Ultraviolet Photodissociation of the ,-Dimethylformamide Cation.

,-Dimethylformamide (DMF) provides a useful small-molecule model for studying features of the peptide bond that forms the backbone of proteins. We report results from a comprehensive multimass velocity-map imaging study into the ultraviolet (UV) photolysis of the ,-dimethylformamide cation (DMF) at wavelengths of 225, 245, and 280 nm. Electronic structure calculations on DMF and DMF were employed to help interpret the experimental results.

Ultrafast dynamics of fluorene initiated by highly intense laser fields.

We present an investigation of the ultrafast dynamics of the polycyclic aromatic hydrocarbon fluorene initiated by an intense femtosecond near-infrared laser pulse (810 nm) and probed by a weak visible pulse (405 nm). Using a multichannel detection scheme (mass spectra, electron and ion velocity-map imaging), we provide a full disentanglement of the complex dynamics of the vibronically excited parent molecule, its excited ionic states, and fragments. We observed various channels resulting from the strong-field ionization regime.

The Role of Momentum Partitioning in Covariance Ion Imaging Analysis.

We present results from a covariance ion imaging study, which employs extensive filtering, on the relationship between fragment momenta to gain deeper insight into photofragmentation dynamics. A new data analysis approach is introduced that considers the momentum partitioning between the fragments of the breakup of a molecular polycation to disentangle concurrent fragmentation channels, which yield the same ion species. We exploit this approach to examine the momentum exchange relationship between the products, which provides direct insight into the dynamics of molecular fragmentation.

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes site-selective ionization.

C-I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy.

Endoscopic 5-Aminolevulinic Acid-Induced Fluorescence-Guided Intraparenchymal Brain Tumor Resection-Can the Endoscope Detect More Fluorescence Than the Microscope?

Objectives: Using a laboratory-based optical setup, we show that 5-aminolevulinic acid (5ALA) fluorescence is better detected using the endoscope than the microscope. Furthermore, we present our case series of fully endoscopic 5ALA-guided resection of intraparenchymal tumors.

Methods: A Zeiss Pentero microscope was compared with the Karl Storz Hopkins endoscope.

Design and characterization of an optical-fiber-coupled laser-induced desorption source for gas-phase dynamics experiments.

Preparation of neutral non-volatile molecules intact in the gas phase for mass spectrometry or chemical dynamics experiments remains a challenge for many classes of molecules. Here, we report the design and characterization of a fiber-coupled laser-based thermal desorption source capable of preparing intact neutral molecules at high molecular densities in the gas phase for use in velocity-map imaging experiments. Within this source, the sample is deposited onto a thin tantalum foil.

Photodissociation dynamics of tetrahydrofuran at 193 nm.

Tetrahydrofuran (THF), a cyclic ether with the chemical formula CHO, can be considered the simplest analog of the deoxyribose backbone component of deoxyribonucleic acid (DNA). As such, it provides a useful model for probing the photochemistry of such biomolecular motifs. We present a velocity-map imaging study into the ultraviolet dissociation of THF at a wavelength of 193 nm.

Development of High Throughput Microscope Mode Secondary Ion Mass Spectrometry Imaging.

This paper describes the development and initial results from a secondary ion mass spectrometer coupled with microscope mode detection. Stigmatic ion microscope imaging enables us to decouple the primary ion (PI) beam focus from spatial resolution and is a promising route to attaining higher throughput for mass spectrometry imaging (MSI). Using a commercial C PI beam source, we can defocus the PI beam to give uniform intensity across a 2.

A localized view on molecular dissociation via electron-ion partial covariance.

Inner-shell photoelectron spectroscopy provides an element-specific probe of molecular structure, as core-electron binding energies are sensitive to the chemical environment. Short-wavelength femtosecond light sources, such as Free-Electron Lasers (FELs), even enable time-resolved site-specific investigations of molecular photochemistry. Here, we study the ultraviolet photodissociation of the prototypical chiral molecule 1-iodo-2-methylbutane, probed by extreme-ultraviolet (XUV) pulses from the Free-electron LASer in Hamburg (FLASH) through the ultrafast evolution of the iodine 4d binding energy.

Photodissociation dynamics of -dimethylformamide at 225 nm and 245 nm.

-Dimethylformamide, (CH)NCHO, is the simplest tertiary amide and a model compound for investigating the photofragmentation of peptide bonds. We report the results of a velocity-map imaging study into the photodissociation dynamics of DMF following excitation at 225 nm and 245 nm. Excitation at either wavelength generates a variety of products, with the primary dissociation pathways involving cleavage of either the N-CO amide bond or an N-CH bond.

