Chemical reaction thresholds according to classical-limit quantum dynamics.

Classical-limit quantum dynamics is used to explain the origin of the quantum thresholds of chemical reactions from their classical dynamics when these are vibrationally nonadiabatic across the interaction region. This study is performed within the framework of an elementary model of chemical reaction that mimics the passage from the free rotation of the reagents to the bending vibration at the transition state to the free rotation of the products.

From mothership to drip-and-ship: Effects of staff shortages at a comprehensive stroke center.

BACKGROUND: Mechanical thrombectomy (MT) has been shown to be effective in the acute phase of ischemic stroke. Current data suggests that the drip-and-ship and mothership telestroke models are equally effective for its administration. We describe the consequences of changing the telestroke model due to staff shortages in a comprehensive stroke center (Besançon), which was replaced by a more distant one (Dijon). METHODS: We conducted a retrospective analysis of all patients referred for MT from January 2015 to December 2018. We analyzed the time between symptom onset and arrival in the angiography suite. We also calculated number of thrombectomies divided by number of days on call, and rate of thrombectomies relative to the number of strokes in each group. RESULTS: In Besançon, 205 patients underwent an MT procedure, versus 43 patients in Dijon. A further four patients were transferred to Dijon but not treated. The time from symptom onset to arrival in the angiography suite was longer for Dijon; 334min versus 281min for Besançon (p<0.001). The percentage of thrombectomies performed per day on call was higher for Besançon: 18.6% versus 13.2% in Dijon (p=0.026). CONCLUSIONS: Over the study period, the time from symptom onset to angiography suite was longer for patients who were transferred to Dijon. The period in which the Besançon hospital experienced the greatest lack of personnel corresponded to a decrease in the number of MTs performed.

Statistical properties of quantum probability fluctuations in complex-forming chemical reactions.

The energy dependence of quantum complex-forming reaction probabilities is well known to involve sharp fluctuations, but little seems to be known about their amplitudes. We develop here, for triatomic reactions, an analytical approach of their statistical distribution. This approach shows that the fluctuation amplitudes depend essentially on the number of available quantum states in the reagent and product channels. Moreover, the more numerous the product states, the more efficiently the fluctuations of their populations compensate each other when they add up to give the reaction probability. The predictions of our approach appear to be in good quantitative agreement with quantum scattering calculations for the prototypical reaction H+ + H2.

Theoretical Study of Barrierless Chemical Reactions Involving Nearly Elastic Rebound: The Case of S(1D) + X2, X = H, D.

For some values of the total angular momentum consistent with reaction, the title processes involve nonreactive trajectories proceeding through a single rebound mechanism during which the internal motion of the reagent diatom is nearly unperturbed. When such paths are in a significant amount, the classical reaction probability is found to be markedly lower than the quantum mechanical one. This finding was recently attributed to an unusual quantum effect called diffraction-mediated trapping, and a semiclassical correction was proposed in order to take into account this effect in the classical trajectory method. In the present work, we apply the resulting approach to the calculation of opacity functions as well as total and state-resolved integral cross sections (ICSs) and compare the values obtained with exact quantum ones, most of which are new. As the title reactions proceed through a deep insertion well, mean potential statistical calculations are also presented. Seven values of the collision energy, ranging from 30 to 1127 K, are considered. Two remarkable facts stand out: (i) The corrected classical treatment strongly improves the accuracy of the opacity function as compared to the usual classical treatment. When the entrance transition state is tight, however, those trajectories crossing it with a bending vibrational energy below the zero point energy must be discarded. (ii) The quantum opacity function, particularly its cutoff, is finely reproduced by the statistical approach. Consequently, the total ICS is also very well described by the two previous approximate methods. These, however, do not predict state-resolved ICSs with the same accuracy, proving thereby that (i) one or several genuine quantum effects involved in the dynamics are missed by the corrected classical treatment and (ii) the dynamics are not fully statistical.

Adult moyamoya angiopathy in Bourgogne-Franche-Comté: Epidemiology, diagnosis and management.

