Direct Experimental Observation of the Tetrabromine Cluster Br4 by Synchrotron Photoionization Mass Spectrometry.

We present a first spectroscopic characterization of the homoatomic polyhalogen tetrabromine, Br4 , in the gas phase. Photolysis of CHBr3 at 248 nm is used to generate atomic bromine radicals in a flow tube reactor. Resulting combination products are detected by photoionization mass spectrometry at the Advanced Light Source of the Lawrence Berkeley National Laboratory. Interpretation of the experimental mass spectra is informed by calculated adiabatic ionization energies carried out at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ//cam-B3LYP/6-311++g** levels of theory. Tunable VUV synchrotron radiation enables the collection of the mass-selected photoionization spectra by which Br4 is assigned using Franck-Condon simulations of a Br2 dimer with a stretched tetrahedral geometry.

Absolute Photoionization Cross Section and Dissociative Ionization Pathways of Alpha-Pinene.

The absolute photoionization cross section of the monoterpenoid, alpha-pinene (AP), is presented together with the relative photoionization cross sections of its dissociative fragments for the first time. Experiments are performed via multiplexed vacuum ultraviolet (VUV) synchrotron photoionization (PI) mass spectrometry in the 8.0-11.0 eV energy range. Experimental work is conducted at the Advanced Light Source of the Lawrence Berkeley National Laboratory. Dissociative fragments were identified at m/z 121, 94, 93, 92, and 80. The photoionization cross section for the parent mass at 11.0 eV was determined to be 17±4 Mb with a total ionization cross section of 92±23 Mb at the same photon energy. Experimental appearance energies of dissociative ionization fragments and potential dissociative ionization pathways calculated at the G4 level of theory are presented as well.

Estimate of the C-Cl photoionization cross section and absolute photoionization cross sections of chlorinated organic compounds.

Chlorinated organic compounds are prominently used for industrial production, but their vapors and emission byproducts can cause detrimental effects to human health and the environment. To accurately quantify organochlorine compounds, the absolute photoionization cross section of tetrachloroethylene, chlorobenzene, 1,2-dichlorobenzene, and chloroacetone are measured using multiplexed synchrotron photoionization mass spectrometry at the Advanced Light Source at Lawrence Berkeley National Laboratory. These measurements allow for the estimation of the C-Cl photoionization cross section, increasing quantification accuracy of chlorinated emissions for kinetic modeling and pollutant mitigation. CBS-QB3 calculations of adiabatic ionization energies and thermochemical appearance energies are also presented and agree well with the experimental results.

Correction: Theoretical and experimental study on the O(3P) + 2,5-dimethylfuran reaction in the gas phase.

Correction for 'Theoretical and experimental study on the O(3P) + 2,5-dimethylfuran reaction in the gas phase' by Andrea Giustini et al., Phys. Chem. Chem. Phys., 2021, 23, 19424-19434, DOI: 10.1039/D1CP01724A.

Photoionization of Two Potential Biofuel Additives: γ-Valerolactone and Methyl Butyrate.

The photoionization of two potential biofuel additives, γ-valerolactone (GVL, C5H8O2) and methyl butyrate (MB, C5H10O2) has been studied by imaging photoelectron photoion coincidence spectroscopy (iPEPICO) at the VUV beamline of the Swiss Light Source (SLS). The vibrational fine structure in the photoelectron spectrum is compared with a Franck-Condon simulation for the electronic ground-state band of the GVL cation. In the lowest energy dissociative photoionization channel of GVL, CO2 is lost, resulting in a 1-butene fragment ion with a 0 K appearance energy of E0 = 10.35 ± 0.01 eV. A newly calculated 1-butene ionization energy of 9.595 ± 0.015 eV establishes the reverse barrier height to CO2 loss as 66.6 ± 4.3 kJ mol-1. Methyl butyrate cations undergo McLafferty rearrangement, which explains the missing ion signal at the computed adiabatic ionization energy of 9.25 eV. After H transfer, ethylene is lost in the lowest energy dissociation channel to yield the methyl acetate enol ion at E0 = 10.24 ± 0.04 eV. This value connects the energetics of methyl butyrate with that of methyl acetate enol ion, which is established at ΔfHo0K[CH2C(OH)OCH3+] = 502 ± 6 kJ mol-1. Parallel to ethylene loss, methyl loss is also observed from the enol tautomer of the parent ion. Both samples exhibit low-energy nonstatistical dissociative ionization channels. In GVL, the methyl-loss abundance rises quickly but levels off suddenly in the energy range of the first electronically excited states, indicating nonstatistical competition between CH3 and CO2 loss. In MB, the major parallel dissociation channel is the loss of a methoxy radical. Calculations indicate that McLafferty rearrangement is inhibited on the excited-state surface. Indeed, breakdown curve modeling of this and a sequential CO-loss channel confirms a second statistical regime in dissociative photoionization, decoupled from ethylene loss.

