Dissociation of GaN2+ and AlN2+ in APT: Electronic structure and stability in strong DC field.

We investigate from a theoretical point of view the stability of AlN2+ and GaN2+ dications produced under high static electric fields like those reached in Atom Probe Tomography (APT) experiments. By means of quantum chemical calculations of the electronic structure of these molecules, we show that their stability is governed by two independent processes. On the one hand, the spin-orbit coupling allows some molecular excited states to dissociate by inter-system crossing. On the other hand, the action of the electric field lowers the potential energy barrier, which ensures the dication stability in standard conditions. We present a detailed example of field emission dynamics in the specific case of the 11Δ states for a parabolic tip, which captures the essentials of the process by means of a simplified model. We show that the dissociation dynamics of AlN2+ and GaN2+ is completely different despite the strong resemblance of their electronic structure.

Dissociation of GaN2+ and AlN2+ in APT: Analysis of experimental measurements.

The use of a tip-shaped sample for the atom probe tomography technique offers the unique opportunity to analyze the dynamics of molecular ions in strong DC fields. We investigate here the stability of AlN2+ and GaN2+ dications emitted from an Al0.25Ga0.75N sample in a joint theoretical and experimental study. Despite the strong chemical resemblance of these two molecules, we observe only stable AlN2+, while GaN2+ can only be observed as a transient species. We simulate the emission dynamics of these ions on field-perturbed potential energy surfaces obtained from quantum chemical calculations. We show that the dissociation is governed by two independent processes. For all bound states, a mechanical dissociation is induced by the distortion of the potential energy surface in the close vicinity of the emitting tip. In the specific case of GaN2+, the relatively small electric dipole of the dication in its ground 13Σ- and excited 11Δ states induces a weak coupling with the electric field so that the mechanical dissociation into Ga+ + N+ lasts for sufficient time to be observed. By contrast, the AlN2+ mechanical dissociation leads to Al2+ + N which cannot be observed as a correlated event. For some deeply bound singlet excited states, the spin-orbit coupling with lower energy triplet states gives another chance of dissociation by system inter-system crossing with specific patterns observed experimentally in a correlated time of flight map.

RASPT2 Analysis of the F-(H2O) n=1-7 and OH-(H2O) n=1-7 CTTS States.

We analyze the electronic structure of the lowest excited states of the F-(H2O) n=1-7 and OH-(H2O) n=1-7 anionic clusters in the framework of RASPT2 theory. At the ground-state geometry, these clusters can bind the excess electron in the first excited singlet and triplet states for n ≥ 3 for F- and n ≥ 2 for OH-. The geometry relaxation of the F-(H2O) n=1-7 clusters in their lowest-energy triplet state produces two series of minima. A first series is made of a F radical weakly bound to a negatively charged water cluster to form F-(H2O) n-. A second series associated with hydrogen transfer from a water molecule to the fluorine atom is built on a HF molecule and a OH radical bound to a negatively charged water cluster to form OH-HF-(H2O) n-1-. This second series provides the lowest-energy isomers of F-(H2O) n for the excited state. These two series of minima are inherited from the neutral fluorine water cluster structure only weakly perturbed by the excess electron. They are similar to the OH-(H2O) n isomers obtained for the lowest-energy triplet state, which are also made of a neutral OH radical inserted in the water molecule network of a (H2O) n- cluster. For all of these clusters in the lowest-energy excited state, the excess electron is localized outside of the cluster near unbound hydrogen atoms. Its binding energy is well correlated to the electric dipole of the cluster, and a lower limit of 4.1 D is necessary to bind it to the cluster. The two series of F-(H2O) n isomers offer two very different routes for geminate recombination observed in water solutions. Our calculation suggests that the recombination takes place with the OH radical left after hydrogen transfer rather than with the F radical.

Electronic structure and stability of the SiO2+ dications produced in tomographic atom probe experiments.