INTRODUCTION: Moyamoya angiopathy (MMA) is a progressive steno-occlusive disease of the distal internal carotid arteries mainly described in Asia. It induces the development of collateral vascular networks to reduce chronic cerebral hypoperfusion. Symptoms depend on the patient's age in Asia: children are at greater risk of transient or constituted ischemic events, whereas adults are more exposed to hemorrhagic stroke. Data from the literature seem to show that the pattern of MMA in western countries differs from that in Asia. MATERIAL AND METHODS: A retrospective study of patients with MMA was conducted in Bourgogne-Franche-Comté (mid-eastern France). Clinical data (symptoms, risk factors, age at diagnosis, number and timing of recurrences, type of treatment) as well as radiological data (angiographic findings, Suzuki's grade) were analyzed. RESULTS: Seventeen adult patients (9 men, 53%) were followed at the university hospitals of Besançon and Dijon from 2009 to 2016. Fourteen patients (83%) had bilateral disease. The mean age at diagnosis was 49 years (±16), 83% of the patients were Caucasian and 17% originated from Maghreb. Only 17% of the hemispheres had a hemorrhagic form. Ischemic form was more frequent before diagnosis with transient ischemic attack (24% of patients) and stroke (83% of patients). With medical treatment, 9 patients suffered from stroke recurrence (53% of patients) with an average delay of 22.7±34 months. Three patients (18%) had combined surgical management by encephelo-synangiosis and superficial temporal artery-to-middle cerebral artery (STA-MCA) anastomosis, without symptom recurrence after treatment with an average follow up of 14 months. CONCLUSION: MMA remains a rare cerebrovascular disease in Europe and requires multidisciplinary care. Epidemiological analysis showed differences with the Asian population, especially the predominance of ischemic forms in adults.

Semiclassical initial value theory of rotationally inelastic scattering: Some remarks on the phase index in the interaction picture.

This paper deals with the treatment of quantum interferences in the semiclassical initial value theory of rotationally inelastic scattering in the interaction picture. Like many semiclassical methods, the previous approach involves a phase index related to sign changes of a Jacobian whose square root is involved in the calculations. It is shown that replacing the original phase index by a new one extends the range of applicability of the theory. The resulting predictions are in close agreement with exact quantum scattering results for a model of atom-rigid diatom collision involving strong interferences. The developments are performed within the framework of the planar rotor model, but are readily applicable to three-dimensional collisions.

Semiclassical Wigner theory of photodissociation in three dimensions: Shedding light on its basis.

The semiclassical Wigner theory (SCWT) of photodissociation dynamics, initially proposed by Brown and Heller [J. Chem. Phys. 75, 186 (1981)] in order to describe state distributions in the products of direct collinear photodissociations, was recently extended to realistic three-dimensional triatomic processes of the same type [Arbelo-González et al., Phys. Chem. Chem. Phys. 15, 9994 (2013)]. The resulting approach, which takes into account rotational motions in addition to vibrational and translational ones, was applied to a triatomic-like model of methyl iodide photodissociation and its predictions were found to be in nearly quantitative agreement with rigorous quantum results, but at a much lower computational cost, making thereby SCWT a potential tool for the study of polyatomic reaction dynamics. Here, we analyse the main reasons for this agreement by means of an elementary model of fragmentation explicitly dealing with the rotational motion only. We show that our formulation of SCWT makes it a semiclassical approximation to an approximate planar quantum treatment of the dynamics, both of sufficient quality for the whole treatment to be satisfying.

New insights into the semiclassical Wigner treatment of photodissociation dynamics.

