Time-domain theoretical analysis of the noncoincidence effect, diagonal frequency shift, and the extent of delocalization of the C=O stretching mode of acetone/dimethyl sulfoxide binary liquid mixtures

A time-domain method for simulating vibrational band profiles that simultaneously takes into account both the diagonal and off-diagonal effects is developed and applied to the C=O stretching bands of neat liquid acetone and the acetone/dimethyl sulfoxide (DMSO) binary liquid mixtures. By using this method, it is possible to examine the influence of liquid dynamics on the noncoincidence effect (NCE), which arises from the off-diagonal vibrational interactions, as well as the frequency shifts and band broadening, which are related to both the diagonal and off-diagonal effects. It is shown that the simulations for the C=O stretching bands of acetone in acetone/DMSO binary liquid mixtures on the basis of this method can reproduce the experimentally observed concave curvature of the concentration dependence of the NCE and the unusually large frequency shift of the anisotropic Raman band. The widths of the infrared, isotropic Raman, and anisotropic Raman bands calculated for neat liquid acetone are also in good agreement with those observed. Based on these calculations, the extent of delocalization of the C=O stretching vibrational motions is examined by referring to two quantitative measures of this property, one calculated in the frequency domain and the other in the time domain. It is shown that the extent of delocalization gets larger as the mole fraction of acetone increases, the C=O stretching vibrations being delocalized over a few tens of molecules in neat liquid acetone. It is also shown that the extent of delocalization is related to the quantity called NCE detectability, which is the ratio between the magnitude of NCE and the bandwidth. It is therefore suggested that the extent of delocalization of vibrational motions may be estimated from observable features of Raman band profiles.     

New calibrations and time stability of the response of the INTERCAST CR-39

We present new calibrations of different production batches (from 1989 to 1999) of the INTERCAST CR-39, using the BNL-AGS 1 A GeV iron beam. The comparison with previous results, obtained with the 158 A GeV lead beam from the CERN-SPS shows that, while each production batch has a different calibration curve (mainly due to minor differences in the production conditions), the aging effect is negligible. We also tested the dependence of the CR-39 response from the time elapsed between exposure and analysis (fading effect). The fading effect, if present, is less then 10%. It may be compatible with the experimental uncertainties on the bulk etching rate v_B.     

The Raman noncoincidence effect of the ν(CO) band of ME6N liquid crystal across the nematic–isotropic phase transition studied by a micro‐spectroscopy experiment

The Raman spectroscopic noncoincidence effect (NCE) of the ν(CO) band of the liquid crystal ME6N (4‐cyanophenyl‐4′‐hexylbenzoate) has been measured at different temperatures (47–52 °C) around the nematic‐isotropic phase transition (47.8 °C) employing a micro‐Raman experiment under confocal conditions and performed on a homogeneously aligned thin sample. The low value of NCE (0.9 cm⁻¹) obtained over the whole temperature range suggests that the orientational structure of the liquid crystal in both phases is governed by the steric hindrances in the proximity of the carbonyl group, rather than by dipolar interactions. This hypothesis is supported by the results of a supplementary investigation of the NCE of the ν(CO) Raman band in liquid ketones and esters, made progressively more hampered by the insertion of bulky (phenyl) groups in proximity of the carbonyl group. The NCE of the ν(CO) band, in fact, decreases from 5.5 cm⁻¹ in acetone (the less hampered) to 0.7 cm⁻¹ in benzophenone (the most hampered among the studied ketones), and from 6.2 cm⁻¹ in methyl acetate (the less hampered) to 2.2 cm⁻¹ in phenyl benzoate (the most hampered among the studied esters). To our best knowledge, this represents the first attempt to analyze the NCE in terms of steric hindrance of the substituents around the target oscillator. A parallel analysis of the difference between the anisotropic and the isotropic bandwidths of the ν(CO) Raman band in these molecular liquids indicates that reorientational dynamics plays only a marginal role, if any. Copyright © 2006 John Wiley & Sons, Ltd.     

Nuclear orbiting and anomalies in nuclear reactions

In this paper, we report our measurements of back-angle oxygen and carbon particle yields from ¹⁶O+⁸⁹Y, ¹²C+⁹³Nb reactions forming the same compound nucleus ¹⁰⁵Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence at high excitation energies from ¹⁶O+⁸⁹Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission is also discussed.     

Chiral interactions in azobenzene dimers: a combined experimental and theoretical study

To investigate interchromophore interactions in azobenzene polymers, we have undertaken a thorough spectroscopic analysis of the azodye [(S)-3-pivaloyloxy-1-(4'-nitro-4-azobenzene)pyrrolidine] by modeling the repeating unit of poly[(S)-3-methacryloyloxy-1-(4'-nitro-4-azobenzene)pyrrolidine) and its dimeric derivative whose synthesis is presented here. The analysis of the electronic and Raman spectra of the azodye in several solvents is based on a previously proposed model for polar chromophores in solution. Electronic and CD spectra of the dimeric unit are collected and analyzed within the framework of a new model. On the basis of the information collected from the spectroscopic analysis of the solvated dye, this model accounts for interchromophore interactions in the dimer. The large CD signal measured for the dimer (amounting to about a third of the signal measured for the polymer) suggests the presence of important chiral interactions in the dimeric unit, and is modeled in terms of a right-handed relative orientation of the two chromophores.     

