Novel correction procedure for compensating thermal contraction errors in the measurement of the magnetic field of superconducting undulator coils in a liquid helium cryostat.

Superconducting undulators (SCUs) can offer a much higher on-axis undulator field than state-of-the-art cryogenic permanent-magnet undulators with the same period and vacuum gap. The development of shorter-period and high-field SCUs would allow the free-electron laser and synchrotron radiation source community to reduce both the length of undulators and the dimensions of the accelerator. Magnetic measurements are essential for characterizing the magnetic field quality of undulators for operation in a modern light source. Hall probe scanning is so far the most mature technique for local field characterization of undulators. This article focuses on the systematic error caused by thermal contraction that influences Hall probe measurements carried out in a liquid helium cryostat. A novel procedure, based on the redundant measurement of the magnetic field using multiple Hall probes at known relative distance, is introduced for the correction of such systematic error.

Modeling the Ground- and Excited-State Unimolecular Decay of the Simplest Fluorinated Criegee Intermediate, HFCOO, Formed from the Ozonolysis of Hydrofluoroolefin Refrigerants.

Hydrofluoroolefins (HFO) are fourth-generation refrigerants designed to function as efficient refrigerants with no ozone depletion potential and zero global warming potential. Despite extensive studies on their chemical and physical properties, the ground- and excited-state chemistry of their atmospheric oxidation products is less well understood. This study focuses on the ground- and excited-state chemistry of the simplest fluorinated Criegee intermediate (CI), fluoroformaldehyde oxide (HFCOO), which is the simplest fluorinated CI formed from the ozonolysis of HFOs. HFCOO contains syn- and anti-conformers, which have Boltzmann populations of, respectively, 87 and 13% at 298 K. For both conformers, the calculated ground-state reaction energy profiles associated with cyclization to form fluorodioxirane is lower than the equivalent unimolecular decay path in the simplest CI, H2COO, with anti-HFCOO returning a barrier height more than half of that of H2COO. The excited-state dynamics reveal that photoexcitation to the bright S2 state of syn-HFCOO and anti-HFCOO is expected to undergo a prompt O-O fission─with the former conformer expected to dissociate with an almost unity quantum yield and to form both O (1D) + HFCO (S0) and O (3P) + HFCO (T1) products. In contrast, photoexcitation of anti-HFCOO is expected to undergo an O-O bond fission with a non-unity quantum yield. The fraction of photoexcited anti-HFCOO that dissociates is predicted to exclusively form O (1D) + HFCO (S0) products, which is in sharp contrast to H2COO. The wider implications of our results are discussed from both physical and atmospheric chemistry perspectives.

Electronic Absorption Spectroscopy and Photochemistry of Criegee Intermediates.

Interest in Criegee intermediates (CIs), often termed carbonyl oxides, and their role in tropospheric chemistry has grown massively since the demonstration of laboratory-based routes to their formation and characterization in the gas phase. This article reviews current knowledge regarding the electronic spectroscopy of atmospherically relevant CIs like CH2 OO, CH3 CHOO, (CH3 )2 COO and larger CIs like methyl vinyl ketone oxide and methacrolein oxide that are formed in the ozonolysis of isoprene, and of selected conjugated carbene-derived CIs of interest in the synthetic chemistry community. Of the aforementioned atmospherically relevant CIs, all except CH2 OO and (CH3 )2 COO exist in different conformers which, under tropospheric conditions, can display strikingly different thermal loss rates via unimolecular and bimolecular processes. Calculated photolysis rates based on their absorption properties suggest that solar photolysis will rarely be a significant contributor to the total loss rate for any CI under tropospheric conditions. Nonetheless, there is ever-growing interest in the absorption cross sections and primary photochemistry of CIs following excitation to the strongly absorbing 1 ππ* state, and how this varies with CI, with conformer and with excitation wavelength. The later part of this review surveys the photochemical data reported to date, including a range of studies that demonstrate prompt photo-induced fission of the terminal O-O bond, and speculates about possible alternate decay processes that could occur following non-adiabatic coupling to, and dissociation from, highly internally excited levels of the electronic ground state of a CI.

Insights into the Ultrafast Photodissociation Dynamics of Isoprene-Derived Criegee Intermediates.

