dominated by 1O2. X-ray photoelectron spectroscopy (XPS) and degradation experiments in different gas atmosphere demonstrated that the sources of 1O2 were closely related to the existence of oxygen vacancies (OVs), the conversion of dissolved oxygen as well as the introduction of active sites (N, Mn and Fe). Furthermore, the good degradation rate of 1-naphthol in real water confirmed the feasibility of MnFe2O4 @N-PC-GM/PMS system in practical application. This work provided a new strategy for the treatment of persistent organic pollutants in water.

Temoporfin-Conjugated Upconversion Nanoparticles for NIR-Induced Photodynamic Therapy: Studies with Pancreatic Adenocarcinoma Cells In Vitro and In Vivo.

Upconverting nanoparticles are interesting materials that have the potential for use in many applications ranging from solar energy harvesting to biosensing, light-triggered drug delivery, and photodynamic therapy (PDT). One of the main requirements for the particles is their surface modification, in our case using poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) and temoporfin (THPC) photosensitizer to ensure the colloidal and chemical stability of the particles in aqueous media and the formation of singlet oxygen after NIR irradiation, respectively. Codoping of Fe2+, Yb3+, and Er3+ ions in the NaYF4 host induced upconversion emission of particles in the red region, which is dominant for achieving direct excitation of THPC. Novel monodisperse PMVEMA-coated upconversion NaYF4:Yb3+,Er3+,Fe2+ nanoparticles (UCNPs) with chemically bonded THPC were found to efficiently transfer energy and generate singlet oxygen. The cytotoxicity of the UCNPs was determined in the human pancreatic adenocarcinoma cell lines Capan-2, PANC-01, and PA-TU-8902. In vitro data demonstrated enhanced uptake of UCNP@PMVEMA-THPC particles by rat INS-1E insulinoma cells, followed by significant cell destruction after excitation with a 980 nm laser. Intratumoral administration of these nanoconjugates into a mouse model of human pancreatic adenocarcinoma caused extensive necrosis at the tumor site, followed by tumor suppression after NIR-induced PDT. In vitro and in vivo results thus suggest that this nanoconjugate is a promising candidate for NIR-induced PDT of cancer.

Topotactically transformable antiphase boundaries with enhanced ionic conductivity

Engineering lattice defects have emerged as a promising approach to effectively modulate the functionality of devices. Particularly, antiphase boundaries (APBs) as planar defects have been considered major obstacles to optimizing the ionic conductivity of mixed ionic-electronic conductors (MIECs) in solid oxide fuel applications. Here our study identifies topotactically transformable APBs (tt-APBs) at the atomic level and demonstrates that they exhibit higher ionic conductivity at elevated temperatures as compared to perfect domains. In-situ observation at the atomic scale tracks dynamic oxygen migration across these tt-APBs, where the abundant interstitial sites between tetrahedrons facilitate the ionic migration. Furthermore, annealing in an oxidized atmosphere can lead to the formation of interstitial oxygen at these APBs. These pieces of evidence clearly clarify that the tt-APBs can contribute to oxygen conductivity as anion diffusion channels, while the topotactically non-transformable APBs cannot. The topotactic transformability opens the way of defect engineering strategies for improving ionic transportation in MIECs.

REVISÃO DO FOTOSSENSIBILIZADOR FTALOCIANINA UTILIZADA NA TERAPIA FOTODINÂMICA E SUA APLICABILIDADE FRENTE AO TRATAMENTO DE DIVERSOS AGENTES PATOGÊNICOS

Photodynamic therapy (PDT) is a treatment modality already used in several countries to treat invasive and topical diseases. In these treatments, the combination of a photoactive drug (PS), visible light, and molecular oxygen results in the formation of singlet oxygen, a type of highly reactive/cytotoxic oxygen species. Phthalocyanines incorporated into solubilization/monomerization systems are photosensitizing substances used in PDT, even given their high hydrophobicity. Its inhibitory capacity against microorganisms and its photodynamic action against various cancer cell lines have made it the protagonist of several scientific articles. This review article provides a brief overview of the concept of PDT and its potential use in the treatment of diseases - an emerging treatment modality in Brazil.

Application of comparative sonochemical, photochemical, and sono-photochemical methods to obtain new silicon phthalocyanine with high singlet oxygen efficiency

Nowadays, non-invasive and nontoxic therapy methods are preferred to treat diverse types of cancer. Sono-photodynamic therapy (SPDT) is one of these alternative methods, combining the properties of PDT (photodynamic therapy) and SDT (sonodynamic therapy) and resulting in a higher singlet oxygen generation. The efficiency of this method is increased by synthesizing a complex with enhanced photochemical properties to use as a sensitizer. Phthalocyanines, especially with added derivatives holding diamagnetic metals such as Si4+, are often compounds used in PDT studies owing to their efficient yields of singlet oxygen formation. In this study, 4‑hydroxy-7-methoxyquinoline silicon phthalocyanine was synthesized and its anti-cancer therapy effect rates were calculated and compared by photochemical and sono-photochemical methods in DMSO. This research will help the studies that aim to obtain high singlet oxygen efficiency in therapeutic methods.

Cyano-rich carbon nitride with tunable n → π* electronic transition for enhanced broad-spectrum photocatalytic H2O2 production

The development of photocatalysts that effectively utilize broad-spectrum light, which occupies a primary percentage of the solar spectrum, remains a great challenge. In this paper, we propose a salt-assisted method mediated by sodium oxalate template to achieve both oxygen doping and formation cyano group defects in carbon nitride materials (CNNO). The simultaneous introduction of oxygen and cyano defects not only induced the distortion of the heptazine structure thus effectively activated the n → π* electron transition, but also can achieve the qualitative changes of broad-spectrum photocatalytic H2O2 production from “0″ to “1” (λ ≥ 700 nm) of CNNO, which has rarely been reported in single photocatalysts. DFT calculations show that the electronic structure of CNNO is rearranged to favor O2 adsorption as well as the formation of the key intermediate OOH*. The present work achieves the co-optimization of electronic structure and light absorption of CN through the synergistic effect of oxygen doping and the construction of cyano defects, which provides a new strategy for the design and synthesis of CN materials that effectively utilize sunlight.

Measurement of argon excimers, Ar2*, in a cold atmospheric plasma jet using cavity ringdown spectroscopy

The argon excimer (Ar2*) species is considered to play an important role in the chemistry of cold atmospheric plasma jets, notably in the formation of reactive oxygen and nitrogen species. In the present work, we demonstrate that cavity ringdown spectroscopy can be used to detect and quantitatively measure Ar2* in the effluent of a cold atmospheric plasma jet, the so-called kINPen-Sci. The spectroscopic features of the 5p π3Πg ← a3Σu+Δν = 0 and 7p σ3Σg+ ← a3Σu+ (ν′ - ν″) systems were clearly identified allowing unambiguous assignment to the Ar2* species. A predominant absorption feature at 512 nm was used to determine the integrated density along the axis perpendicular to the gas flow. Assuming a homogeneous density distribution in the kINPen-Sci effluent, Ar2* densities from 1.8 × 1011 molecule · cm−3 at 0 mm to 1.3 × 1010 molecule · cm−3 at 4.2 mm below the nozzle tip were determined.