Temperature Dependence Of Kinetics Research Articles

GSAG:Ce scintillator: insights from yttrium admixture.

The GSAG:Ce scintillator represents a promising and cost-effective alternative to the expensive GGAG:Ce. Recent studies have attributed its low light yield to the thermal quenching effect. In this study, we employed the strategy of adding an yttrium (Y) admixture to the GSAG matrix to increase the thermal activation energy of thermal quenching. The scintillation, optical, and luminescence properties of Gd(3-x)Y x Sc2Al3O12:Ce (x = 0, 0.2, 0.5, 0.8) grown using the micro-pulling-down method are thoroughly studied and reported. We further investigated the correlation between the Y content and other characteristics (scintillation rise time, light yield, decay, etc.). The magnitude of thermal quenching was evidenced by combination of the temperature-dependent photoluminescence decay kinetics and thermally stimulated luminescence. Excitation spectra were measured down to 30 nm in the VUV range under the synchrotron radiation at DESY to monitor the energy transfer efficiency from the host under excitation above the band gap. Results suggested that thermal ionization was not the primary reason for the low performance of the GSAG:Ce composition, and other defects related to the presence of scandium (Sc) must play a role. Furthermore, it was found that the stoichiometric GSAG host provided a noticeably higher light yield than the previously studied congruent one. This research provides valuable insights into the characteristics of GSAG:Ce scintillators.

Sensing of n-butanol vapours using an oxygen vacancy-enriched Zn2SnO4-SnO2 hybrid-composite.

The precise identification of various toxic gases is important to prevent health and environmental hazards using cost-effective, efficient, metal oxide-based chemiresistive sensing methods. This study explores the sensing properties of a chemiresistive sensor based on a Zn2SnO4-SnO2 microcomposite for detecting n-butanol vapours. The microcomposite, enriched with oxygen vacancies, was thoroughly characterized, confirming its structure, crystallinity, morphology and elemental composition. The sensor demonstrated high repeatability across a temperature range of 275-350 °C and concentrations from 100 to 1000 ppm, with the highest response observed at 350 °C. The concentration-dependent response of the sensor towards n-butanol follows a linear relationship within the studied operating temperature range. The response time increases as the concentration of n-butanol increases. Conductance transients were modelled using the Langmuir-Hinshelwood mechanism, showing temperature-dependent oxidation kinetics. At lower temperatures, the rate-determining step involved n-butanol oxidation, while at higher temperatures, simultaneous oxidation and desorption processes dominated. The calculated activation energy for the n-butanol oxidation step was 0.12 eV. Furthermore, principal component analysis (PCA) effectively discriminated n-butanol from other volatile organic compounds (VOCs), emphasizing the sensor's potential for selective n-butanol detection through a combination of kinetic modelling and statistical analysis.

Temperature-Dependent Reaction Kinetics of the Carbanions Cn- and CnH- (n = 2 and 4) with H Atoms in a Cryogenic Ion Trap.

We report on the temperature-dependent reactions of the carbon-chain anions C2- and C4-, as well as the hydrocarbons C2H- and C4H- with H atoms in the temperature regime between 8 and 296 K. The experiments have been carried out in a temperature-variable radiofrequency multipole ion trap. From the measured kinetics, we have derived reaction rate coefficients that are constant for all considered systems in the measured temperature regime. For the C2-, C4-, and C4H- anions, the values are about a factor of 2 smaller than the Langevin capture rate coefficient, while for C2H-, the measured value agrees with the Langevin value. No theoretical calculations are available at present to explain this. All rate coefficients are in good agreement with previous measurements at room temperature.

Temperature-Dependent Water Oxidation Kinetics: Implications and Insights.