Isoprene is the most abundant nonmethane volatile organic compound emitted into the troposphere by terrestrial vegetation. Reaction with ozone represents an important isoprene removal process from the troposphere and is a well-known source of Criegee intermediates (CIs), which are reactive carbonyl oxides. Three CIs, formaldehyde oxide (CH2 OO), methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide) are formed during isoprene ozonolysis. All three CIs contain strongly absorbing ππ* states, electronic excitation, which leads to dissociation to form aldehyde/ketone + oxygen products. Here, we compare the excited state chemistry of CH2 OO, MVK-oxide and MACR-oxide in order to ascertain how increasing molecular complexity affects their photodynamics. In CH2 OO, vertical excitation to the S2 state leads to prompt O-O bond fission with a unity quantum yield. Branching into both the O (1 D) + H2 CO (S0 ) and O (3 P) + H2 CO (T1 ) product channels is predicted, with 80% of trajectories dissociating to form the former product pair. Analogous vertical excitation of the lowest energy conformers of MVK-oxide and MACR-oxide also undergoes O-O bond fission to form O + MVK/MACR products-albeit with a nonunity quantum yield. In the latter case, ca. 10% and 25% of trajectories remain as the parent MVK-oxide and MACR-oxide molecules, respectively. Additionally, at most only 5% of the dissociating trajectories form O (3 P) + MVK/MACR (T1 ) products, with a greater fraction forming O (1 D) + MVK/MACR (S0 ) products (cf. CH2 OO). This latter observation coupled with the greater fraction of undissociated trajectories aligns with the bathochromic shift in the electronic absorption of the MACR-oxide and MVK-oxide (cf. CH2 OO). We discuss the implications of the results in a broader context, including those that are relevant to the atmosphere.

Tin-based metal organic framework catalysts for high-efficiency electrocatalytic CO2 conversion into formate.

Electrochemical reduction of carbon dioxide (ERCO2) allows for the conversion of CO2 to value-added low-carbon chemicals. Catalysts are indispensable for an efficient ERCO2 process. In this work, a Sn-based metal-organic framework (Sn-MOF) was synthesized as an electrocatalyst for the conversion of CO2 to formate (HCOO-). Such a Sn-MOF electrocatalyst exhibits an outstanding performance with a formate selectivity up to 92% and a current density of 23.2 mA cm-2 at -1.2 VRHE. Density functional theory calculations were used to probe and analyze the catalytic ERCO2 mechanism. This work shows the possibility to achieve a high efficiency of a pure Sn-MOF in catalyzing ERCO2 directly. In addition, this work provides insights into the design and synthesis of highly efficient ERCO2 electrocatalysts for practical applications.

A direct dynamics study of the exotic photochemistry of the simplest Criegee intermediate, CH2OO.

Criegee intermediates are amongst the most fascinating molecules in modern-day chemistry. They are highly reactive intermediates that find vital roles that range from atmospheric chemistry to organic synthesis. Their excited state chemistry is exotic and complicated, and a myriad of electronic states can contribute to their photodissociation dynamics. This article reports a multi-state direct dynamics (full-dimensional) study of the photoinduced fragmentation of the simplest Criegee intermediate, CH2OO, using state-of-the-art MS-CASPT2 trajectory surface hopping. Following vertical excitation to the strongly absorbing S2(1ππ*) state, internal conversion, and thus changes in the electronic state character of the separating O + CH2O fragments, is observed between parent electronic states at separations that, traditionally, might be viewed as the classically asymptotic region of the potential energy surface. We suggest that such long-range internal conversion may account for the unusual and non-intuitive total kinetic energy distribution in the O(1D) + CH2O(S0) products observed following photoexcitation of CH2OO. The present results also reveal the interplay between seven singlet electronic states and dissociation to yield the experimentally observed O(1D) + CH2O(S0) and O(3P) + CH2O(T1) products. The former (singlet) products are favored, with a branching ratio of ca. 80%, quantifying the hitherto unknown product branching ratios observed in velocity map imaging experiments. To the best of our knowledge, such long-range internal conversions that lead to changes in the electronic state character of the fragment pairs originating from a common parent - at classically asymptotic separations - have not been recognized hitherto in the case of a molecular photodissociation.

