Mutual Neutralization of NO

We have studied the mutual neutralization reaction of vibronically cold NO^{+} with O^{-} at a collision energy of ≈0.1 eV and under single-collision conditions. The reaction is completely dominated by production of three ground-state atomic fragments. We employ product-momentum analysis in the framework of a simple model, which assumes the anion acts only as an electron donor and the product neutral molecule acts as a free rotor, to conclude that the process occurs in a two-step mechanism via an intermediate Rydberg state of NO which subsequently fragments.

The mutual neutralization of hydronium and hydroxide.

Mutual neutralization of hydronium (H3O+) and hydroxide (OH-) ions is a very fundamental chemical reaction. Yet, there is only limited experimental evidence about the underlying reaction mechanisms. Here, we report three-dimensional imaging of coincident neutral products of mutual-neutralization reactions at low collision energies of cold and isolated ions in the cryogenic double electrostatic ion-beam storage ring (DESIREE). We identified predominant H2O + OH + H and 2OH + H2 product channels and attributed them to an electron-transfer mechanism, whereas a minor contribution of H2O + H2O with high internal excitation was attributed to proton transfer. The reported mechanism-resolved internal product excitation, as well as collision-energy and initial ion-temperature dependence, provide a benchmark for modeling charge-transfer mechanisms.

Cervical spine flexion-extension radiography versus magnetic resonance imaging in pediatric patients following blunt traumatic injury.

Background: In pediatric trauma patients, 60-80% of spinal cord injuries involve the cervical vertebrae. While the American College of Radiology offers guidelines for best imaging practices in the setting of acute pediatric trauma, there is a lack of uniformity in imaging-decision protocols across institutions. MRI has been shown to demonstrate high sensitivity for both bony and ligamentous injuries while also avoiding unnecessary radiation exposure in the pediatric patient population. However, the efficacy of flexion-extension (FE) radiography following initial MRI has not been evaluated in children. Our hypothesis is that FE radiography conducted following an initial MRI does not contribute significant diagnostic information or reduce time to cervical collar removal and thus can be removed from institutional protocols in order to avoid unnecessary testing and reduce pediatric radiation exposure. Methods: Trauma data were collected for pediatric patients presenting with suspected acute cervical spine injury from 2014 to 2021. A total of 108 patients were subdivided into 41 patients who received "MRI Only" and 67 patients who received both "MRI and FE" diagnostic cervical spine imaging. Chi-square testing and t-tests were performed to determine differences between MRI and FE radiographic detection rates of bony and ligamentous injuries in the subgroups. Results: In patients for whom FE did not find any injury, MRI detected bony and ligamentous injuries in 9/63 and 12/65 cases, respectively. In 3/21 (14.3%) cases in which MRI detected a bony and/or ligamentous injury and FE did not, patients eventually required surgical intervention for c-spine stabilization. No patients required surgical fixation when FE radiography showed an abnormality and MRI was normal. Addition of follow-up FE radiography after initial MRI did not have a significant effect on overall hospital length of stay (MRI Only vs MRI+FE: 9.2±12.0 days vs 8.6±13.5 days, p=0.816) or on rates of collar removal at discharge or greater than 48 hours after imaging (MRI Only vs MRI+FE: 41.5% vs 56.7%, p=0.124). Conclusions: FE radiography following initial MRI did not have a significant effect on reducing time to cervical collar removal or overall hospital length of stay. In addition, in 3 of 6 cases (50.0%) in which surgical fixation was required, MRI detected ligamentous and/or bony injury while FE radiography was normal. Level of Evidence: This study contributes Level 2b scientific evidence consistent with a well-designed cohort or case-control analytic study.

Clinical and radiographic predictors of the need for facial CT in pediatric blunt trauma: a multi-institutional study.