The molecular electronic states of the SiO2+ dication have been investigated in a joint theoretical and experimental analysis. The use of a tip-shaped sample for tomographic atom probe analysis offers the unique opportunity to produce and to analyze the lifetime of some excited states of this dication. The perturbation brought by the large electric field of the polarized tip along the ion trajectory is analyzed by means of molecular dynamics simulation. For the typical electric fields used in the experiment, the lowest energy triplet states spontaneously dissociate, while the lowest energy singlet states do not. We show that the emission process leads to the formation of some excited singlet state, which dissociates by means of spin-orbit coupling with lower-energy triplet states to produce specific patterns associated with Si+ + O+ and Si2+ + O dissociation channels. These patterns are recorded and observed experimentally in a correlated time-of-flight map.

Role of a Neighbor Ion in the Fragmentation Dynamics of Covalent Molecules.

Fragmentation of molecular nitrogen dimers (N_{2})_{2} induced by collision with low energy 90 keV Ar^{9+} ions is studied to evidence the influence of a molecular environment on the fragmentation dynamics of N_{2} cations. Following the capture of three or four electrons from the dimer, the three-body N_{2}^{+}+N^{m+}+N^{n+} [with (m,n)=(1,1) or (1, 2)] fragmentation channels provide clean experimental cases where molecular fragmentation may occur in the presence of a neighbor molecular cation. The effect of the environment on the fragmentation dynamics within the dimer is investigated through the comparison of the kinetic energy release (KER) spectra for these three-body channels and for isolated N_{2}^{(m+n)+} monomer cations. The corresponding KER spectra exhibit energy shifts of the order of 10 eV, attributed to the deformation of the N^{m+}+N^{n+} potential energy curves in the presence of the neighboring N_{2}^{+} cation. The KER structures remain unchanged, indicating that the primary collision process is not significantly affected by the presence of a neighbor molecule.

Spin-orbit coupling in the dissociative excitation of alkali atoms at the surface of rare gas clusters: A theoretical study.

We analyze the role of the spin-orbit (SO) coupling in the dissociative dynamics of excited alkali atoms at the surface of small rare gas clusters. The electronic structure of the whole system is deduced from a one-electron model based on core polarization pseudo-potentials. It allows us to obtain in the same footing the energy, forces, and non-adiabatic couplings used to simulate the dynamics by means of a surface hopping method. The fine structure state population is analyzed by considering the relative magnitude of the SO coupling ξ, with respect to the spin-free potential energy. We identify three regimes of ξ-values leading to different evolution of adiabatic state population after excitation of the system in the uppermost state of the lowest np (2)P shell. For sufficiently small ξ, the final population of the J=12 atomic states, P12, grows up linearly from P12=13 at ξ = 0 after a diabatic dynamics. For large values of ξ, we observe a rather adiabatic dynamics with P12 decreasing as ξ increases. For intermediate values of ξ, the coupling is extremely efficient and a complete transfer of population is observed for the set of parameters associated to NaAr3 and NaAr4 clusters.

Spectroscopic properties of alkali atoms embedded in Ar matrix.

We present a theoretical investigation of visible absorption and related luminescence of alkali atoms (Li, Na, and K) embedded in Ar matrix. We used a model based on core polarization pseudopotentials, which allows us to determine accurately the gas-to-matrix shifts of various trapping sites. The remarkable agreement between our calculated results and the experimental spectra recorded by several authors allows us to establish a clear assignment of the observed spectra, which are made of contributions from crystalline sites on the one hand, and of grain boundary sites on the other hand. Our study reveals remarkably large Stokes shifts, up to 9000 cm(-1), which could be observed experimentally to identify definitely the trapping sites.

Nonadiabatic molecular dynamics of photoexcited Li2(+) Ne(n) clusters.

