Ion Imaging Research Articles

Depth Correction of 3D SIMS Images of Mammalian Cells with Secondary Ion Images Captures the Effects of Differential Sputtering.

Depth Correction of 3D SIMS Images of Mammalian Cells with Secondary Ion Images Captures the Effects of Differential Sputtering.

Investigation of Small-Molecule Constituents in Voacanga africana Seeds and Mapping of Their Spatial Distributions Using Laser Ablation Direct Analysis in Real-Time Imaging-Mass Spectrometry (LADI-MS).

Plant seeds are a renewable resource that can furnish access to medicinal natural products that can only otherwise be isolated from aerial or root parts, the harvest of which may be destructive to the plant or threaten its viability. However, optimization of the isolation of such compounds from seeds would be greatly assisted if the spatial distribution of the molecules of interest within the plant tissue were known. For example, iboga alkaloids that hold promise for the treatment of opioid use disorder are typically isolated from the leaves, bark, or roots of Tabernanthe or Voacanga spp. trees, but it would be more environmentally sustainable to isolate such compounds from their seeds. Here, we leveraged the unique capabilities of the ambient mass spectral imaging technique termed laser ablation direct analysis in real-time imaging-mass spectrometry (LADI-MS) to reveal the spatial distributions of a range of molecules, including alkaloids within V. africana seeds. In addition to six compounds previously reported in these seeds, namely, tetradecanoic acid, n-hexadecanoic acid, (Z,Z)-9,12-octadecadienoic acid, (Z)-9-octadecenoic acid, octadecanoic acid, and Δ14-vincamine, an additional 31 compounds were newly identified in V. africana seeds. The compound classes included alkaloids, terpenes, and fatty acids. The ion images showed that the fatty acids were localized in the embryo of the seed. The alkaloids, which were mainly localized in the seed endosperm, included strictamine, akuammidine, polyneruidine, vobasine, and Δ14-vincamine. This information can be exploited to enhance the efficiency of secondary metabolite isolation from V. africana seeds while eliminating the destruction of other plant parts.

Photodissociation dynamics of SO2 between 193 and 201 nm.

The nonadiabatic interactions between the C̃ state and neighboring electronic states of SO2 have attracted much attention; however, the predissociation mechanisms are not yet completely understood. In this work, the predissociation dynamics of SO2 via its C̃ state have been investigated at λ = 193-201nm by using the time-sliced velocity map ion imaging technique. The translational energy distributions and the branching ratios of the O(3PJ=2,1,0) spin-orbit products at six photolysis wavelengths have been acquired. The SO(3Σ-) product population gradually decreases in v = 0 and increases in v = 2 as the photolysis wavelength decreases. The branching ratios of O(3P J=2,1,0) products are almost similar at most wavelengths, except at 194.8nm. Our data suggest that the predissociation between 193 and 201nm is via an avoided crossing between the C̃ state and the repulsive triplet 23A' state. The state-to-state dynamical pictures shown in this work provide a rigorous test of the potential energy surfaces (PESs) of the SO2 and the nonadiabatic couplings between these PESs.

Synthesis of nucleus-satellite like Ag nanoparticles based on dielectric barrier discharge system for prolonged chemiluminescence imaging of mercury ions

Noble metal nanomaterials were unique in the field of chemiluminescence (CL) because of their high catalytic activity and surface plasmon resonance (SPR). Herein, polyhedral oligomeric silsesquioxanes modified silver nanoparticles (POSS-Ag NPs) were firstly synthesized by dielectric barrier discharge system within 40 min. Amino modified POSS (AE-POSS), as both a reducing agent and protective agent, was bonded to the surface of Ag NPs to stabilized Ag NPs through the three-dimensional framework structure to form “nucleus-satellite” like structures, which specially showed enhanced CL intensity due to increased specific surface area and SPR characteristics. Subsequently, a prolonged CL signal for over 1 h by POSS-Ag NPs - luminol system happened, which could be well observed in the CL imaging. The presence of Ag0/Ag+ and O2/·O2– charge cycling transfer on the surface of POSS-Ag NPs continuously provided large amounts of catalysts (Ag0) and CL reactants (Ag+), continuously reacting with luminol to greatly prolong the CL reaction time. Significantly, due to the mercury (Hg)-Ag alloys production in Ag NPs solution to inhibit catalytic and SPR effects, this intense and long-time CL system for the specific imaging detection of Hg2+ was developed. The detection limit of this method was 3 × 10−8 M. The enhanced prolonged CL phenomenon could improve the accuracy of chemical analysis and have promising applications in CL imaging.

