Quantum tunneling of oxygen atoms on very cold surfaces.

Any evolving system can change state via thermal mechanisms (hopping a barrier) or via quantum tunneling. Most of the time, efficient classical mechanisms dominate at high temperatures. This is why an increase of the temperature can initiate the chemistry. We present here an experimental investigation of O-atom diffusion and reactivity on water ice. We explore the 6-25 K temperature range at submonolayer surface coverages. We derive the diffusion temperature law and observe the transition from quantum to classical diffusion. Despite the high mass of O, quantum tunneling is efficient even at 6 K. As a consequence, the solid-state astrochemistry of cold regions should be reconsidered and should include the possibility of forming larger organic molecules than previously expected.

Water formation through O2 + D pathway on cold silicate and amorphous water ice surfaces of interstellar interest.

The formation of the first monolayer of water molecules on bare dust grains is of primary importance to understand the growth of the icy mantles that cover dust in the interstellar medium. In this work, we explore experimentally the formation of water molecules from O(2) + D reaction on bare silicate surfaces that simulates the grains present in the diffuse interstellar clouds at visual extinctions (A(V) < 3 mag). For comparison, we also study the formation of water molecules on surfaces covered with amorphous water ice representing the dense clouds (A(V) ≥ 3 mag). Our studies focus on the formation of water molecules in the sub-monolayer and monolayer regimes using reflection absorption infrared spectroscopy and temperature-programmed desorption techniques. We provide the fractions of the products, such as D(2)O and D(2)O(2) molecules formed on three astrophysically relevant surfaces held at 10 K (amorphous olivine-type silicate, porous amorphous water ice, and nonporous amorphous water ice). Our results showed that the formation of D(2)O molecules occurs with an efficiency of about 55%-60% on nonporous amorphous water ice and about 18% on bare silicate grains surfaces. We explain the low efficiency of D(2)O water formation on the silicate surfaces by the desorption upon formation of certain products once the reaction occurs between O(2) and D atoms on the surface. A kinetic model taking into account the chemical desorption of newly formed water supports our conclusions.

Analysis of molecular hydrogen formation on low-temperature surfaces in temperature programmed desorption experiments.

The study of the formation of molecular hydrogen on low-temperature surfaces is of interest both because it enables the exploration of elementary steps in the heterogeneous catalysis of a simple molecule and because of its applications in astrochemistry. Here, we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments, beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations, and the energy barriers of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results are used in order to evaluate the formation rate of H2 on dust grains under the actual conditions present in interstellar clouds. It is found that, under typical conditions in diffuse interstellar clouds, amorphous silicate grains are efficient catalysts of H2 formation when the grain temperatures are between 9 and 14 K. This temperature window is within the typical range of grain temperatures in diffuse clouds. It is thus concluded that amorphous silicates are good candidates to be efficient catalysts of H2 formation in diffuse clouds.

[Computerized recording of physiologic parameters monitored during anesthesia]. / Registrazione computerizzata dei parametri fisiologici monitorizzati durante anestesia.

STUDY OBJECTIVE: The aim of the study is to describe a multifunctional anesthesia record system PC-based, for use in operating room, and to verify the possibility of statistical analysis of some of the signals registered. DESIGN: Anesthesia records with data entered automatically were performed in 650 patients undergoing anesthesia for abdominal or thoracic surgery. A randomized trial in patients allocated into two groups was performed too. The first group was ventilated with non rebreathing system, the second group was ventilated with circle system. SETTING: Inpatient surgery clinic at a medical center. PATIENTS: 24 patients ASA I undergoing general anesthesia for laparoscopic cholecystectomy. INTERVENTIONS: The first group was ventilated with O2 = 4 1/min-1 and N2O = 6 1/min-1; the second group was ventilated with O2 = 350 ml/min-1 and N2O = 250 ml/min-1, reducing the N2O flow in order to keep FIO2 = 0.4. MEASUREMENTS: Esophageal temperature was registered every 90 sec and automatically copied on a Microsoft Excel spread sheet for statistical analysis. RESULTS: The automated anesthesia record was easy to use and different information about anesthesia and surgery were recorded. The automated analysis of the signals can be performed if no artifacts exist. With this method we found a statistical difference in the esophageal temperature between the two groups after 45 min of anesthesia. CONCLUSIONS: Computerized records capture many more data than handwritten records and give the possibility to give a rationale in their customs.