How to get access to long range states of highly excited molecules

Due to competition between ionic and covalent dissociation, the excited potential curves of the alkali dimers display long range structures, leading in some cases to secondary wells. We discuss the possibility of populating the well (with a depth of 1614.8 cm^-1, located at R _e = 30.5a ₀ ) that is present in the Na₂ potential curve and propose detection schemes. Received: 28 May 1998 / Revised: 5 August 1998 / Accepted: 24 September 1998     

A novel electrochemical approach for fabrication of photoluminescent erbium-doped porous silicon

21 /cm³. After this new ECD treatment, PS:Er was found to emit much more intense room-temperature visible photoluminescence than both the porous silicon control and the PS:Er prepared by constant-current ECD. Room-temperature IR photoluminescence around 1.54 μm was observed for the first time without any post-doping annealing. Received: 3 September 1998/Accepted: 9 September 1998     

Behavior of intruder based states in light Bi and Tl isotopes: the study of 187Bi α decay

The excitation energies of the single-particle normal and intruder levels in both ¹⁸³Tl and ¹⁸⁷Bi were measured for the first time via the α decay of ¹⁸⁷Bi produced in the ⁹⁷Mo(⁹²Mo,pn)¹⁸⁷Bi reaction. The previously unobserved ¹⁸⁷Bi ground state (h_9/2) to ¹⁸³Tl ground state (s_1/2) α transition was identified, establishing the ¹⁸⁷Bi intruder state excitation energy to be 112(21) keV, 70 keV less than that of the same level in ¹⁸⁹Bi. Received: 10 September 1998 / Revised version: 18 December 1998     

Photoelectron and photoion spectroscopy on atomic Lu in the region of the 5p excitation

The resonances of atomic Lu have been investigated by photoelectron and photoion spectroscopy using monochromatized synchrotron radiation in the vacuum ultraviolet energy region. The total photoion yield has been compared to calculations in which the extended Fano theory (Mies formalism) and the Hartree-Fock method were applied. The resonance structure is dominated by the spin-orbit splitting of the 5p core hole. In the photoion yield spectra of singly and doubly charged ions a high fraction of Lu²⁺ ions has been found in the region of the 5p ^-1 (² P _1/2 )nd resonances. Photoelectron spectra, recorded in this resonance region, have been investigated with respect to deexcitation channels connected with Lu²⁺ ions. The 5p ^-1 (² P _1/2 )nd resonances predominantly autoionize by spin-flip into states, which decay in the second step into Lu²⁺ final ionic states. Received: 2 September 1998 / Accepted: 17 September 1998     

Sum-frequency vibrational spectroscopy of a monolayer self-assembled on gold: interference between resonant and nonresonant contributions of nonlinear polarization

zzz ^(R) is dominant in the observed resonant signals, whereas all of the ijk components contribute to the nonresonant signal. The transition frequencies and the relative amplitude of resonant signals are also determined for the CH₃ vibrational modes of ODT on gold. Received: 21 August 1998 / Revised version: 16 September 1998 / Published online: 24 February 1999     

Gamma-spectroscopy of the 199At nucleus with the Recoil Filter Detector

The neutron deficient ¹⁹⁹At nucleus has been studied in the ¹⁷⁵Lu+²⁸Si reaction at E_b= 141 MeV. In order to select events of interest in the presence of the very strong background caused by fission, γ-rays have been detected in coincidence with recoiling evaporation residues. The excited states of ¹⁹⁹At observed for the first time may indicate that this nucleus is deformed. Received: 17 September 1998 / Revised version: 14 October 1998     

Influence of hydrodynamics on the dynamics of a homopolymer

We present an analytical approach of the dynamics of a polymer when it is quenched from a solvent into a good or bad solvent. The dynamics is studied by means of a Langevin equation, first in the absence of hydrodynamic effect, then taking into account the hydrodynamic interactions with the solvent. The variation of the radius of gyration is studied as a function of time. In both cases, for the first stage of collapse or swelling, the evolution is described by a power law with a characteristic time proportional to N ^4/3 (N), where N is the number of monomers, without (with) hydrodynamic interactions. At larger times, scaling laws are derived for the diffusive relaxation time. Received: 10 March 1998 / Received in final form: 15 September 1998 / Accepted: 25 September 1998     