As a vital process for solar fuel synthesis, water oxidation remains a challenging reaction to perform using durable and cost-effective systems. Despite decades of intense research, our understanding of the detailed processes involved is still limited, particularly under photochemical conditions. Recent research has shown that the overall kinetics of water oxidation by a molecular dyad depends on the coordination between photocharge generation and the subsequent chemical steps. This work explores similar effects of heterogeneous solar water oxidation systems. By varying a key variable, the reaction temperature, we discovered distinctly different behaviors on two model systems, TiO2 and Fe2O3. TiO2 exhibited a monotonically increasing water oxidation performance with rising temperature across the entire applied potential range, between 0.1 and 1.5 V vs the reversible hydrogen electrode (RHE). In contrast, Fe2O3 showed increased performance with increasing temperature at high applied potentials (>1.2 V vs RHE) but decreased performance at low applied potentials (<1.2 V vs RHE). This decrease in performance with temperature on Fe2O3 was attributed to an increased level of electron-hole recombination, as confirmed by intensity-modulated photocurrent spectroscopy (IMPS). The origin of the differing temperature dependences on TiO2 and Fe2O3 was further ascribed to their different surface chemical kinetics. These results highlight the chemical nature of charge recombination in photoelectrochemical (PEC) systems, where surface electrons recombine with holes stored in surface chemical species. They also indicate that PEC kinetics are not constrained by a single rate-determining chemical step, highlighting the importance of an integrated approach to studying such systems. Moreover, the results suggest that for practical solar water splitting devices higher temperatures are not always beneficial for reaction rates, especially under low driving force conditions.

Bimolecular kinetics of Criegee intermediate (CH2OO) with 2-pentanone: experimental and theoretical analysis in atmospheric conditions.

Temperature-dependent kinetics of Criegee intermediate (CH2OO) with 2-pentanone were performed at 258-318 K and 50 Torr using pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS) technique. The measured room temperature rate coefficient was (3.84 ± 0.24) × 10-13 cm3 molecule-1 s-1. The reaction follows a negative temperature dependency, and the corresponding Arrhenius equation is k4 = (1.76 ± 0.36) × 10-15exp{(3.18 ± 0.11) kcal mol-1/RT}. The high-P limit rate coefficients obtained using CVT/SCT at CCSD(T)/aug-cc-pVTZ//B3LYP/6-311 + G(2df,2p) level of theory deviate from the experimental results, especially in the low-temperature region. At 258 K, the computed high-P limit rate coefficient exceeded the experimental value by more than a factor of four. Comparing all the reaction pathways, HCOOH was the major product formed in the title reaction. The atmospheric lifetime of 2-pentanone due to its reaction with CH2OO was calculated to be ~ 3000 days, rendering the reaction insignificant for inclusion in models of atmospheric 2-pentanone.

Nighttime chemistry of furanoids and terpenes: Temperature dependent kinetics with NO3 radicals and insights into the reaction mechanism

In this study, the gas phase reaction of NO3 radical with three furanoids, furan (F), 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) were investigated using a relative rate method in a temperature regulated atmospheric simulation chamber (THALAMOS). As part of this study, the temperature dependence of two monoterpenes, α-pinene (α-P) and 2-carene (2-C), that were used as reference molecules, is also reported. The kinetic measurements were performed in the range of 263–373 K, atmospheric pressure using zero air as bath gas. The reaction was followed using Selected ion flow tube mass spectrometry (SIFT-MS) to monitor in real time the mixing ratios of the investigated species. The corresponding Arrhenius expressions obtained were:kα−P+NO3(263−378K)=(1.32±0.16)×10−12×e462±70Tcm3molecule‐1s‐1.k2−C+NO3296–433K=8.77±2.71×10−13×e904±96Tcm3molecule‐1s‐1.kF+NO3263−353K=7.55±1.96×10−13×e254±79Tcm3molecule‐1s‐1.k2−MF+NO3263−373K=7.76±2.62×10−13×e922±262Tcm3molecule‐1s‐1.k2,5−DMF+NO3298–353K=2.58±0.77×10−13×e1692±136Tcm3molecule‐1s‐1.Where the estimated uncertainties include the 1σ precision of the fit and the estimated uncertainty in the precision of the Arhenius fit of the reference compound. In the case of furanoids, the negative temperature-dependence of the rate coefficients shows that the reaction mechanism is complex, indicating that the reaction involves the formation of an adduct that could lead either to NO3 addition to the double bond, as well as, in the case of 2-MF and 2,5-DMF, the H-abstraction from the methyl group attached to the ring. In addition to the kinetics measurements, the major products formed from the reaction of furan and 2,5-DMF with NO3 were studied. The two identified products from the reaction of furan with NO3, were 3H-furan-2-one (C4H4O2) and 2-butenedial (C4H4O2), formed by NO3 addition to the double bond of the furan ring. 3-Hexene-2,5-dione (C6H8O2) and 5-methylfurfural (C6H6O2) are the two major products of 2,5-DMF reaction with NO3, linked to the addition and abstraction pathways, respectively. Considering that 5-methylfurfural is the only primary product of the H elimination pathway of 2,5-DMF, the determination of its formation yields as a function of temperature, allowed us to extract the temperature dependence of the rate coefficients of the abstraction and addition pathways.Overall, the NO3 oxidation of the studied furanoids, is expected to be the dominant tropospheric loss process, in the studied temperature range.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically-Stable Low-Temperature Lithium-Ion Batteries.