The semiclassical Wigner treatment of Brown and Heller [J. Chem. Phys. 1981, 75, 186] is applied to direct triatomic (or triatomic-like polyatomic) photodissociations with the aim of accurately predicting final state distributions at relatively low computational cost, and having available a powerful interpretative tool. For the first time, the treatment takes rotational motions into account. The proposed formulation closely parallels the quantum description as far as possible. An approximate version is proposed, which is still accurate while numerically much more efficient. In addition to being weighted by usual vibrational Wigner distributions, final phase space states appear to be weighted by new rotational Wigner distributions. These densities have remarkable structures clearly showing that classical trajectories most contributing to rotational state j are those reaching the products with a rotational angular momentum close to [j(j + 1)](1/2) (in ℏ units). The previous methods involve running trajectories from the reagent molecule onto the products. The alternative backward approach [L. Bonnet, J. Chem. Phys., 2010, 133, 174108], in which trajectories are run in the reverse direction, is shown to strongly improve the numerical efficiency of the most rigorous method in addition to being state-selective, and thus, ideally suited to the description of state-correlated distributions measured in velocity imaging experiments. The results obtained by means of the previous methods are compared with rigorous quantum results in the case of Guo's triatomic-like model of methyl iodide photodissociation [J. Chem. Phys., 1992, 96, 6629] and close agreement is found. In comparison, the standard method of Goursaud et al. [J. Chem. Phys., 1976, 65, 5453] is only semi-quantitative.

Insights into the semiclassical Wigner treatment of bimolecular collisions.

The semiclassical Wigner treatment of bimolecular collisions, proposed by Lee and Scully on a partly intuitive basis [J. Chem. Phys. 73, 2238 (1980)], is derived here from first principles. The derivation combines Heller's ideas [J. Chem. Phys. 62, 1544 (1975); ibid. 65, 1289 (1976); ibid. 75, 186 (1981)], the backward picture of molecular collisions [L. Bonnet, J. Chem. Phys. 133, 174108 (2010)] and the microreversibility principle.

How Adsorbed Oxygen Atoms Inhibit Hydrogen Dissociation on Tungsten Surfaces.

Hydrogen molecules dissociate on clean W(110) surfaces. This reaction is progressively inhibited as the tungsten surface is precovered with oxygen. We use density functional theory and ab initio molecular dynamics to rationalize, at the atomic scale, the influence of the adsorbed O atoms on the H2 dissociation process. The reaction probability is calculated for kinetic energies below 300 meV and different O nominal coverages. We show that the adsorbed O atoms act as repulsive centers that modulate the dynamics of the impinging H2 molecules by closing dissociation pathways. In agreement with existing experimental information, H2 dissociation is absent for an O coverage of half a monolayer. The results show that the influence of O adsorbates on the dissociation dynamics on W(110) goes much beyond the blocking of possible H adsorption sites. Adsorbed O atoms create a sort of chemical shield at the surface that prevents further approach and dissociation of the H2 molecules.

High-harmonic transient grating spectroscopy of NO2 electronic relaxation.

We study theoretically and experimentally the electronic relaxation of NO(2) molecules excited by absorption of one ∼400 nm pump photon. Semiclassical simulations based on trajectory surface hopping calculations are performed. They predict fast oscillations of the electronic character around the intersection of the ground and first excited diabatic states. An experiment based on high-order harmonic transient grating spectroscopy reveals dynamics occurring on the same time scale. A systematic study of the detected transient is conducted to investigate the possible influence of the pump intensity, pump wavelength, and rotational temperature of the molecules. The quantitative agreement between measured and predicted dynamics shows that, in NO(2), high harmonic transient grating spectroscopy encodes vibrational dynamics underlying the electronic relaxation.

The O((1)D) + H2 (X (1)Σ+, v, j) → OH(X (2)Π, v', j') + H((2)S) reaction at low collision energy: when a simple statistical description of the dynamics works.

In this communication, we highlight that statistical approaches for chemical reactions describe reasonably well the low energy dynamics of the title process. Consequently, such methods prove to be valuable to compute rate constants from low to room temperatures. Results are compared with experiment and recent precise quantum wave packet calculations [J. Phys. Chem. A, 2009, 113, 5285].

Classical description in a quantum spirit of the prototype four-atom reaction OH + D2.

Classical mechanics is the only practical way to simulate internuclear motion in many complex systems that are important for biology, materials science, and technology. It is therefore important to test classical dynamics on simpler systems. The OH + H(2) or OH + D(2) system is the prototype four-body chemical reaction for fundamental studies of this nature, and high-resolution experiments have been reported by Davis and co-workers. Here we use those experiments to test state-resolved quasi-classical trajectory calculations in a quantum spirit, and find good agreement with experiment. Our simulations correctly predict that the newly formed oxygen-deuterium bond in the HOD product is preferentially excited to the vibrational state v = 2, and they yield a state-resolved product translational energy distribution. Of special interest is that the triple (angle-velocity) differential cross section shows the same state-resolved structure associated with the product vibrational states that were analyzed. This level of accuracy has previously been achieved only for triatomic systems, and these new simulations demonstrate that the quasi-classical method with quantum corrections may represent a reasonable alternative to quantum scattering approaches for the description of polyatomic reaction dynamics.

