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1.
J Chem Phys ; 143(17): 174301, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26547164

RESUMO

We report absolutely calibrated isotropic Raman lineshapes for Kr2 and Xe2 and for KrXe at 294.5 K and compare them to quantum-mechanically generated lineshapes by using state-of-the-art second-order Møller-Plesset and DFT/B3LYP data sets for the induced mean dipole polarizability á¾±. A very good agreement between the numerical and the experimental data was observed but the large uncertainty margins and the short Raman frequency interval probed in our experiment prevented us from rating on a more refined scale the performance of the tested á¾± models. These drawbacks are inherent in isotropic Raman spectrum measurements and amplified for dissimilar pairs because, for such systems and spectra, the unreliable operation of subtracting optical signals of comparable magnitude occurs twice per Raman frequency shift value, thus penalizing twice the quality of the measured data. In light of our findings and of previously reported evidence about related electric properties in Kr2 and Xe2 and in KrXe, we are left with no doubt as to the consistency of the induced-polarizability and interatomic-potential data used for these three systems at the reported level of accuracy.

2.
J Chem Phys ; 140(12): 124308, 2014 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-24697442

RESUMO

Of the six normal vibrations of SF6, ν3 has a key role in the mechanisms of radiative forcing. This vibration, though inactive in Raman, shows up through the transition 2ν3 allowing for a complementary view on the asymmetric stretch of the molecule. Here, we look back into this topic, which has already caught some interest in the past but with some points been left out. We make a systematic incoherent-light-scattering analysis of the overtone with the use of different gas pressures and polarization orientations for the incident beam. Absolute-scale isotropic and anisotropic spectra are reported along with natural and pressure-induced widths and shifts, and other spectral features such as the peaks corresponding to the (experimentally indistinguishable) interfering channels Eg and F2g hitherto seen solely as two-photon IR-absorption features. We make the first-ever prediction of the SF6 polarizability second derivative with respect to the ν3-mode coordinate and we develop a heuristic argument to explain why the superposition of the three degenerate stretching motions that are related to the ν3 mode cannot but generate a polarized Raman band.

3.
J Chem Phys ; 140(3): 034308, 2014 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-25669380

RESUMO

Long known as a fully polarized band with a near vanishing depolarization ratio [ηs = 0.05, W. Holzer and R. Ouillon, Chem. Phys. Lett. 24, 589 (1974)], the 2ν5 Raman overtone of SF6 has so far been considered as of having a prohibitively weak anisotropic spectrum [D. P. Shelton and L. Ulivi, J. Chem. Phys. 89, 149 (1988)]. Here, we report the first anisotropic spectrum of this overtone, at room temperature and for 13 gas densities ranging between 2 and 27 amagat. This spectrum is 10 times broader and 50 times weaker than the isotropic counterpart of the overtone [D. Kremer, F. Rachet, and M. Chrysos, J. Chem. Phys. 138, 174308 (2013)] and its profile much more sensitive to pressure effects than the profile of the isotropic spectrum. From our measurements an accurate value for the anisotropy matrix-element |⟨000020|Δα|000000⟩| was derived and this value was found to be comparable to that of the mean-polarizability 000020α¯000000. Among other conclusions our study offers compelling evidence that, in Raman spectroscopy, highly polarized bands or tiny depolarization ratios are not necessarily incompatible with large polarizability anisotropy transition matrix-elements. Our findings and the way to analyze them suggest that new strategies should be developed on the basis of the complementarity inherent in independent incoherent Raman experiments that run with two different incident-beam polarizations, and on concerted efforts to ab initio calculate accurate data for first and second polarizability derivatives. Values for these derivatives are still rarities in the literature of SF6.