We investigate the relaxation of photoexcited Li(2)(+) chromophores solvated in Ne(n) clusters (n = 2-22) by means of molecular dynamics with surface hopping. The simplicity of the electronic structure of these ideal systems is exploited to design an accurate and computationally efficient model. These systems present two series of conical intersections between the states correlated with the Li+Li(2s) and Li+Li(2p) dissociation limits of the Li(2)(+) molecule. Frank-Condon transition from the ground state to one of the three lowest excited states, hereafter indexed by ascending energy from 1 to 3, quickly drives the system toward the first series of conical intersections, which have a tremendous influence on the issue of the dynamics. The states 1 and 2, which originate in the Frank-Condon area from the degenerated nondissociative 1(2)Π(u) states of the bare Li(2)(+) molecule, relax mainly to Li+Li(2s) with a complete atomization of the clusters in the whole range of size n investigated here. The third state, which originates in the Frank-Condon area from the dissociative 1(2)Σ(u)(+) state of the bare Li(2)(+) molecule, exhibits a richer relaxation dynamics. Contrary to intuition, excitation into state 3 leads to less molecular dissociation, though the amount of energy deposited in the cluster by the excitation process is larger than for excitation into state 1 and 2. This extra amount of energy allows the system to reach the second series of conical intersections so that approximately 20% of the clusters are stabilized in the 2(2)Σ(g)(+) state potential well for cluster sizes n larger than 6.

Structure and photoabsorption properties of cationic alkali dimers solvated in neon clusters.

We present a theoretical investigation of the structure and optical absorption of M(2)(+) alkali dimers (M=Li,Na,K) solvated in Ne(n) clusters for n=1 to a few tens Ne atoms. For all these alkali, the lowest-energy isomers are obtained by aggregation of the first Ne atoms at the extremity of the alkali molecule. This particular geometry, common to other M(2)(+)-rare gas clusters, is intimately related to the shape of the electronic density of the X (2)Σ(g)(+) ground state of the bare M(2)(+) molecules. The structure of the first solvation shell presents equilateral Ne(3) and capped pentagonal Ne(6) motifs, which are characteristic of pure rare gas clusters. The size and geometry of the complete solvation shell depend on the alkali and were obtained at n=22 with a D(4h) symmetry for Li and at n=27 with a D(5h) symmetry for Na. For K, our study suggests that the closure of the first solvation shell occurs well beyond n=36. We show that the atomic arrangement of these clusters has a profound influence on their optical absorption spectrum. In particular, the XΣ transition from the X (2)Σ(g)(+) ground state to the first excited (2)Σ(u)(+) state is strongly blueshifted in the Frank-Condon area.

An accurate model potential for alkali neon systems.

We present a detailed investigation of the ground and lowest excited states of M-Ne dimers, for M=Li, Na, and K. We show that the potential energy curves of these Van der Waals dimers can be obtained accurately by considering the alkali neon systems as one-electron systems. Following previous authors, the model describes the evolution of the alkali valence electron in the combined potentials of the alkali and neon cores by means of core polarization pseudopotentials. The key parameter for an accurate model is the M(+)-Ne potential energy curve, which was obtained by means of ab initio CCSD(T) calculation using a large basis set. For each MNe dimer, a systematic comparison with ab initio computation of the potential energy curve for the X, A, and B states shows the remarkable accuracy of the model. The vibrational analysis and the comparison with existing experimental data strengthens this conclusion and allows for a precise assignment of the vibrational levels.

Solvation of Na(2) (+) in Ar(n) clusters. I. Structures and spectroscopic properties.

We present a theoretical study of Na(2) (+) solvation in an argon matrix Ar(n) for n=1 to a few tens. We use a model based on an explicit description of valence electron interaction with Na(+) and Ar cores by means of core polarization pseudopotential. The electronic structure determination is thus reduced to a one-electron problem, which can be handled efficiently. We investigate the ground state geometry and related optical absorption of Na(2) (+)Ar(n) clusters. For nA (2)Sigma(u) (+)), which reveals the confinement of the excited A (2)Sigma(u) (+) state. The Na(2) (+) energy spectrum is so strongly perturbed that the A (2)Sigma(u) (+) state becomes higher than the B (2)Pi(u) (+) states. The closure of the first solvation shell is observed at n=17. Above this size, the second solvation shell develops. Its structure is dominated by a pentagonal organization around the Na(2) (+) molecular axis. The optical transitions vary smoothly with n and the A (2)Sigma(u) (+) and B (2)Pi(u) states are no longer inverted, though the first optical transition remains strongly blueshifted.

