1,721,282 research outputs found
Methylene Singlet-Triplet Energy Splitting by Molecular Beam Photodissociation of Ketene
No full textFemtosecond extreme ultraviolet ion imaging of ultrafast dynamics in electronically excited helium nanodroplets
No full textA novel femtosecond extreme ultraviolet (EUV) ion-imaging technique is applied to study ultrafast dynamics in electronically excited helium nanodroplets. Ion mass spectra recorded by single-photon EUV ionization and by transient EUV-pump/IR-probe two-photon ionization differ significantly for EUV photon energies below and above similar to 24 eV, in agreement with recently performed synchrotron measurements. Pump-probe time-delay-dependent ion kinetic energy (KE) spectra exhibit two major contributions: a decaying high KE component and a rising low KE component, which are attributed to the different excitation regimes. A model is presented that describes the excitation energy dependence of the relaxation and ionization dynamics within the framework of bulk and surface states. The model is supported by recent ab initio calculations on electronically excited states of 25-atom clusters. An intraband relaxation mechanism is proposed that proceeds on a similar to 10-20-ps time scale and that corresponds to the transfer of electronic excitation in the Rydberg n = 2 manifold from bulk to surface states
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Anion Photoelectron Spectroscopy of Exotic Species
Full text linkAbstractAnion Photoelectron Spectroscopy of Exotic SpeciesByTerry A. YenDoctor of Philosophy in ChemistryUniversity of California, BerkeleyProfessor Daniel M. Neumark, ChairAnion photoelectron spectroscopy is performed on a variety of small, unstable species in both the gas and condensed phases. For the gas-phase studies, the properties of the astrophysically significant molecules C3N- and C5N- and the biologically meaningful deprotonated DNA nucleobases were investigated. Spectra of C3N- and C5N- were obtained at 283 nm using slow electron velocity-map imaging and at 213 nm using field-free time-of-flight, respectively. Adiabatic electron affinities for both species, a term value for the first excited state of C5N, and vibrational frequencies for the degenerate cis and trans bending modes of C3N were determined. Spectra of deprotonated thymine and deprotonated cytosine at 213 nm were obtained to explore their excited state dynamics to understand the photostability of DNA. For the condensed phase studies, a new spectrometer, the liquid microjet apparatus, was assembled and used to measure the vertical binding energy of the solvated electron. A microjet flowing a salt solution intersects a laser at either 266 nm or 213 nm. Two photons from a single nanosecond laser pulse are used to first generate solvated electrons using charge-transfer-to-solvent excitation and to then eject them into vacuum, where they are detected using field-free time-of-flight
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Femtosecond Photoelectron Spectroscopy of the Dynamics of Electron Attachment and Photodissociation in Iodide-Nucleobase Clusters
Full text linkDNA and RNA photodamage mechanisms are of significant importance but remain relatively poorly understood. The attachment of low-energy electrons to nucleic acid constituents has been shown to induce single and double strand breaks, although the mechanism of electron attachment and subsequent fragmentation remains debated. Nucleobases have been suggested to be the most likely target for attachment. The transient negative ions (TNIs) that form as a result of attachment have been implicated as important species in the damage mechanism. In addition, nucleobases exhibit strong photoabsorption cross-sections for UV light that may create a photoexcited species vulnerable to electron attachment. In vivo, local water molecules may stabilize TNIs and affect dissociation barriers, among other effects.Time-resolved photoelectron spectroscopy (TRPES) of gas phase iodide-nucleobase clusters is a powerful tool to probe ultrafast reductive damage pathways in nucleic acid constituents. This femtosecond pump-probe technique employs an ultraviolet (UV) pump pulse to either initiate charge transfer from the iodide to the nucleobase or directly photoexcite the nucleobase species. A UV or infrared (IR) probe pulse can photodetach nascent transient negative ions (TNIs) or anionic photofragments to trace the ultrafast dynamics of TNI formation, decay, and cluster dissociation. In this thesis, we employ TRPES in conjunction with excited state calculations and photofragment action spectroscopy to probe the dynamics of electron attachment and photodissociation in a variety of iodide-nucleobase clusters, including iodide-uracil, iodide-uracil-water, and the simpler model system iodide-nitromethane. Photofragment action spectroscopy and excited state calculations have revealed two distinct regimes of UV photoabsorption in iodide-nucleobase clusters: near the cluster vertical detachment energy (VDE) and near 4.8 eV. Near-VDE photoexcitation corresponds to optical excitation from an I(5p) orbital to form a dipole-bound (DB) anion, in which the excess electron is bound by the large dipole moment of the base. Photoexcitation from 4.6 - 5.2 eV is expected to correspond to base-centered pi-pi* photoexcitation of the nucleobase. In addition