HIGH-RESOLUTION INFRARED AND RAMAN SPECTROSCOPY OF SF6_6: THE STATE-OF-THE-ART IN JUNE 2006

Author Institution: LPUB -- CNRS UMR 5027, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France; Instituto de Estructura de la Materia, CSIC Serrano 123, E-28006 Madrid, Spain; Fachbereich C -- Anorganische Chemie, Bergische Universitat Wuppertal, D-42097 Wuppertal, Germany; LADIR -- CNRS UMR 7075, Case Courrier 49, 4 Place Jussieu, F-75252 Paris Cedex 05, FranceSulfur hexafluoride is recognized by the Kyoto Protocol as a powerful greenhouse gas whose emissions should be monitored and reduced. Although its abundance is still relatively small ($3.8\times 10^{-6}$ ppmv), it is increasing rapidly ($8$ \%$/$year) while the lifetime of SF$_6$ in the atmosphere is extremely long ($3200$ years) with a Global Warming Potential equal to 23900 compared to CO$_2$} {\bf 24}, 675--678 (1997).}$^,$}. It is thus necessary to correctly model the atmospheric absorption of SF$_6$} (2006).}, especially in the strongly absorbing $\nu_3$ region (near $939$ cm$^{-1}$). Until recently, however, respective spectra were not very well known. In particular, the knowledge of hot bands is very important for atmospheric applications, but this implies to study various vibrational levels, some being only accessible through Raman scattering. During the past decade, we have analyzed different fundamental, harmonic and combination bands for both ${}^{32}$SF$_6$ and ${}^{34}$SF$_6$ using high-resolution infrared and Raman spectra} {\bf 222}, 291--295 (2003), V. Boudon, J. L. Domenech, D. Bermejo and H. Willner, {\em J. Mol. Spectrosc.\/} {\bf 228}, 392--400 (2004) and references therein.}. In this talk, we will discuss the present status and prospects of SF$_6$ spectroscopy. In particular, new spectra and analyses of ${}^{34}$SF$_6$ will be reported and discussed. We will also show that a correct modelling of absorption intensities is still a pending question

Fourier transform microwave spectrum of (HCCCN)-N-15 and global analysis of the high resolution infrared and rotational spectra up to 1700 cm(-1)

The rotational spectrum of an enriched sample of HC C-C N-15 was measured in the range 8-27 GHz by means of a waveguide Fourier transform microwave spectrometer. New transitions were also measured in the millimetre- and submillimetre ranges. These measurements combined with the available rovibrational and rotational data [Fayt et al., J. Mol. Struct. 695-696 (2004) 295], with many newly assigned infrared bands, were used for a global rovibrational analysis of all vibrational states up to 1700 cm(-1). A full set of 243 molecular parameters for the modes upsilon(4)-upsilon(7) has been deduced. (C) 2008 Elsevier B.V. All rights reserved

The Si–H stretching–bending overtone polyads of SiHF₃: Assignments, band intensities, internal coordinate force field, and ab initio dipole moment surfaces

Fourier transform overtone spectra of SiHF were recorded in the region of 2500–9000 cm−1 and vibrationally assigned. Experimental intensities were estimated. The 3ʋ1 overtone band at 6753 cm−1 was observed to be more than 10 times weaker than the 4ʋ1 band. A reduced three-dimensional Hamiltonian model in terms of internal coordinates was employed to study the Si–H stretching and bending vibrations including 5ʋ1 and 6ʋ1 which were recently recorded using optoacousticspectroscopy. Potential energy parameters were optimized by fitting to experimental band centers. The Fermi resonance between the Si–H stretching and bending motions was found to be insignificant. Band intensities were computed using ab initio one- and three-dimensional dipole momentsurfaces (DMS) expanded to polynomials in terms of symmetrized internal coordinates. The intensity anomaly of 3ʋ1 is understood as resulting from cancellation of contributions by the linear and quadratic terms in the DMS expansion. The behavior of X–H stretching overtone intensities as excitation increases was also studied in the low and medium energy regions. Whether a rapid or a slow decrease of intensity occurs with increasing excitation depends strongly on the nonlinearity of the DMS. For some molecules, there is an almost complete cancellation of contributions from the lower order terms in the DMS so that the accuracy of the computed overtone intensities is mainly limited by the uncertainty of the higher order expansion coefficients in the DMS

Comparison of Mechanical Power During Adaptive Support Ventilation Versus Nonautomated Pressure-Controlled Ventilation-A Pilot Study

Objectives: The aim of this pilot study was to compare the amount of "mechanical power of ventilation" under adaptive support ventilation with nonautomated pressure-controlled ventilation. Design: Single-center, observational prospective pilot study adjoining unitwide implementation of adaptive support ventilation in our department. Setting: The ICU of a nonacademic teaching hospital in the Netherlands. Patients: Twenty-four passive invasively ventilated critically ill patients expected to need of invasive ventilation beyond the following calendar day. Measurements and Main Results: In patients under adaptive support ventilation, only positive end-expiratory pressure and Fio2 were set by the caregivers-all other ventilator settings were under control of the ventilator; in patients under pressure-controlled ventilation, maximum airway pressure (Pmax), positive end-expiratory pressure, Fio2, and respiratory rate were set by the caregivers. Mechanical power of ventilation was calculated three times per day. Compared with pressure-controlled ventilation, mechanical power of ventilation with adaptive support ventilation was lower (15.1 [10.5-25.7] vs 22.9 [18.7-28.8] J/min; p = 0.04). Tidal volume was not different, but Pmax (p = 0.012) and respiratory rate (p = 0.012) were lower with adaptive support ventilation. Conclusions: This study suggests adaptive support ventilation may have benefits compared with pressure-controlled ventilation with respect to the mechanical power of ventilation transferred from the ventilator to the respiratory system in passive invasively ventilated critically ill patients. The difference in mechanical power of ventilation is not a result of a difference in tidal volume, but the reduction in applied pressures and respiratory rate. The findings of this observational pilot study need to be confirmed in a larger, preferably randomized clinical trial

Effect of intellivent‐asv versus conventional ventilation on ventilation intensity in patients with covid‐19 ards— an observational study

Driving pressure (ΔP) and mechanical power (MP) are associated with outcomes in critically ill patients, irrespective of the presence of Acute Respiratory Distress Syndrome (ARDS). INTELLiVENT‐ASV, a fully automated ventilatory mode, controls the settings that affect ΔP and MP. This study compared the intensity of ventilation (ΔP and MP) with INTELLiVENT‐ASV versus conventional ventilation in a cohort of COVID‐19 ARDS patients in two intensive care units in the Netherlands. The coprimary endpoints were ΔP and MP before and after converting from conventional ventilation to INTELLiVENT‐ASV. Compared to conventional ventilation, INTELLiVENT‐ASV delivered ventilation with a lower ΔP and less MP. With conventional ventilation, ΔP was 13 cmH2O, and MP was 21.5 and 24.8 J/min, whereas with INTELLiVENT‐ASV, ΔP was 11 and 10 cmH2O (mean difference –2 cm H2O (95 %CI –2.5 to –1.2 cm H2O), p < 0.001) and MP was 18.8 and 17.5 J/min (mean difference –7.3 J/Min (95% CI –8.8 to –5.8 J/min), p < 0.001). Conversion from conventional ventilation to INTELLiVENT‐ASV resulted in a lower intensity of ventilation. These findings may favor the use of INTELLiVENT‐ASV in COVID‐19 ARDS patients, but future studies remain needed to see if the reduction in the intensity of ventilation translates into clinical benefits