Background: Facial injuries are common in children with blunt trauma. Most are soft tissue lacerations and dental injuries readily apparent on clinical examination. Fractures requiring operative intervention are rare. Guidelines for utilization of maxillofacial CT in children are lacking. We hypothesized that head CT is a useful screening tool to identify children requiring dedicated facial CT. Methods: We conducted a multicenter retrospective review of children aged 18 years and under with blunt facial injury who underwent both CT of the face and head from 2014 through 2018 at five pediatric trauma centers. Penetrating injuries and animal bites were excluded. Imaging and physical examination findings as well as interventions for facial fracture were reviewed. Clinically significant fractures were those requiring an intervention during hospital stay or within 30 days of injury. Results: 322 children with facial fractures were identified. Head CT was able to identify a facial fracture in 89% (287 of 322) of children with facial fractures seen on dedicated facial CT. Minimally displaced nasal fractures, mandibular fractures, and dental injuries were the most common facial fractures not identified on head CT. Only 2% of the cohort (7 of 322) had facial injuries missed on head CT and required an intervention. All seven had mandibular or alveolar plate injuries with findings on physical examination suggestive of injury. Discussion: In pediatric blunt trauma, head CT is an excellent screening tool for facial fracture. In the absence of clinical evidence of a mandibular or dental injury, a normal head CT will usually exclude a clinically significant facial fracture. Level of evidence: III.

A localized view on molecular dissociation via electron-ion partial covariance.

Inner-shell photoelectron spectroscopy provides an element-specific probe of molecular structure, as core-electron binding energies are sensitive to the chemical environment. Short-wavelength femtosecond light sources, such as Free-Electron Lasers (FELs), even enable time-resolved site-specific investigations of molecular photochemistry. Here, we study the ultraviolet photodissociation of the prototypical chiral molecule 1-iodo-2-methylbutane, probed by extreme-ultraviolet (XUV) pulses from the Free-electron LASer in Hamburg (FLASH) through the ultrafast evolution of the iodine 4d binding energy. Methodologically, we employ electron-ion partial covariance imaging as a technique to isolate otherwise elusive features in a two-dimensional photoelectron spectrum arising from different photofragmentation pathways. The experimental and theoretical results for the time-resolved electron spectra of the 4d3/2 and 4d5/2 atomic and molecular levels that are disentangled by this method provide a key step towards studying structural and chemical changes from a specific spectator site.

Mutual neutralisation of O+ with O-: investigation of the role of metastable ions in a combined experimental and theoretical study.

The mutual neutralisation of O+ with O- has been studied in a double ion-beam storage ring with combined merged-beams, imaging and timing techniques. Branching ratios were measured at the collision energies of 55, 75 and 170 (± 15) meV, and found to be in good agreement with previous single-pass merged-beams experimental results at 7 meV collision energy. Several previously unidentified spectral features were found to correspond to mutual neutralisation channels of the first metastable state of the cation (O+(2Do), τ ≈ 3.6 hours), while no contributions from the second metastable state (O+(2Po), τ ≈ 5 seconds) were observed. Theoretical calculations were performed using the multi-channel Landau-Zener model combined with the anion centered asymptotic method, and gave good agreement with several experimentally observed channels, but could not describe well observed contributions from the O+(2Do) metastable state as well as channels involving the O(3s 5So) state.

Isolated Facet Joint Arthritis in Juvenile Idiopathic Arthritis.

Juvenile idiopathic arthritis (JIA) is a group of childhood inflammatory arthropathies which has variable clinical presentations and can affect multiple joints including the spine. Arthritis in facet joints is rare and very unusual to be the only presentation of JIA. We report a 16-year-old female who presented with back pain and stiffness, in which CT of the lumbar spine showed evidence of facet joint erosion and pelvis MRI showed facet joint arthritis consistent with juvenile idiopathic arthritis.

Acetabula Osteoid Osteoma Mimicking Juvenile Idiopathic Arthritis and Chronic Recurrent Multifocal Osteomyelitis.