Graphite (Gr)-based lithium-ion batteries with admirable electrochemical performance below -20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+-solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically-stable solid electrolyte interphase (SEI) without compromising strong Li+-solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature-dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low-temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e-) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4-based, inorganics-enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e- blocking and rapid desolvation, and as a result, much suppressed Li-metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low-temperature battery performances. Overall, our work originally provides visualized guides to improve low-temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

Field-domain rapid-scan EPR at 240 GHz for studies of protein functional dynamics at room temperature

We present field-domain rapid-scan (RS) electron paramagnetic resonance (EPR) at 8.6T and 240GHz. To enable this technique, we upgraded a home-built EPR spectrometer with an FPGA-enabled digitizer and real-time processing software. The software leverages the Hilbert transform to recover the in-phase (I) and quadrature (Q) channels, and therefore the raw absorptive and dispersive signals, χ′ and χ′′, from their combined magnitude (I2+Q2). Averaging a magnitude is simpler than real-time coherent averaging and has the added benefit of permitting long-timescale signal averaging (up to at least 2.5×106 scans) because it eliminates the effects of source-receiver phase drift. Our rapid-scan (RS) EPR provides a signal-to-noise ratio that is approximately twice that of continuous wave (CW) EPR under the same experimental conditions, after scaling by the square root of acquisition time. We apply our RS EPR as an extension of the recently reported time-resolved Gd-Gd EPR (TiGGER) [Maity et al., 2023], which is able to monitor inter-residue distance changes during the photocycle of a photoresponsive protein through changes in the Gd-Gd dipolar couplings. RS, opposed to CW, returns field-swept spectra as a function of time with 10ms time resolution, and thus, adds a second dimension to the static field transients recorded by TiGGER. We were able to use RS TiGGER to track time-dependent and temperature-dependent kinetics of AsLOV2, a light-activated phototropin domain found in oats. The results presented here combine the benefits of RS EPR with the improved spectral resolution and sensitivity of Gd chelates at high magnetic fields. In the future, field-domain RS EPR at high magnetic fields may enable studies of other real-time kinetic processes with time resolutions that are otherwise difficult to access in the solution state.

Development and validation of an oil palm model for a wide range of planting densities and soil textures in Malaysian growing conditions

A semi-mechanistic oil palm growth and yield model called Sawit.jl was developed to account for a wide range of planting densities and soil textures under Malaysia's climate conditions. The model comprises components related to meteorology, photosynthesis, energy balance, soil water content, and crop growth. The model simulates instantaneous meteorological properties using daily weather data, calculates simultaneous evaporation from crop and soil with the Shuttleworth-Wallace model, determines soil water content through Darcy's law, and adapts a biochemical C3 model for photosynthesis. The model is also parameterized using updated measurements from the newer tenera oil palm, including temperature-dependent Rubisco kinetics, specific leaf area, and the partitioning of nutrients and dry matter between various tree parts. Sawit.jl was validated using historical field measurement data from seven Malaysian oil palm sites, encompassing palm ages spanning 1–23 years. These seven sites differed in soil type (Inceptisols and Ultisols), planting density (82–299 palms ha−1), soil texture (27–59 % clay and 7–67 % sand), and rainfall (1800–2800 mm yr−1). The model showed overall good accuracy in simulating oil palm parameters (except for trunk weight) across diverse conditions, with model agreement metrics ranging from 6 to 27 % for model absolute errors, −22 to +17 % for model bias, and 0.38 to 0.98 for the Kling-Gupta Efficiency index. The model also predicted the response of oil palm yield to abrupt rainfall changes, such as those during El Niño and La Niña events, while accounting for how soil texture, rainfall, and other meteorological factors influence water deficits and crop photosynthesis. However, model accuracy varied by site, planting density, and oil palm parameter. Model accuracy can be increased by more accurately representing the oil palm microclimate, incorporating fruiting activity, and refining the dry matter partitioning mechanism for the trunk.