Mitochondrial targeting fluorescent probe for specific detection of nickel ions and biological imaging

Nickel ion, a kind of essential trace element, is indispensable for maintaining life health. Nickel ions in excess will induce a series of reactions in the body and be correlative with the diseases and even cancer. As one of the most important organelles, mitochondrion is responsible for maintaining the homeostasis of metal ions in cells. Therefore, sensitive detection of nickel ions in mitochondria contributes to further study the physiological function of mitochondria, and is of great significance for investigating body health. In this study, a simple and effective fluorescence probe method for the detection of nickel ions in organisms and environment was proposed. The probe has shown excellent spectral performance in vitro experiments, and the detection limits was as low as 17 nM. And it can be applied to the detection of nickel ions in environmental water samples with satisfactory results, the recovery rate is higher than 85%. More importantly, the probe can specifically target to mitochondria to realize the imaging of nickel ions in cells and provide an effective auxiliary tool for in-depth study of the relationship between mitochondrial function and metal ions. In addition, the probe has been successfully applied to the detection of nickel ions in zebrafish model, which further demonstrates the great potential and value of the probe in biological applications.

Velocity-selected spatial map ion imaging spectrometer for direct imaging of near-surface catalytic activity

We propose and demonstrate an approach permitting direct imaging of the spatial distribution of gas-surface reaction products with <60 μm lateral spatial resolution using a velocity filtered ion imaging technique. We demonstrate direct imaging of the density of hydrogen deuteride (HD) molecules desorbed from a patterned platinum (Pt) thin film exposed to molecular beams of hydrogen (H2) and deuterium (D2). Resonance enhanced multiphoton absorption was performed with a 2 + 1 scheme through the E,F state using a nanosecond UV laser at ∼201 nm. The generated cations of HD, D2, and H2 were velocity filtered and accelerated with ion imaging optics toward a multichannel plate and phosphor screen. To reduce the significant image blur caused by the translational energy of the parent molecules, a grounded pinhole with 50 μm diameter is placed at the velocity-mapped imaging plane of the ion optics, which velocity-filters the ions that form the image of the near-surface origination plane, improving the ion imaging resolution by a factor of ∼10. The instrument demonstrates the capability to directly image catalytic output in the gas phase in the near-surface region with tens of micrometers of spatial resolution simultaneously with mass and molecular velocity resolution.

Sublimation application of 5-chloro-2-mercaptobenzothiazole matrix for matrix-assisted laser desorption/ionization mass spectrometry imaging of mouse kidney.

Sublimation is a solvent-free technique used to apply a uniform matrix coating over a large sample plate, improving the matrix's purity and enhancing the analyte signal. Although the 5-chloro-2-mercaptobenzothiazole (CMBT) matrix was introduced years ago, there are no reports of its application via sublimation. We investigated the experimental parameters that are optimal for CMBT matrix sublimation on mouse kidney samples. We also evaluated the stability of the sublimed CMBT matrix under a vacuum environment. Using kidney samples prepared with a sublimated CMBT matrix, we conducted matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) analysis of specific phospholipids (phosphatidylcholine and phosphatidylglycerol in the positive ion mode and phosphatidylinositol in the negative ion mode). We also explored various spatial resolutions (50, 20, and 10μm) and performed sequential MALDI-hematoxylin and eosin (H&E) staining. The CMBT matrix was applied to kidney samples using a sublimation apparatus connected to a vacuum pump to achieve a pressure of 0.05 Torr. The matrix was then subjected to different temperatures and sublimation times to determine the optimal conditions for matrix application. Subsequently, a Q-Exactive mass spectrometer equipped with a Spectroglyph MALDI ion source was employed for MALDI-MSI experiments. Standard protocols were followed for H&E staining after MALDI analysis. A matrix thickness of 0.15 mg/cm2 yielded high-quality images. The sublimated matrix exhibited minimal loss after approximately 20 h of exposure to a vacuum of 7Torr, indicating its stability under these conditions. Ion images were successfully obtained at spatial resolutions of 50, 20, and 10μm. Furthermore, orthogonal histological information was obtained through sequential MALDI-H&E staining. We demonstrate that samples prepared for MALDI-MSI using sublimation to apply the CMBT matrix yield high-quality mass spectrometric images of mouse kidney sections. We also provide data for the impact of various experimental parameters on image quality (e.g., temperature, time, matrix thickness, and spatial resolution).