Osteoid osteoma (OO) is a benign bone tumor that usually presents between 10 and 35 years of age. The metaphysis and diaphysis of the femur and tibia are the typical locations. The diagnosis is usually straightforward when images reveal a radiolucent nidus surrounded by reactive sclerosis. However, the diagnosis is more difficult when it occurs at atypical locations with nonspecific and misleading appearance on images. OO may mimic juvenile idiopathic arthritis (JIA), bone infection, or malignancy. We present a 14-year-old male with a 4-month history of left hip pain. His pain was worse with playing hockey and lacrosse and in the morning and sometimes woke him up at night. His examination was significant for pain with flexion and external rotation of the left hip and for mild limitation of full external rotation. Blood work revealed normal complete blood count, erythrocyte sedimentation rate, and C-reactive protein. Left hip X-ray was unremarkable. Left hip MR arthrogram showed marked edema of the medial and posterior walls of the left acetabulum. CT-guided biopsy of the left acetabulum showed unremarkable flow cytometry and chronic inflammatory component raising concern about chronic recurrent multifocal osteomyelitis (CRMO). Bone scan revealed focal increased uptake in the left acetabulum and no additional abnormality. Repeat MRI with intravenous contrast showed a left hip effusion, focal synovial enhancement in the medial left hip, and acetabula edema. The patient failed treatment for presumed JIA and CRMO with nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, methotrexate, and adalimumab. CT scan of the left hip was performed for further evaluation of the bone and showed 11 × 6 mm low attenuation focus with subtle internal nidus in the posteromedial aspect of the acetabular rim, suggestive of intra-articular OO. Radiofrequency ablation was performed with no complications, and the left hip pain improved. The atypical location resulted in delay of diagnosis for 12 months after presentation. We highlight the diagnostic pitfalls observed in atypical OO locations and the difficulties this creates with making the diagnosis. OO mimicking JIA has previously been described. We submit CRMO as another differential diagnosis which may be mimicked and demonstrate the vital role of CT scan in the diagnosis.

Photoionization Dynamics of the Tetraoxo Complexes OsO4 and RuO4.

The photoionization dynamics of OsO4 and RuO4, chosen as model systems of small-size mononuclear heavy-metal complexes, has been theoretically studied by the time-dependent density functional theory (TDDFT). Accurate experimental measurements of photoionization dynamics as a benchmarking test for the theory are reported for the photoelectron asymmetry parameters of outer valence ionizations of OsO4, measured in the 17-90 eV photon energy range. The theoretical results are in good agreement with the available experimental data. The observed dynamical behavior of partial cross sections and asymmetry parameters has been related to both the coupling to the continuum of discrete excited states, giving strong modulations in the photon energy dependency, and the atomic composition of the initial ionized states, which determines the rate of decay of ionization probability for increasing excitation energies. Overall, an extensive analysis of the photoionization dynamics for valence and core orbitals is presented, showing good agreement with all the available experimental data. This provides confidence for the validity of the TDDFT approach in describing photoionization of heavy transition element compounds, with the perspective of being used for larger systems. Further experimental work is suggested for RuO4 to gather evidence of the sensitivity of the theoretical method to the nature of the metal atom.

Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole.

The excited state relaxation pathways of isoxazole and oxazole upon excitation with UV-light were investigated by nonadiabatic ab initio dynamics simulations and time-resolved photoelectron spectroscopy. Excitation of the bright ππ*-state of isoxazole predominantly leads to ring-opening dynamics. Both the initially excited ππ*-state and the dissociative πσ*-state offer a combined barrier-free reaction pathway, such that ring-opening, defined as a distance of more than 2 Å between two neighboring atoms, occurs within 45 fs. For oxazole, in contrast, the excited state dynamics is about twice as slow (85 fs) and the quantum yield for ring-opening is lower. This is caused by a small barrier between the ππ*-state and the πσ*-state along the reaction path, which suppresses direct ring-opening. Theoretical findings are consistent with the measured time-resolved photoelectron spectra, confirming the timescales and the quantum yields for the ring-opening channel. The results indicate that a combination of time-resolved photoelectron spectroscopy and excited state dynamics simulations can explain the dominant reaction pathways for this class of molecules. As a general rule, we suggest that the antibonding σ*-orbital located between the oxygen atom and a neighboring atom of a five-membered heterocyclic system provides a driving force for ring-opening reactions, which is modified by the presence and position of additional nitrogen atoms.