Machine learning assisted reflectance spectral characterisation of coronary thrombi correlates with microvascular injury in patients with ST-segment elevation acute coronary syndrome.

Aims: We set out to further develop reflectance spectroscopy for the characterisation and quantification of coronary thrombi. Additionally, we explore the potential of our approach for use as a risk stratification tool by exploring the relation of reflectance spectra to indices of coronary microvascular injury.

Methods And Results: We performed hyperspectral imaging of coronary thrombi aspirated from 306 patients presenting with ST-segment elevation acute coronary syndrome (STEACS).

Imaging the Dynamics of the Electron Ionization of CF.

The dissociation of CF following electron ionization at 100 eV has been studied using multimass velocity-map ion imaging and covariance-map imaging analysis. Single ionization events form parent CF cations in an ensemble of electronic states, which follow a multiplex of relaxation pathways to eventually dissociate into ionic and neutral fragment products. We observe CF, CF, CF, C, F, CF, CF, CF, and CF ions, all of which can reasonably be formed from singly charged parent ions.

Disentangling sequential and concerted fragmentations of molecular polycations with covariant native frame analysis.

We present results from an experimental ion imaging study into the fragmentation dynamics of 1-iodopropane and 2-iodopropane following interaction with extreme ultraviolet intense femtosecond laser pulses with a photon energy of 95 eV. Using covariance imaging analysis, a range of observed fragmentation pathways of the resulting polycations can be isolated and interrogated in detail at relatively high ion count rates (∼12 ions shot). By incorporating the recently developed native frames analysis approach into the three-dimensional covariance imaging procedure, contributions from three-body concerted and sequential fragmentation mechanisms can be isolated.

The kinetic energy of PAH dication and trication dissociation determined by recoil-frame covariance map imaging.

We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.

Electron-induced dissociation dynamics studied using covariance-map imaging.

Recently, covariance analysis has found significant use in the field of chemical reaction dynamics. When coupled with data from product time-of-flight mass spectrometry and/or multi-mass velocity-map imaging, it allows us to uncover correlations between two or more ions formed from the same parent molecule. While the approach has parallels with coincidence measurements, covariance analysis allows experiments to be performed at much higher count rates than traditional coincidence methods.

Partial and Contingent Recoil-Frame Covariance-Map Imaging.

When applied to multimass velocity-map imaging data, covariance analysis reveals correlations between different fragment ions formed from the same parent molecule and can provide detailed insights into the fragmentation dynamics. Covariances between the time-of-flight signals for two different ions show that they are formed in the same event, while covariances between their velocity-map images, often referred to as "recoil-frame covariances", reveal details of the correlated motion of the two fragments. In many cases, covariance analysis is complicated by the fact that fluctuations in experimental parameters such as laser or molecular beam intensities can lead to apparent correlations between unrelated ions.

All-Optical Three-Dimensional Electron Momentum Imaging.

We report a new implementation of three-dimensional (3D) momentum imaging for electrons, employing a two-dimensional (2D) imaging detector and a silicon photomultiplier tube (siPMT). To achieve the necessary time resolution for 3D electron imaging, a poly(-phenylene)-dye-based fast scintillator (Exalite 404) was used in the imaging detector instead of conventional phosphors. The system demonstrated an electron time-of-flight resolution comparable with that of electrical MCP pick-off (tens of picoseconds), while achieving an unprecedented dead time reduction (∼0.

Multi-channel photodissociation and XUV-induced charge transfer dynamics in strong-field-ionized methyl iodide studied with time-resolved recoil-frame covariance imaging.

The photodissociation dynamics of strong-field ionized methyl iodide (CH3I) were probed using intense extreme ultraviolet (XUV) radiation produced by the SPring-8 Angstrom Compact free electron LAser (SACLA). Strong-field ionization and subsequent fragmentation of CH3I was initiated by an intense femtosecond infrared (IR) pulse. The ensuing fragmentation and charge transfer processes following multiple ionization by the XUV pulse at a range of pump-probe delays were followed in a multi-mass ion velocity-map imaging (VMI) experiment.

Covariance-Map Imaging: A Powerful Tool for Chemical Dynamics Studies.

Over the past decade or so, the state-of-the-art in the field of chemical reaction dynamics has progressed from studies of few-atom systems to wide-ranging investigations into a variety of photoinduced and collision-induced processes in much larger molecules. Many of these studies are of direct relevance to a wide audience of chemists, spanning fields such as atmospheric chemistry, astrochemistry, synthetic chemistry, and chemical biology. Key to this work has been the technique of velocity-map imaging, which allows complete product scattering distributions to be recorded for the process of interest.