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 C60+ PI beam source, we can defocus the PI beam to give uniform intensity across a 2.5 mm2 area. By coupling the beam with a position-sensitive spatial detector, we can achieve mass spectral imaging of positive and negative secondary ions (SIs), which we demonstrate using samples comprising metals and dyes. Our approach involves simultaneous desorption of ions across a large field of view, enabling mass spectral images to be recorded over an area of 2.5 mm2 in a matter of seconds. Our instrument can distinguish spatial features with a resolution of better than 20 μm, and has a mass resolution of >500 at 500 u. There is considerable scope to improve this, and through simulations we estimate the future performance of the instrument.

An Orbitrap/Time-of-Flight Mass Spectrometer for Photofragment Ion Imaging and High-Resolution Mass Analysis of Native Macromolecular Assemblies.

We discuss the design, development, and evaluation of an Orbitrap/time-of-flight (TOF) mass spectrometry (MS)-based instrument with integrated UV photodissociation (UVPD) and time/mass-to-charge ratio (m/z)-resolved imaging for the comprehensive study of the higher-order molecular structure of macromolecular assemblies (MMAs). A bespoke TOF analyzer has been coupled to the higher-energy collisional dissociation cell of an ultrahigh mass range hybrid quadrupole-Orbitrap MS. A 193 nm excimer laser was employed to photofragment MMA ions. A combination of microchannel plates (MCPs)-Timepix (TPX) quad and MCPs-phosphor screen-TPX3CAM assemblies have been used as axial and orthogonal imaging detectors, respectively. The instrument can operate in four different modes, where the UVPD-generated fragment ions from the native MMA ions can be measured with high-mass resolution or imaged in a mass-resolved manner to reveal the relative positions of the UVPD fragments postdissociation. This information is intended to be utilized for retrieving higher-order molecular structural details that include the conformation, subunit stoichiometry, and molecular interactions as well as to understand the dissociation dynamics of the MMAs in the gas phase.

Infrared Activated Signatures and Jahn-Teller Dynamics of NO-CH4 Collision Complexes.

Bimolecular collision outcomes sensitively depend on the chemical functionality and relative orientations of the colliding partners that define the accessible reactive and nonreactive pathways. Accurate predictions from multidimensional potential energy surfaces demand a full characterization of the available mechanisms. Therefore, there is a need for experimental benchmarks to control and characterize the collision conditions with spectroscopic accuracy to accelerate the predictive modeling of chemical reactivity. To this end, the bimolecular collision outcomes can be investigated systematically by preparing reactants in the entrance channel prior to reaction. Herein, we investigate the vibrational spectroscopy and infrared-driven dynamics of the bimolecular collision complex between nitric oxide and methane (NO-CH4). We recorded the vibrational spectroscopy of NO-CH4 in the CH4 asymmetric stretching region using resonant ion-depletion infrared spectroscopy and infrared action spectroscopy, thus revealing a significantly broad spectrum centered at 3030 cm-1 that extends over 50 cm-1. The asymmetric CH stretch feature of NO-CH4 is explained by CH4 internal rotation and attributed to transitions involving three different nuclear spin isomers of CH4. The vibrational spectra also show extensive homogeneous broadening due to the ultrafast vibrational predissociation of NO-CH4. Additionally, we combine infrared activation of NO-CH4 with velocity map imaging of NO (X2Π, ν″ = 0, J″, Fn, Λ) products to develop a molecular-level understanding of the nonreactive collisions of NO with CH4. The anisotropy of the ion image features is largely determined by the probed rotational quantum number of NO (J″) products. For a subset of NO fragments, the ion images and total kinetic energy release (TKER) distributions show an anisotropic component at low relative translation (∼225 cm-1) indicating a prompt dissociation mechanism. However, for other detected NO products, the ion images and TKER distributions are bimodal, in which the anisotropic component is accompanied by an isotropic feature at high relative translation (∼1400 cm-1) signifying a slow dissociation pathway. In addition to the predissociation dynamics following vibrational excitation, the Jahn-Teller dynamics prior to infrared activation need to be considered to fully describe the product spin-orbit distributions. Therefore, we correlate the Jahn-Teller mechanisms of NO-CH4 to the symmetry-restricted NO (X2Π, ν″ = 0, J″, Fn, Λ) + CH4 (ν″) product outcomes.

