Precision infrared spectroscopy in CF379Br by means of infrared-microwave double resonance

From the observation of double resonance effects on the microwave spectrum two coincidences between 9.4 μm CO₂ laser lines and infrared transitions of the ν₆ → (ν₆ + ν₁) band of CF₃⁷⁹Br have been determined: R(30) laser line coincident with ^qR₂(7), F = 17/2→17/2 transition, R(28) laser line coincident with all four ΔF = 0 hyperfine components of the ^qQ₈(13) transition. In both cases other infrared transitions lay within the tuning range of the laser. The frequencies of these two laser lines allowed calculations of the band center frequency ν₀ = 1083.530 ± 0.001cm^?1 and α_A = 11.93 ± 0.3MHz, for the ν₆ → (ν₆ + ν₁) band.α_B constants were determined for the vibrational states v₆, (v₆ + v₁), v₁, and v₃.     

"Safe" Coulomb excitation of 30Mg

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion."     

Anomalous spin dephasing in (110) GaAs quantum wells: anisotropy and intersubband effects

A strong anisotropy of electron spin decoherence is observed in GaAs/(AlGa)As quantum wells grown on a (110) oriented substrate. The spin lifetime of spins perpendicular to the growth direction is about one order of magnitude shorter compared to spins along [110]. The spin lifetimes of both spin orientations decrease monotonically above temperatures of 80 and 120 K, respectively. The decrease is very surprising for spins along the [110] direction and cannot be explained by the usual Dyakonov-Perel dephasing mechanism. A novel spin dephasing mechanism is put forward that is based on scattering of electrons between different quantum well subbands.     

Final-state interaction as the origin of the Cronin effect

The Cronin effect that refers to the enhancement of hadron spectra at intermediate p(T) with increasing A in pA collisions is traditionally explained in terms of the broadening of the parton transverse momentum in the initial state. We show that recent data on the nuclear modification factor at eta=0 for d+Au collisions can be understood in terms of the recombination of soft and shower partons in the final state. It is the centrality dependence of the soft parton density that leads to the Cronin effect.     

Numerical simulations of pulsed and quasi-cw regimes of synchronously pumped Raman oscillators

Synchronously pumped Raman oscillators allow for an efficient frequency conversion of pump pulses whose power is well below the threshold for extracavity stimulated Raman scattering (SRS). Numerical simulations show that the cavity mismatch of pump laser and Raman oscillator is critical for maximum conversion efficiency and minimum pulse duration for transient and stationary SRS. At a certain mismatch the simulations predict a quasi-cw Raman oscillator output even at moderate cavity quality factors. Optimum operation conditions are discussed for pump pulse trains of finite lengths. The results of the numerical calculations are in qualitative agreement with a simple phenomenological model. PACS 42.55.Ye; 42.65.Dr; 42.55.Lt     

Immunomagnetic separation and detection of Salmonella cells using newly designed carriers

A new method for simultaneous determination of alkoxyethanols (2-methoxyethanol, 2-ethoxyethanol, 2-isopropoxyethanol, and 2-butoxyethanol) by high-performance liquid chromatography (HPLC) with fluorescence detection has been developed. The alkoxyethanols and an internal standard (2-phenoxyethanol) were derivatized by treatment with 1-anthroylnitrile to give the anthroyl esters. The esterification was completed in 30 min in the presence of quinuclidine as base catalyst at room temperature. After stopping the reaction, an aliquot of the final solution was injected into the HPLC. The resulting anthroyl esters of the alkoxyethanols and the internal standard were separated on a C18 reversed-phase column with acetonitrile-water-acetic acid (65:35:0.1, v/v) as the mobile phase and detected fluorimetrically at excitation and emission wavelengths of 360 nm and 460 nm, respectively. The detection limits of the derivatives as alkoxyethanols at a signal-to-noise ratio of 3 were in the range of 1-3 pg per injection. The minimal amounts of alkoxyethanols derivatized in the reaction mixture for derivatization to determine the limits of detection were approximately 0.5 ng. This HPLC method was applied to the determination of some of alkoxyethanols in the air of the workplace where the thinner containing alkoxyethanols was used for painting.     

Experimental and ab Initio Equilibrium Structure and Harmonic Force Field of 1,2,5-Oxadiazole

The equilibrium structure of 1,2,5-oxadiazole has been calculated ab initio at the CCSD(T) level using a polarized valence quadruple zeta basis set. The harmonic force field has also been calculated at the MP2/cc-pVTZ, B3LYP/6-311++G(3df, 2pd), and B3LYP/cc-pVQZ levels. These force fields have been subsequently scaled and further refined by fitting them to the experimental values of the vibrational fundamentals of three isotopomers and the centrifugal distortion constants of the parent molecule. The specific refinement of those scaled force constants particularly sensitive to the experimental data set was decisive for obtaining a more reliable harmonic potential. The resulting force fields are presented and used, together with the ground state rotational constants, to calculate an r(z) structure. The experimental r(0), r(s), and r(m) structures have also been determined. The different results have been compared and it is concluded that the ab initio structure is a good approximation of the equilibrium structure. It is also shown that the magnetic correction is not negligible, particularly for the inertial defect. Another interesting conclusion is that the anharmonicity of the C-H stretching might be unusually small. Copyright 2001 Academic Press.