Intermolecular and diffusive dynamics of pure acetonitrile isotopomers studied by depolarized Rayleigh scattering and femtosecond optical kerr effect

The relaxation dynamics of pure acetonitrile isotopomers has been investigated in the temperature range 8 to 75 ^° C. The overall response of the liquid is measured either recording directly the decay of the optical Kerr signal with heterodyne detection (OHD-OKE) and Fourier transforming the depolarized Rayleigh scattering spectra (DRS). The OHD-OKE signals show a decay that can be described by a bi-exponential law. At some temperatures, stressing to a maximum level the sensitivity of the OHD-OKE experimental set-up, a damped oscillation is observed on top of the fast decay component. The two techniques provide same results with a high level of reproducibility, as far as the slow component is concerned. This latter is described by an exponential law with the time constants ranging in the interval 2.0 to 0.85 ps in the light and approximately in the same interval in the deuterated molecule. The decays are, at all temperatures, well reproduced by the extended diffusion J-model. The fast component, better observed with the OHD-OKE experiments in a restricted temperature range, has time constants ranging from 550 to 350 fs. After the subtraction of the curve due to the slower decay component, the data have also been analyzed by Fourier transforming the fast part of the decay. The spectrum then consists of a broad (approximately 80 cm^-1 wide) band centered at 50 cm^-1. This band is interpreted as the manifestation of intermolecular vibrational motions. Received 21 July 2002 Published online 1st October 2002 RID="a" ID="a"e-mail: foggi@colonnello.lens.unifi.it     

Momentum distribution of a Fermi gas of atoms in the BCS-BEC crossover

We observe dramatic changes in the atomic momentum distribution of a Fermi gas in the crossover region between the BCS theory superconductivity and Bose-Einstein condensation (BEC) of molecules. We study the shape of the momentum distribution and the kinetic energy as a function of interaction strength. The momentum distributions are compared to a mean-field crossover theory, and the kinetic energy is compared to theories for the two weakly interacting limits. This measurement provides a unique probe of pairing in a strongly interacting Fermi gas.     

Molecular associations between indolizines and tetracyanoethylene

Spectroscopic, thermodynamic and kinetic properties of molecular interactions between indolizines and tetracyanoethylene are reported. The interactions involved in the complexes are weak as evidenced by the low formation constants. The kinetic behaviour indicates the initial formation of a pI-complex that is rapidly transformed into a σ-complex and thereafter into the final adduct(s). Apart from the results obtained by other techniques, infrared data clearly evidence vibrational contributes characteristic of the complexes, the tricyanovinyl derivatives and the tetracyanoethylene radical anion.     

Molecular associations of hydrazones. X. Dihydrazones as twin-site donors

Molecular associations of dihydrazones of 1,2-diketones with tetracyanoethylene are investigated and compared with those of the corresponding monohydrazones, in order to verify the influence of the second donor centre on the equilibrium constants. As proved by X-ray determinations (complex 2,3-butandionemonophenylhydrazone/tetracyanoethylene), hydrogen bonding appears to play an important role in the lattice stabilization of monohydrazones complexes. C₁₀H₁₂N₂O·1/2C₆N₄,M _r =240.66, monoclinic,C2/c,a=12.216(2),b=12.824(3),c=16.784(2)Å,=93.74(2)°,Z=8,D _x=1.22 g cm^–3,V=2623.8(8)ų, room temperature, CuK, =1.5418 Å,=6.28 cm^–1,F(000)=1008,R=0.059 for 1398 independent observed reflections. The aromatic ring is planar and the tetracyanoethylene atoms are far more than 3.40 Å from its barycentre. Together with van der Waals forces, H-bonding between two faced hydrazono molecules realizes the packing in the crystal.     

A portable laser system for high-precision atom interferometry experiments

We present a modular rack-mounted laser system for the cooling and manipulation of neutral rubidium atoms which has been developed for a portable gravimeter based on atom interferometry that will be capable of performing high-precision gravity measurements directly at sites of geophysical interest. This laser system is constructed in a compact and mobile design so that it can be transported to different locations, yet it still offers improvements over many conventional laboratory-based laser systems. Our system is contained in a standard 19″ rack and emits light at five different frequencies simultaneously on up to 12 fibre ports at a total output power of 800 mW. These frequencies can be changed and switched between ports in less than a microsecond. The setup includes two phase-locked diode lasers with a phase noise spectral density of less than 1 μrad/Hz^1/2 in the frequency range in which our gravimeter is most sensitive to noise. We characterise this laser system and evaluate the performance limits it imposes on an interferometer.