Nonequilibrium Scattering/Evaporation Dynamics at the Gas-Liquid Interface: Wetted Wheels, Self-Assembled Monolayers, and Liquid Microjets.

ConspectusWe often teach or are taught in our freshman courses that there are three phases of matter─gas, liquid and solid─where the ordering reflects increasing complexity and strength of interaction between the molecular constituents. But arguably there is also a fascinating additional "phase" of matter associated with the microscopically thin interface (<10 molecules thick) between the gas and liquid, which is still poorly understood and yet plays a crucial role in fields ranging from chemistry of the marine boundary layer and atmospheric chemistry of aerosols to the passage of O2 and CO2 through alveolar sacs in our lungs. The work in this Account provides insights into three challenging new directions for the field, each embracing a rovibronically quantum-state-resolved perspective. Specifically, we exploit the powerful tools of chemical physics and laser spectroscopy to pose two fundamental questions. (i) At the microscopic level, do molecules in all internal quantum-states (e.g., vibrational, rotational, electronic) colliding with the interface "stick" with unit probability? (ii) Can reactive, scattering, and/or evaporating molecules at the gas-liquid interface avoid collisions with other species and thereby be observed in a truly "nascent" collision-free distribution of internal degrees of freedom? To help address these questions, we present studies in three different areas: (i) reactive scattering dynamics of F atoms with wetted-wheel gas-liquid interfaces, (ii) inelastic scattering of HCl from self-assembled monolayers (SAMs) via resonance-enhanced photoionization (REMPI)/velocity map imaging (VMI) methods, and (iii) quantum-state-resolved evaporation dynamics of NO at the gas-water interface. As a recurring theme, we find that molecular projectiles reactively, inelastically, or evaporatively scatter from the gas-liquid interface into internal quantum-state distributions substantially out of equilibrium with respect to the bulk liquid temperatures (TS). By detailed balance considerations, the data unambiguously indicate that even simple molecules exhibit rovibronic state dependences to how they "stick" to and eventually solvate into the gas-liquid interface. Such results serve to underscore the importance of quantum mechanics and nonequilibrium thermodynamics in energy transfer and chemical reactions at the gas-liquid interface. This nonequilibrium behavior may well make this rapidly emergent field of chemical dynamics at gas-liquid interfaces more complicated but even more interesting targets for further experimental/theoretical exploration.

Non-equilibrium dynamics at the gas-liquid interface: State-resolved studies of NO evaporation from a benzyl alcohol liquid microjet.

First measurements of internal quantum-state distributions for nitric oxide (NO) evaporating from liquid benzyl alcohol are presented over a broad range of temperatures, performed by liquid-microjet techniques in an essentially collision-free regime, with rotational/spin-orbit populations in the 2Π1/2,3/2 manifolds measured by laser-induced fluorescence. The observed rotational distributions exhibit highly linear (i.e., thermal) Boltzmann plots but notably reflect rotational temperatures (Trot) as much as 30 K lower than the liquid temperature (Tjet). A comparable lack of equilibrium behavior is also noted in the electronic degrees of freedom but with populations corresponding to spin-orbit temperatures (TSO) consistently higher than Trot by ∼15 K. These results unambiguously demonstrate evaporation into a non-equilibrium distribution, which, by detailed-balance considerations, predict quantum-state-dependent sticking coefficients for incident collisions of NO at the gas-liquid interface. Comparison and parallels with previous experimental studies of NO thermal desorption and molecular-beam scattering in other systems are discussed, which suggests the emergence of a self-consistent picture for the non-equilibrium dynamics.

Quantum-state-resolved studies of aqueous evaporation dynamics: NO ejection from a liquid water microjet.

This work presents the first fully quantum-state-resolved measurements of a solute molecule evaporating from the gas-liquid interface in vacuum. Specifically, laser-induced fluorescence detection of NO(2Π1/2, 3/2, v = 0, J) evaporating from an ∼5 mM NO-water solution provides a detailed characterization of the rotational and spin-orbit distributions emerging from a ⌀4-5 µm liquid microjet into vacuum. The internal-quantum-state populations are found to be well described by Boltzmann distributions, but corresponding to temperatures substantially colder (up to 50 K for rotational and 30 K for spin-orbit) than the water surface. The results therefore raise the intriguing possibility of non-equilibrium dynamics in the evaporation of dissolved gases at the vacuum-liquid-water interface. In order to best interpret these data, we use a model for evaporative cooling of the liquid microjet and develop a model for collisional cooling of the nascent NO evaporant in the expanding water vapor. In particular, the collisional-cooling model illustrates that, despite the 1/r drop-off in density near the microjet greatly reducing the probability of collisions in the expanding water vapor, even small inelastic cross sections (≲ 20 Å2) could account for the experimentally observed temperature differences. The current results do not rule out the possibility of non-equilibrium evaporation dynamics, but certainly suggest that correct interpretation of liquid-microjet studies, even under conditions previously considered as "collision-free," may require more careful consideration of residual collisional dynamics.