Competition between ring-puckering and ring-opening excited state reactions exemplified on 5H-furan-2-one and derivatives.

The influence of ring-puckering on the light-induced ring-opening dynamics of heterocyclic compounds was studied on the sample 5-membered ring molecules γ-valerolactone and 5H-furan-2-one using time-resolved photoelectron spectroscopy and ab initio molecular dynamics simulations. In γ-valerolactone, ring-puckering is not a viable relaxation channel and the only available reaction pathway is ring-opening, which occurs within one vibrational period along the C-O bond. In 5H-furan-2-one, the C=C double bond in the ring allows for ring-puckering which slows down the ring-opening process by about 150 fs while only marginally reducing its quantum yield. This demonstrates that ring-puckering is an ultrafast process, which is directly accessible upon excitation and which spreads the excited state wave packet quickly enough to influence even the outcome of an otherwise expectedly direct ring-opening reaction.

Dissociation kinetics of excited ions: PEPICO measurements of Os3(CO)12 - The 7-35 eV single ionization binding energy region.

In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os3(CO)12, in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behavior was observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 ± 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 ± 0.4 eV, corresponding to one electron being ejected from the Os3 center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.

Dynamics in higher lying excited states: Valence to Rydberg transitions in the relaxation paths of pyrrole and methylated derivatives.

The involvement of intermediate Rydberg states in the relaxation dynamics of small organic molecules which, after excitation to the valence manifold, also return to the valence manifold is rarely observed. We report here that such a transiently populated Rydberg state may offer the possibility to modify the outcome of a photochemical reaction. In a time resolved photoelectron study on pyrrole and its methylated derivatives, N-methyl pyrrole and 2,5-dimethyl pyrrole, 6.2 eV photons (200 nm) are used to excite these molecules into a bright ππ* state. In each case, a π3p-Rydberg state, either the B1(π3py) or the A2(π3pz) state, is populated within 20-50 fs after excitation. The wavepacket then proceeds to the lower lying A2(πσ*) state within a further 20 fs, at which point two competing reaction channels can be accessed: prompt N-H (N-CH3) bond cleavage or return to the ground state via a conical intersection accessed after ring puckering, the latter of which is predicted to require an additional 100-160 fs depending on the molecule.

Chirally sensitive collision induced dissociation of proton-bound diastereomeric complexes of tryptophan and 2-butanol.

In this work we report the stereo-dependent collision-induced dissociation (CID) of proton-bound complexes of tryptophan and 2-butanol. The dissociation efficiency was measured as a function of collision energy in single collision mode. The homochiral complex was found to be less stable against CID than a heterochiral one. Additional gas dependence measurements were performed with diastereomeric complexes that confirm the findings.

Substituent effects on the relaxation dynamics of furan, furfural and ß-furfural: a combined theoretical and experimental approach.

For the series furan, furfural and ß-furfural we investigated the effect of substituents and their positioning on the photoinduced relaxation dynamics in a combined theoretical and experimental approach. Using time resolved photoelectron spectroscopy with a high intensity probe pulse, we can, for the first time, follow the whole deactivation process of furan through a two photon probe signal. Using the extended 2-electron 2-orbital model [Nenov et al., J. Chem. Phys., 2011, 135, 034304] we explain the formation of one central conical intersection and predict the influence of the aldehyde group of the derivatives on its geometry. This, as well as the relaxation mechanisms from photoexcitation to the final outcome was investigated using a variety of theoretical methods. Complete active space self consistent field was used for on-the-fly calculations while complete active space perturbation theory and coupled cluster theory were used to accurately describe critical configurations. Experiment and theory show the relaxation dynamics of furfural and ß-furfural to be slowed down, and together they disclose an additional deactivation pathway, which is attributed to the nO lonepair state introduced with the aldehyde group.

Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study.