A combined experimental and computational investigation on the OH radical and Cl atom-initiated reaction of 2,3-dichloropropene in troposphere

Temperature-dependent kinetics of OH radical and Cl atom-initiated reaction of an important halogenated alkene, 2,3-Dichloropropene (23DCP), were investigated using absolute and relative methods over 278–363 K. Pulsed laser photolysis – laser induced fluorescence technique and relative rate method using gas chromatography with flame ionization detector were employed for studying the kinetics of 23DCP with OH radical and Cl atom, respectively. The obtained Arrhenius expressions were kOH(expt)=(4.08 ± 1.63) × 10−13exp{(1043 ± 124)/T} cm3 molecule−1 s−1 and kCl(expt)=(1.54 ± 0.24) × 10−11exp{(705 ± 48)/T} cm3 molecule−1 s−1. Computational calculations were conducted to validate our experimental kinetic results and provide new insights into the importance of a particular pathway among all based on thermodynamic parameters. The addition of OH/Cl to the terminal carbon of the double bond present in 23DCP proved to be the predominant pathway across the selected temperature range for the present study (200–400 K). The degradation mechanism of these reactions was proposed by analyzing the products with the aid of gas chromatography with mass spectrometry. Calculating various atmospheric implication parameters can help to understand how the release of 23DCP may affect the troposphere.

CHIRAL SWITCHING CONTROL OF PHARMACEUTICAL SUBSTANCES

Objective: The aim of this study was to demonstrate that chiral switching should be recognized as a widespread phenomenon that extends beyond the production of pure enantiomeric drugs. Methods: To investigate the optical activity of substances from various chemical classes, enantiomers of chiral compounds (Sigma-Aldrich, USA) were chosen: valine and its racemic form (D-valine, L-valine, and racemic valine with optical purity ≥ 99%), L-ascorbic acid (content ≥ 99%), carbohydrates (D-glucose, D-galactose, L-galactose, contents ≥ 99.5%). Solutions were prepared using deuterium-depleted water (DDW–"light" water, D/H=4 ppm), natural deionized high-ohmic water (BD, D/H=140 ppm), and heavy water (99.9% D2O; Sigma-Aldrich). Optical activity was measured using the Atago POL-1/2 polarimeter. Results: One of the components in the racemic medication mixture can act as an inert agent, exhibit toxicity, or undergo undesirable biotransformation mechanisms, resulting in the formation of products with unknown properties. It has been established that a change in the deuterium/protium (D/H) ratio in water leads to a change in the equilibrium and kinetic characteristics of optically active compounds across various chemical classes, such as amino acids, carboxylic acids, and carbohydrates. An inequality was observed in the absolute values of the optical rotation of the L-and D-isomers of valine and galactose, depending on the D/H isotope ratio. The impact of chiral water clusters on optical rotation accounts for the sudden shift in the specific rotation of dilute solutions (less than 0.5%) of L-ascorbic acid in water, based on the D/H ratio. The influence of the isotopic composition of water was confirmed by studying the temperature-dependent mutarotation kinetics of D-glucose and L-and D-galactose in Arrhenius coordinates. The mutarotation process in natural high-resistivity water is characterized by an activation energy (Ea) of 40.8±1.4 kJ mol-1, while in deuterium-depleted water, Ea = 63.6±3.5 kJ mol-1. This results in a kinetic isotope effect for deuterium (KIED) of 1.6. Conclusion: Methodological approaches have been developed to control chiral switching based on the isotopic composition of water in vivo and in vitro. The study of changes in the optical activity of hierarchical structures in the human body, the influence of solvent properties on the mechanisms of optical rotation, as well as the use of KIED values, can be utilized to monitor various chiral transitions in vitro and living organisms.