Photodissociation Dynamics of the i-Methylvinoxy Radical at 308, 248, and 225 nm Using Fast Beam Photofragment Translational Spectroscopy.

The photodissociation dynamics of the i-methylvinoxy (CH3COCH2) radical have been studied by means of fast beam coincidence translational spectroscopy. The radical was produced by photodetachment of the i-methylvinoxide anion at 700 nm, followed by dissociation at 225 nm (5.51 eV), 248 nm (5.00 eV), and 308 nm (4.03 eV). At all three dissociation energies, the major products were found to be CH3 + CH2CO, with a small amount of CO + C2H5 produced at the higher dissociation energies. Photofragment mass distributions and translational energy distributions were recorded for each wavelength. Comparison of the mass distributions with dissociation of fully deuterated i-methylvinoxy aided the assignment of the observed channels. Electronic structure calculations were performed to determine the relative energies of minima and transition states involved in the dissociation and to aid interpretation of the experimental results. The proposed dissociation mechanism involves internal conversion from the initially excited electronic state, followed by dissociation over a barrier on the ground state.

Investigation of the two- and three-fragment photodissociation of the tert-butyl peroxy radical at 248 nm.

The photodissociation dynamics of the tert-butyl peroxy (t-BuOO) radical are studied by fast-radical-beam coincidence translational spectroscopy. The neutral t-BuOO radical is formed by photodetachment of the corresponding t-BuOO- anion at 700 nm (1.77 eV), followed by dissociation at 248 nm (5.00 eV). Photofragment mass and translational energy distributions are obtained. The major channel is found to be three-body fragmentation to form O, CH3, and acetone (83%), with minor two-body fragmentation channels leading to the formation of O2 + tert-butyl radical (10%) and HO2 + isobutene (7%). Experimental results show that the translational energy distribution for two-body dissociation peaks is close to zero translational energy, with an isotropic angular distribution of fragments. These results indicate that two-body fragmentation proceeds via internal conversion to the ground electronic state followed by statistical dissociation. For three-body dissociation, the translational energy distribution peaks closer to the maximal allowed translational energy and shows an anisotropic distribution of the plane of the dissociating fragments, implying rapid dissociation on an excited-state surface. A small shoulder in the three-body translational energy distribution suggests that some three-fragment dissociation events proceed by a different mechanism, involving internal conversion to the ground electronic state followed by sequential dissociation.

Photodissociation dynamics of the methyl perthiyl radical at 248 and 193 nm using fast-beam photofragment translational spectroscopy.

The photodissociation dynamics of the methyl perthiyl radical (CH3SS) have been investigated using fast-beam coincidence translational spectroscopy. Methyl perthiyl radicals were produced by photodetachment of the CH3SS(-) anion followed by photodissociation at 248 nm (5.0 eV) and 193 nm (6.4 eV). Photofragment mass distributions and translational energy distributions were measured at each dissociation wavelength. Experimental results show S atom loss as the dominant (96%) dissociation channel at 248 nm with a near parallel, anisotropic angular distribution and translational energy peaking near the maximal energy available to ground state CH3S and S fragments, indicating that the dissociation occurs along a repulsive excited state. At 193 nm, S atom loss remains the major fragmentation channel, although S2 loss becomes more competitive and constitutes 32% of the fragmentation. The translational energy distributions for both channels are very broad at this wavelength, suggesting the formation of the S2 and S atom products in several excited electronic states.

Investigation of 3-fragment photodissociation of O3 at 193.4 and 157.6 nm by coincident measurements.

Photodissociation of the ozone molecule at 193.4 nm (6.41 eV) and 157.6 nm (7.87 eV) is studied by fast-beam translational spectroscopy. Coincident detection of the dissociation products allows direct observation of the 3-fragment channel and determination of its kinematic parameters. The results indicate that at each wavelength, 3-fragment dissociation proceeds through synchronous concerted bond breaking, but the energy partitioning among the fragments is different. The branching fraction of the 3-fragment channel increases from 5.2(6)% at 193.4 nm to 26(4)% at 157.6 nm, in agreement with previous studies. It is shown that vibrational excitation of the symmetric stretch mode in O3 molecules created by photodetachment of O(3)(-) anion enhances the absorption efficiency, especially at 193.4 nm, but does not have a strong effect on the 3-fragment dissociation.

