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The time-resolved diffraction signal from a laser-excited solution has three principal components: the solute-only term, the solute-solvent cross term, and the solvent-only term. The last term is very sensitive to the thermodynamic state of the bulk solvent, which may change during a chemical reaction due to energy transfer from light-absorbing solute molecules to the surrounding solvent molecules and the following relaxation to equilibrium with the environment around the scattering volume. The volume expansion coefficient α for a liquid is typically ∼1×10-3 K-1, which is about 1000 times greater than for a solid. Hence solvent scattering is a very sensitive on-line thermometer. The decomposition of the scattered x-ray signal has so far been aided by molecular dynamics (MD) simulations, a method capable of simulating the solvent response as well as the solute term and solute/solvent cross terms for the data analysis. Here we present an experimental procedure, applicable to most hydrogen containing solvents, that directly measures the solvent response to a transient temperature rise. The overtone modes of OH stretching and CH3 asymmetric stretching in liquid methanol were excited by near-infrared femtosecond laser pulses at 1.5 and 1.7 μm and the ensuing hydrodynamics, induced by the transfer of heat from a subset of excited CH3OH* to the bulk and the subsequent thermal expansion, were probed by 100 ps x-ray pulses from a synchrotron. The time-resolved data allowed us to extract two key differentials: the change in the solvent diffraction from a temperature change at constant density, seen at a very short time delay ∼100 ps, and a term from a change in density at constant temperature. The latter term becomes relevant at later times ∼1 μs when the bulk of liquid expands to accommodate its new temperature at ambient pressure. These two terms are the principal building blocks in the hydrodynamic equation of state, and they are needed in a self-consistent reconstruction of the solvent response during a chemical reaction. We compare the experimental solvent terms with those from MD simulations. The use of experimentally determined solvent differentials greatly improved the quality of global fits when applied to the time-resolved data for C2H4I2 dissolved in methanol. [ABSTRACT FROM AUTHOR]

A time-resolved x-ray-diffraction experiment is presented that aims to study the recombination of laser-dissociated iodine molecules dissolved in CCl4. This process is monitored over an extended time interval from pico- to microseconds. The variations of atom-atom distances are probed with a milliangstrom resolution. A recent theory of time-resolved x-ray diffraction is used to analyze the experimental data; it employs the correlation function approach of statistical mechanics. The most striking outcome of this study is the experimental determination of time-dependent I–I atom-atom distribution functions. The structure of the CCl4 solvent changes simultaneously; the solvent thus appears as a reaction partner rather than an inert medium hosting it. Thermal expansion of the system is nonuniform in time, an effect due to the presence of the acoustic horizon. One concludes that a time-resolved x-ray diffraction permits real-time visualization of solvent and solute motions during a chemical reaction. [ABSTRACT FROM AUTHOR]

A theory is proposed to study time-resolved x-ray diffraction on the pico- and subpicosecond time scales. Electromagnetic fields are treated in the frame of Maxwellian electrodynamics, whereas the molecular system is treated by using quantum mechanics. An expression is given for the time-resolved x-ray signal; it involves a three-time correlation function of the Fourier transformed electronic density and of the electric dipole moment of the system. This theory is applied to the study of the recombination of photodissociated iodine molecules in solution. Both geminate and nongeminate recombination are considered. The feasibility of the real time visualization of atomic motions is discussed. [ABSTRACT FROM AUTHOR]

Using femtosecond resolution X-ray solution scattering at a free electron laser we were able to directly observe metal–metal bond cleavage upon photolysis at 400 nm of Ru3(CO)12, a prototype for the photochemistry of transition metal carbonyls. This leads to the known single intermediate Ru3(CO)11(μ-CO)*, with a bridging ligand (μCO) and where the asterisk indicates an open Ru3-ring. This loses a CO ligand on a picosecond time scale yielding a newly observed triple bridge intermediate, Ru3(CO)8(μ-CO)3*. This loses another CO ligand to form the previously observed Ru3(CO)10, which returns to Ru3(CO)12via the known single-bridge Ru3(CO)10(μ-CO). These results indicate that contrary to long standing hypotheses, metal–metal bond breakage is the only chemical reaction immediately following the photolysis of Ru3(CO)12 at 400 nm. Combined with previous picosecond resolution X-ray scattering data and time resolved infrared spectroscopy these results yield a new mechanism for the photolysis of Ru3(CO)12. [ABSTRACT FROM AUTHOR]

Neutron diffraction from a polycrystalline sample of 242Pu2O3 (La2O3 structure) has been used to solve the magnetic structure below TN=19 K. The magnetic unit cell requires a doubling in all three crystallographic directions of the chemical unit cell. Below 4 K the magnetic and chemical unit cells become identical. The moments point along the unique c axis at all temperatures below TN. The magnetic moment is 0.60(2)μB per Pu ion and the C2 coefficient in the Pu3+ form factor is 4.5(3). The value of the moment, its direction within the unit cell, and the C2 coefficients are all consistent with the |±3/2> Kramers doublet being the ground state of the Pu3+ ion. [ABSTRACT FROM AUTHOR]

Presents a study which examined spin and orbital moments in actinide compounds. Experimental details and techniques; Analysis of the magnetic form data; Results and discussion.