Quantum Yield Data Research Articles

Physiological Responses of Pak Choi (Brassica rapa Subsp. Chinensis) Genotypes to Salt Tolerance

Salinity stress poses a significant challenge to Pak Choi (Brassica rapa subsp. Chinensis) production. To address this limitation, we conducted an evaluation of 24 Korean native Pak Choi species to identify genotypes with resistance to salt stress. Through cluster analysis of electrolyte leakage data, we discovered ‘IT262109’, ‘IT279432’, and ‘IT185735’ as native accessions displaying the strongest salt tolerance. Additionally, our assessment of the maximum quantum yield of photosystem II revealed a 3.7% reduction in seaweed yield in the highly salt-tolerant system compared with the control group, while the weak salt-tolerant system experienced a substantial reduction rate of 45.7% to 49.4%. Notably, salt stress had a significant impact on Pak Choi growth, but the salt-tolerant genotype exhibited less growth reduction compared with the salt-sensitive genotype. Based on the electrolyte leakage and maximum quantum yield data, it was evident that ‘IT185735’ demonstrated poorer growth compared with ‘IT262109’ and ‘IT279432’. Consequently, ‘IT262109’ and ‘IT279432’ show great potential as parent varieties for enhancing salt tolerance in Pak Choi.

Fluorescence Quantum Yield Standards for the UV/Visible/NIR: Development, Traceable Characterization, and Certification

The rational design of next generation molecular and nanoscale reporters and the comparison of different emitter classes require the determination of the fluorometric key performance parameter fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. Main prerequisites for reliable Φf measurements, which are for transparent luminophore solutions commonly done relative to a reference, i.e., a fluorescence quantum yield standard of known Φf, are reliable and validated instrument calibration procedures to consider wavelength-, polarization-, and time-dependent instrument specific signal contributions, and sufficiently well characterized fluorescence quantum yield standards. As the standard's Φf value directly contributes to the calculation of the sample's Φf, its accuracy presents one of the main sources of uncertainty of relative Φf measurements. To close this gap, we developed a first set of 12 fluorescence quantum yield standards, which absorb and emit in the wavelength region of 330-1000 nm and absolutely determined their Φf values with two independently calibrated integrating sphere setups. Criteria for standard selection and the configuration of these novel fluorescence reference materials are given, and the certification procedure is presented including homogeneity and stability studies and the calculation of complete uncertainty budgets for the certified Φf values. The ultimate goal is to provide the community of fluorescence users with available reference materials as a basis for an improved comparability and reliability of quantum yield data since the measurement of this spectroscopic key property is an essential part of the characterization of any new emitter.

Spatial and temporal drivers of fluorescence quantum yield variability in the Southern Ocean

AbstractFluorescence quantum yield is a powerful tool for assessing phytoplankton photophysiology and photosynthetic efficiency, but there is a paucity of in situ studies. Here we present the first wavelength‐specific fluorescence quantum yield data from high spatial and temporal resolution real‐time measurements made in the Southern Ocean. This dataset represents both winter and summer conditions across a broad latitudinal range of the Atlantic and Indian South Ocean and the presented analysis assesses the potential influence of a range of physical, chemical, and biological drivers of variability. The results indicate that both light history and potential iron limitation play significant roles in constraining the magnitude of fluorescence quantum yield on a seasonal basis, with links to specific pigment composition of carotenoids involved in fluorescence quenching. Whereas community structure and associated pigment content play a strong role in dictating the spectral shape of fluorescence quantum yield both seasonally and spatially, with larger diatom‐dominated communities fluorescing more in the blue region of the spectrum and smaller phycoerythrin‐containing phytoplankton fluorescing more in the green‐orange region of the spectrum. This study provides a better understanding of the drivers of variability of in situ fluorescence quantum yield, which is useful for informing interpretations of studies based on remotely sensed signals, which are essential for investigating spatial and temporal variability in photophysiological characteristics on longer time scales.