Modeling the Conformer-Dependent Electronic Absorption Spectra and Photolysis Rates of Methyl Vinyl Ketone Oxide and Methacrolein Oxide.

Criegee intermediates are important atmospheric oxidants, formed via the reaction of ozone with volatile alkenes emitted into the troposphere. Small Criegee intermediates (e.g., CH2OO and CH3CHOO) are highly reactive, and their removal via unimolecular decay or bimolecular chemistry dominates their atmospheric lifetimes. As the molecular complexity of Criegee intermediates increases, their electronic absorption spectra show a bathochromic shift within the solar spectrum relevant to the troposphere. In these cases, solar photolysis may become a competitive contributor to their atmospheric removal. In this article, we report the conformer-dependent simulated electronic absorption spectra of two four-carbon-centered Criegee intermediates, methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide). Both MVK-oxide and MACR-oxide contain four low-energy conformers, which are convoluted in the experimentally measured spectra. Here, we deconvolute each conformer and estimate contributions from each of the four conformers to the experimentally measured spectra. We also estimate the photolysis rates and predict that solar photolysis should be a more competitive removal process for MVK-oxide and MACR-oxide (cf. CH2OO and CH3CHOO).

Achieving high selectivity towards electro-conversion of CO2 using In-doped Bi derived from metal-organic frameworks.

Metal-organic frameworks (MOFs) and their derivatives have shown great potential as electrocatalysts, in virtue of their ease of functionalization and abundance of active sites. Here, we report a series of indium-doped bismuth MOF-derived composites (BiInX-Y@C) for the direct conversion of carbon dioxide (CO2) to hydrocarbon derivatives. Amongst the catalysts studied, BiIn5-500@C demonstrated high selectivity for the production of formate and intrinsic activity in a wide potential window, ranging from - 1.16 to - 0.76 V vs. RHE (VRHE). At - 0.86 VRHE, the Faradaic efficiency and total current density were determined as 97.5% and - 13.5 mA cm-2, respectively. In addition, a 15-h stability test shows no obvious signs of deactivation. Complementary density functional theory (DFT) calculations revealed that the In-doped Bi2O3 are the predominant active centers for HCOOH production in the reduction of CO2 under the action of the BiInX-Y@C catalyst. This work provides new detailed insights into reaction mechanism, and selectivity for reduction of CO2via MOFs, which are expected to inspire and guide the design of novel, selective and efficient catalysts.

Insights into the Ultrafast Dynamics of CH2 OO and CH3 CHOO Following Excitation to the Bright 1 ππ* State: The Role of Singlet and Triplet States.

Criegee intermediates make up a class of molecules that are of significant atmospheric importance. Understanding their electronically excited states guides experimental detection and provides insight into whether solar photolysis plays a role in their removal from the troposphere. The latter is particularly important for large and functionalized Criegee intermediates. In this study, the excited state chemistry of two small Criegee intermediates, formaldehyde oxide (CH2 OO) and acetaldehyde oxide (CH3 CHOO), was modeled to compare their specific dynamics and mechanisms following excitation to the bright ππ* state and to assess the involvement of triplet states to the excited state decay process. Following excitation to the bright ππ* state, the photoexcited population exclusively evolves to form oxygen plus aldehyde products without the involvement of triplet states. This occurs despite the presence of a more thermodynamically stable triplet path and several singlet/triplet energy crossings at the Franck-Condon geometry and contrasts with the photodynamics of related systems such as acetaldehyde and acetone. This work sets the foundations to study Criegee intermediates with greater molecular complexity, wherein a bathochromic shift in the electron absorption profiles may ensure greater removal via solar photolysis.

The states that hide in the shadows: the potential role of conical intersections in the ground state unimolecular decay of a Criegee intermediate.