to DB anions, the canonical nucleobases are known to support conventional, valence-bound (VB) anionic states. Like the canonical nucleobases, nitromethane (CH3NO2) also possesses a large dipole moment and is known to support both DB and VB anion states and thus serves as a valuable small molecule model for the dynamics in larger nucleobase species. TRPES of iodide-nitromethane clusters with a near-VDE photon energy UV pump pulse yields instantaneous formation of the iodide-nitromethane DB anion with complete or nearly complete conversion to form a VB state in 400 - 500 fs. The VB state exhibits bi-exponential decay in 2 ps and 1200 ps. A UV probe pulse measures the formation of iodide as the major dissociation channel of the cluster, with mono-exponential formation in approximately 20 ps. Rice-Ramsperger-Kassel-Marcus (RRKM) calculations to model the statistical unimolecular dissociation of the cluster predict dissociation to form iodide in only 300 fs. The lack of a charged intermediate decay state suggests that intramolecular vibrational energy redistribution (IVR) in the cluster is the rate-limiting step in the nonstatistical dissociation of the cluster. TRPES of iodide-uracil binary clusters shows some similarities to iodide-nitromethane, with only partial DB to VB anion conversion following near-VDE photoexcitation likely due to the reversed energetic ordering of the two TNI states. In this pump energy regime, bi-exponential formation of iodide in 15 ps and 150 ps is measured and is expected to correspond to internal conversion and dissociation from each of the two relatively long-lived TNIs. Based on our TRPES results for iodide-nitromethane, we expect the long dissociation time constant to correspond to decay of the VB anion, with delayed dissociation due to inefficient IVR from vibrationally excited ring modes to the iodide---uracil stretch coordinate. In the pi-pi* photoexcitation regime, the VB anion of the iodide-uracil complex is found to form instantaneously despite the lack of a direct optical excitation to form this state. No DB anion is detected in this pump regime. We have suggested that VB anion formation occurs by charge transfer from iodide to fill the empty hole in the pi orbital following base-centered excitation. Autodetachment decay signal is measured in this photoexcitation regime to be approximately commensurate with the prompt formation and decay of the VB state. Thus, we expect that the decay of the nascent VB state is by autodetachment. Iodide formation is measured to occur in 10s of ps, and we expect that cluster dissociation to form iodide likely occurs as a result of internal conversion of the pi-pi* photoexcited base. The addition of a single water molecule to iodide-uracil is found to have two major effects: near-VDE photoexcitation yields a somewhat more pronounced DB to VB anion conversion in iodide-uracil-water than in iodide-uracil, and pi-pi* photoexcitation yields bi-exponential formation of iodide. In the near-VDE photoexcitation regime, the nascent DB anion may undergo relatively prompt water binding site reorientation to reach a conformer with a lower DB to VB anion conversion barrier resulting in delayed VB anion formation and thus more prominent conversion. Pi-pi* photoexcited iodide-uracil-water clusters may have other decay channels that can contribute to the bi-exponential formation of iodide such as the formation of iodide-water
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Slow Photoelectron Velocity-Map Imaging and Infrared Photodissociation Spectroscopy of Cryogenically-Cooled Ions
Full text linkBoth slow photoelectron velocity-map imaging of cryogenically cooled anions (cryo-SEVI) and infrared photodissociation (IRPD) spectroscopy are employed to probe anions and cations, respectively. Such techniques are capable of providing insight into the vibrational, electronic, and geometric properties of these small molecules, which are facilitated by the high resolution afforded by each method. Further, recent developments have enhanced the abilities of cryo-SEVI to probe vibrationally excited anions (IR-cryo-SEVI), and plans are underway on further improving the cooling abilities of the machine (cryo-cryo-SEVI), allowing for an expanded range of viable molecular targets. In the meantime, there is a vast array of viable molecular species accessible to both cryo-SEVI and IRPD, with systems studied here falling into the categories of free radicals, interstellar species, and metal oxide clusters.Anion photoelectron spectroscopy (PES) is a powerful technique for studying transient neutral species, owing to the ease with which stable anions are photodetached to access these states. Cryo-SEVI is a high-resolution variant of anion PES that exploits the resolving properties of velocity-map imaging by employing a tunable laser source to achieve sub milli-electronvolt (meV) resolution for many species. This is further enhanced by the cryogenic cooling of anions in a radiofrequency ion trap prior to photodetachment, greatly improving spectral clarity and giving access to a larger array of systems. The systems capable of being studied by cryo-SEVI, however, are limited by the ability to cool them sufficiently. To this end, development of a second ion trap has begun, allowing for the study of larger species, especially metal oxides, which are of considerable