We have reinvestigated the excited state dynamics of cyclohexa-1,3-diene (CHD) with time-resolved photoelectron spectroscopy and fewest switches surface hopping molecular dynamics based on linear response time-dependent density functional theory after excitation to the lowest lying ππ* (1B) state. The combination of both theory and experiment revealed several new results: First, the dynamics progress on one single excited state surface. After an incubation time of 35 ± 10 fs on the excited state, the dynamics proceed to the ground state in an additional 60 ± 10 fs, either via a conrotatory ring-opening to hexatriene or back to the CHD ground state. Moreover, ring-opening predominantly occurs when the wavepacket crosses the region of strong nonadiabatic coupling with a positive velocity in the bond alternation coordinate. After 100 fs, trajectories remaining in the excited state must return to the CHD ground state. This extra time delay induces a revival of the photoelectron signal and is an experimental confirmation of the previously formulated model of two parallel reaction channels with distinct time constants. Finally, our simulations suggest that after the initially formed cis-Z-cis HT rotamer the trans-Z-trans isomer is formed, before the thermodynamical equilibrium of three possible rotamers is reached after 1 ps.

Successful treatment of IgG-4 related sclerosing disease with rituximab: a novel case report.

IgG4-related sclerosing disease (IgG4-RSD) is a rare inflammatory disease that can affect multi organs. We describe a paediatric patient with ocular, nerve, and renal involvement successfully treated twice with corticosteroids and rituximab.

Experimental studies of H13CO+ recombining with electrons at energies between 2-50,000 meV.

An investigation into the dissociative recombination process for H(13)CO(+) using merged ion-electron beam methods has been performed at the heavy ion storage ring CRYRING, Stockholm, Sweden. We have measured the branching fractions of the different product channels at ∼ 0 eV collision energy to be the following: CO + H 87 ± 2%, OH + C 9 ± 2%, and O + CH 4 ± 2%. The formation of electronically excited CO in the dominant reaction channel has also been studied, and we report the following tentative branching fractions for the different CO product electronic states: CO(X (1)Σ(+)) + H, 54 ± 10%; CO(a (3)Π) + H, 23 ± 4%; and CO(a' (3)Σ(+)) + H, 23 ± 4%. The absolute cross section between ∼ 2-50 000 meV was measured and showed resonance structures between 3 and 15 eV. The cross section was fitted in the energy range relevant to astrophysics, i.e., between 1 and 300 meV, and was found to follow the expression σ = 1.3 ± 0.3 × 10(-16) E(-1.29 ± 0.05) cm(2) and the corresponding thermal rate constant was determined to be k(T) = 2.0 ± 0.4 × 10(-7)(T/300)(-0.79 ± 0.05) cm(3) s(-1). Radioastronomical observations with the IRAM 30 m telescope of HCO(+) toward the Red Rectangle yielded an upper column density limit of 4 × 10(11) cm(-2) of HCO(+) at the 1σ level in that object, indicating that previous claims that the dissociative recombination of HCO(+) plays an important role in the production of excited CO molecules emitting the observed Cameron bands in that object are not supported.

Dissociative recombination of CH4(+).

CH4(+) is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres. However, the rate of one of the common destruction mechanisms for molecular ions in these regions, dissociative recombination (DR), is somewhat uncertain. Here, we present absolute measurements for the DR of CH4(+) made using the heavy ion storage ring CRYRING in Stockholm, Sweden. From our collision-energy dependent cross-sections, we infer a thermal rate constant of k(Te) = 1.71(±0.02) × 10(­6)(Te/300)(−0.66(±0.02)) cm3 s(­1) over the region of electron temperatures 10 ≤ Te ≤ 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH4 (0.00 ± 0.00); CH3 + H (0.18 ± 0.03); CH2 + 2H (0.51 ± 0.03); CH2 + H2 (0.06 ± 0.01); CH + H2 + H (0.23 ± 0.01); and CH + 2H2 (0.02 ± 0.01), indicating that two or more C­H bonds are broken in 80% of all collisions.