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The available knowledge of the electronically excited states of the copper dimer is limited. This is common for transition metals, as the high density of states hinders both experimental assignment and computation. In this work, two-color resonant four-wave mixing spectroscopy was applied to neutral Cu2in the gas phase. The method yielded accurate positions of individual rovibrational lines in the I-X and J-X electronic systems. This revealed the term symbols for the I and J states as 1Πu(1u) and 1Σu+(0u+), respectively. For the 63Cu2isotopologue, accurate molecular constants were obtained. The characterization of the J state finally allowed decisive determination of its electron configuration. The J state is obtained from the ground state by promotion of a 3dπgelectron into the weakly bonding 4pπumolecular orbital. From the data analysis, lifetimes of the I state (between 10 ps and 5 ns) and J state (66 ns) were inferred.

The extension of transient grating spectroscopy to the x-ray regime will create numerous opportunities, ranging from the study of thermal transport in the ballistic regime to charge, spin, and energy transfer processes with atomic spatial and femtosecond temporal resolution. Studies involving complicated split-and-delay lines have not yet been successful in achieving this goal. Here we propose a novel, simple method based on the Talbot effect for converging beams, which can easily be implemented at current x-ray free electron lasers. We validate our proposal by analyzing printed interference patterns on polymethyl methacrylate and gold samples using ∼3  keV X-ray pulses.

We demonstrate the feasibility of the time-delayed femtosecond CARS (fs-CARS) technique in a dense gas environment. The experiments were performed on N2 molecules between 0.2 and 5 bar pressure. The method provides several advantages compared with its wavenumber-resolved counterpart, e.g. the possible separation of the non-resonant contributions to the signal, and is more suitable when the isolated lines approximations collapse and complex line mixing and energy transfer models have to be implemented in the signal description. The experimental results are in good agreement with theoretical considerations based on collision-induced rotational energy transfer (RET) models such as the common energy-corrected sudden approximation (ECS). Moreover, it is shown that the structure of the time-delayed signals is very sensitive to the applied pressures. Therefore, fs-CARS is an ideal supplementary tool for investigations of collision-induced spectroscopic effects, which are decisive for temperature and concentration determination in combustion processes. Copyright © 2002 John Wiley & Sons, Ltd.

A novel approach to the preparation and monitoring of molecules in high vibrational levels in their electronic ground state is presented. An ultrashort laser pulse prepares a well defined wavepacket in the electronic excited state and, following the evolution of this wavepacket, the proper frequency and timing are selected to optimize its coupling back down to high vibrational levels in the ground state. The evolution of the wavepacket in the ground state is then monitored by a time-delayed coherent scattering from the polarization that has been induced in the ground state by the first two pulses. The ability to populate vibrations as high as v = 26 for molecular iodine is demonstrated experimentally and the potential of the new method [which is termed (TD)²CARS] for further developments towards mode-selective excitations is discussed. Copyright © 2000 John Wiley & Sons, Ltd.

In this study, we report the ultrafast dissociation and recombination dynamics of I2 enclosed in well-defined cages formed by the electroneutral host framework of the crystalline microporous SiO2 modification decadodecasil 3R (DDR). In this composite, each cage is occupied by one guest molecule, corresponding to a high density of I2. The dynamics are investigated by femtosecond pump−probe spectroscopy with variable probe wavelengths. After excitation into the bound B state, collision-induced predissociation is observed followed by recombination onto the A and A‘ states, where the molecules undergo vibrational relaxation. A kinetic model is applied to simulate the experimental data. The results are compared with results from a former study [Materny et al. J. Phys. Chem. 1996, 100, 18650] where I2 predissociation and caging dynamics in compressed argon were probed along the reaction coordinate. Geminate primary recombination (within the cage) is characterized by rate constants which are nearly identical to those found for I2 in Ar at 200−400 bar. No geminate secondary recombination (diffusive, outside the cage) is observed. However, approximately 10% of the recombinations are assumed to be nongeminate with a rate that corresponds to the motion of iodine atoms into the adjacent cages.