temperature entering the trap. Installing this second trap should then give access to larger clusters, as well as allow for the introduction of a reaction gas to study how such species react with small molecules, possibly elucidating catalytic reaction mechanisms.Meanwhile, IRPD spectroscopy, a complementary method to cryo-SEVI, can readily characterize the structures of large metal oxide clusters. Here, cations (I) are mass selected, collected in an ion trap, and messenger-tagged with He. These species are then irradiated with intense, tunable IR light and extracted into a time-of-flight mass spectrometer to determine the depletion of IHe as a function of photon energy. IRPD spectra then yield vibrational frequencies with comparable resolution to cryo-SEVI, allowing for the determination of geometries and vibrational frequencies when compared with simulation.Carbon and silicon carbide clusters are structurally complex species of great interest in interstellar, plasma, and combustion chemistry. Cryo-SEVI spectra of C and C allow for the extraction of previously unresolved vibrational frequencies, as well as evidence of vibronic coupling effects to numerous electronic excited states. Small silicon carbides are important astrochemically as a number of them have been observed in interstellar space, though the relative energetics of many of these species are in question, as there exist multiple low-lying stable isomers. SEVI spectra of 4-atom silicon carbides (SiC, SiC, and SiC) shed light on this energetic ordering, elucidate new vibrational frequencies in these species, and observe the first SiC structure with a permanent dipole. Among the free radicals studied are the nitrate radical (NO) and the hydroxy radical (OH). Cryo-SEVI spectra of NO reveal the extent to which vibronic coupling shapes this molecule's vibrational structure, quelling a controversy surrounding the position of the mode of this species. Study of the hydroxy radical was facilitated by recent development of IR-cryo-SEVI, wherein anions are vibrationally pre-excited prior to photodetachment, allowing for the probing of previously inaccessible regions of the neutral potential energy surface. This method, showcased by the photodetachment of vibrationally-excited OH, results in newly allowed features to arise in the spectra of this molecule as well as characterization of the anion's vibrational frequency without the use of a messenger-tag, as is in IRPD.Transition metal oxides serve as a catalysts for many fundamental reactions in chemistry, with the active site often occurring at molecular-scale defects. Given the challenge of studying such active sites, it has become commonplace to use small gas-phase clusters as models for these defect sites, which have the benefit of being easy to produce and tractable for theoretical comparison. The cryo-SEVI spectra of ZrO reacting with HO revealed the coexistence of two structural isomers of the product, arising from a ``hot'' ion distribution ``frozen in" to the cold, trapped population. Comparison of the electron affinities of this and the titanium analogue of the system, as well as the un-reacted clusters, provides insight into the reactivity of these clusters. Further, the IRPD spectra of (NiO)(AlO)(AlO) with = 1-2 and = 1-3, a model for Ni/AlO - industrial catalyst for oxidative dehydrogenation with high selectivity, are presented. Comparison with theory shows that the structures formed lead to under-coordinated Nickel centers that may elucidate the catalytic mechanism of bulk Ni/AlO. Finally, cryo-SEVI spectra of NdO characterize the energetics of this species, including detachment transitions to high-lying excited states that may help explain previous observations from atmospheric release experiments
Dynamics in Helium Nanodroplets Induced via Multiphoton Absorption in the XUV and X-ray Regimes
Full text linkUpon formation, helium nanodroplets evaporatively cool to 0.37 K and thus are in a superfluid state. The ultracold droplets have a very low binding energy and are optically transparent. In contrast, when exposed to extreme ultraviolet (XUV) and x-ray radiation, a variety of complex relaxation and disintegration dynamics may ensue. This dissertation explores dynamics induced in droplets via multiphoton absorption in the XUV and x-ray regimes. In the XUV regime, helium droplets become electronically excited, with two broad absorption features originating from atomic helium states. The lower absorption feature at 21.6 eV originates from n=2 atomic helium states, while the upper feature centered at 23.7 eV arises from higher-lying atomic Rydberg states. After single photon absorption, a variety of relaxation mechanisms have been observed, such as ejection of Rydberg atoms, interband relaxation and Hen* formation. Multiphoton absorption leads to additional deexcitation pathways as a result of interactions between excited helium atoms. At higher photon energies, in the soft x-ray regime, individual atoms in the droplet are ionized via single photon ionization. With high intensity x-ray free electron laser (X-FEL) light sources, droplets can become highly ionized. The ionized droplet may disintegrate from the Coulomb repulsion between ions. Alternatively, if the droplet is sufficiently ionized, the freed electrons are trapped by the collective Coulomb potential of the parent ions, resulting in