Photodissociation dynamics of the thiophenoxy radical at 248, 193, and 157 nm.

The photodissociation dynamics of the thiophenoxy radical (C6H5S) have been investigated using fast beam coincidence translational spectroscopy. Thiophenoxy radicals were produced by photodetachment of the thiophenoxide anion followed by photodissociation at 248 nm (5.0 eV), 193 nm (6.4 eV), and 157 nm (7.9 eV). Experimental results indicate two major competing dissociation channels leading to SH + C6H4 (o-benzyne) and CS + C5H5 (cyclopentadienyl) with a minor contribution of S + C6H5 (phenyl). Photofragment mass distributions and translational energy distributions were measured at each dissociation wavelength. Transition states and minima for each reaction pathway were calculated using density functional theory to facilitate experimental interpretation. The proposed dissociation mechanism involves internal conversion from the initially prepared electronic excited state to the ground electronic state followed by statistical dissociation. Calculations show that SH loss involves a single isomerization step followed by simple bond fission. For both SH and S loss, C-S bond cleavage proceeds without an exit barrier. By contrast, the CS loss pathway entails multiple transition states and minima as it undergoes five membered ring formation and presents a small barrier with respect to products. The calculated reaction pathway is consistent with the experimental translational energy distributions in which the CS loss channel has a broader distribution peaking farther away from zero than the corresponding distributions for SH loss.

Improved sliced velocity map imaging apparatus optimized for H photofragments.

Time-sliced velocity map imaging (SVMI), a high-resolution method for measuring kinetic energy distributions of products in scattering and photodissociation reactions, is challenging to implement for atomic hydrogen products. We describe an ion optics design aimed at achieving SVMI of H fragments in a broad range of kinetic energies (KE), from a fraction of an electronvolt to a few electronvolts. In order to enable consistently thin slicing for any imaged KE range, an additional electrostatic lens is introduced in the drift region for radial magnification control without affecting temporal stretching of the ion cloud. Time slices of ∼5 ns out of a cloud stretched to ⩾50 ns are used. An accelerator region with variable dimensions (using multiple electrodes) is employed for better optimization of radial and temporal space focusing characteristics at each magnification level. The implemented system was successfully tested by recording images of H fragments from the photodissociation of HBr, H2S, and the CH2OH radical, with kinetic energies ranging from <0.4 eV to >3 eV. It demonstrated KE resolution ≲1%-2%, similar to that obtained in traditional velocity map imaging followed by reconstruction, and to KE resolution achieved previously in SVMI of heavier products. We expect it to perform just as well up to at least 6 eV of kinetic energy. The tests showed that numerical simulations of the electric fields and ion trajectories in the system, used for optimization of the design and operating parameters, provide an accurate and reliable description of all aspects of system performance. This offers the advantage of selecting the best operating conditions in each measurement without the need for additional calibration experiments.

Investigation of Soft Magnetic Material Fe-6.5Si Fracture Obtained by Additive Manufacturing.

The freeform capability additive manufacturing (AM) technique and the magnetic efficiency of Fe-6.5Si steel have the potential for the development of electromechanical component designs with thin body sections. Moreover, the directional anisotropy of the material, which is formed during growth, improves the magnetic and electrical properties of Fe-6.5 wt%Si. We obtained the range of optimal technological modes of Laser Power Bed Fusion process (volume energy density (VED) of 100−140 J/mm3, scanning speed of 750−500 mm/s) to produce the samples from Fe-6.5 wt%Si powder, but even at the best of them cracks may appear. The optical microscopy and SEM with EDX analysis of the laser-fabricated structures are applied for investigation of this phenomena. We detected a carbon content at the boundaries of the cracks. This suggests that one of the reasons for the crack formation is the presence of Fe3C in the area of the ordered α'FeSi (B2)+Fe3Si(D03) phases. Quantitative analysis based on crack initiation criteria (CIC) showed that the safe level of internal stresses in terms of the CIC criteria in the area of discontinuities is exceeded by almost 190%. Local precipitates of carbides in the area of cracks are explained by the heterogeneity and high dynamics of temperature fields, as well as the transfer of substances due to Marangoni convection, which, as a result, contributes to a significant segregation of elements and the formation of precipitate phases.

A direct comparison of high-speed methods for the numerical Abel transform.