4.
J Chem Phys ; 138(17): 174308, 2013 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-23656135

RESUMO

The room-temperature isotropic spectrum of SF6 was recorded at the frequency of the 2ν5 overtone by running high-sensitivity incoherent Raman experiments for two independent polarizations of the incident beam and for gas densities varying from 2 to 27 amagat. Weak yet observable pressure effects were found. A transparent analysis of the Raman cross-section problem along with the first-ever prediction of the value of the mean polarizability second derivative ∂(2)α/∂q5(2) are made and the hitherto underestimated role of the hot bands of SF6 is brought to the wider public. The emergence of an analytic hotband factor is shown whose magnitude is dramatically increased with the order of the overtone and the gas temperature and all the more so upon considering low-frequency molecular vibrations. Our formulas, which in the harmonic approximation are exact, are still applicable to real situations provided certain conditions are fulfilled. For nondegenerated modes, generalization to higher order overtones is made, an issue addressing the much challenging problem of the IR-allowed second overtone bands. The content of this paper is also an invitation towards ab initio derivative-calculations for sulfur hexafluoride, especially given the today's needs in interpreting spectra of significance for greenhouse atmospheric issues.

5.
J Chem Phys ; 134(22): 224301, 2011 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-21682508

RESUMO

A line-mixing shape analysis of the isotropic remnant Raman spectrum of the 2ν(3) overtone of CO(2) is reported at room temperature and for densities, ρ, rising up to tens of amagats. The analysis, experimental and theoretical, employs tools of non-resonant light scattering spectroscopy and uses the extended strong collision model (ESCM) to simulate the strong line mixing effects and to evidence motional narrowing. Excellent agreement at any pressure is observed between the calculated spectra and our experiment, which, along with the easy numerical implementation of the ESCM, makes this model stand out clearly above other semiempirical models for band shape calculations. The hitherto undefined, explicit ρ-dependence of the vibrational relaxation rate is given. Our study intends to improve the understanding of pressure-induced phenomena in a gas that is still in the forefront of the news.

6.
J Chem Phys ; 134(19): 194305, 2011 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-21599057

RESUMO

In a recent article we showed that the 2ν(3) transition of CO(2) gives rise to a Raman spectrum that is almost entirely depolarized [M. Chrysos, I. A. Verzhbitskiy, F. Rachet, and A. P. Kouzov, J. Chem. Phys. 134, 044318 (2011)]. In the present article, we go further forward in the study of this overtone by reporting a first-principles shape analysis of its depolarized spectrum at room temperature. As a first step in our analysis, a model assuming isolated Lorentzian line shapes was applied, which at low gas densities turns out to be sufficient for qualitative conclusions. As the next step, a sophisticated approach was developed on the basis of the extended strong-collision model in order to properly account for the heavy line mixing between rotational lines. Whereas a marked deviation between model and measured spectra was observed upon application of the simpler model, striking agreement even at the highest CO(2) density was found on applying the sophisticated one. Accurate calculated data were used for the rotational line broadening coefficients without resort to arbitrary parameters. Values for the vibrational shift scaling linearly with the density of the gas are given.

7.
J Chem Phys ; 134(10): 104310, 2011 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-21405168

RESUMO

In a recent paper [M. Chrysos, I. A. Verzhbitskiy, F. Rachet, and A. P. Kouzov, J. Chem. Phys. 134, 044318 (2011)], we showed that, in CO(2), the 2ν(3) transition generates a Raman line spectrum that is 98% depolarized, a property in agreement with general symmetry rules. Here, we present an extensive analysis, experimental and theoretical, of the isotropic remnant of this overtone. The isotropic spectrum turned out to be 45 times less intense than its anisotropic counterpart and to have a moment that is 350 times smaller than the moment of the anisotropic spectrum, in excellent agreement with theoretical predictions. Once the measured intensity (along with other data exclusively experimental) was fed back into the formula of the moment, a value for the CO(2) mean-polarizability asymmetric stretch derivative ∂(2)α/∂q(3)(2) was returned that matches the best ab initio prediction to better than 4%. Agreement, in order of magnitude, was found between the intensity reported herein and that reported in the sole prior study of this overtone [G. Tejeda, B. Mat, and S. Montero, J. Chem. Phys. 103, 568 (1995)].