Wavelength trends of photoproduction of reactive transient species by chromophoric dissolved organic matter (CDOM), under steady-state polychromatic irradiation

The formation quantum yields of photochemically produced reactive intermediates (PPRIs) by irradiated CDOM (in this study, Suwannee River Natural Organic Matter and Upper Mississippi River Natural Organic Matter) decrease with increasing irradiation wavelength. In particular, the formation quantum yields of the excited triplet states of CDOM (3CDOM*) and of singlet oxygen (1O2) have an exponentially decreasing trend with wavelength. The •OH wavelength trend is different, because more effective •OH production occurs under UVB irradiation than foreseen by a purely exponential function. We show that the parameter-adjustable Weibull function (which adapts to both exponential and some non-exponential trends) is suitable to fit the mentioned quantum yield data, and it is very useful when CDOM irradiation is carried out under polychromatic lamps as done here. Model calculations suggest that, thanks to the ability of CDOM to also absorb visible radiation, and despite its decreasing quantum yield of •OH generation with increasing wavelength, CDOM would be able to trigger •OH photogeneration in deep waters, to a higher extent than UVB-absorbing nitrate or UVB + UVA-absorbing nitrite.

Alternative Co-Initiators for Photocurable Biomaterials: Polymerisation, Quantum Yield of Conversion and Cytotoxicity

Cyclic acetals such as 1,3 benzodioxole (BZD), piperonyl alcohol (PA), and N-phenyl glycine (NPG) are naturally occurring compounds capable of acting as co-initiators during free-radical polymerisation, and potentially serve to offer non-allergic and biologically less toxic alternatives to conventional (tertiary) amines. The current study aimed to evaluate the use of cyclic acetals in concentrations of 0.5-6.0 mol % for photopolymerisation of an unfilled model dimethacrylate resin system, bisphenol-A-glycidyldimethacrylate (BisGMA), and triethylene glycol dimethacrylate (tegDMA), 1:1 wt.%) using the photosensitiser camphorquinone (CQ; λmax = 469 nm) in concentrations of 0.5-1.5 mol %. Conventional tertiary amines, namely, ethyl-4-dimethyamino benzoate (EDMAB) (aromatic) and dimethylaminoethyl methacrylate (DMAEMA) (aliphatic) were utilised for comparison purposes. Real-time degree of conversion (DC) was evaluated using Fourier transform near-infrared spectroscopy. To measure the effectiveness of these alternative compounds in facilitating CQ photon absorption, quantum yield of conversion of CQ per absorbed photon was calculated using UV-Vis spectroscopy. Cytotoxicity of NPG and cyclic acetals were assessed using MTT and Calcien AM to determine metabolic activity and cell viability, respectively. The result indicated that cyclic acetals were capable of facilitating free radical polymerisation as co-initiators at all three CQ concentrations (0.5, 1.0 and 1.5 mol %). Further, the use of NPG as a co-initiator resulted in post-irradiation DC values that were comparable to both EDMAB and DMAEMA across all three CQ concentrations. Based on the quantum yield of conversion of CQ, alternative compounds facilitated the hydrogen abstraction process, which provided high conversion of CQ molecules. UV-Vis absorption and quantum yield data revealed that NPG exhibited competitive effects in absorbing blue light photons, which might be attributed to the photolytic degradation of NPG and the formation of N-methylaniline. Indirect treatment of human dental pulp cells (HDPCs) with eluted extracts of NPG, BZD and PA exhibited relatively lower cytotoxicity when compared with HDPCs groups treated with no eluted extracts. The relative cytotoxicity of DMAEMA was comparable to that of PA. However EDMAB, CQ and the neat model resin media extracts resulted in significant cytotoxicity, with highest relative reduction in the number of viable cells observed in groups treated with neat model resin extracts, suggesting that bisGMA and tegDMA monomers played significant role in the overall cytotoxicity of photocurable systems involving HDPCs.

