Chaotic phenomena of charged particles in crystal lattices

In this article, we have applied the methods of chaos theory to channeling phenomena of positive charged particles in crystal lattices. In particular, we studied the transition between two ordered types of motion; i.e., motion parallel to a crystal axis (axial channeling) and to a crystal plane (planar channeling), respectively. The transition between these two regimes turns out to occur through an angular range in which the particle motion is highly disordered and the region of phase space spanned by the particle is much larger than the one swept in the two ordered motions. We have evaluated the maximum Lyapunov exponent with the method put forward by Rosenstein et al. [Physica D 65, 117 (1993)] and by Kantz [Phys. Lett. A 185, 77 (1994)]. Moreover, we estimated the correlation dimension by using the Grassberger-Procaccia method. We found that at the transition the system exhibits a very complex behavior showing an exponential divergence of the trajectories corresponding to a positive Lyapunov exponent and a noninteger value of the correlation dimension. These results turn out to be linked to a physical interpretation. The Lyapunov exponents are in agreement with the model by Akhiezer et al. [Phys. Rep. 203, 289 (1991)], based on the equivalence between the ion motion along the crystal plane described as a "string of strings" and the "kicked" rotator. The nonintegral value of the correlation dimension can be explained by the nonconservation of transverse energy at the transition.     

Interpretation of the 13C16O2 spectrum at 4.4 μm

The overlapping structure observed in the region of the ν₃ fundamental of ¹³C¹⁶O₂ at 4.4 μm has been assigned to several transitions belonging to not only the 13-C variety of carbon dioxide (¹³C¹⁶O₂) but also to ¹³C¹⁶O¹⁷O and ¹³C¹⁶O¹⁸O species occurring in the sample. Molecular constants have been evaluated for the assigned transitions.     

Instrumental neutron activation analysis of an enriched 28Si single-crystal

The determination of the Avogadro constant plays a key role in the redefinition of the kilogram in terms of a fundamental constant. The present experiment makes use of a silicon single-crystal highly enriched in ²⁸Si that must have a total impurity mass fraction smaller than a few parts in 10⁹. To verify this requirement, we previously developed a relative analytical method based on neutron activation for the elemental characterization of a sample of the precursor natural silicon crystal WASO 04. The method is now extended to fifty-nine elements and applied to a monoisotopic ²⁸Si single-crystal that was grown to test the achievable enrichment. Since this crystal was likely contaminated, this measurement tested also the detection capabilities of the analysis. The results quantified contaminations by Ge, Ga, As, Tm, Lu, Ta, W and Ir and, for a number of the detectable elements, demonstrated that we can already reach the targeted 1 ng/g detection limit.     

The ablation of quartz wall by SF6 under radiofrequency discharge

The behaviour of SF₆ in quartz and alumina tubes of a flow reactor capacitively coupled to a 35 MHz radiofrequency generator has been investigated at pressure of 20 torr, with power levels of 3.5÷5.5 cal cm^?3 sec^?1 and gas flow rates ranging between 0.1 and 2 1(STP) min^?1. A combination of gaschromatographic, mass spectrometric and infrared spectrophotometric techniques has shown the presence of SO₂F₂, SOF₄, SOF₂, SiF₄, F₂, O₂ together with unreacted SF₆ in the discharge products.A detailed quantitative investigation of the effluent products and of their concentration profiles versus space time and power is presented and a general mechanism for the ablation process of the quartz wall is suggested.     

Rotational spectra of rare isotopic species of bromofluoromethane: determination of the equilibrium structure from ab initio calculations and microwave spectroscopy