CO2 Activation Within a Superalkali-Doped Fullerene.

With the aim of finding a suitable synthesizable superalkali species, using the B3LYP/6-31G* density functional level of theory we provide results for the interaction between the buckminsterfullerene C60 and the superalkali Li3F2. We show that this endofullerene is stable and provides a closed environment in which the superalkali can exist and interact with CO2. It is worthwhile to mention that the optimized Li3F2 structure inside C60 is not the most stable C2v isomer found for the "free" superalkali but the D3h geometry. The binding energy at 0 K between C60 and Li3F2 (D3h) is computed to be 119 kJ mol-1. Once CO2 is introduced in the endofullerene, it is activated, and the O C O ^ angle is bent to 132°. This activation does not follow the previously studied CO2 reduction by an electron transfer process from the superalkali, but it is rather an actual reaction where a F (from Li3F2) atom is bonded to the CO2. From a thermodynamic analysis, both CO2 and the encapsulated [Li3F2⋅CO2] are destabilized in C60 with solvation energies at 0 K of 147 and < -965 kJ mol-1, respectively.

Theoretical and experimental study on the O(3P) + 2,5-dimethylfuran reaction in the gas phase.

In this work we report a joint experimental and computational study on the 2,5-dimethylfuran oxidation reaction in the gas phase initiated by atomic oxygen O(3P). The experiments have been performed by using vacuum-ultraviolet synchrotron radiation at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory (LBNL), at a temperature of 550 K and a pressure of 8 Torr. The experimental data were supported by quantum-chemical calculations along with a kinetic model, also taking into account the possible involvement of different magnetic states, performed in the framework of the RRKM theory. Propyne, acetaldehyde, methylglyoxal, dimethylglyoxal, 3-penten-2-one, 2,5-dimethylfuran-3(2H)-one, and 1,2-diacetyl ethylene have been identified as the main primary products arising under the conditions of the experiment. Our computational model suggests that these species can be formed at the concentration and branching ratio experimentally observed only in the presence of a non-negligible fraction of non-thermalized intermediates.

Study of the Synchrotron Photoionization Oxidation of Alpha-Angelica Lactone (AAL) Initiated by O(3P) at 298, 550, and 700 K.

In recent years, biofuels have been receiving significant attention because of their potential for decreasing carbon emissions and providing a long-term renewable solution to unsustainable fossil fuels. Currently, lactones are some of the alternatives being produced. Many lactones occur in a range of natural substances and have many advantages over bioethanol. In this study, the oxidation of alpha-angelica lactone initiated by ground-state atomic oxygen, O(3P), was studied at 298, 550, and 700 K using synchrotron radiation coupled with multiplexed photoionization mass spectrometry at the Lawrence Berkeley National Lab (LBNL). Photoionization spectra and kinetic time traces were measured to identify the primary products. Ketene, acetaldehyde, methyl vinyl ketone, methylglyoxal, dimethyl glyoxal, and 5-methyl-2,4-furandione were characterized as major reaction products, with ketene being the most abundant at all three temperatures. Possible reaction pathways for the formation of the observed primary products were computed using the CBS-QB3 composite method.

Exploring the variability of radiomic features of lung cancer lesions on unenhanced and contrast-enhanced chest CT imaging.

PURPOSE: The aim of this methods work is to explore the different behavior of radiomic features resulting by using or not the contrast medium in chest CT imaging of non-small cell lung cancer. METHODS: Chest CT scans, unenhanced and contrast-enhanced, of 17 patients were selected from images collected as part of the staging process. The major T1-T3 lesion was contoured through a semi-automatic approach. These lesions formed the lesion phantoms to study features behavior. The stability of 94 features of the 3D-Slicer package Radiomics was analyzed. Feature discrimination power was quantified by means of Gini's coefficient. Correlation between distance matrices was evaluated through Mantel statistic. Heatmap, cluster and silhouette plots were applied to find well-structured partitions of lesions. RESULTS: The Gini's coefficient evidenced a low discrimination power, <0.05, for four features and a large discrimination power, around 0.8, for five features. About 90% of features was affected by the contrast medium, masking tumor lesions variability; thirteen features only were found stable. On 8178 combinations of stable features, only one group of four features produced the same partition of lesions with the silhouette width greater than 0.51, both on unenhanced and contrast-enhanced images. CONCLUSIONS: Gini's coefficient highlighted the features discrimination power in both CT series. Many features were sensitive to the use of the contrast medium, masking the lesions intrinsic variability. Four stable features produced, on both series, the same partition of cancer lesions with reasonable structure; this may merit being objects of further validation studies and interpretative investigations.

