A new instrumentation for simultaneous terahertz and mid-infrared spectroscopy in corrosive gaseous mixtures

The correct interpretation of infrared (IR) observations of planetary atmospheres requires an accurate knowledge of temperature and partial and global pressures. Precise laboratory measurements of absorption intensities and line profiles, in the 200-350 K temperature range, are, therefore, critical. However, for gases only existing in complex chemical equilibria, such as nitrous or hypobromous acids, it is not possible to rely on absolute pressure measurements to measure absolute integrated optical absorption cross sections or IR line intensities. To overcome this difficulty, a novel dual-beam terahertz (THz)/mid-IR experimental setup has been developed, relying on the simultaneous use of two instruments. The setup involves a newly constructed temperature-controlled (200-350 K) cross-shaped absorption cell made of inert materials. The cell is traversed by the mid-IR beam from a high-resolution Fourier transform spectrometer using along a White-cell optical configuration providing absorption path lengths from 2.8 to 42 m and by a THz radiation beam (82.5 GHz to 1.1 THz), probing simultaneously the same gaseous sample. The THz channel records pure rotational lines of molecules for which the dipole moment was previously measured with high precision using Stark spectroscopy. This allows for a determination of the partial pressure in the gaseous mixture and enables absolute line intensities to be retrieved for the mid-IR range. This new instrument opens a new possibility for the retrieval of spectroscopic parameters for unstable molecules of atmospheric interest. The design and performance of the equipment are presented and illustrated by an example of simultaneous THz and mid-IR measurement on nitrous acid (HONO) equilibrium.

Characterization of the Observed Electric Field and Molecular Relaxation Times for Millimeter-Wave Chirped Pulse Instrumentation

In a chirped pulse experiment, the strength of the signal level is proportional to the amplitude of the electric field, which is weaker in the millimeter-wave or submillimeter-wave region than in the microwave region. Experiments in the millimeter region thus require an optimization of the coupling between the source and the molecular system and a method to estimate the amplitude of the electric field as seen by the molecular system. We have developed an analytical model capable of reproducing the coherent transient signals obtained with a millimeter-wave chirped pulse setup operated in a monochromatic pulse mode. The fit of the model against the experimental data allowed access to the amplitude of the electric field and, as a byproduct, to the molecular relaxation times T ₁ and T ₂.

Conformational landscape and inertial defect of methoxyphenol isomers studied by mm-wave spectroscopy and quantum chemistry calculations

Because methoxyphenols (MP) are emitted in significant quantities during biomass fires and contribute to the secondary organic aerosols formation which impacts the climate, their gas phase monitoring in the atmosphere is crucial and requires accurate rovibrational cross sections determined with a good knowledge of their ground state (GS) and vibrationally excited state (ES) molecular parameters. Therefore, the rotational spectra of the two isomers, 2-MP (guaïacol) and 4-MP (mequinol), have been measured in absorption and in emission at room temperature using a frequency multiplication chain and a mm-wave Fourier transform chirped-pulse spectrometer, respectively. Guided by quantum chemistry calculations, the conformational landscape has been characterised and the observation of only one rotamer in the spectra of 2-MP and 4-MP has been explained. For 2-MP, the most stable conformation is justified by an intramolecular O-H⋯OCH₃ hydrogen-bond which has been characterised by a topology analysis of the electron density. In a global fit including more than 30 000 line assignments, rotational and quartic centrifugal constants of the GS and the three lowest energy ES have been determined allowing to reproduce the millimeter-wave spectra at the experimental accuracy. The same work has been performed on the cis-rotamer of 4-MP highlighting some perturbations marring the fit quality for two vibrationally ES. Finally, the isomeric dependence of the negative inertial defect ΔI agrees with that of the lowest energy out of plane mode ν₄₅, and the variation of ΔI with the degree of vibrational excitation allows a fine estimation of v₄₅ = 1 vibrational wavenumber.

[Preoperative betablockers use in vascular and thoracic surgery]

OBJECTIVE

The aim of this study was to evaluate betablockers use and effect in the preoperative period in vascular and thoracic surgery.

PATIENTS AND METHODS

Retrospective study concerning patients scheduled for high or intermediate surgical risk procedure (n = 321) in a French vascular and thoracic surgery department during 2002. Eligibility for betablocker therapy was defined as previously described for inclusion criteria in Mangano's Study (N Engl J Med 1996;335:1713-20). Therapy effect was evaluated with heart rate in the operating room.

RESULTS

Forty-six percent (99/213) of eligible patients for betablockers were really treated in the preoperative period. In patients treated with betablockers, 40% appeared in the operating room with the most favorable heart rate (55-65 b/min). During surgical procedure, heart rate over 80 b/min was observed in more than 30% of patients with betablocker therapy. In patients eligible for betablocker therapy but untreated with these drugs, only 12% have received betablockers in the preoperative period.

CONCLUSION

Betablockers underuse is important in the preoperative period, and effect on heart rate is rarely optimal. This fact should encourage physicians to apply protocols for perioperative betablockers administration.