Guided by theoretical predictions, the rotational spectra of the mono- and bideuterated species of bromofluoromethane, CDH(79)BrF, CDH(81)BrF, CD(2) (79)BrF, and CD(2) (81)BrF, have been recorded for the first time. Assignment of a few hundred rotational transitions led to the accurate determination of the ground-state rotational constants, all of the quartic and most of the sextic centrifugal distortion constants, as well as the full bromine quadrupole-coupling tensor for both (79)Br and (81)Br, in good agreement with corresponding theoretical predictions based on high-level coupled-cluster calculations. The rotational spectra of the (13)C containing species (13)CH(2) (79)BrF and (13)CH(2) (81)BrF have been observed in natural abundance and have been assigned, thus allowing the determination of the rotational and centrifugal distortion constants as well as the bromine quadrupole-coupling tensor. Furthermore, empirical equilibrium structures have been obtained within a least-squares fit procedure using the available experimental ground-state rotational constants for various isotopic species. Vibrational effects have been accounted for in the analysis using vibration-rotation interaction constants derived from anharmonic force fields computed at the second-order Moller-Plesset perturbation theory as well as coupled-cluster (CC) levels. The empirical equilibrium geometries obtained in this way agree well with the corresponding theoretical predictions obtained from CC calculations [at the CCSD(T) level] after extrapolation to the complete basis set limit and inclusion of core-valence correlation corrections and relativistic effects.     

High-resolution FTIR, microwave, and ab initio investigations of CH2 79BrF: ground, v(5) = 1, and v(6) = 1, 2 state constants

A spectroscopic study of CH279BrF in the infrared and microwave regions has been carried out. The rovibrational spectrum of the nu5 fundamental interacting with 2nu6 has been investigated by high-resolution FTIR spectroscopy. Owing to the weakness of the 2nu6 band, the v6 = 2 state constants have been derived from v6 = 1. For this reason, the rotational spectra of the ground and v6 = 1 states have been observed by means of microwave spectroscopy. Highly accurate ab initio computations have also been performed at the CCSD(T) level of theory in order to support the experimental investigation. As far as the nu5 band is concerned, the analysis of the rovibrational structure led to the identification of more than 3000 transitions, allowing the determination of a set of spectroscopic parameters up to sextic distortion terms and pointing out first-order c-type Coriolis interaction with the v6 = 2 state. With regard to the pure rotational spectra measurements, the assignment of several DeltaJ = 0, +1 transitions allowed the determination of the rotational, all the quartic, and most of the sextic centrifugal distortion constants, as well as the full bromine quadrupole coupling tensor for both the ground and v6 = 1 states.     

Packed capillary liquid chromatography–electrospray mass spectrometry analysis of organophosphorus chemical warfare agents

Packed capillary column liquid chromatography (LC)–electrospray mass spectrometry (ESI-MS) was used for the first time to detect and identify four common organophosphorus chemical warfare agents in aqueous samples. Aqueous samples containing the organophosphorus chemical warfare agents in the 0.01 to 0.1 mg/ml range were analyzed directly by packed capillary LC–ESI-MS with the chemical warfare agents and several minor related impurities being well resolved under acetonitrile–water gradient elution conditions. The ESI-MS data for isopropyl methylphosphonofluoridate (sarin or GB), O-ethyl N,N-dimethylphosphoramidocyanidate (tabun or GA), cyclohexyl methylphosphonofluoridate (GF) and pinacolyl methylphosphonofluoridate (soman or GD) were acquired with a sampling cone voltage setting that promoted collisionally activated dissociation, and resulted in the acquisition of informative mass spectra containing both molecular and product ion information. The developed method appears to be an attractive alternative to GC–MS for the analysis of aqueous samples containing organophosphorus chemical warfare agents and their hydrolysis products, since they may be analyzed directly without the need for additional sample handling.     

Characterization of PEO-lithium triflate polymer electrolytes: Conductivity, DSC and Raman Investigations

Polymeric membranes to be used as electrolytic separators in lithium batteries were prepared from Poly Ethylene Oxide (PEO) and Lithium Triflate salt (LiTf) via a solventfree procedure. Several membranes, having different PEO/LiTf molar ratios, were characterized by Electrochemical Impedance Spectroscopy (EIS) to obtain their ionic conductivity. Most of the compositions exhibit an Arrhenius-like behaviour with two different activation energies above and below 60 °C. Only the sample having the highest LiTf concentration showed a non-Arrhenius trend. Differential Scanning Calorimetry (DSC) study was performed to determine the various phases present in the system. The degree of association of the mobile ions changes vs. composition and temperature was investigated by Raman spectroscopy, a powerful technique which allows to follow these changes in details by studying the spectral parameters of the SO₃ stretching vibration of triflate ions. These data were correlated with the conductivity and thermodynamic data. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.