Synchrotron Photoionization Study of the Diisopropyl Ether Oxidation.

Scientific evidence has shown oxygenates help to reduce dangerous pollutants arising from burning fossil fuel in the automotive sector. For this reason, their use as additives has spread widely. The aim of this work consists in providing a comprehensive identification of the main primary oxidation products of diisopropyl ether (DIPE), one of the most promising among etheric oxygenates. The Cl-initiated oxidation of DIPE is examinated by using a vacuum ultraviolet (VUV) synchrotron radiation at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory (LBNL). Products are identified on the basis of their mass-to-charge ratio, shape of photoionization spectra, adiabatic ionization energies, and chemical kinetic profiles, at three different temperatures (298, 550, and 650 K). Acetone, propanal, propene, and isopropyl acetate have been identified as major reaction products. Acetone is the main primary product. Theoretical calculations using the composite CBS-QB3 method provided useful tools to validate the postulated reaction mechanisms leading to experimentally observed species. The formation of other species is also discussed.

Reducing Properties of Superalkalis on Pyridinic Graphene Surfaces: a Computational Study.

The hyperlithiated species Li k + 1 F k (k=1, 2, 3, and 4) have been studied by quantum mechanical (QM) methods. Different structures have been localized for each molecule by the CBS-QB3 composite method: all the isomers show superalkali properties and strong tendency to donate an electron to carbon dioxide forming stable Li k + 1 F k · · · CO 2 complexes. With the aim to find molecular systems able to stabilize superalkalis, geometries of complexes between superalkalis and pyridine and superalkalis and graphene surfaces doped with a pyridinic vacancy were calculated. The pyridinic graphene sheets were modeled with two finite molecular systems C69 H21 N3 and C117 H27 N3 . The interaction with one pyridine molecule is quite weak and the superalkali maintains its structure and electron properties. The affinity for graphene sheets is instead stronger and the superalkalis tend to deform their geometry to better interact with the graphene surface. However, the superalkalis continue to show the tendency to transfer electrons to carbon dioxide reducing CO2 , as found in graphene absence.

Prostate cancer dose-response, fractionation sensitivity and repopulation parameters evaluation from 25 international radiotherapy outcome data sets.

OBJECTIVE: This study was undertaken to model the biochemical free survival at 5 years and to evaluate the parameters defining dose-response curve, dose-fractionation radiosensitivity and repopulation. METHODS: It was carried out a literature search on Pubmed to retrieve data sets of patients treated with external beam radiation therapy of 1.8-4.0 Gy per fraction and overall treatment time of 3 to 10 weeks. 10 groups were identified, based on risk class and androgen deprivation therapy (ADT). Dose-response curve D50 (dose at 50% probability of control) and g50 (steepness), α/ß (dose-fractionation radiosensitivity), and repopulation parameters, dprolif and Tprolif , were calculated. Bootstrap-based cross-validation was performed and median and 95% CI (confidence interval) were evaluated. RESULTS: 25 data sets, including 20,310 patients, were considered. The median (95% CI) D50 and g50 values were 62 (CI 53 - 66) Gy and 1.6 (0.8 - 2.4). ADT patients showed lower values of D50 and g50 (57 ± 5 Gy and 1.1 ± 0.4) compared to no-ADT patients (65 ± 2 Gy and 2.3 ± 0.6), with p < 0.0001 and p = 0.002. If we did not consider any dependence on overall treatment time, the median (95% CI) value of α/ß was 1.4 (1.0 - 1.9) Gy with p < 0.0001 for all patients. The median values of dproli f and Tprolif were 0.0 to 0.3 Gy/d and 18-40 days. CONCLUSION: Dose-response curve resulted dependent on risk class and ADT, with higher steepness for no-ADT patients. Low values of dose-fractionation radiosensitivity were found, supporting the use of moderate hypofractionated radiotherapy in each risk class. A limited dependence on repopulation was observed. ADVANCES IN KNOWLEDGE: Prostate cancer response to moderate hypofractionated radiotherapy was reliably quantified considering risk class and androgen deprivation therapy.

Peroxy self-reaction leading to the formation of furfural.