Correlated cryo-SEM and CryoNanoSIMS imaging of biological tissue

BackgroundThe development of nanoscale secondary ion mass spectrometry (NanoSIMS) has revolutionized the study of biological tissues by enabling, e.g., the visualization and quantification of metabolic processes at subcellular length scales. However, the associated sample preparation methods all result in some degree of tissue morphology distortion and loss of soluble compounds. To overcome these limitations an entirely cryogenic sample preparation and imaging workflow is required.ResultsHere, we report the development of a CryoNanoSIMS instrument that can perform isotope imaging of both positive and negative secondary ions from flat block-face surfaces of vitrified biological tissues with a mass- and image resolution comparable to that of a conventional NanoSIMS. This capability is illustrated with nitrogen isotope as well as trace element mapping of freshwater hydrozoan Green Hydra tissue following uptake of 15N-enriched ammonium.ConclusionWith a cryo-workflow that includes vitrification by high pressure freezing, cryo-planing of the sample surface, and cryo-SEM imaging, the CryoNanoSIMS enables correlative ultrastructure and isotopic or elemental imaging of biological tissues in their most pristine post-mortem state. This opens new horizons in the study of fundamental processes at the tissue- and (sub)cellular level.TeaserCryoNanoSIMS: subcellular mapping of chemical and isotopic compositions of biological tissues in their most pristine post-mortem state.

Photodissociation dynamics of H2S+ near 325 nm

We study the photodissociation dynamics of the hydrogen sulfide cations (H2S+) using the time-sliced velocity map ion imaging (VMI) technique and high-accuracy calculations. High-resolution ion images of the S+(4S) products were measured at four photolysis wavelengths of 325.158, 325.200, 325.243, 325.307 nm, which correspond to the excitation to the A2A1(0,13,0) K=1 state of H2S+. Rotational state-resolved total kinetic energy releases and angular distributions have been derived as a function of the photolysis wavelengths. Notably, photolysis wavelength dependent product rotational state and anisotropy parameter distributions have been clearly observed. Full-dimensional potential energy surface characterization suggests that nonadiabatic coupling between A2A1 and B2B2 states at C2v configurations, as well as relaxation of the symmetry to Cs in the conical intersection region between the two states, plays a key role in the photodissociation process.

Singlet O2 from Ultraviolet Excitation of the Quinoline-O2 Complex.

We report results from experiments with the quinoline-O2 complex, which was photodissociated using light near 312 nm. Photodissociation resulted in formation of the lowest excited state of oxygen, O2 a 1Δg, which we detected using resonance enhanced multiphoton ionization and velocity map ion imaging. The O2+ ion image allowed for a determination of the center-of-mass translational energy distribution, P(ET), following complex dissociation. We also report results of electronic structure calculations for the quinoline singlet ground state and lowest energy triplet state. From the CCSD/aug-cc-pVDZ//(U)MP2/cc-pVDZ calculations, we determined the lowest energy triplet state to have ππ* electronic character and to be 2.69 eV above the ground state. We also used electronic structure calculations to determine the geometry and binding energy for several quinoline-O2 complexes. The calculations indicated that the most strongly bound complex has a well depth of about 0.11 eV and places the O2 moiety above and approximately parallel to the quinoline ring system. By comparing the experimental P(ET) with the energy for the singlet ground state and the lowest energy triplet state, we concluded that the quinoline product was formed in the lowest energy triplet state. Finally, we found the experimental P(ET) to be in agreement with a Prior translational energy distribution, which suggests a statistical dissociation for the complex.

Bichromatic UV detection system for atomically-resolved imaging of ions.

We present a compact bichromatic imaging system, located outside of the vacuum chamber of a trapped ion apparatus that collects the fluorescence of 230.6 and 369.5nm photons simultaneously on a shared electron-multiplying charge-coupled device (EMCCD) camera. The system contains two lens doublets, consisting of a sphere and an asphere. They provide a numerical aperture of 0.45 and 0.40 at 230.6 and 369.5nm, respectively, and enable spatially resolved state detection with a large field of view of 300 μm for long 115In+/172Yb+ Coulomb crystals. Instead of diffraction-limited imaging for one wavelength, the focus in this system is on simultaneous single-ion resolved imaging of both species over a large field, with special attention to the deep UV wavelength (230.6nm) and the low scattering rate of In+ ions. The introduced concept is applicable to other dual-species applications.