Leveraging Temperature-Dependent (Electro)Chemical Kinetics for High-Throughput Flow Battery Characterization

The library of redox-active organics that are potential candidates for electrochemical energy storage in flow batteries is exceedingly vast, necessitating high-throughput characterization of molecular lifetimes. Demonstrated extremely stable chemistries require accurate yet rapid cell cycling tests, a demand often frustrated by time-denominated capacity fade mechanisms. We have developed a high-throughput setup for elevated temperature cycling of redox flow batteries, providing a new dimension in characterization parameter space to explore. We utilize it to evaluate capacity fade rates of aqueous redox-active organic molecules, as functions of temperature. We demonstrate Arrhenius-like behavior in the temporal capacity fade rates of multiple flow battery electrolytes, permitting extrapolation to lower operating temperatures. Collectively, these results highlight the importance of accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime flow batteries.

Temperature-Dependent Kinetics of the Reactions of the Criegee Intermediate CH2OO with Hydroxyketones.

Though there is a growing body of literature on the kinetics of CIs with simple carbonyls, CI reactions with functionalized carbonyls such as hydroxyketones remain unexplored. In this work, the temperature-dependent kinetics of the reactions of CH2OO with two hydroxyketones, hydroxyacetone (AcOH) and 4-hydroxy-2-butanone (4H2B), have been studied using a laser flash photolysis transient absorption spectroscopy technique and complementary quantum chemistry calculations. Bimolecular rate constants were determined from CH2OO loss rates observed under pseudo-first-order conditions across the temperature range 275-335 K. Arrhenius plots were linear and yielded T-dependent bimolecular rate constants: kAcOH(T) = (4.3 ± 1.7) × 10-15 exp[(1630 ± 120)/T] and k4H2B(T) = (3.5 ± 2.6) × 10-15 exp[(1700 ± 200)/T]. Both reactions show negative temperature dependences and overall very similar rate constants. Stationary points on the reaction energy surfaces were characterized using the composite CBS-QB3 method. Transition states were identified for both 1,3-dipolar cycloaddition reactions across the carbonyl and 1,2-insertion/addition at the hydroxyl group. The free-energy barriers for the latter reaction pathways are higher by ∼4-5 kcal mol-1, and their contributions are presumed to be negligible for both AcOH and 4H2B. The cycloaddition reactions are highly exothermic and form cyclic secondary ozonides that are the typical primary products of Criegee intermediate reactions with carbonyl compounds. The reactivity of the hydroxyketones toward CH2OO appears to be similar to that of acetaldehyde, which can be rationalized by consideration of the energies of the frontier molecular orbitals involved in the cycloaddition. The CH2OO + hydroxyketone reactions are likely too slow to be of significance in the atmosphere, except at very low temperatures.

Relaxation kinetics of interface states and bulk traps in atomic layer deposited ZrO2/β-Ga2O3 metal-oxide-semiconductor capacitors

The study of interface states and bulk traps and their connection to device instability is highly demanded to achieve reliable β-Ga2O3 metal-oxide-semiconductor (MOS) devices. However, a comprehensive analysis of the capture/emission behavior of interface states and bulk traps can be challenging due to widespread time constant distribution. In this study, using capacitance transient measurement tools, trap states of the ZrO2/β-Ga2O3 MOS gate stack were explicitly investigated, particularly its bias- and temperature-dependent relaxation kinetics. As forward bias is enlarged, it is observed that the interface state density (Dit) increases by 12.6%. Two bulk traps with discrete levels identified as 0.43 eV (E1) and 0.74 eV (E2) below the conduction band minimum were extracted by deep-level transient spectroscopy. It is further revealed that the emission processes of E1 and E2 are thermally enhanced, while the capture processes remain insensitive to temperature. The electric-field dependence of E1 indicates that the dominant mechanism follows the rule of Poole–Frenkel emission. The capacitance–voltage (C–V) hysteresis deteriorated at a higher forward bias due to the higher trap density and increased population of trapped charges. These findings provide an important framework for future device optimization to improve the reliability and performance of β-Ga2O3 MOS devices.