Comparison of the RADM2 and RACM chemical mechanisms in O3 simulations: effect of the photolysis rate constant

Since the photolysis rate plays an important role in any photoreaction leading to compound sink and radical formation/destruction and eventually O3 formation, its impact on the simulated O3 concentration was evaluated in the present study. Both RADM2 and RACM were adopted with and without updated photolysis rate constants. The newly developed photolysis rates were determined based on two major absorption cross-section and quantum yield data sources. CMAQ in conjunction with meteorological MM5 and emission data retrieved from Taiwan and East Asia were employed to provide spatial and temporal O3 predictions over a one-week period in a three-level nested domain [from 81 km × 81 km in Domain 1 (East Asia) to 9 km × 9 km in Domain 3 (Taiwan)]. Four cases were analyzed, namely, RADM2, with the original photolysis rates applied in Case 1 as a reference case, RADM2, with the updated photolysis rates applied in Case 2, and RACM, with and without the updated photolysis rates applied in Cases 3 and 4, respectively. A comparison of the simulation and observed results indicates that both the application of updated photolysis rate constants and RACM instead of RADM2 enhanced all three error analysis indicators (unpaired peak prediction accuracy, mean normalized bias error and mean absolute normalized gross error). Specifically, RADM2 with the updated photolysis rates resulted in an increase of 12 ppb (10%) in the daily maximum O3 concentration in southwestern Taiwan, while RACM without the updated photolysis rates resulted in an increase of 20 ppb (17%) in the daily maximum O3 concentration in the same area. When RACM with the updated photolysis rate constants was applied in the air quality model, the difference in the daily maximum O3 concentration reached up to 30 ppb (25%). The implication of Case 4 (RACM with the updated photolysis rates) for the formation and degradation of α-pinene and d-limonene was examined.

Photophysical Properties of Some Fluorescent Dyes in SDS Micellar Solutions.

Photophysical properties of fluorescent dyes such as Safranin T, Acridine Orange, Pyronin B and Pyronin Y in SDS micelles were examined by using spectroscopic techniques. Firstly, spherical micelles in deionized water were prepared with Sodium Dodecyl Sulfate (SDS) surfactants and they were transformed into their layered structures (lamellar micelles) by the aid of NaCl (sodium chloride). SEM studies confirmed the transformation of SDS micelles from the spherical structures to the lamellar structures. Secondly, absorption and fluorescence characteristics of the dyes in deionized water and the SDS micelles aqueous solutions were characterized in the presence of various NaCl concentrations at above the critical micelle concentration (CMC). Moreover, the photophysical properties of the dyes in various media were discussed by fluorescence quantum yield and fluorescence lifetime data. The micellar structures called a mimetic membrane system changed the photophysical properties of the dyes compared to those in deionized water.

Ratiometric oxygen probes with a cell-penetrating peptide for imaging oxygen levels in living cells

We investigated the photophysical and intracellular properties of two newly designed molecule-based ratiometric oxygen probes, 7DEAC-R8-BTQphen (R8) and 7DEAC-R12-BTQphen (R12), to evaluate their suitability for intracellular O2 measurements. R8 and R12 consist of a blue fluorescent coumarin derivative (7DEAC) and a red phosphorescent iridium(III) complex (BTQphen) connected respectively by an octa- or dodecaarginine linker to promote intracellular delivery of the probes. The probes showed oxygen-sensitive dual emissions in acetonitrile, lipid bilayer membrane, and in living cells. Energy state diagrams showing the relaxation processes of R8 and R12 in the excited state were constructed using emission spectra, quantum yield, and lifetime data. Efficient photon absorption at 405 nm due to the 7DEAC chromophore is followed by intramolecular energy transfer to the BTQphen moiety, resulting in 7DEAC fluorescence and BTQphen phosphorescence with an intensity ratio and spectral separation suitable for ratiometric measurements. The validities of O2 concentrations derived from the ratios between the phosphorescence and fluorescence intensities of R8 and R12 were verified in lipid membranes, as well as in solution by phosphorescence lifetime measurements of the BTQphen moiety. The cellular uptake efficiencies of R8 and R12 were significantly enhanced due to their oligoarginine linkers compared to previous probes with oligoproline linkers. These ratiometric oxygen probes allowed visualization of the O2 gradient produced by placing a thin coverslip onto a HeLa cell monolayer.