Molecular characterization of human peripheral nerves using desorption electrospray ionization mass spectrometry imaging.

Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) is a molecular imaging method that can be used to elucidate the small-molecule composition of tissues and map their spatial information using two-dimensional ion images. This technique has been used to investigate the molecular profiles of variety of tissues, including within the central nervous system, specifically the brain and spinal cord. To our knowledge, this technique has yet to be applied to tissues of the peripheral nervous system (PNS). Data generated from such analyses are expected to advance the characterization of these structures. The study aimed to: (i) establish whether DESI-MSI can discriminate the molecular characteristics of peripheral nerves and distinguish them from surrounding tissues and (ii) assess whether different peripheral nerve subtypes are characterized by unique molecular profiles. Four different nerves for which are known to carry various nerve fiber types were harvested from a fresh cadaveric donor: mixed, motor and sensory (sciatic and femoral); cutaneous, sensory (sural); and autonomic (vagus). Tissue samples were harvested to include the nerve bundles in addition to surrounding connective tissue. Samples were flash-frozen, embedded in optimal cutting temperature compound in cross-section, and sectioned at 14 μm. Following DESI-MSI analysis, identical tissue sections were stained with hematoxylin and eosin. In this proof-of-concept study, a combination of multivariate and univariate statistical methods was used to evaluate molecular differences between the nerve and adjacent tissue and between nerve subtypes. The acquired mass spectral profiles of the peripheral nerve samples presented trends in ion abundances that seemed to be characteristic of nerve tissue and spatially corresponded to the associated histology of the tissue sections. Principal component analysis (PCA) supported the separation of the samples into distinct nerve and adjacent tissue classes. This classification was further supported by the K-means clustering analysis, which showed separation of the nerve and background ions. Differences in ion expression were confirmed using ANOVA which identified statistically significant differences in ion expression between the nerve subtypes. The PCA plot suggested some separation of the nerve subtypes into four classes which corresponded with the nerve types. This was supported by the K-means clustering. Some overlap in classes was noted in these two clustering analyses. This study provides emerging evidence that DESI-MSI is an effective tool for metabolomic profiling of peripheral nerves. Our results suggest that peripheral nerves have molecular profiles that are distinct from the surrounding connective tissues and that DESI-MSI may be able to discriminate between nerve subtypes. DESI-MSI of peripheral nerves may be a valuable technique that could be used to improve our understanding of peripheral nerve anatomy and physiology. The ability to utilize ambient mass spectrometry techniques in real time could also provide an unprecedented advantage for surgical decision making, including in nerve-sparing procedures in the future.

A Photodissociation dynamics study utilizing spatial orientation control of asymmetric top molecules

AbstractBackgroundThe hexapole state selection had been developed mainly as a measure of rotational state selection and orientation control of symmetric top molecules.ObjectiveThis review aims to reorganize the results that the state selection technique was applied to study the photodissociation dynamics of an asymmetric top molecule 2‐bromobutane.Methods2‐Bromobutane molecules have been state‐selected and spatially oriented using a hexapole state selector. The oriented molecules were then photolyzed to emit Br (2P1/2) photofragments. The photofragments were observed by using the slice ion imaging technique.ResultsThe photofragment scattering distribution was experimentally observed to present a characteristic top‐bottom asymmetry, which allows us to extract geometric information of molecular vector properties related to the photodissociation dynamics. Besides, a theoretical study suggested a possibility of chiral discrimination by the scattering angular distributions.ConclusionThis review introduces the overview of the theoretical formulation of the angular distributions and representative experimental results using the orientational control technique as an effective tool for studies of photodissociation dynamics.

Highly Rotationally Excited N2 Reveals Transition-State Character in the Thermal Decomposition of N2O on Pd(110).

We employ time-slice and velocity map ion imaging methods to explore the quantum-state resolved dynamics in thermal N2O decomposition on Pd(110). We observe two reaction channels: a thermal channel that is ascribed to N2 products initially trapped at surface defects and a hyperthermal channel involving a direct release of N2 to the gas phase from N2O adsorbed on bridge sites oriented along the [001] azimuth. The hyperthermal N2 is highly rotationally excited up to J = 52 (v″ = 0) with a large average translational energy of 0.62 eV. Between 35 and 79% of the estimated barrier energy (1.5 eV) released upon dissociation of the transition state (TS) is taken up by the desorbed hyperthermal N2. The observed attributes of the hyperthermal channel are interpreted by post-transition-state classical trajectories on a density functional theory-based high-dimensional potential energy surface. The energy disposal pattern is rationalized by the sudden vector projection model, which attributes to unique features of the TS. Applying detailed balance, we predict that in the reverse Eley-Rideal reaction, both N2 translational and rotational excitation promote N2O formation.