Temperature-dependent aqueous OH kinetics of C2–C10 linear and terpenoid alcohols and diols: new rate coefficients, structure–activity relationship, and atmospheric lifetimes

Abstract. Aliphatic alcohols (AAs), including terpenoic alcohols (TAs), are ubiquitous in the atmosphere due to their widespread emissions from natural and anthropogenic sources. Hydroxyl radical (OH) is the most important atmospheric oxidant in both aqueous and gas phases. Consequently, the aqueous oxidation of the TAs by the OH inside clouds and fogs is a potential source of aqueous secondary organic aerosols (aqSOAs). However, the kinetic data, necessary for estimating the timescales of such reactions, remain limited. Here, bimolecular rate coefficients (kOHaq) for the aqueous oxidation of 29 C2–C10 AAs by hydroxyl radicals (OH) were measured with the relative rate technique in the temperature range 278–328 K. The values of kOHaq for the 15 AAs studied in this work were measured for the first time after validating the experimental approach. The kOHaq values measured for the C2–C10 AAs at 298 K ranged from 1.80 × 109 to 6.5 × 109 M−1 s−1. The values of activation parameters, activation energy (7–17 kJ mol−1), and average Gibbs free energy of activation (18 ± 2 kJ mol−1) strongly indicated the predominance of the H-atom abstraction mechanism. The estimated rates of the complete diffusion-limited reactions revealed up to 44 % diffusion contribution for the C8–C10 AAs. The data acquired in this work and the values of kOHaq for AAs, carboxylic acids, and carboxylate ions available in the literature were used to develop a modified structure–activity relationship (SAR). The SAR optimized in this work estimated the temperature-dependent kOHaq for all compounds under investigation with much higher accuracy compared to the previous models. In the new model, an additional neighboring parameter was introduced (F≥ (CH2)6), using the kOHaq values for the homolog (C2–C10) linear alcohols and diols. A good overall accuracy of the new SAR at 298 K (slope = 1.022, R2=0.855) was obtained for the AAs and carboxylic acids under investigation. The kinetic database (kOHaq values in this work and compiled literature data) was also used to further enhance the ability of SAR to predict temperature-dependent values of kOHaq in the temperature range 278–328 K. The calculated atmospheric lifetimes indicate that terpenoic alcohols and diols can react with the OH in aerosol, cloud, and fog water with liquid water content (LWC) ≥0.1 g m−3 and LWC ≥ 10−4 g m−3, respectively. The preference of terpenoic diols to undergo aqueous oxidation by the OH under realistic atmospheric conditions is comparable with terpenoic acids, making them potentially effective precursors of aqSOAs. In clouds, a decrease in the temperature will strongly promote the aqueous reaction with the OH, primarily due to the increased partitioning of WSOCs into the aqueous phase.

Temperature-Dependent Kinetics for the Reactions of Fen- (n = 2-17) and FexNiy- (x + y = 3-9) with O2: Comparison of Pure and Mixed Metal Clusters with Relevance to Meteor Radio Afterglows and Surface Oxidation.

Rate constants and product branching fractions were measured from 300-600 K for Fen- + O2 (n = 2-17) and for 300-500 K for FexNiy- + O2 (x + y = 3-9) using a selected-ion flow tube (SIFT) apparatus. Rate constants for 46 species are reported. All rate constants increased with increasing temperature, and several were in excess of the Langevin-Gioumousis-Stevenson (LGS) capture rate at elevated temperatures. As with previously studied transition metal anion oxidation reactions, the collision limit is treated as the sum of the LGS limit along with a hard-sphere contribution, allowing for determination of activation energies. These values are compared to each other along with previous results for Nin-. Measured rate constants for all three series (Fen-, Nin-, and FexNy-) vary over a relatively narrow range (1-5 × 10-10 cm3 s-1 at 300 K) being at least 15% of the collision rate constant. All reaction rate constants increase with temperature, described by small activation energies of 0.5-4 kJ mol-1. The data are consistent with an anticorrelation between the electron binding energy and rate constant, previously noted in other systems. The Fen- reaction produces a larger population of higher energy electrons than do the Nin- reactions, with FexNiy- producing an intermediate amount. The results suggest that the overall rate constant is limited by a small energetic barrier located at a large internuclear distance where electrostatic forces dominate, causing the potentials to be similar across systems, while the product formation is determined by the shorter-range, valence portion of the potential, which varies widely between systems.