NIR optical carbon dioxide gas sensor based on simple azaBODIPY pH indicators.

Two simple boron-dipyrromethene-type fluorophore (azaBODIPYs) dyes are synthesized and tested for the determination of CO2 gas by an inner filter process. The indicators are noncovalently entrapped in suitable polymers according to their polarity, featuring absorption maxima at 620 nm and fluorescent emission maxima in the range 675-720 nm. Molar absorptivity and fluorescence quantum yield data were determined for these two synthesized azaBODIPYs. These indicators have high molar absorption coefficients of 7.1 × 104 and 2.1 × 104 M-1 cm-1 and quantum yields of 21 and 9%. The pKa values of the indicators are determined from absorbance and fluorescence measurements with values of 7.9 and 8.5, depending on the positioning of the substitution pattern of the electron-donating functionalities. The two azaBODIPYs present excellent photostability, making them suitable for long duration measurements. These azaBODIPY dyes act as fluorescent pH indicators in a polymeric sensing membrane along with microcrystalline powder of chromium-doped gadolinium aluminium borate as the luminophore, a transfer phase agent (tetraoctyl or tetramethyl ammonium hydroxide) and a plasticizer or surfactant to improve membrane permeability to gaseous CO2. The response time ranges from 42 to 60 s and recovery time from 103 to 120 s, with a detection limit of 0.04 and 0.57% CO2. The store time of the sensing membranes is longer than 570 days in the best case, and it does not need to be kept in any special atmosphere other than darkness.

Arginine-Substituted Phthalocyanine with Concentration-Driven Self-Disaggregation Performance: Synthesis, Properties and Mechanistic Study.

An arginine-substituted zinc phthalocyanine (ArgZnPc) capable of disaggregating at high concentrations in polar non-aqueous solvents through concentration-driven hydrogen bond type transformation has been prepared. The ArgZnPc was prepared through a guanidine-meditated self-catalytic ester hydrolysis reaction. The concentration-driven disaggregation of ArgZnPc was confirmed by UV-Vis absorption spectra, fluorescence emission spectra and lifetimes, and singlet oxygen quantum yield data.

Quantum yield and lifetime data analysis for the UV curable quantum dot nanocomposites.

The quantum yield (QY) and lifetime are the important parameters for the photoluminescent materials. The data here report the changes of the QY and lifetime for the quantum dot (QD) nanocomposite after the UV curing of the urethane acrylate prepolymer. The data were collected based on the water soluble CdTe QDs and urethane acrylate prepolymer. Colloidal QDs were in various concentration from 0.5×10−3 molL−1 to 10×10−3 molL−1, and 1% (wt%) 1173 was the photoinitiator. The QY before the curing was 56.3%, 57.8% and 58.6% for the QDs 510 nm, 540 nm and 620 nm, respectively. The QY after the curing was changed to 8.9%, 9.6% and 13.4% for the QDs 510 nm, 540 nm and 620 nm, respectively. Lifetime data showed that the lifetime was changed from 23.71 ns, 24.55 ns, 23.52 ns to 1.29 ns, 2.74 ns, 2.45 ns for the QDs 510 nm, 540 nm and 620 nm, respectively.

Asymmetrically Crowded "Push-Pull" Octaphenylporphyrins with Modulated Frontier Orbitals: Syntheses, Photophysical, and Electrochemical Redox Properties.