Radiofrequency, Centimeter-Wave, Millimeter-Wave, and Infrared Spectra of SiHF(3): Investigation of the Ground, v(4) = 1, and v(6) = 1 Vibrational States

The present paper deals with the analysis of the microwave, millimeter-wave, and infrared spectra of (28)SiHF(3) in its ground, v(6) = 1 and v(4) = 1 excited states. The former was observed up to 1055 GHz leading to the determination of one octic centrifugal distortion constant, L(J) = -0.0749(55) µHz. Furthermore the <k ||H ||k +/- 6> interaction term ||h(3,GS) || = 1.1032(70) mHz has been fitted from splittings of six K = 3 lines. The excited states have been regarded as isolated ones. This enabled fits according the Q-, D-, and QD-reduction schemes proposed by E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev, (J. Mol. Spectrosc. 126, 159-170 (1987)) and further developed by J. K. G. Watson, C. Gerke, H. Harder, and K. Sarka, (J. Mol. Spectrosc. 187, 131-141 (1997)) and Harder (J. Mol. Spectrosc. 194, 145 (1999)). A multiple fit analysis was performed confirming the assumption that the excited states are not affected by intervibrational resonances. Finally the millimeter spectrum of (29)SiHF(3) and (30)SiHF(3) in their ground state was also measured up to 460 GHz and accurate rotational and centrifugal distortion parameters were derived. Copyright 2000 Academic Press.

[Antiphospholipid antibody syndrome in pediatric neurosurgery: a hemostasis problem]

The case of a 11-year-old boy under anticoagulant therapy for a familial antiphospholipid antibody syndrome (SAAPF), who underwent surgery for a cerebrovascular malformation responsible for an intracerebral haematoma, is reported. Antivitamins K (AVK) were changed for unfractioned heparin (HNF), three days before. Heparin was discontinued two hours prior to surgery to obtain a normal peroperative coagulation. A vascular dural fistula was removed without any haemostatic problem. The neurological status rapidly returned to normal and tomodensitometry at day 1 showed a normal intracranial status. Heparin was readministered at h 16. Thrombocytopenia occurred at day 4 of heparin treatment. The change for a low weight molecular heparinoid, danaparoid (Orgaran), normalized the platelet count. The platelets aggregation tests were negative during thrombopenia. However, the test for antibodies against the PF4-heparin complex with the Elisa technique, was in favour of a heparin induced thrombocytopenia (TIH). In spite of its anecdotic occurrence due to cumulative thrombotic risks from the association of immunologic disorders (TIH and SAAPF), this case report underlines the value but also the risks of anticoagulant therapy in neurosurgery, when patients are at high risk for thrombosis.

Analysis of Rotational and Rovibrational Spectra of SiDF(3) in the Ground and v(4) = 1 Excited States

This paper presents the analysis of the spectra of SiDF(3) in its vibrational ground and v(4) = 1 states. The pure rotational spectrum of the ground state was measured up to 903 GHz (J" = 65). Rotational, quartic, and sextic centrifugal distortion constants were accurately determined. Furthermore the parameter ||h(3) || = 7.64(11) x 10(-4) Hz was derived from the observation of A(1)-A(2) splittings of six K = 3 lines. The assignment of the v(4) = 1 spectrum was performed by combining 140 pure rotational frequencies and more than 2300 rovibrational transitions. Among them, because of the strong (+/-2, -/+4) interaction, there are more than 90 A(1)-A(2) resolved split transitions between the (l = 0, k = +/-3) ground state levels and the (l = +/-2, k = -/+1) v(4) = 1 levels. Although the v(4) band is located at about 994.3 cm(-1), the energies of the other fundamental bands are at a distance of more than 140 cm(-1). The assumption of the isolated character of the state was confirmed by the small differences between the v(4) = 1 state and the ground state parameters and by the possibility of using the D and Q reduction schemes proposed by E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev [J. Mol. Spectrosc. 126, 159-170 (1987)]. Copyright 1999 Academic Press.

Radio-Frequency, Centimeter-Wave, Millimeter-Wave, and Infrared Spectra of SiDF(3) in the v(6) = 1 Excited State

This paper deals with the first study of high-resolution radio-frequency, centimeter-wave, millimeter-wave, and infrared spectra of the deuterated isotopomer of trifluorosilane, SiDF(3), in its lowest degenerate excited v(6) = 1 state. Following the work of E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev, (J. Mol. Spectrosc. 126, 159-170 (1987)) and Harder (J. Mol. Spectrosc. 194, 145 (1999)), the data (18 A(1)-A(2) transitions, 229 l-type resonance transitions, 189 pure rotational transitions, and 1167 rovibrational transitions) have been fitted using three equivalent Q, D, and QD reduction schemes enabling the fit of one of the three interaction parameters d, q(12), and epsilon, respectively, while the other two are fixed to zero. In addition to further higher order constants, either f(K)(22) or tau(K) also had to be constrained. By checking the standard deviation of each data set and the relations between parameters determined within different constrains, the six reduction schemes have been shown to be unitary equivalent. Furthermore, the axial rotational ground state constant C(0) has been accurately determined. Copyright 1999 Academic Press.

The Ground State Rotational Spectra of HDCO and D2CO

The ground state rotational spectra of HDCO and D2CO have been measured from 5 to 2000 GHz. These new measurements together with older ones have been fitted to a standard A-reduced Watson-type Hamiltonian. The accuracy of the rotational and centrifugal distortion constants has been significantly improved. It has to be noted that it was necessary to include octic constants. The experimental constants are compared to ab initio predictions. Copyright 1999 Academic Press.

Gas filter correlation instrument for air monitoring at submillimeter wavelengths

A gas filter correlation (GFC) instrument for air monitoring at submillimeter wavelengths has been developed. We used a high-power terahertz radiation source in combination with a specific gas filter cell to obtain a highly selective instrument to differentiate species present in an unknown mixture. This approach provides a new method for survey measurements in the spectrum from 100 to 1000 GHz, in which many molecular rotational lines appear. Basic operational considerations and preliminary experiments with hydrogen sulfide are described.