Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule.

Potassium and sodium-potassium eutectic dissolve slightly (of the order of lo-* g.-atom/l.) in certain ethers to give unstable blue solutions which are considered to be similar to the well-known blue solutions of alkali metals in ammonia and amines. Absorption spectra of the solutions show maxima a t about 7000 A.An attempt has been made to correlate the ability to give a blue solution with the structure and basicity of the ethers.IT has previously been reported that moderately stable blue solutions of potassium and sodium-potassium alloy in some ethers may be obtained. Solubility has since been observed in some fifteen ethers and one amino-ether. The solutions are immediately decolorised by air but they can be filtered through a sintered-glass disc in VIECZCO. Filtered solutions decolorise at room temperature, rapidly in some cases and slowly in others, owing principally to attack on the solvent by the alkali metal. The nature of the decomposition products has not been investigated. Generally, the total alkali-metal concentration appears €0 increase with decrease in temperature; in some ethers, viz., the dimethyl ethers oi polyethylene glycols, the surface of the sodium-potassium alloy exhibits a coppercoloured lustre at low temperature, presumably on account of the formation of alkali-metal Down, Lewis, Moore, and Wilkinson, PYOC. Chem. Soc., 1957, 209 (where references t o previous work with water and alcohols are given). EXPERIMENTALAs the solutions were unstable to air they were handled in vacuo or in oxygen-free nitrogen, methods similar to those described previously 8 being used. Preparation and Purification of Materials.-Solvents.Several ethers were available commercially. Others were prepared from available hydroxy-compounds by the Williamson method. The products were fractionally distilled, freed from alcohols by refluxing them over sodium, and distilled from lithium aluminium hydride in a stream of nitrogen.The cyclic tetramer of propylene oxide was prepared by polymerisation with boron trifluonde-ether complex, according to a method kindly provided by Mr. W. J. Toussaint of Union Carbide Chemicals Co., which is as follows: Dry propylene oxide (2198 g.) was added to a flask equipped with a stirrer, a brine-cooled condenser, and a feed tank for catalyst addition. The

The development of ultrafast gas electron diffraction with nonrelativistic electrons has enabled the determination of molecular structures with atomic spatial resolution. It has, however, been challenging to break the picosecond temporal resolution barrier and achieve the goal that has long been envisioned—making space- and-time resolved molecular movies of chemical reaction in the gas-phase. Recently, an ultrafast electron diffraction (UED) apparatus using mega-electron-volt (MeV) electrons was developed at the SLAC National Accelerator Laboratory for imaging ultrafast structural dynamics of molecules in the gas phase. The SLAC gas-phase MeV UED has achieved 65 fs root mean square temporal resolution, 0.63 Å spatial resolution, and 0.22 Å−1 reciprocal-space resolution. Such high spatial-temporal resolution has enabled the capturing of real-time molecular movies of fundamental photochemical mechanisms, such as chemical bond breaking, ring opening, and a nuclear wave packet crossing a conical intersection. In this paper, the design that enables the high spatial-temporal resolution of the SLAC gas phase MeV UED is presented. The compact design of the differential pump section of the SLAC gas phase MeV UED realized five orders-of-magnitude vacuum isolation between the electron source and gas sample chamber. The spatial resolution, temporal resolution, and long-term stability of the apparatus are systematically characterized.

Pump-probe measurements aim to capture the motion of electrons and nuclei on their natural timescales (femtoseconds to attoseconds) as chemical and physical transformations take place, effectively making "molecular movies" with short light pulses. However, the quantum dynamics of interest are filtered by the coordinate-dependent matrix elements of the chosen experimental observable. Thus, it is only through a combination of experimental measurements and theoretical calculations that one can gain insight into the internal dynamics. Here, we report on a combination of structural (relativistic ultrafast electron diffraction, or UED) and spectroscopic (time-resolved photoelectron spectroscopy, or TRPES) measurements to follow the coupled electronic and nuclear dynamics involved in the internal conversion and photodissociation of the polyatomic molecule, diiodomethane (CH 2 I 2). While UED directly probes the 3D nuclear dynamics, TRPES only serves as an indirect probe of nuclear dynamics via Franck-Condon factors, but it is sensitive to electronic energies and configurations, via Koopmans' correlations and photoelectron angular distributions. These two measurements are interpreted with trajectory surface hopping calculations, which are capable of simulating the observables for both measurements from the same dynamics calculations. The measurements highlight the nonlocal dynamics captured by different groups of trajectories in the calculations. For the first time, both UED and TRPES are combined with theory capable of calculating the observables in both cases, yielding a direct view of the structural and nonadiabatic dynamics involved.

Conformer-specific dynamics Conformation-dependent dynamics play an important role in organic chemistry syntheses such as electrocyclic reactions, as well as in biological processes such as protein folding. However, current time-resolved experimental methods struggle to distinguish conformers from each other, and conformational isomerism is usually analyzed through reactant and product distributions. Using a combination of mega–electron volt ultrafast electron diffraction and quantum wave packet simulations, Champenois et al . directly followed the photochemical electrocyclic ring opening of the molecule α-phellandrene with femtosecond time resolution and confirmed that the transformation of a specific molecular conformer follows the famous Woodward-Hoffmann rules. The proposed method is potentially a powerful tool to follow conformer specificity in various organic and biological systems in real time. —YS