Flow equations and the Ruderman-Kittel-Kasuya-Yosida interaction

In the past different models for the magnetic salt vanadyl pyrophosphate (VO)₂P₂O₇ were discussed. Neither a spin ladder nor an alternating chain are capable to describe recently measured magnetic excitations. In this paper we propose a 2D model that fits better to experimental observations. Received: 29 May 1998 / Received in final form: 25 September 1998 / Accepted: 30 September 1998     

Elastic and inelastic scattering of 58Ni +90,94Zr

Pure elastic and inelastic scattering cross sections have been measured for the systems ⁵⁸Ni +^90,94Zr at energies near the Coulomb barrier where not only quasi-elastic and fusion but also deep-inelastic process come into play. Coupled channels calculations including both projectile and target inelastic excitations can successfully explain the elastic and inelastic scattering angular distributions with an energy-independent semi-empirical bare potential. The calculation reproduces also the sum of the total quasi-elastic, fusion and deep-inelastic cross sections. Received: 14 September 1998 / Revised version: 21 October 1998     

New excitation scheme of 139Cs

¹³²Te was produced via the ²³²Th (α, fission) reaction at the Variable Energy Cyclotron , Calcutta. ¹³²Te was separated in carrier-free form from the fission products by radiochemical separation and the half-lives for the 50 keV and 162 keV states of ¹³²I were determined to be 2.94±0.11 ns and 0.55±0.04 ns respectively. The present results differ significantly from the previously reported half-lives of 7.14 ns and 3.57 ns for the 50 keV and 162 keV states respectively. Received: 28 July 1998 / Revised version: 23 September 1998     

Praseodymium-doped Ti:LiNbO3 waveguides

3 by diffusion doping is investigated by means of secondary neutral mass spectrometry and secondary ion mass spectrometry. The diffusion of praseodymium in LiNbO₃ can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient and a limited solubility of praseodymium in LiNbO₃ increasing exponentially with rising temperature. The diffusion depends on the Li₂O content of the LiNbO₃ crystal. For LiNbO₃ crystals with a nominal slight difference in the congruent composition, the diffusion constants and activation energies for Z-cut LiNbO₃ are 3.28×10^-5 cm²/s and 2.27 eV, and 1.39×10^-5 cm²/s and 2.24 eV, respectively. Titanium-doped waveguides are formed in Pr:LiNbO₃ and characterised in relation to waveguide loss and absorption in the visible and near infrared. Received: 17 September 1998 / Accepted: 11 November 1998     

A new polymeric material for optical switching

′ -(2^′′,4^′′,6^′′-trichlorophenazoamino)-phenazo-4-nitrobenzene, was studied. Large nonresonant optical nonlinearity (χ⁽³⁾≥10^-28 C⁴m/J³ or 10^-9 esu) and fast response time (t<20 ps) were measured by forward degenerate four-wave mixing experiment. Optical bistable behavior in a quasi-waveguide interferometer with the thin film of the material was observed. The potential of the material for optical switching was evaluated. Received: 20 July 1998/Revised version: 11 September 1998     

Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV

The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by defolding the p_t spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions of resonances are obtained from the invariant masses of (p, π^±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c² relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass values of 2000 MeV/c². The observed differences between (p, π⁻) and (p, π⁺) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e. to rather low temperatures and large expansion velocities. Received: 26 June 1998 / Revised version: 2 September 1998     

Analysis of degenerate four-wave mixing spectra of NO in a CH4/N2/O2 flame

4 /N₂/O₂ flame to spectral simulations based on a two-level theory for stationary, saturable absorbers by Abrams et al. Temperatures determined from least-squares fits of simulations to experimental spectra in the A²Σ⁺?X²Π⁺(0,0) band are compared to temperatures obtained from OH absorption spectroscopy and a radiation-corrected thermocouple. We find that DFWM rotational temperatures derived from Q-branch spectra agree with thermocouple and are independent of pump laser intensity for low to moderate saturation (I≈I_sat). However, the temperatures are systematically low and depend on pump intensity if the analysis neglects saturation effects. We demonstrate a method for obtaining an effective pump saturation intensity for use with the two-level model. This approach for analyzing saturated DFWM line intensities differs from previous work in that the use of the theory of Abrams et al. rather than a transition-dipole-moment power law allows treatment of a much wider range of saturation. Based on the observed signal-to-noise ratio an NO detection sensitivity of 25 ppm is projected, limited by a DFWM background interference specific to hydrocarbon flames. Received: 15 September 1998 / Revised version: 18 November 1998 / Published online: 24 February 1999     