8.
J Chem Phys ; 134(4): 044318, 2011 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-21280736

RESUMO

Molecular vibrations that are not totally symmetrical give rise to depolarized lines [P. Atkins and J. de Paula, Atkins' Physical Chemistry (Oxford University Press, UK, 2006), p. 464]. But in the case of stretching vibrations in centrosymmetric molecules, the statement has so far not been conclusively verified. It is the purpose of this article to report a rigorous experimental and theoretical analysis of the 2ν(3) band of CO(2)--the first overtone of the asymmetrical stretch vibration. The anisotropic spectrum was extracted and its spectral moment calculated from light-scattering measurements, taken at room temperature and for a wide range of CO(2)-gas densities. Evidence for a near-entirely depolarized Raman band is provided, with integrated depolarization ratio η(int)=6/7.16, closely approaching the upper bound η(max)=6/7. Agreement with theoretical predictions is found, on the basis of quality ab initio data for polarizability properties, provided that electro-optical and mechanical anharmonicity and intermode coupling effects between symmetric ν(1) and antisymmetric ν(3) stretching vibrations are incorporated.

9.
J Chem Phys ; 131(7): 074304, 2009 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-19708744

RESUMO

We report anisotropic collision-induced Raman scattering intensities by the Kr-Xe atomic pair recorded in a gas mixture of Kr and Xe at room temperature. We compare them to quantum-mechanical calculations on the basis of modern incremental polarizability models of either ab initio post-Hartree-Fock or density functional theory methods.

10.
Phys Rev Lett ; 100(13): 133007, 2008 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-18517948

RESUMO

Exact and general analytic expressions are reported for the integrated intensity and the width of collision-induced absorption (CIA) and collision-induced scattering (CIS) bands by gases of centrosymmetric linear molecules. These expressions provide significant insight and allow assignment of partial second moments to the degrees of freedom of the colliding molecules. The expressions are applied to ambient CO(2), whose collisional spectra are reputed to be useful probes for terrestrial and planetary atmospheres. Compelling evidence of the substantial role of hitherto missing polarization and polarizability mechanisms is provided and is in remarkable agreement with experimental observation. Our findings allow the long-overdue simple interpretation of CIA and CIS by CO(2)-CO(2) without the need to resort to short-range interactions to offset the discrepancies between theory and experiment.

11.
J Chem Phys ; 124(23): 234303, 2006 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-16821914

RESUMO

We present a collision-induced light scattering spectrum of Ne(2) and analyze it, together with an induced spectrum of Ar(2), in terms of a model for the pair-polarizability anisotropy beta of an atomic gas. This model, which is in essence a slight modification of one introduced by Ceccherini et al. [J. Chem. Phys. 111, 6316 (1999)], is shown to describe the measured spectra much farther into the wings than does the original model. The agreement of our measurements with quantum-mechanical spectra from the most reliable, now available, ab initio computation methods for beta produces evidence in support of the data and counters criticism of our experiment.

12.
Phys Rev Lett ; 84(10): 2120-3, 2000 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-11017223

RESUMO

Contrary to what has been observed thus far collision-induced light scattering (CILS) can be completely polarized. This exceptional behavior characterizes the very far wing of the binary CILS spectrum by gaseous helium. This conclusion is drawn from an experimental study of the depolarization ratio of He (2) in a much extended, previously unexplored, spectral domain. Our analysis shows that this property, unique thus far, is mainly due to an almost perfect cancellation between polarization and exchange pair polarizability contributions to the depolarized spectrum, taking place at internuclear distances shorter than the atomic diameter.