In this paper we report femtosecond studies of the influence of rare-gas collisions on the dissociation reaction of NaI molecules by investigating the coherent wave packet motion in NaI at a temperature of 670 °C and rare-gas pressures ranging from 0 to 1000 bar. The photodissociation dynamics of NaI is influenced by the interaction between the excited covalent and the ionic ground state potential energy surfaces, which cross at a certain internuclear separation. Due to the adiabaticity of the so formed potential, studies of the elementary nuclear motion and reaction dynamics along the covalent (Na + I) and the ionic (Na⁺ + I^-) channels are possible. The probing is made for the transition-state complex [Na···I]^&thermod;*. Even at low rare-gas pressures a considerable influence of collisions on the wave packet motion within the adiabatic potential well is found. Only few collisions between NaI molecules and surrounding rare-gas atoms result in fast vibrational relaxation and loss of coherence. Furthermore, a stabilization of the transition state is observed due to the decrease of the Landau−Zener escape probability. The reaction cross section for the interaction of the transition state molecules with helium atoms is found to be smaller than for the interaction with argon atoms. The intensity of the detected laser-induced fluorescence arising from the transition Na ← Na* decreases with increasing rare-gas pressure. Here, the effect for argon atoms is smaller than for helium atoms.

X-ray diffraction and dielectric measurements have been performed on the molecular crystal CsCN as a function of temperature. The order parameter of the cubic to rhombohedral phase transition (Tc=186 K) was determined and interpreted by a coupling of the (CN)- orientations to the shear strain. At lower temperatures the dielectric response is dominated by thermally activated relaxations processes rather than by electrical ordering of the CN dipoles.

Femtosecond time-resolved CARS measurements on benzene, toluene, and binary mixtures of these molecules have been performed in the gas phase. Whereas a two-pulse excitation process prepares benzene in a single vibrational state, a vibrational wave packet is excited in toluene, which gives rise to oscillatory patterns in the CARS signal. For the mixed system one finds beats between modes coherently excited in both molecules. The results are analyzed using perturbative quantum calculations. It is shown that the rotational degree of freedom is responsible for the decay of the CARS signal in all cases. Furthermore, it is demonstrated that the details of the excitation process have to be incorporated in the calculation to obtain the correct amplitudes of the oscillating signals.

Elastic and inelastic neutron scattering studies of the Kondo lattice CeCu2Ge2 were performed. AtTN=4.1 K an incommensurate magnetic order develops with an ordering wave vectorq0=(0.28, 0.28, 0.54) and an ordered moment µs=0.74 µB. The crystalline electric field splits the 4f1-J-multiplet of the Ce ion into a ground state doublet and a quartet at 191 K. The wave function of the ground state yields an ordered moment of 1.54µB. Thus, due to the onset of the formation of a Kondo singlet the magnetic moment is considerably reduced. The magnetic relaxation rate ? was investigated via quasielastic neutron scattering. The temperature dependence of ?(T) is characteristic of heavy-fermion systems with a high temperature square root dependence and a limiting low temperature value, yielding a Kondo temperatureTK˜10K. The quasielastic component of the scattered neutron intensities persists down to the lowest temperatures, well belowTN. This quasielastic line is regarded as a characteristic feature of heavy-fermion systems and corresponds to the enhanced value of the linear term of the specific heat.

In this study, we have employed femtosecond time-resolved CARS (coherent anti-Stokes Raman scattering) spectroscopy in order to gain information about the molecular dynamics evolving on the electronic excited as well as ground state potential energy surfaces (PES) of iodine and bromine in the gas phase. The coherences of the wave packet in the temporal transients of the molecules excited by the ultrashort laser pulses are analyzed by means of fast Fourier transform calculations as well as by a simple model describing the purely rotational contribution. The latter is able to describe the rotational coherence seen for the excited but not for the ground-state dynamics. Information about vibrational dynamics is extracted from the transients reflecting the wave packet motion on both the ground and excited-state PES.

An inelastic neutron scattering study is performed on the new magnetically ordered heavy-fermion systems CeCu2Ge2and CeAg2Ge2. The temperature dependence of the quasielastic line can be interpreted in terms of a Kondo type of behavior. In addition crystalline electric field transition energies are reported.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.