Criegee intermediates are of great significance to Earth's troposphere - implicated in altering the tropospheric oxidation cycle and in forming low volatility products that typically condense to form secondary organic aerosols (SOAs). As such, their chemistry has attracted vast attention in recent years. In particular, the unimolecular decay of thermal and vibrationally-excited Criegee intermediates has been the focus of several experimental and computational studies, and it is now recognized that Criegee intermediates undergo unimolecular decay to form OH radicals. In this contribution we reveal insight into the chemistry of Criegee intermediates by highlighting the hitherto neglected multi-state contribution to the ground state unimolecular decay dynamics of the Criegee intermediate products. The two key intermediates of present focus are dioxirane and vinylhydroperoxide - known to be active intermediates that mediate the unimolecular decay of CH2OO and CH3CHOO, respectively. In both cases the unimolecular decay path encounters conical intersections, which may play a pivotal role in the ensuing dynamics. This hitherto unrecognized phenomenon may be vital in the way in which the reactivity of Criegee intermediates are modelled and is likely to affect the ensuing dynamics associated with the unimolecular decay of a given Criegee intermediate.

Photodissociation dynamics of methyl vinyl ketone oxide: A four-carbon unsaturated Criegee intermediate from isoprene ozonolysis.

The electronic spectrum of methyl vinyl ketone oxide (MVK-oxide), a four-carbon Criegee intermediate derived from isoprene ozonolysis, is examined on its second π* ← π transition, involving primarily the vinyl group, at UV wavelengths (λ) below 300 nm. A broad and unstructured spectrum is obtained by a UV-induced ground state depletion method with photoionization detection on the parent mass (m/z 86). Electronic excitation of MVK-oxide results in dissociation to O (1D) products that are characterized using velocity map imaging. Electronic excitation of MVK-oxide on the first π* ← π transition associated primarily with the carbonyl oxide group at λ > 300 nm results in a prompt dissociation and yields broad total kinetic energy release (TKER) and anisotropic angular distributions for the O (1D) + methyl vinyl ketone products. By contrast, electronic excitation at λ ≤ 300 nm results in bimodal TKER and angular distributions, indicating two distinct dissociation pathways to O (1D) products. One pathway is analogous to that at λ > 300 nm, while the second pathway results in very low TKER and isotropic angular distributions indicative of internal conversion to the ground electronic state and statistical unimolecular dissociation.

Photodissociation Dynamics of CH2OO on Multiple Potential Energy Surfaces: Experiment and Theory.

UV excitation of the CH2OO Criegee intermediate across most of the broad span of the (B 1A')-(X 1A') spectrum results in prompt dissociation to two energetically accessible asymptotes: O (1D) + H2CO (X 1A1) and O (3P) + H2CO (a 3A''). Dissociation proceeds on multiple singlet potential energy surfaces that are coupled by two regions of conical intersection (CoIn). Velocity map imaging (VMI) studies reveal a bimodal total kinetic energy release (TKER) distribution for the O (1D) + H2CO (X 1A1) products with the major and minor components accounting for ca. 40% and ca. 20% on average of the available energy (Eavl), respectively. The unexpected low TKER component corresponds to highly internally excited H2CO (X 1A1) products accommodating ca. 80% of Eavl. Full dimensional trajectory calculations suggest that the bimodal TKER distribution of the O (1D) + H2CO (X 1A1) products originates from two different dynamical pathways: a primary pathway (69%) evolving through one CoIn region to products and a smaller component (20%) sampling both CoIn regions enroute to products. Those that access both CoIn regions likely give rise to the more highly internally excited H2CO (X 1A1) products. The remaining trajectories (11%) dissociate to O (3P) + H2CO (a 3A'') products after traversing through both CoIn regions. The complementary experimental and theoretical investigation provides insight on the photodissociation of CH2OO via multiple dissociation pathways through two regions of CoIn that control the branching and energy distributions of products.

A Simple and Efficient Method for Simulating the Electronic Absorption Spectra of Criegee Intermediates: Benchmarking on CH2OO and CH3CHOO.