Interest in alternative fuels to petroleum and classical fuels has been growing very rapidly in recent years. Furan and its alkyl derivatives, such as methylfuran (2MF), have been identified as valid alternative biofuels. This study focuses on the self-reaction of the peroxy radical generated in the first oxidation step of 2MF, initiated by Cl atoms at 323 K and 4 Torr. The experiments have been carried out by a multiplexed synchrotron photoionization mass spectrometer (mSPIMS) at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory (USA). The presence of a peak at m/z = 96 reveals that furfural is the dominant product of 2MF oxidation. Various reaction mechanisms for furfural formation are proposed here. The potential energy surfaces for singlet and triplet spin states have been mapped using quantum mechanical methods, such as CCSD(T), DFT-B3LYP, and composites models (CBS-QB3), to optimize the products, transition states, and intermediates. Experimental and theoretical results provide evidence that furfural does not form by primary reaction chemistry. Self-reaction of the peroxy radical generated in the first oxidation step of 2MF has been proposed as the pathway leading to the formation of furfural. Among various reaction channels, we indentified some entirely exothermic pathways involving oxygen-oxygen coupling and the formation of ROOOOR Russell intermediates.

Computational investigation of LiF containing hypersalts.

This study explores the design of possible hypersalts starting from the hyperhalogen Li3F4 plus a Li atom and the hyperalkali Li4F3 plus a F atom. The investigation uses a multistep composite computational job that follows the same setup of the CBS-QB3 method, and uses B3LYP in combination with the CBSB7 + basis set for geometry optimizations. Adiabatic ionization energies (AIE), adiabatic electron affinities (AEA), HOMO-LUMO energy gaps, and NBO's are calculated for each presented species. Results confirm that the newly constructed hyperalkalis Li4F3, which has two isomers A and B, result in even lower AIE (3.83 eV and 3.65 eV for hyperalkali A and B, respectively) than the starting superalkali Li2F. The study also confirms the structures for the designed hyperhalogens Li3F4 (two isomers A and B) with higher AEA (7.70 eV and 5.63 eV for hyperhalogen A and B, respectively) than the superhalogen LiF2 building block. Hyperhalogens A and B in combination with a Li atom and hyperalkali A and B in combination with a F atom are used to create hypersalts. This yields three possible hypersalts A, B(C), and D with the formula Li4F4. Hypersalt A has the larger binding energy for dissociation into neutral fragments equal to 7.82 eV. Hypersalt C has the lower binding energy for dissociation into neutrals of 7.17 eV and hypersalt D the larger binding energy for dissociation into ions.

Investigation of Oxidation Reaction Products of 2-Phenylethanol Using Synchrotron Photoionization.

A photolytically Cl-initiated oxidation reaction of 2-phenylethanol (2PE) was carried out at the Advanced Light Source (ALS) in the Lawrence Berkeley National Laboratory. Using the multiplex photoionization mass spectrometer, coupled with the tunable vacuum ultraviolet radiation of the ALS, data were collected at low pressure (4-6 Torr) and temperature (298-550 K) regimes. Data analysis was performed via characterization of the reaction species photoionization spectra and kinetic traces. Products and reaction pathways are also computed using the CBS-QB3 composite method. The present results suggest primary products m/ z = 30 (formaldehyde), 106 (benzaldehyde), and 120 (phenylacetaldehyde) at 298 K, and m/ z = 120 (phenylacetaldehyde) at 550 K. Branching fractions at room temperature are 27 ± 6.5% for formaldehyde, 24 ± 4.5% for benzaldehyde, and 25 ± 5.8% for phenylacetaldehyde and 60 ± 14% for phenylacetaldehyde at 550 K.

Study of Methylidyne Radical (CH and CD) Reaction with 2,5-Dimethylfuran Using Multiplexed Synchrotron Photoionization Mass Spectrometry.

At 298 K the reactions of 2,5-dimethlyfuran + CH(X2Π) and + CD radicals were investigated using synchrotron radiation coupled with multiplexed photoionization mass spectrometry at the Lawrence Berkeley National Laboratory. Reaction products were characterized based on their photoionization spectra and kinetic time traces. The CBS-QB3 level of theory was used for all energy calculations, and potential energy surface scans were used to determine thermodynamically favorable reaction mechanisms. The two entrance pathways observed in the reactions are CH insertion within the C-O bond and CH addition to the π-bond system. Both yield initial 6-membered ring radical intermediates. Primary products from the CH addition pathway were observed at m/ z = 108, 66, and 42. The two C7H8O isomers at m/ z = 108 formed are 1,2,4-heptatrien-6-one and 3-hepten-5-yne-2-one. At m/ z = 66, the three C5H6 isomers observed are 1,3-cyclopentadiene, 3-penten-1-yne (E), and 1-pent-4-yne. Ketene ( m/ z = 42) is also observed. From CH insertion entrance channel, the three C6H8 isomers produced are 1,2,4-hexatriene (Z), 2-hexen-4-yne (E), and 1,3,4-hexatriene. Patterns of H-loss, CHO-loss, and CO-loss observed were also in agreement with trends observed in other similar studies. H-assisted isomerization pathways have been considered as well for the formation of m/ z = 66, 80, and 108 isomers.