MALDI Mass Spectrometry Imaging sample preparation with wet-interface matrix deposition for lipid analysis.

Sample preparation is one of the most crucial steps for MALDI mass spectrometry imaging (MALDI-MSI). The scientists beginning their adventure with this technique may be overwhelmed by the variety of matrices, solvents, concentrations, the ways of their applications, and the lack of widely available knowledge about the influence of these parameters on the results. Here we would like to present our experiences with detailed aspects of matrices deposition, hopefully helpful for the scientific community. In our article, we have tested several MALDI matrices applied by the SunCollect® system: wet-interface matrix deposition in the context of lipids analysis. Among them: 2,5-dihydroxybenzoic acid (DHB), norharmane, N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC), 9-aminoacridine (9AA). We have optimized the number of matrix layers and nozzle settings in terms of spectra intensity and the overall quality of obtained ion maps. Our research presents the influence of the number of matrix layers and nozzle settings on the results and allows for choosing the optimal parameters for the analyses. In positive ionization mode, DHB matrix could be chosen as the first selection. In the negative ionization mode, DAN matrix produces higher peak intensity in a lower mass range and seems to provide more information than 9AA. We recommended NEDC for particular tasks such as glucose analysis. Comparably to remaining matrices, norharmane significantly changes received ion maps. Dealing with such a great amount of data allows us to notice an interesting conclusion the obtained ion picture for a particular ion could differ dramatically with changing the matrix, the solvent composition, or even the number of matrix layers. This must be considered when interpreting the result and forces us to compare the results obtained with different matrices with extreme caution.

Time-Domain Rotational Raman Spectroscopy of the Ethylene Dimer and Trimer by Coulomb Explosion Imaging of Rotational Wave Packets.

We report rotational Raman spectroscopy of the ethylene dimer and trimer, based on time-resolved Coulomb explosion imaging of rotational wave packets. Rotational wave packets were created in the gas-phase ethylene clusters upon nonresonant ultrashort pulse irradiation. The subsequent rotational dynamics were traced as spatial distribution of monomer ions ejected from the clusters via the Coulomb explosion process induced by a strong probe pulse. The observed images of monomer ions show multiple kinetic energy components. The time-dependence of the angular distribution for each component was analyzed, and the Fourier transformation spectra, which correspond to rotational spectra, were obtained. A lower kinetic energy component was mainly attributed to a signal from the dimer and a higher energy component mainly from the trimer. We have successfully observed rotational wave packets up to a delay time of ∼20 ns and achieved a spectral resolution of 70 MHz after Fourier transformation. Owing to this higher resolution than the previous studies, improved rotational and centrifugal distortion constants were obtained from the spectra. In addition to improving the spectroscopic constants, this study opens the way for rotational spectroscopy of larger molecular clusters than dimers through Coulomb explosion imaging of rotational wave packets. Details of spectral acquisition and analyses of each kinetic energy component are also reported.

Spin-dependent reactivity and spin-flipping dynamics in oxygen atom scattering from graphite

The formation of two-electron chemical bonds requires the alignment of spins. Hence, it is well established for gas-phase reactions that changing a molecule’s electronic spin state can dramatically alter its reactivity. For reactions occurring at surfaces, which are of great interest during, among other processes, heterogeneous catalysis, there is an absence of definitive state-to-state experiments capable of observing spin conservation and therefore the role of electronic spin in surface chemistry remains controversial. Here we use an incoming/outgoing correlation ion imaging technique to perform scattering experiments for O(3P) and O(1D) atoms colliding with a graphite surface, in which the initial spin-state distribution is controlled and the final spin states determined. We demonstrate that O(1D) is more reactive with graphite than O(3P). We also identify electronically nonadiabatic pathways whereby incident O(1D) is quenched to O(3P), which departs from the surface. With the help of molecular dynamics simulations carried out on high-dimensional machine-learning-assisted first-principles potential energy surfaces, we obtain a mechanistic understanding for this system: spin-forbidden transitions do occur, but with low probabilities.