Criegee intermediates (CIs) play a vital role in the atmosphere-known most prominently for enhancing the oxidizing capacity of the troposphere. Knowledge of their electronic absorption spectra is of vital importance for two reasons: (1) to aid experimentalists in detecting CIs and (2) in deciding if their removal is affected by solar photolysis. In this article we report a simple and efficient method based on the nuclear ensemble method that may be effectively used to compute the electronic absorption spectra of Criegee intermediates without the need for extensive computation of preparing the initial configurations of the starting geometry. We use this method to benchmark several excited-state electronic structure methods and their efficacy in reproducing the electronic absorption spectra of two well-known cases of CI: CH2OO and CH3CHOO. The success and computational feasibility of the methodology are crucial for its applicability to CIs of increasing molecular complexity, which have no known experimentally measured electronic absorption spectra, allowing a guide for experimentalists. Application of the methodology to more complex CIs (e.g., those with extended conjugation or those derived from endocyclic alkenes) will also reveal if solar photolysis becomes a competitive removal process when compared to unimolecular decay or bimolecular chemistry.

The Role of Norrish Type-I Chemistry in Photoactive Drugs: An ab initio Study of a Cyclopropenone-Enediyne Drug Precursor.

We present a contemporary mechanistic description of the light-driven conversion of cyclopropenone containing enediyne (CPE) precusors to ring-opened species amenable to further Bergman cyclization and formation of stable biradical species that have been proposed for use in light-induced cancer treatment. The transformation is rationalized in terms of (purely singlet state) Norrish type-I chemistry, wherein photoinduced opening of one C-C bond in the cyclopropenone ring facilitates non-adiabatic coupling to high levels of the ground state, subsequent loss of CO and Bergman cyclization of the enediyne intermediate to the cytotoxic target biradical species. Limited investigations of substituent effects on the ensuing photochemistry serve to vindicate the experimental choices of Popik and coworkers (J. Org. Chem., 2005, 70, 1297-1305). Specifically, replacing the phenyl moiety in the chosen model CPE by a 1,4-benzoquinone unit leads to a stronger, red-shifted parent absorption, and increases the exoergicity of the parent → biradical conversion.

Oxidative Addition of Singlet Oxygen to Model Building Blocks of the Aerucyclamide A Peptide: A First-Principles Approach.

Singlet oxygen (1O2) is a significant source of biodamage in living organisms. 1O2 is a highly reactive excited electronic-state spin-configuration of molecular oxygen and is usually prepared via organic molecule sensitization. Despite the wealth of experimental studies on the 1O2-induced oxidation of several bio-organic molecules, the detailed mechanism of the oxidation process is largely unknown. Using high-level quantum chemical methods, we compute the potential energy profiles of the various electronic states associated with the [4 + 2]-cycloaddition reaction of O2 with a class of model peptide precursors that are based on derivatives of oxazole and thiazole. Experiments have shown that such oxazole/thiazole-based model peptides show a favorable reaction with 1O2. Upon increasing the molecular complexity, the bimolecular rate constant decreases and is attributed to the π-perturbing effects of the substituent of the oxazole/thiazole moiety. Our theoretical predictions are in excellent agreement with the experimental measurements and reveal a deep insight into the myriad electronic states that may hinder/promote the reaction of a given bio-organic molecule with 1O2.

Simulation studies for characterizing ultrashort bunches using novel polarizable X-band transverse deflection structures.

Transverse deflection structures are useful devices for characterizing the longitudinal properties of bunches in electron accelerators. With efforts to produce ever-shorter bunches for applications such as external injection into novel accelerator structures, e.g. plasma cells or dielectric structures, the applicability of deflection structures to measuring ultrashort bunches has been considered. In this paper, charge-density and bunch-length measurements of femtosecond and subfemtosecond bunches at the ARES linac at the SINBAD facility at DESY are studied with simulations and the limitations discussed in detail. The novel polarizable X-band transverse deflection structure (PolariX-TDS) will allow the streaking of bunches at all transverse angles, making a 3D charge-density reconstruction of bunches possible, in addition to the standard 1D charge-density reconstruction and bunch-length measurements. These various measurements of the charge-density distributions of bunches have been simulated, and it is shown that useful information about ultrashort bunches down to subfemtosecond lengths may be obtained using the setup planned for the ARES linac.