A new series of β-substituted octaphenylporphyrins were synthesized and the influence of unsymmetrical substitution on the photophysical and electrochemical properties of the compounds is elucidated. The examined compounds are represented as MOPP(R)X2 where OPP = the dianion of octaphenylporphyrin, R = NO2, CHO, or CH2OH, X = Br or CN, and M is Co(II), Cu(II), Ni(II), or Zn(II). Routes to the trifunctionalized β-octaphenylporphyrins begin with the synthesis of MOPP(R) (R = NO2, CHO, and CH2OH) and the conversion of MOPP(NO2) to MOPP(NO2)X2 (X = Br and CN). These "push-pull" octaphenylporphyrins exhibit high dipole moments, tunable redox properties, and red-shifted electronic spectral features due to asymmetric β-substitution. Photophysical data on the series of MOPP(R)X2 compounds also reflect the nonplanar conformation of these porphyrins. Quantum yield and lifetime data are invariably lower than what has been reported in the literature for related β-substituted porphyrins. The spectroscopic properties and electrochemical redox potentials of the porphyrins are influenced by both the peripheral substituents and nature of the core metal ion. A decrease in the HOMO-LUMO gap and increase in Δb1 is observed as the number of electron withdrawing groups on the molecule was increased. In addition, a tuning of the redox potentials could be achieved by introducing both electron donating (CH2OH) and withdrawing (CN, NO2, CHO, and Br) substituents into the MOPP skeleton which led to a "cross-polarized push-pull effect" of the β-substituents and a nonplanarity of the molecule. Metal-centered oxidations were exhibited for all of the Co(II) porphyrins and an M(II)/M(III) process was also observed to occur for NiOPP(R) (R = CH2OH, H, CHO, and NO2) and CuOPP(NO2)(CN)2. These electrode reactions for the latter two series of compounds occur after an initial conversion of the neutral porphyrin to its dicationic form under the electrochemical conditions. Evidence for the site of electron transfer is given in part by comparison with data in the literature for related compounds and in part by theoretical calculations and thin-layer spectroelectrochemical data carried out in the current study.

Triphenylamine substituted dipyrrinato metal complexes: Synthesis, optical and electrochemical studies

A series of triphenylamine substituted dipyrrinato metal complexes (1–8) have been synthesized. The mononuclear type complexes 1–6 have Ni(II), Co(II), Pd(II), In(III), and Zn(II) metal ions in the core. The binuclear type complexes 7 and 8 have Zn(II) metal ion in the center. All the compounds (1–8) were characterized by HRMS, NMR, IR, UV–vis absorption, cyclic voltammetry and fluorescence techniques. The presence of large electron rich triphenylamine moiety at dipyrrin ligands affected the spectral properties of complexes. Except Co(II) complex, other metal complexes exhibited blue shifted absorption maxima in UV–vis studies. The In(III) and Zn(II) metal complexes 4–6 showed red shifted emission maxima in fluorescence compared to their corresponding phenyl analogues. Complexes 3–8 exhibited good Stokes shifts in the range of 4600 to 7000cm−1 with reduced quantum yields. Singlet state lifetimes of complexes 3–8 were in the range of 2 to 4ns; also the decrease in radiative decay constants kr and the increase in non-radiative decay constants knr were in line with the quantum yield data. CV studies of complexes 1–8 showed anodic shifts in the oxidation potentials, suggesting that meso-triphenylamine group has affected the electronic properties of complexes by making them difficult to oxidize.

A photolysis coefficient for characterizing the response of aqueous constituents to photolysis

UV photolysis and UV based advanced oxidation processes (AOPs) are gaining more and more attention for drinking water treatment. Quantum yield (o) and molar absorption coefficient (e) are the two critical parameters measuring the effectiveness of photolysis of a compound. The product of the two was proposed as a fundamental measure of a constituent’s amenability to transformation by photolysis. It was shown that this product, named the photolysis coefficient, k p , can be determined using standard bench tests and captures the properties that govern a constituent’s transformation when exposed to light. The development showed the photolysis coefficient to be equally useful for microbiological, inorganic and organic constituents. Values of k p calculated by the authors based on quantum yield and molar absorption coefficient data from the literature were summarized. Photolysis coefficients among microorganisms ranged from 8500 to more than 600000 and are far higher than for inorganic and organic compounds, which varied over a range of approximately 10 to 1000 and are much less sensitive to UV photolysis than the microorganisms.