The Abel transform is a mathematical operation that transforms a cylindrically symmetric three-dimensional (3D) object into its two-dimensional (2D) projection. The inverse Abel transform reconstructs the 3D object from the 2D projection. Abel transforms have wide application across numerous fields of science, especially chemical physics, astronomy, and the study of laser-plasma plumes. Consequently, many numerical methods for the Abel transform have been developed, which makes it challenging to select the ideal method for a specific application. In this work, eight published transform methods have been incorporated into a single, open-source Python software package (PyAbel) to provide a direct comparison of the capabilities, advantages, and relative computational efficiency of each transform method. Most of the tested methods provide similar, high-quality results. However, the computational efficiency varies across several orders of magnitude. By optimizing the algorithms, we find that some transform methods are sufficiently fast to transform 1-megapixel images at more than 100 frames per second on a desktop personal computer. In addition, we demonstrate the transform of gigapixel images.

Baseline and postoperative levels of C-reactive protein and interleukins as inflammatory predictors of atrial fibrillation following cardiac surgery: a systematic review and meta-analysis.

BACKGROUND: Postoperative atrial fibrillation (POAF) is a leading arrhythmia with high incidence and serious clinical implications after cardiac surgery. Cardiac surgery is associated with systemic inflammatory response including increase in cytokines and activation of endothelial and leukocyte responses. AIM: This systematic review and meta-analysis aimed to determine the strength of evidence for evaluating the association of inflammatory markers, such as C-reactive protein (CRP) and interleukins (IL), with POAF following isolated coronary artery bypass grafting (CABG), isolated valvular surgery, or a combination of these procedures. METHODS: We conducted a meta-analysis of studies evaluating measured baseline (from one week before surgical procedures) and postoperative levels (until one week after surgical procedures) of inflammatory markers in patients with POAF. A compre-hensive search was performed in electronic medical databases (Medline/PubMed, Web of Science, Embase, Science Direct, and Google Scholar) from their inception through May 2017 to identify relevant studies. A comprehensive subgroup analysis was performed to explore potential sources of heterogeneity. RESULTS: A literature search of all major databases retrieved 1014 studies. After screening, 42 studies were analysed including a total of 8398 patients. Pooled analysis showed baseline levels of CRP (standard mean difference [SMD] 0.457 mg/L, p < 0.001), baseline levels of IL-6 (SMD 0.398 pg/mL, p < 0.001), postoperative levels of CRP (SMD 0.576 mg/L, p < 0.001), postoperative levels of IL-6 (SMD 1.66 pg/mL, p < 0.001), postoperative levels of IL-8 (SMD 0.839 pg/mL, p < 0.001), and postoperative levels of IL-10 (SMD 0.590 pg/mL, p < 0.001) to be relevant inflammatory parameters significantly associated with POAF. CONCLUSIONS: Perioperative inflammation is proposed to be involved in the pathogenesis of POAF. Therefore, perioperative assessment of CRP, IL-6, IL-8, and IL-10 can help clinicians in terms of predicting and monitoring for POAF.

La2TeI2: a new layered telluride iodide with unusual electrical properties.

A new layered metal-rich telluride halide, La2TeI2, has been synthesized by heating stoichiometric mixtures of LaI3, La, and Te under argon at 900 degrees C, and its structure has been refined from X-ray powder diffraction data. The compound crystallizes in the 3R-Lu2CCl2 structure type (rhombohedral space group R(-)3m with a = 4.5074(4) A, c = 32.528(2) A, and Z = 3). The crystal structure is composed of infinite layers of edge-sharing, Te-centered metal atom octahedra and iodine atoms separating these layers to form three close-packed I-Ln-Te-Ln-I slabs within the unit cell. The title compound is metallic at room temperature and exhibits an anomaly in the resistivity around 140 K which is closely related to changes in the a lattice parameter with temperature. The chemical bonding and metallic properties of La2TeI2 can be plausibly understood in terms of an ionic description (Ln3+)2Te2-(I-)2(e)2 where two electrons are delocalized in the La 5d conduction band.

New synthesis route to and physical properties of lanthanum monoiodide.

A fast procedure to produce LaI by reduction of LaI2 or LaI3 in a Na melt under argon at 550 degrees C is given. The structural studies performed by means of powder X-ray diffraction as well as transmission electron microscopy are consistent with previous single-crystal results. Measurements of the electrical resistance on polycrystalline samples reveal metallic behavior for LaI in the range 10-300 K. Upon cooling, a small maximum in the resistivity has been observed at 67 K. This anomaly disappears upon heating a sample, however, yielding a hysteresis in rho(T) above 70 K. From the Pauli susceptibility, an electron density of states at the Fermi level of about 0.3 eV(-1).formula unit(-1) has been estimated, as compared with a value of 1.0 eV(-1).formula unit(-1) derived from ab initio LMTO band structure calculations.