Importância da experiência clínica para a mensuração da curva escoliótica de crianças pela técnica de Cobb / La importancia de la experiencia clínica en la medición de la curva escoliótica de niños mediante la técnica de Cobb / The importance of clinical experience for the measurement of scoliosis curve in children by Cobb technique

RESUMO A escoliose é definida como uma deformidade com desvio lateral da coluna no plano coronal, torsão da coluna e do tronco e distúrbio no perfil sagital. Essa alteração postural é avaliada por meio de radiografia de incidência anteroposterior, utilizando-se o método de Cobb. O objetivo do estudo é verificar a influência da experiência do avaliador sobre a confiabilidade intraexaminador e interexaminador do ângulo Cobb em curvaturas escolióticas de crianças. Foram incluídas na pesquisa 39 crianças portadoras de escoliose idiopática, com idade entre 7 e 18 anos. Os exames foram avaliados por dois fisioterapeutas, um quiropraxista e um estudante de fisioterapia - cada um avaliando duas vezes cada exame. A segunda avaliação ocorreu após sete dias, para confiabilidade intraexaminador. Ademais, as primeiras avaliações forneceram dados para confiabilidade interexaminador. A análise estatística foi realizada com coeficiente de correlação intraclasse (CCI), análise de Bland e Altman e análise descritiva do desvio absoluto médio, erro-padrão de medição e mínima mudança detectável. Observou-se boa confiabilidade (CCI>0,5) para as análises intraexaminadores entre os profissionais, e confiabilidade fraca (CCI=0,4) para o avaliador inexperiente. A confiabilidade interexaminador dos profissionais foi boa (CCI=0,6), e com a presença do avaliador inexperiente foi fraca (CCI=0,3). As avaliações entre os profissionais apresentaram menor variabilidade das medidas e valores de desvio-padrão quando comparadas com as do avaliador inexperiente. A mensuração dos ângulos da escoliose por meio do método de Cobb realizada por profissionais experientes apresentou melhores índices de concordância e de confiabilidade intra e interexaminadores e menor desvio-padrão e variabilidade entre as medidas.

RESUMEN La escoliosis se define como una alteración con curvatura lateral de la columna vertebral en el plano coronal, torsión de la columna vertebral y del tronco y trastorno en el perfil sagital. Esta alteración postural se evalúa mediante radiografía anteroposterior, utilizando el método de Cobb. El presente estudio tiene como objetivo verificar la influencia de la experiencia del evaluador para la fiabilidad intraexaminador e interexaminador del ángulo de Cobb en las curvaturas escolióticas de los niños. El estudio incluyó a 39 niños con escoliosis idiopática entre 7 y 18 años de edad. Los exámenes fueron evaluados por dos fisioterapeutas, un quiropráctico y un estudiante de fisioterapia, siendo que cada uno evaluó cada examen dos veces. Tras siete días, ocurrió una segunda evaluación para la fiabilidad intraexaminador. Además, las primeras evaluaciones proporcionaron datos para la fiabilidad interexaminador. El análisis estadístico se realizó con el coeficiente de correlación intraclase (ICC), con el análisis de Bland y Altman y con el análisis descriptivo de la desviación media absoluta, del error estándar de medición y del cambio mínimo detectable. Se observó una alta fiabilidad (ICC>0,5) en los análisis intraexaminadores entre los profesionales, y una baja fiabilidad (ICC=0,4) en los de evaluadores inexpertos. La fiabilidad interexaminador de los profesionales fue buena (ICC=0,6), y la presencia del evaluador inexperto fue baja (ICC=0,3). Las evaluaciones entre los profesionales mostraron una menor variabilidad de las medidas y valores de desviación estándar en comparación con los del evaluador inexperto. La medición de los ángulos de escoliosis utilizando el método de Cobb que había sido realizada por profesionales con experiencia mostró mejores índices de concordancia y fiabilidad intra e interexaminadores y una menor desviación estándar y variabilidad entre las mediciones.