Classical photodissociation dynamics with Bohr quantization.

The standard classical expression of the state-resolved photodissociation cross section is not consistent with an efficient Bohr quantization of product internal motions. A new and strictly equivalent expression not suffering from this drawback is proposed. This expression opens the way to more realistic classical simulations of direct polyatomic photodissociations in the quantum regime where only a few states are available to the products.

The method of Gaussian weighted trajectories. V. On the 1GB procedure for polyatomic processes.

In recent years, many chemical reactions have been studied by means of the quasiclassical trajectory (QCT) method within the Gaussian binning (GB) procedure. The latter consists of "quantizing" the final vibrational actions in Bohr spirit by putting strong emphasis on the trajectories reaching the products with vibrational actions close to integer values. A major drawback of this procedure is that if N is the number of product vibrational modes, the amount of trajectories necessary to converge the calculations is ∼10(N)×larger than with the standard QCT method. Applying it to polyatomic processes is thus problematic. In a recent paper, however, Czakó and Bowman propose to quantize the total vibrational energy instead of the vibrational actions [G. Czakó and J. M. Bowman, J. Chem. Phys. 131, 244302 (2009)], a procedure called 1GB here. The calculations are then only ∼10 times more time consuming than with the standard QCT method, allowing thereby for considerable numerical saving. In this paper, we propose some theoretical arguments supporting the 1GB procedure and check its validity on model test cases as well as the prototype four-atom reaction OH+D(2)→HOD+D.

Transformation from angle-action variables to Cartesian coordinates for polyatomic reactions.

The transformation from angle-action variables to Cartesian coordinates is an important step of the semiclassical description of bimolecular collisions and photofragmentations. The basic reason is that dynamical conditions corresponding to molecular beam experiments are ideally generated in angle-action variables, whereas the classical equations of motion are ideally solved in Cartesian coordinates by standard numerical approaches. To our knowledge, this transformation is available in the literature only for atom-diatom arrangements. The goal of the present work is to derive it for diatom-polyatom ones. The analogous transformation for any type of arrangement may then be straightforwardly deduced from that presented here.

When Classical Trajectories Get to Quantum Accuracy: The Scattering of H2 on Pd(111).

When elementary reactive processes occur at such low energies that only a few states of reactants and/or products are available, quantum effects strongly manifest and the standard description of the dynamics within the classical framework fails. We show here, for H2 scattering on Pd(111), that by pseudoquantizing in the spirit of Bohr the relevant final actions of the system, along with adequately treating the diffraction-mediated trapping of the incoming wave, classical simulations achieve an unprecedented agreement with state-of-the-art quantum dynamics calculations.

Moya-Moya syndrome after cranial radiation for optic glioma with NF1. Case report and literature review of syndromic cases.

INTRODUCTION: Moya-Moya angiopathy is a neurovascular disease that predisposes to ischemic or hemorrhagic strokes. It is generated by a steno-occlusion of the terminal portion of the internal carotid arteries, which induces the development of abnormal neovessels in the deep regions of the brain. Some pathologies such as sickle cell disease, Down syndrome or Graves' disease may be associated with Moya-Moya angiopathy. These syndromic forms harbor several differences compared with idiopathic Moya-Moya disease. CASE REPORT: We report the case of a young patient who presented with a syndromic form of Moya-Moya angiopathy after cranial radiation therapy for an optic glioma associated with type 1 neurofibromatosis treated by combined revascularization. We discuss the particularities of syndromic forms, in their presentation and management based on a review of the literature. CONCLUSION: Many diseases can be associated with Moya-Moya syndrome. Symptomatic patients should undergo surgery, but the risk of postoperative complications appears to be greater than that encountered in patients with non-syndromic Moya-Moya angiopathy.