Electron diffraction data on structural transformations in free clucters of argon

The analysis of ultrafast electron diffraction (UED) data from low-symmetry single crystals of small molecules is often challenged by the difficulty of assigning unique Laue indices to the observed Bragg reflections. For a variety of technical and physical reasons, UED diffraction images are typically of lower quality when viewed from the perspective of structure determination by single-crystal X-ray or electron diffraction. Nevertheless, time series of UED images can provide...

We present the result of our calculations of ultrafast electron diffraction (UED) for cyclobutanone excited into $S_2$ electronic state, which are based on the non-adiabatic dynamics simulations with \textit{Ab Initio} Multiple Cloning (AIMC) method with the electronic structure calculated at the SA(3)-CASSCF(12,12)/aug-cc-pVDZ level of theory. The key features in the UED pattern were identified that can be used to distinguish between the reaction pathways observed in the AIM...

We investigate the wavelength dependent ionization, heating, and expansion dynamics of medium-sized rare-gas clusters (Ar$_{923}$) under intense femtosecond short-wavelength free electron laser pulses by quasi-classical molecular dynamics simulations. A comparison of the interaction dynamics for pulses with $\hbar\omega$=20, 38, and 90\,eV photon energy at fixed total excitation energy indicates a smooth transition from plasma-driven cluster expansion, where predominantly sur...

Upon melting, the molecules in the crystal explore numerous configurations, reflecting an increase in disorder. The molar entropy of disorder can be defined by Bolzmann's formula dSd = Rln(Wd) where Wd is the increase in the number of microscopic states, so far inaccessible experimentally. We found that the Arrhenius frequency factor A of the electron diffraction signal decay provides Wd via an experimental equation A = AINTWd where AINT is an inelastic scattering cross-secti...

The fractionation of isotopes of natural Ar near the condensation (Tc) and freezing point has been studied using mass spectrometry (MS), numerical modeling and density functional theory. The heat of formation of 0.30, 0.52 and 0.70 kJ per Ar atom of the clusters Ar2, Ar3 and Ar4, respectively, shows the tendency of Ar to clusterization. At T > Tc apparent separation coefficients {\alpha}40 = 0.80, {\alpha}38 = 1.07 and {\alpha}36 = 1.28 for 40Ar, 38Ar and 36Ar, respectively, ...

A simple mass spectrometric method has been developed to quantify dopant levels in heteronuclear clusters in the gas phase. The method is demonstrated with reference to quantification of the water content in supersonic beams of water-doped argon clusters. Such doped clusters have assumed much importance in the context of recently-reported doping-induced enhancement in the emission of energetic charged particles and photons upon their interaction with intense laser pulses. We ...

Because of their high pulse energies, X-ray free-electron lasers (FEL) allow to resolve the structure of individual nanoparticles via coherent diffractive imaging (CDI) within a single X-ray pulse. Since the inevitable rapid destruction of the sample limits the achievable resolution, a thorough understanding of the spatiotemporal evolution of matter on the nanoscale following the irradiation is crucial. We present a technique to track X-ray induced structural changes in time ...

A comparison is made between the three principal methods for analysis of neutron and X-ray diffraction data from noble gas fluids by direct Fourier transform. All three methods (standard Fourier transform, Lorch modification and Soper-Barney modification) are used to analyse four different sets of diffraction data from noble gas fluids. The results are compared to the findings of a full-scale real space structure determination, namely Empirical Potential Structure Refinement....

The formation of $O^{-}$ and $O_{2}^{-}$ ions via dissociative electron attachment to a pulsed supersonic jet of $O_{2}$ molecules containing weakly bound small van der Waals clusters seeded in a beam of argon is reported. The energy dependence of the $O^{-}$ and $O_{2}^{-}$ yield exhibits three peaks near 7, 11 and 16 eV incident electron energies. The 7 eV peak arises from the $^{2}\Pi_{u}$ state of $O_{2}^{-}$ whereas, the 11 and 16 eV peaks are ascribed to two distinct re...

We present results predicting experimentally measurable structural quantities from molecular dynamics studies of hydrogen. In doing this, we propose a paradigm shift for experimentalists -- that the predictions from such calculations should be seen as the most likely hypotheses. Specifically, the experimental results should be aiming to distinguish between the candidate low-energy structures, rather than aiming to solve the simplest structure consistent with the data. We show...