NIR to NIR upconversion in KYb2F7: RE3+ (RE = Tm, Er) nanoparticles for biological imaging.

Until recently, many contrast agents widely used in biological imaging have absorbed and emitted in the visible region, limiting their usefulness for deeper tissue imaging. In order to push the boundaries of deep tissue imaging with non-ionizing radiation, contrast agents in the near infrared (NIR) regime, which is not strongly absorbed or scattered by most tissues, are being sought after. Upconverting nanoparticles (UCNPs) are attractive candidates since their upconversion emission is tunable with a very narrow bandwidth and they do not photobleach or blink. The upconversion produced by the nanoparticles can be tailored for NIR to NIR by carefully choosing the lanthanide dopants and dopant ratios such as KYb2F7: RE3+ (RE = Tm, Er). Spectroscopic characterization was done by analyzing absorption, fluorescence, and quantum yield data. In order to study the toxicity of the nanoparticles Monkey Retinal Endothelial Cells (MREC) were cultivated in 24 well plates and then treated with nanoparticles at different concentrations in triplicate to obtain the optimal concentration for in vivo experiments. It will be shown that these UCNPs do not elicit a strong toxic response such as quantum dots and some noble metal nanoparticles. 3-D optical slices of nanoparticle treated fibroblast cells were imaged using a confocal microscope where the nucleus and cytoplasm were stained with DAPI and Alexa Fluor respectively. These results presented support the initial assumption, which suggests that KYb2F7: RE3+ would be excellent candidates for NIR contrast agents.

Fluorescence Properties of Twenty Fluorescein Derivatives: Lifetime, Quantum Yield, Absorption and Emission Spectra

The fluorescence lifetime (τf), emission quantum yield (Φf), absorption and emission spectral data of 20 fluorescein derivatives were measured under the same conditions by using time-correlated single photon counting, steady state fluorescence and absorption methods to get comparable data. Based on the results, the factors and mechanism that control the fluorescence properties of the fluorescein dyes are discussed. Both Φf and τf are remarkably dependent on the substitution on either xanthene or phenyl rings, but their ratio (Φf/τf), i.e. rate constant of radiation process, is a constant value (0.20 × 10(9) s(-1)). The rate constant of nonradiation process, on the other hand, is varied with both the structure and the solvent used.

BDE-209: Kinetic Studies and Effect of Humic Substances on Photodegradation in Water

BDE-209 is a brominated flame retardant and a priority contaminant, which has been found in several environmental matrices, namely, in water. To date, there are no quantum yield data for BDE-209 photodegradation by sunlight in water, to allow predicting half-life times in aquatic systems. In this work, the kinetics of BDE-209 photodegradation in water was studied and the influence of different fractions of aquatic humic substances (HS) was evaluated. Aqueous solutions of BDE-209 exposed for different periods of time to simulated sunlight were analyzed by HPLC-UV after being concentrated using dispersive liquid-liquid microextraction (DLLME) or solid-phase extraction (SPE). The photodegradation of BDE-209 in aqueous solution followed pseudo-first-order kinetics. The average quantum yield obtained of 0.010 ± 0.001 (about 20-fold lower than the quantum yield determined in ethanol) allow to predict an outdoor half-life time of 3.5 h. The photodegradation percentage of BDE-209 was not significantly affected by the XAD-4 fraction of HS, but it decreased substantially in the presence of humic and fulvic acids. Light screening by the humic substances could not explain this delay, which is probably the result of the association of the compound with the hydrophobic sites of the humic material.

Photophysical properties of powder and solutions of N-(p-methoxyphenyl)-4-octylamino-1,8-naphthalimide

The photophysical properties of N-(p-methoxyphenyl)-4-octylamino-1,8-naphthalimide (OANI) were investigated. The molar extinction coefficient, quantum yield, fluorescence lifetime, and other data were presented for OANI in EtOH. Intramolecular electron-transfer processes in addition to the influence of intermolecular repulsion on the shape of the absorption and fluorescence spectra of this compound were discussed.