13.
Therapie ; 53(2): 151-5, 1998.
Artigo em Francês | MEDLINE | ID: mdl-9773115

RESUMO

PHOLY is a study of drug Prescription in Hospices civils of LYon by a transverse and descriptive survey. It aims at studying the methodology of such an investigation in a large university medical centre, elaborating a methodology for continuous assessment of prescribing, comparing prescriptions with scientific knowledge and identifying specific therapies. We collected 1525 questionnaires from 4333 hospitalized patients in 11 hospitals (prescriptions and indications). The main difficulties we encountered concerned communications (4 letters), fewer questionnaires collected than expected (1525/3018), many missing data, and the lack of a specific budget, thus allowing only partial data exploitation and control. This study revealed many problems such as relevant information for physicians, training and management of investigators, control, data capture and analysis. However, a prescription study may be possible with limited means.


Assuntos
Revisão de Uso de Medicamentos , Hospitais para Doentes Terminais/organização & administração , França , Projetos Piloto , Setor Público , Inquéritos e Questionários
14.
Therapie ; 53(2): 157-64, 1998.
Artigo em Francês | MEDLINE | ID: mdl-9773116

RESUMO

As shown in many studies, up-to-date knowledge is not reflected in prescribing behaviours. The aim of pilot study PHOLY (Prescription aux Hospices civils de LYon) was to study methodological and technical conditions of a drug utilization study in a large university medical centre and to evaluate the discrepancy between drug prescribing and up-to-date knowledge. Data of 1115 in-patients of Hospices Civils de Lyon were collected. We have shown the feasibility of such a study in spite of many difficulties (52.15 per cent of questionnaires received, missing data...). Reference treatments such as ACE inhibitors in heart failure treatment or betablockers for high blood pressure represent respectively only 14.6 per cent and 6.7 per cent of the prescriptions in these indications. Within the framework of quality of care improvement, the study of the appropriateness of the treatments enables identification of domains where better therapeutic information is necessary.


Assuntos
Revisão de Uso de Medicamentos , Hospitais para Doentes Terminais/organização & administração , Antagonistas Adrenérgicos beta/uso terapêutico , Inibidores da Enzima Conversora de Angiotensina/uso terapêutico , Anti-Hipertensivos/uso terapêutico , Baixo Débito Cardíaco/tratamento farmacológico , França , Humanos , Hipertensão/tratamento farmacológico , Projetos Piloto , Setor Público , Qualidade da Assistência à Saúde
16.
Arch Mal Coeur Vaiss ; 87(9): 1225-32, 1994 Sep.
Artigo em Francês | MEDLINE | ID: mdl-7646237

RESUMO

There are many causes of left main coronary artery disease, the first of which is atherosclerosis. Other rarer causes may be observed, such as acute and chronic occlusions, spasm and primary and secondary dissection. The prevalence of stenosis of the left main coronary artery at coronary angiography is about 5%. The risk factors are the same as for coronary artery disease. The symptoms are angina, especially unstable angina. The diagnosis is suspected on the finding of an extremely positive exercise stress test, confirmed by coronary angiography. The results of the prospective large scale Veterans Administration trial showed surgery to be the treatment of choice with a 30 months survival of 80% in the surgical group compared with 64% in the medical group. The operative morbidity and mortality is less than 10% at present. Recent studies have reported a medium-term mortality of 4.3 to 10.25% with follow-up periods of 24 and 43 months respectively. The long-term survival and functional improvement are excellent, with values of nearly 80%. Chronic occlusion of the left main stem is rare, 0.01 to 0.7% in coronary angiographic studies. There is no difference in presentation, electrocardiographic or stress test features compared with other severe coronary artery disease. The diagnosis is angiographic and the treatment surgical because of the mediocre natural history with risks of sudden death and severe infarction. Acute occlusion of the left main coronary is rare for generally fatal. The mechanism is acute thrombosis and the clinical presentation is that of extensive infarction usually with cardiogenic shock.(ABSTRACT TRUNCATED AT 250 WORDS)


Assuntos
Doença das Coronárias , Adulto , Angioplastia Coronária com Balão , Aterectomia Coronária , Angiografia Coronária , Ponte de Artéria Coronária , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Prognóstico , Taxa de Sobrevida
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