Capturing Volatile Organic Compounds Employing Superalkali Species.

In this study, the interactions between the superalkali species Li3 F2 and four volatile organic compounds (VOCs), methanol, ethanol, formaldehyde, and acetaldehyde, are assessed using the CBS-QB3 composite model. Adiabatic ionization energy (AIE), adiabatic electron affinity (AEA), binding energy (BE), charge transfer (▵q), and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gaps have been computed. Stronger interactions are observed between Li3 F2 and the aldehydes than alcohols. The smaller aldehydes show a larger BE with Li3 F2 than the bigger aldehydes. However, alcohol clusters do not show this trend due to their weak interactions (low BEs). Both alcohol clusters increase their binding energies as they become cations. This unexpected behavior is explained based on molecular orbital arguments.

Study of low temperature chlorine atom initiated oxidation of methyl and ethyl butyrate using synchrotron photoionization TOF-mass spectrometry.

The initial oxidation products of methyl butyrate (MB) and ethyl butyrate (EB) are studied using a time- and energy-resolved photoionization mass spectrometer. Reactions are initiated with Cl˙ radicals in an excess of oxygen at a temperature of 550 K and a pressure of 6 Torr. Ethyl crotonate is the sole isomeric product that is observed from concerted HO2-elimination from initial alkylperoxy radicals formed in the oxidation of EB. Analysis of the potential energy surface of each possible alkylperoxy radical shows that the CH3CH(OO)CH2C([double bond, length as m-dash]O)OCH2CH3 (RγO2) and CH3CH2CH(OO)C([double bond, length as m-dash]O)OCH2CH3 (RßO2) radicals are the isomers that could undergo this concerted HO2-elimination. Two lower-mass products (formaldehyde and acetaldehyde) are observed in both methyl and ethyl butyrate reactions. Secondary reactions of alkylperoxy radicals with HO2 radicals can decompose into the aforementioned products and smaller radicals. These pathways are the likely explanation for the formation of formaldehyde and acetaldehyde.

Synchrotron Photoionization Study of Furan and 2-Methylfuran Reactions with Methylidyne Radical (CH) at 298 K.

The reactions of furan and 2-methylfuran with methylidyne CH (X2Π) radical were investigated at 298 K using synchrotron radiation produced at the Advanced Light Source of the Lawrence Berkeley National Laboratory. Reaction products were observed by multiplexed photoionization mass spectrometry and characterized based on their photoionization spectra and kinetic time traces. Primary products observed in furan + CH are 2,4-cyclopentadien-1-one (m/z = 80), 2-penten-4-ynal (m/z = 80), and vinylacetylene (m/z = 52). From 2-methylfuran + CH, 2-4-cyclopentadien-1-carbaldehyde (m/z = 94), 2,3,4-hexatrienal (m/z = 94), 1,3 cyclopentadiene (m/z = 66), 3-penten-1-yne (Z) (m/z = 66), and vinylacetylene (m/z = 52) are the primary products observed. Using potential energy surface scans, thermodynamically favorable reaction pathways are proposed. CH addition to the π-bonds in furan and 2-methylfuran rings was found to be the entrance channel that led to formation of all identified primary products. Both reactions follow patterns of H loss and CHO loss, as well as formation of cyclic and acyclic isomers.

Activation of Dinitrogen with a Superalkali Species, Li3 F2.

The capability of the superalkali Li3 F2 to activate dinitrogen (N2 ) is presented. The (Li3 F2 )nN2 clusters (n=1-6) were investigated first at the MP2/6-311+G(3d2f,2df,2p)//B3LYP/6-311G(2d,d,p) level of theory. Clusters up to n=4 were also optimized through the CBS-QB3 composite model. The complete dissociation of N2 was confirmed through visualized molecular orbitals and bond order calculation. The N-N bond is weakened by the addition of Li3 F2 superalkali units. The enthalpy of atomization ΔatH0∘ and formation (ΔfH0∘ ), charge flows (Δq), binding energies, and the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are calculated to help explain the N2 activation.