ABSTRACT Scoliosis is defined as a deformity with lateral deviation of the spine in the coronal plane, torsion of the spine and trunk, and disturbances in the sagittal profile. This postural alteration is evaluated by anteroposterior incidence radiography using the Cobb method. The objective of this study was to verify the influence of evaluator experience on inter- and intra-rater reliability of the Cobb angle of scoliosis curvatures in children. In total, 39 patients aged 7 to 18 years with idiopathic scoliosis were included in this study. The exams were evaluated by two physical therapists, a chiropractor and a physical therapy student. Each evaluator rated each exam twice and the second evaluation occurred after seven days, characterizing the intra-rater reliability. Furthermore, the first evaluations provided the inter-rater reliability. Statistical analysis was performed with intraclass correlation coefficient (ICC), Bland-Altman analysis, descriptive analysis of mean absolute deviation, standard error of measurement, and minimum detectable chance. Correlations ranged from good (ICC>0.5) for intra-rater reliability among professionals to weak (ICC=0.4) for the inexperienced evaluator. The inter-rater reliability of the professional's evaluations was good (ICC=0.6) and the same analysis with the presence of an inexperienced evaluator was weak (ICC=0.3). Evaluations among professionals showed less variability of measurements and standard deviation values compared to the inexperienced evaluator. The measurement of the angles of the scoliosis through the Cobb method carried out by experienced professionals showed better agreement as well as intra- and inter-rater reliability, lower standard deviation, and variability among the measurements.

Synthesis, Electronic Spectroscopy, and Photochemistry of Methacrolein Oxide: A Four-Carbon Unsaturated Criegee Intermediate from Isoprene Ozonolysis.

Ozonolysis of isoprene, one of the most abundant volatile organic compounds in the earth's atmosphere, generates the four-carbon unsaturated methacrolein oxide (MACR-oxide) Criegee intermediate. The first laboratory synthesis and direct detection of MACR-oxide is achieved through reaction of photolytically generated, resonance-stabilized iodoalkene radicals with oxygen. MACR-oxide is characterized on its first π* ← π electronic transition using a ground-state depletion method. MACR-oxide exhibits a broad UV-visible spectrum peaked at 380 nm with weak oscillatory structure at long wavelengths ascribed to vibrational resonances. Complementary theory predicts two strong π* ← π transitions arising from extended conjugation across MACR-oxide with overlapping contributions from its four conformers. Electronic promotion to the 11ππ* state agrees well with experiment, and results in nonadiabatic coupling and prompt release of O 1D products observed as anisotropic velocity-map images. This UV-visible detection scheme will enable study of its unimolecular and bimolecular reactions under thermal conditions of relevance to the atmosphere.

Exploring Norrish type I and type II reactions: an ab initio mechanistic study highlighting singlet-state mediated chemistry.

Norrish reactions are important photo-induced reactions in mainstream organic chemistry and are implicated in many industrially and biologically relevant processes and in the processing of carbonyl molecules in the atmosphere. The present study reports multi-reference electronic structure calculations designed to assess details of the potential energy profiles associated with the Norrish type-I and type-II reactions of a prototypical ketone 5-methyl-hexan-2-one. We show that the well-established 'triplet state mediated' reaction pathways following initial population of a singlet excited state can be complemented by (hitherto rarely recognized) 'singlet state only' Norrish type-I and type-II reaction mechanisms that involve no spin-forbidden transitions along the respective reaction paths, and suggest how the efficiencies of such reactions might be affected by strategic substitutions at selected sites within the parent ketone.

Origins of Photodamage in Pheomelanin Constituents: Photochemistry of 4-Hydroxybenzothiazole.

4-Hydroxybenzothiazole (4-HBT) is a molecular constituent of pheomelanin-a polymeric skin centered pigment which acts as a natural photoprotector against harmful solar-UV radiation. Its molecular structure is therefore required to sustain a degree of photostability upon electronic excitation with UV irradiation. Despite its function as a protector against UV, pheomelanin is known to be less photostable than that of its close derivative eumelanin-a dark skin centered pigment. The 4-HBT subunit has long being attributed as a key contributor to the lack of photostability of pheomelanin-a hypothesis which we aim to test in this paper. Using high-level multireference computational methods, coupled with on-the-fly surface-hopping molecular dynamics, we find excited state reaction paths that show potential detriment to 4-HBT, leading to phototoxic radicals and products that are distinct from the original ground state molecule. Such radicals and photoproducts include those formed by classic πσ* photodissociations, intramolecular proton-transfer, and ring-opening reactions. Such reactions shed light on the types of molecular structure that show photodetrimental effects upon UV irradiation, allowing judicious predictions for synthetic analogues that may offer enhanced photoprotection in commercial sunscreens.