[Influence of sex on the prognosis of high risk acute coronary syndromes treated by early angioplasty]. / Influence du sexe sur le pronostic des syndromes coronaires aigus à haut risque traités par angioplastie précoce.

The aim of this study was to evaluate the influence of sex on the prognosis of high risk acute coronary syndromes treated early with angioplasty. Over a period of two years, 694 consecutive patients (151 female, 543 male) underwent revascularisation within the first 24 hours of an acute coronary syndrome without permanent ST elevation (ST depression (52.5%) or relapse of angina despite medical treatment (47.5%). The females were older than the males (67.9 vs 62.3 years; p < 0.0001), smoked less (7.3 vs. 32.8%; p < 0.001) and had a higher prevalence of hypertension (53 vs. 42.1%; p = 0.017). The angiographic characteristics were equivalent in both sexes, except for a lower frequency of thrombus in the females (6.9 vs. 15.2%; p < 0.0001). All lesions were treated with endoprosthesis implantation. The angiographic success rate was comparable (94 vs. 93.7%) as was the rate of major cardiac events while in hospital (3.8 versus 4%). With an average survival of 2 years, the incidence of major cardiac events remained identical in both sexes (15.4 vs 15.7%: p = 0.43): cardiac mortality (3.2 vs 2%; p = 0.18), myocardial infarction (7.3 vs 6.7%; p = 0.37), further revascularisation (8.3 vs 7.2%; p = 0.47). The survival without major cardiac event was comparable at 1 year (87 +/- 0.1 vs 88 +/- 0.3%) and at 2 years (78 +/- 0.2 vs 83 +/- 0.3%; p = 0.58). In conclusion, the progression both in hospital and at two years with a strategy of early revascularisation for high risk acute coronary syndromes was comparable in males and females.

Clinical impact of local implementation of agreed guidelines for the management of patients with acute myocardial infarction.

OBJECTIVE: This study sought to assess the impact of local implementation of clinical practice guidelines on the pattern of care and outcome in patients admitted to the Coronary Care Unit (CCU) with acute myocardial infarction. BACKGROUND: Development of clinical practice guidelines is among the most popular of the methods intended to promote translation of results from clinical trials into routine care. However, very little is known about the actual impact on routine care of the clinical guidelines for managing patients with acute myocardial infarction. METHODS: We reviewed a prospectively collected cohort of consecutive patients discharged with a diagnosis of acute myocardial infarction from S. Maria degli Angeli, a large community-based hospital in northeast Italy. Eighty-six patients treated in 1996 (before guideline implementation) were compared with 70 patients treated in 1997 (after guideline implementation) with respect to patterns of use of guideline-directed pharmacotherapies for acute myocardial infarction, diagnostic testing, length of CCU stay and clinical outcome. RESULTS: The two groups were similar in male gender, age, infarct location and severity. Patients managed before guideline implementation were less likely to receive thrombolysis (36 vs 50%; p = 0.05), i.v. beta-blockers at admission (13 vs 31%; p = 0.002), oral beta-blockers at CCU discharge (45 vs 74%; p = 0.0003). When these were given, patients managed before guideline implementation received lower dosages of i.v. heparin, as manifested by a lower proportion of patients reaching adequate aPTT levels at 24 hours (14 vs 62%, p < 0.0001), and of oral beta-blockers (-50%, p < 0.0001), and higher dosage of aspirin (+100%, p < 0.0001). The time to mobilization (+1 day) and the length of CCU stay (+0.5 day) were longer in patients managed before guideline implementation (p < 0.0001). Incidence of major complications was similar between the two groups (19 vs 13%, respectively; p = ns). CONCLUSIONS: Patients with myocardial infarction managed after local implementation of clinical practice guidelines were more likely to receive evidence-based effective pharmacotherapies, and to have earlier mobilization and earlier discharge from CCU. This study strongly supports the role of local implementation of clinical practice guidelines to optimize management of patients with acute myocardial infarction.

Dual chamber pacing with optimal AV delay in congestive heart failure: a randomized study.