Electron detachment and fragmentation in collisions between 1.25 keV/carbon and clusters and

The destruction cross-section for 22.5 and 50 keV C^1- , for 10 and 50 keV C₈ ^1- and for 50 and 75 keV C₆₀ ^1- clusters in collisions with H₂ has been measured by an attenuation method. The destruction of the cluster anions is dominated by electron detachment rather than fragmentation and is of the order of the geometric cross-section. The cross-sections vary little with bombarding energy. Received: 16 September 1998 / Received in final form: 23 February 1999     

Effect of He+ and H+ ion irradiation on polystyrene films probed by NIR photothermal deflection spectroscopy

+ and H⁺ ions. Photothermal deflection spectroscopy (PDS) technique was used to record the absorption spectrum in the wavelength range 1.20 μm to 2.0 μm. The evolution of the various overtone and combination bands occurring in this range has been related to the changes taking place in the polystyrene structure. Received: 1 September 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999     

A neutral atom and a wire: towards mesoscopic atom optics

A large variety of trapping and guiding potentials can be designed by bringing cold atoms close to charged or current-carrying material objects. Using a current-carrying wire we demonstrate how to build guides and traps for neutral atoms and using a charged wire we study a 1/r ² singularity. The simplicity and versatility of the principles demonstrated in our experiments will allow for miniaturization and integration of atom optical elements into matter-wave quantum circuits. Received: 13 December 1998 / Revised version: 8 July 1999 / Published online: 8 September 1999     

The β+-electron capture decay of 73Kr

The β⁺– electron capture decay of ⁷³Kr, produced at the ISOLDE CERN facility, has been studied by β-delayed proton and gamma emission. The established decay scheme involves 15 up to now unreported gamma emitting levels in ⁷³Br. The total proton branching ratio has been measured to be 0.0025 ± 0.0003. From this work, a spin and parity 3/2⁻ is assigned to the ⁷³Kr ground state, on the basis of the allowed β branch to the ⁷³Br J^π= 1/2⁻ ground state and the feeding of the 5/2⁺ level located at 286 keV in ⁷³Br. Received: 17 September 1998 / Revised version: 25 January 1999     

Isotopically selective infrared multiphoton dissociation of 2-chloro-1,1,1-trifluoroethane: 13C selectivity and mechanism

13 C-selective infrared multiphoton dissociation of CF₃CH₂Cl has been studied by analyzing the distribution of ¹³C concentrations of the main products CF₂=CHCl, CF₂=CH₂, CF₂=CHF, C₂F₆, and the trace products CF₃CH₂CF₃ and CF₃CH=CHF₃. The mechanism mainly concerns the dissociation of energized CF₃CH₂Cl, the collisional stabilization of excited CF₃CH and CF₃CH₂ and the recombination of the nascent radicals. No significant radical–molecule reactions degrade the intrinsic ¹³C dissociation selectivity. High ¹³C production yield and ¹³C concentration can be attained at a laser fluence of 1.6 J/cm². Such low fluence can be used to improve focus condition and enhance photon utilization efficiency for practicable ¹³C separation. Received: 10 March 1998/Revised version: 17 September 1998     

Dopant diffusion and segregation in semiconductor heterostructures: Part 2. B in GexSi1-x/Si structures

x Si_1-x/Si heterostructures have been obtained. Here the chemical effects seem to be of less importance. The Fermi-level effect determines the ionized boron solubilities in Ge_xSi_1-x and in Si, as well as the thermal equilibrium concentration of the singly-positively-charged crystal self-interstitials I⁺ which governs the boron diffusion process. The junction carrier concentration affects the concentration of I⁺ and solubility of B in the region and hence controls B diffusion across the heterojunction. Received: 20 August 1998/Accepted: 23 September 1998