Pressure and temperature dependent kinetics and the reaction mechanism of Criegee intermediates with vinyl alcohol: a theoretical study.

Criegee intermediates (CIs), the key intermediates in the ozonolysis of olefins in atmosphere, have received much attention due to their high activity. The reaction mechanism of the most simple Criegee intermediate CH2OO with vinyl alcohol (VA) was investigated by using the HL//M06-2X/def2TZVP method. The temperature and pressure dependent rate constant and product branching ratio were calculated using the master equation method. For CH2OO + syn-VA, 1,4-insertion is the main reaction channel while for the CH2OO + anti-VA, cycloaddition and 1,2-insertion into the O-H bond are more favorable than the 1,4-insertion reaction. The 1,4-insertion or cycloaddition intermediates are stabilized collisionally at 300 K and 760 torr, and the dissociation products involving OH are formed at higher temperature and lower pressure. The rate constants of the CH2OO reaction with syn-VA and anti-VA both show negative temperature effects, and they are 2.95 × 10-11 and 2.07 × 10-13 cm3 molecule-1 s-1 at 300 K, respectively, and the former is agreement with the prediction in the literature.

Enhanced condensation kinetics in aqueous microdroplets driven by coupled surface reactions and gas-phase partitioning.

Although aqueous microdroplets have been shown to exhibit enhanced chemical reactivity compared to bulk solutions, mechanisms for these enhancements are not completely understood. Here we combine experimental measurements and kinetic modeling to show the strong coupling of interfacial reactions and gas/droplet partitioning in the condensation reaction of pyruvic acid (PA) to yield zymonic acid (ZA) in acidic aqueous microdroplets. Experimental analysis of single microdroplets reveals the substantial influence of evaporation of PA and partitioning of water on the size-, relative humidity (RH)- and temperature-dependent sigmoidal reaction kinetics for the condensation reaction. A newly developed diffusion-reaction-partitioning model is used to simulate the complex kinetics observed in the microdroplets. The model can quantitatively predict the size and compositional changes as the reaction proceeds under different environmental conditions, and provides insights into how microdroplet reactivity is controlled by coupled interfacial reactions and the gas-phase partitioning of PA and water. Importantly, the kinetic model best fits the data when an autocatalytic step is included in the mechanism, i.e. a reaction step where the product, ZA, catalyzes the interfacial condensation reaction. Overall, the dynamic nature of aqueous microdroplet chemistry and the coupling of interfacial chemistry with gas-phase partitioning are demonstrated. Furthermore, autocatalysis of small organic molecules at the air-water interface for aqueous microdroplets, shown here for the first time, has implications for several fields including prebiotic chemistry, atmospheric chemistry and chemical synthesis.

Thermogravimetric study of metal–organic precursors and their suitability for hybrid molecular beam epitaxy

Although metal–organic (MO) precursors are widely used in technologically relevant deposition techniques, reports on their temperature-dependent evaporation and decomposition behaviors are scarce. Here, MO precursors of the metals Ti, V, Al, Hf, Zr, Ge, Ta, and Pt were subjected to thermogravimetric analysis to experimentally determine their vapor pressure curves and to gain insight into their temperature-dependent decomposition kinetics. Benzoic acid was used as a calibration standard and vapor pressure curves were extracted from thermogravimetric measurements using the Langmuir equation. The obtained data is used to discuss the suitability of these MO precursors in chemical vapor deposition-based thin film growth approaches in general, and hybrid molecular beam epitaxy in particular. All MOs, except for Ta- and one Ti-based MOs, were deemed suitable for gas inlet systems. The Ta-based MO demonstrated suitability for an effusion cell, while all MOs showed compatibility with cracker usage.Graphical