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The Chelyabinsk superbolide was caused by the largest asteroid entering the Earth’s atmosphere since the 1908 Tunguska event, and the only confirmed airburst in history known to have caused human injuries. The Chelyabinsk event was also the first superbolide to have been well documented by ground-based casual video cameras. These data formed the basis to accurately model the asteroid’s physical properties and structure, which were further refined from recovered meteorites. Compared to space-based sensors, which with presently available data only measure brightness with time (and hence energy deposition), ground- based cameras have the advantage of providing a measurement of entry dynamics, a crucial constraint for entry models. To date, only half a dozen meter-sized or larger impactors have been instrumentally observed by dedicated fireball cameras. With the widespread use of high-resolution dashcams and security cameras, it is now also possible to record details of fragmentation and bolide wake - features not visible in data derived from space-based sensors. In this work, we present a novel method of calibrating daytime observations of superbolides using casual videos which provides measurements of bolide trajectory, dynamics, and light curve of comparable quality to dedicated instrumental systems. We present open-source software with the implementation of the method and a fireball entry model. We apply these tools to analyze the Novo Mesto superbolide, which occurred on February 28th , 2020, over Slovenia and resulted in the fall of several L5 meteorites. The ~1 m asteroid produced a 0.3 kT airburst which was felt on the ground as a minor earthquake. In contrast to other meter-sized impactors, >80% of the mass loss experienced by the impactor occurred in a single fragmentation point (Figure 1) at a dynamic pressure of 3.5 MPa (at an altitude of 35 km). The observed increase in atmospheric energy deposition is best explained by a massive release of mm-sized dust, evidenced by a bright luminous trail visible for several seconds. Only ~30 kg of the initial body survived the peak dynamic pressure of ~10 MPa. This object, together with one other similar case, provides evidence for a special class of Near-Earth Objects (NEOs) which catastrophically disrupt into small fragments and deposit most of their energy in a single point rather than in a prolonged cascade of fragmentations. This contrasts with classical assumptions of a Weibull strength distribution which assumes a more gradual fragmentation at lower pressures. Such objects present a higher risk as small impactors can create outsized airbursts.

In this thesis, we asked ourselves how well Slovene speakers of English perform at perceiving the General British centring diphthongs /ɪə/, /eə/ and /ʊə/, whether and how often they reproduce them, and if so, to what extent of precision. These three phonemes have been chosen because they are expected to present difficulty in perception and production, because Standard Slovene does not feature similar phonemes (or combinations of phonemes), because they are being increasingly monophthongized in General British English, and because they do not appear in General American English. We have conducted two tests, one for perception and one for production, on first-year students of English. We have discovered that both perception and production of centring diphthongs is problematic, the latter more so than the former, with the majority of participants preferring a pronunciation closer to General American English rather than General British English. Those who reproduce centring diphthongs consistently exhibit more precision in pronunciation than those those who reproduce them sporadically. Finally, there is a slight, but varied, correlation between strong performers in perception and strong performers in production. V tej nalogi se sprašujemo, kako se slovenski govorci angleščine odrežejo pri percepciji standardnih britanskih (General British) centričnih diftongov /ɪə/, /eə/ in /ʊə/, če in kako pogosto jih reproducirajo, in če jih, s kakšno natančnostjo. Te tri foneme smo izbrali, ker se pričakuje, da bodo predstavljali težave pri percepciji in produkciji, saj knjižna slovenščina podobnih fonemov ne vključuje (niti ne v kombinaciji fonemov), ker se v standardni britanski angleščini vse bolj pogosto monoftongizirajo in ker se ne pojavljajo v standardni ameriški angleščini (General American). Izvedli smo dva testa, enega za percepcijo in enega za produkcijo, na študentih Anglistike, ki obiskujejo prvi letnik. Ugotovili smo, da percepcija in produkcija centričnih diftongov predstavljata težave, pri čemer jih produkcija predstavlja več, saj se večina udeležencev nagiba k izgovorjavi, ki je bližja standardni ameriški angleščini kot standardni britanski angleščini. Ti, ki konsistentno reproducirajo centrične diftonge, so bolj natančni v izgovorjavi, kot ti, ki jih reproducirajo občasno. Ugotovili smo, da se kaže delna, a razgibna, korelacija med uspešnimi udeleženci pri percepciji in uspešnimi udeleženci pri produkciji.

On February 28, 2020 at 09:30:32 UTC, a daytime superbolide was observed over southeastern Slovenia and neighbouring countries. In the following days, three meteorite pieces (469, 203, and 48 grams) were recovered nearby the Slovenian city of Novo Mesto by local people. The meteorite was classified as an L5 ordinary chondrite, more or less brecciated and shocked. In this work we reconstruct the trajectory using the available video data which consist of two static security cameras and four dash cameras mounted on cars in motion. We use a new radial distortion method developed by Vida et al. (2021) to accurately model the lens distortion of individual cameras and we determine the position of the vehicles to a precision of several centimeters on every video frame.

The creation of stable molecular monolayers on metallic surfaces is a fundamental challenge of surface chemistry. N-Heterocyclic carbenes (NHCs) were recently shown to form self-assembled monolayers that are significantly more stable than the traditional thiols on Au system. Here we theoretically and experimentally demonstrate that the smallest cyclic carbene, cyclopropenylidene, binds even more strongly than NHCs to Au surfaces without altering the surface structure. We deposit bis(diisopropylamino)cyclopropenylidene (BAC) on Au(111) using the molecular adduct BAC-CO2 as a precursor and determine the structure, geometry, and behavior of the surface-bound molecules through high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Our experiments are supported by density functional theory calculations of the molecular binding energy of BAC on Au(111) and its electronic structure. Our work is the first demonstration of surface modification with a stable carbene other than NHC; more broadly, it drives further exploration of various carbenes on metal surfaces.