A Phase Space Theory for Roaming Reactions

We describe a new, simple theory for predicting the branching fraction of products in roaming reactions, compared to the analogous barrierless bond dissociation products. The theory uses a phase space theory (PST) formalism to divide reactive states in the bond dissociation channel into states with enough translational energy to dissociate and states that may roam. Two parameters are required, ΔEroam, the energy difference between the bond dissociation threshold and the roaming threshold, and the roaming probability, Proam, the probability that states that may roam do roam rather than recombine to form reactants. The PST-roaming theory is tested against experimental and theoretical data on the dissociation dynamics of H2CO, NO3, and CH3CHO. The theory accurately models the relative roaming to bond dissociation branching fraction over the experimental or theoretical energy range available in the literature for each species. For H2CO, fixing ΔEroam = 146 cm(-1), the midpoint of the experimental bounds for the roaming threshold, we obtain Proam = 1. The best-fit value, ΔEroam = 161 cm(-1), is also consistent with the experimental bounds. Using this value, the relative roaming to dissociation branching ratios are predicted to be similar in D2CO and H2CO, consistent with experimental observation. For NO3, we fix ΔEroam = 258.6 cm(-1), the experimental threshold for NO + O2 production, and we model low-temperature experimental branching fractions using the experimental rotational and vibrational temperatures of Trot = 0 K and Tvib = 300 K. The best fit to the experimental data is obtained for Proam = 0.0075, with this very small Proam being consistent with the known geometric constraints to formation of NO + O2. Using Proam = 0.0075, our PST-roaming theory also accurately predicts the low-temperature NO yield spectrum and quantum yield data for room-temperature NO3 photolysis. For CH3CHO, we fix ΔEroam = 385 cm(-1), based on theoretical calculations, and obtain a best-fit value of Proam = 0.21, fitting to reduced dimensional trajectory calculations. These values of ΔEroam and Proam yield PST-roaming theory results that are also consistent with two experimental room-temperature data points. The combination of other kinetic theories and the PST-roaming theory will provide rate coefficients for roaming reactions.

Developing a diagnostic model for estimating terrestrial vegetation gross primary productivity using the photosynthetic quantum yield and Earth Observation data

This article develops a new carbon exchange diagnostic model [i.e. Southampton CARbon Flux (SCARF) model] for estimating daily gross primary productivity (GPP). The model exploits the maximum quantum yields of two key photosynthetic pathways (i.e. C3 and C4 ) to estimate the conversion of absorbed photosynthetically active radiation into GPP. Furthermore, this is the first model to use only the fraction of photosynthetically active radiation absorbed by photosynthetic elements of the canopy (i.e. FAPARps ) rather than total canopy, to predict GPP. The GPP predicted by the SCARF model was comparable to in situ GPP measurements (R(2) >0.7) in most of the evaluated biomes. Overall, the SCARF model predicted high GPP in regions dominated by forests and croplands, and low GPP in shrublands and dry-grasslands across USA and Europe. The spatial distribution of GPP from the SCARF model over Europe and conterminous USA was comparable to those from the MOD17 GPP product except in regions dominated by croplands. The SCARF model GPP predictions were positively correlated (R(2) >0.5) to climatic and biophysical input variables indicating its sensitivity to factors controlling vegetation productivity. The new model has three advantages, first, it prescribes only two quantum yield terms rather than species specific light use efficiency terms; second, it uses only the fraction of PAR absorbed by photosynthetic elements of the canopy (FAPARps ) hence capturing the actual PAR used in photosynthesis; and third, it does not need a detailed land cover map that is a major source of uncertainty in most remote sensing based GPP models. The Sentinel satellites planned for launch in 2014 by the European Space Agency have adequate spectral channels to derive FAPARps at relatively high spatial resolution (20m). This provides a unique opportunity to produce global GPP operationally using the Southampton CARbon Flux (SCARF) model at high spatial resolution.