AIM: A prospective randomized trial was set up to evaluate contractile parameters and quality of life in patients with congestive heart failure. METHODS AND RESULTS: We describe the results from 38 patients in sinus rhythm and with chronic heart failure due to congestive cardiomyopathy, prospectively randomized to optimal medical therapy (Group 1, 19 patients) or optimal medical therapy plus dual chamber pacemaker programmed to optimal AV delay (Group 2, 19 patients). At a 6 month follow-up, 7/19 patients in Group 1 had died compared with 5/19 patients in Group 2. During follow-up, there were few significant changes in evaluated parameters except for mitral regurgitation time, which was prolonged in Group 1 and shortened in Group 2. The systolic left ventricular diameter shortened significantly only in Group 2. An energy and activity questionnaire showed that the effect of DDD pacing in the latter patient population was beneficial. CONCLUSIONS: From these results we may conclude that at the 6 month follow-up DDD pacing with echo-optimized AV interval programming can improve quality of life without affecting survival.

Echocardiography in pulmonary embolism disease.

Pulmonary embolism is a very common disease often misdiagnosed, because of variable and nonspecific clinical manifestations. Therefore it has a burden of high mortality, particularly in nonrecognized cases. Pulmonary angiography, which is usually considered the gold standard, and ventilation/perfusion pulmonary scan have shown good results in this field, but the first is costly and invasive, and both are not easily and rapidly available in all centers. Echocardiography can be helpful in the diagnosis of pulmonary embolism; transthoracic echo in particular is able to recognize indirect signs of the disease, due to acute pressure right overload; it is also possible to evaluate pulmonary artery systolic pressure by continuous wave Doppler. Transthoracic echocardiography can be negative in cases of small pulmonary embolism, in which the pressure overload and therefore haemodynamic impairment is trivial. The sensitivity and specificity of transthoracic echo is low, but its role in the diagnosis and management of pulmonary embolism may be important, because it can easily and rapidly show the presence and degree of right ventricular pressure overload and therefore it can help in addressing therapy and prognosis. Transesophageal echo may directly demonstrate thrombotic masses in the main pulmonary arteries or, less often, floating intracavitary thrombi. In this field it is showing promising results.

Direct demonstration of an air-fluid interface by two-dimensional echocardiography: a new diagnostic sign of hydropneumopericardium.

Hydropneumopericardium is an uncommon condition that requires prompt diagnosis and treatment if hemodynamic compromise is present. Chest roentgenography, computerized tomography, and echocardiography provide important information for the diagnosis. In this article a new distinctive echocardiographic sign of hydropneumopericardium is described: the direct demonstration of the air-fluid interface in the long-axis precordial view.

Relation of right ventricular morphology and function in pectus excavatum to the severity of the chest wall deformity.

Although pectus excavatum (PE) is thought to impair right ventricular (RV) performance, the degree of RV dysfunction, if any, produced by this chest wall deformity remains controversial. To address this issue, we performed 2-dimensional echocardiography and chest wall radiography in 28 subjects with mild-to-severe degrees of PE to assess RV morphology and function in relation to the degree of the chest wall deformity. Measurements of RV anatomy and function obtained in these patients were compared to those of 24 normal control subjects of similar age and sex. In subjects with PE, mean RV outflow tract diameter at the aortic root level was narrower (1.4 +/- 0.3 cm/m2) and end-diastolic (10 +/- 2.3 cm2/m2) and end-systolic (5.8 +/- 1.4 cm2/m2) areas were larger than those in normal controls (1.6 +/- 0.3, 8.6 +/- 1.7, and 4.5 +/- 1.2 cm2/m2, respectively; p < 0.013). The magnitude of these abnormalities was related to the degree of the chest wall deformity evaluated on the chest radiogram (r = 0.54, 0.51, and 0.49, respectively). RV planar emptying fraction, an index of RV systolic function, was reduced in subjects with PE (42 +/- 10%) compared to the normal controls (48 +/- 10%; p = 0.047). No relation could be found, however, between this index and the severity of the chest wall deformity.(ABSTRACT TRUNCATED AT 250 WORDS)