Charge transfer rates at metal/organic interfaces affect the efficiencies of devices for organic based electronics and photovoltaics. A quantitative study of electron transfer rates, which take place on the femtosecond timescale, is often difficult, especially since in most systems the molecular adsorption geometry is unknown. Here, we use X-ray resonant photoemission spectroscopy to measure ultrafast charge transfer rates across pyridine/Au(111) interfaces while also controlling the molecular orientation on the metal. We demonstrate that a bi-directional charge transfer across the molecule/metal interface is enabled upon creation of a core-exciton on the molecule with a rate that has a strong dependence on the molecular adsorption angle. Through density functional theory calculations, we show that the alignment of molecular levels relative to the metal Fermi level is dramatically altered when a core-hole is created on the molecule, allowing the lowest unoccupied molecular orbital to fall partially below the metal Fermi level. We also calculate charge transfer rates as a function of molecular adsorption geometry and find a trend that agrees with the experiment. These findings thus give insight into the charge transfer dynamics of a photo-excited molecule on a metal surface.

A regular 2D array of crown molecules, which would spontaneously self-assemble into disordered molecular clusters, is obtained by exploiting a guest–host process, based on the chemical affinity between amino and carboxylic groups on a gold surface. First a carboxylic organic template is formed, which then serves as a host for amino-functionalized crown molecules. The amino-carboxylic interaction thereby drives the formation of a monolayer of guest molecules, regularly distributed at the nanometer scale, preventing their aggregation in unordered clusters observed on a bare gold surface. This method, which can be applied to other guest molecules, represents a novel route to overcome the shape-matching requirements of the standard guest–host architectures. Furthermore, it is intrinsically selective, due to the chemical nature of the anchoring process.

Primary amines can interact with neighbor molecules or with a metal substrate via weak bonds involving the electron lone pair of their amino functional group. Near edge X-ray absorption spectra (NEXAFS) on the N 1s edge show that the structure of the empty molecular orbitals localized on the nitrogen atom is very sensitive to these interactions. Here we investigate the origin of these changes by means of theoretical calculations. NEXAFS spectra are simulated for the 1,4-benzenediamine (BDA) molecule in its free, crystalline, and monolayer on Au(111) forms. We identify the electronic states which are affected by these amino-based interactions. In the case of the molecular layer grown on the gold substrate, we show how the results of the calculations can be used to identify intermolecular interactions in fluencing adsorption geometries in molecular monolayers. (Figure Presented).

The performance of devices from organic semiconductors is often governed by charge transfer phenomena at structurally and electronically complex interfaces, which remain challenging to access and study with excellent chemical and temporal resolution. Herein, we report the preparation and X-ray spectroscopic characterization of well-defined model organic-inorganic interfaces. We discover an unexpected trend for our systems' associated charge transfer times, and we rationalize this trend with density functional theory calculations. Our findings hold relevance for understanding interfacial charge transfer phenomena in a variety of organic, biological, and bioinspired systems.

A combined theoretical and experimental study of the assembly of triphenylboroxines on Au(111) reveals the charge delocalization properties of the interface., We performed a combined experimental and theoretical study of the assembly of phenylboronic acid on the Au(111) surface, which is found to lead to the formation of triphenylboroxines by spontaneous condensation of trimers of molecules. The interface between the boroxine group and the gold surface has been characterized in terms of its electronic properties, revealing the existence of an ultra-fast charge delocalization channel in the proximity of the oxygen atoms of the heterocyclic group. More specifically, the DFT calculations show the presence of an unoccupied electronic state localized on both the oxygen atoms of the adsorbed triphenylboroxine and the gold atoms of the topmost layer. By means of resonant Auger electron spectroscopy, we demonstrate that this interface state represents an ultra-fast charge delocalization channel. Boroxine groups are among the most widely adopted building blocks in the synthesis of covalent organic frameworks on surfaces. Our findings indicate that such systems, typically employed as templates for the growth of organic films, can also act as active interlayers that provide an efficient electronic transport channel bridging the inorganic substrate and organic overlayer.

The role of additives and thermal treatment in the formation of donor–acceptor copolymer organic films of PFO–DBT (poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole]) with increased transport properties is addressed by resonant Auger photoemission and core-hole clock spectroscopy, which allows an analysis of the competition between the inner shell core-hole lifetime and the motion of photoexcited electrons on a femtosecond time scale. From the branching of the competing core-hole decay channels, we study the delocalization dynamics of excited electrons over empty molecular orbitals. We find evidence of ultrafast charge-carrier transfer from specific orbitals (LUMO+1) and increased coupling in copolymer assemblies when a solvent additive (1,8 diiodooctane) is added and samples are post-treated with thermal annealing. Relative conformational energies and core-hole spectra were calculated by time-dependent density functional theory.

The self-assembly of the naphthylmethylamine molecules (NMA) on the Au(111) surface is investigated by a combined experimental and theoretical approach. Three well-defined phases are observed upon different thermal treatments at the monolayer stage. The role played by the methylamine termination is evidenced in both the molecule–molecule and molecule–substrate interactions. The autorecognition process of the amino groups is identified as the driving factor for the formation of a complex hydrogen bonding scheme in small molecular clusters, possibly acting also as a precursor of a denitrogenation condensation process induced by thermal annealing.