nanoplasma formation. The quasineutral nanoplasma can then disintegrate via hydrodynamic expansion. The simple electronic structure of atomic helium and uniform density of liquid helium make helium droplets an excellent system for studying complex energy transfer, relaxation, and charging dynamics common to condensed phase media. Energy transfer and relaxation following multiphoton absorption into the lower, n=2 helium droplet absorption feature is studied by femtosecond time-resolved photoelectron spectroscopy in combination with XUV intensity-dependent ion yield measurements. With many photoexcited helium atoms in the droplet, resonant interatomic Coulombic decay (ICD) emerges as a possible deexcitation mechanism. In ICD, an excited atom relaxes by transferring its energy to a neighboring excited atom, resulting in ionization with freed electron carrying away the excess energy. This process is common in van der Waals clusters and condensed phase media, such as biological systems. Previous experiments have revealed that beyond ICD between two excited atoms, with high excitation densities, ICD can occur between many excited atoms leading to a host of inelastic processes as well. Here, measurements are performed in a lower XUV intensity regime than previous studies, such that ICD is limited to interactions between two excited atoms. A high-order harmonic pulse at 21.6 eV in the XUV, resonant with the lower droplet absorption feature, is used to electronically excite the droplet. Relaxation dynamics are then measured using a 3.1 eV UV probe pulse at various XUV-UV pump-probe delays. Ion yield measurements reveal a quadratic dependence on the XUV intensity in smaller droplets (~104 atoms/droplet) and a linear relationship in larger droplets (~106 atoms/droplet). The ICD lifetime is measured to be ~1 ps and found to be a competitive mechanism by which the droplet relaxes, even at low excitation densities.The charging and disintegration dynamics of helium droplets exposed to intense (~1016 W/cm2), soft x-ray pulses at 838 eV photon energy are explored via single shot coincidence measurements of ion time of flight spectra and small angle x-ray scattering patterns. Experimental conditions encompass an extended range of ionization conditions in droplets, from the pure Coulomb explosion regime to the formation of nanoplasmas. Interpretation of these ionization dynamics is important for better understanding of a host of complex processes initiated by intense x-ray pulse light—matter interactions, both intentionally and as unavoidable byproducts of X-FEL based experiments. Ion time-of-flight spectra are used to determine the maximum ion kinetic energy resulting from the x-ray—droplet interaction, while scattering images encode the droplet size and absolute photon fluence. In correlating the droplet size, x-ray fluence, and maximum ion kinetic energy, a continuous relationship between the degree of ionization and ion kinetic energy is observed across the transition from weakly to strongly ionized droplets. Across all experimental conditions, results indicate that the maximum ion kinetic energy is governed by Coulomb repulsion from unscreened cations. Additionally, the results are consistent with the emergence of a spherical shell of unscreened ions around a quasineutral plasma core with the onset of frustrated ionization by electron trapping. The thickness of this shell is reduced to less than 2% of the droplet radius at the highest degrees of ionization frustration
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Attosecond X-Ray Pulses for Molecular Electronic Dynamics
Full text linkAttosecond pulses are opening a wide new field on the border of chemistry and physics. They offer the opportunity to initiate and probe electronic rearrangement of atoms, molecules, solids and clusters on the natural timescale of the electron motion. This thesis is about making and measuring attosecond pulses, with the ultimate goal of applying attosecond spectroscopy to molecules. In chapter 1, attosecond spectroscopy is reviewed in general. The applications of attosecond pulses to atoms and molecules, including successful experiments and theoretical predictions, are discussed. In chapter 2, techniques for making and measuring attosecond radiation are presented. This chapter focuses on high harmonic generation from tabletop laser sources, since synchrotron- and free-electron laser-based techniques are not yet experimentally demonstrated. Chapters 3 and 4 discuss in detail the laboratory setup for attosecond pulse generation, including the laser source, optical diagnostics, and attosecond delay line. The attosecond control of free electron motion with few-cycle laser pulses is presented in chapter 5. There, the carrier-envelope phase (CEP), and thus the attosecond temporal evolution of the laser field, leads to quantum interferences between free electron wavefunctions and lends control over the direction of electron emission. Attosecond pulse production is achieved in chapter 6 by gating harmonic generation on the leading edge of the driving laser pulse. The gate mechanism is shown to rely on the macroscopic ionization of the harmonic generation medium. This final chapter also demonstrates a new technique for assessing attosecond pulse temporal structure based on the inversion of the driving laser field in the laboratory frame of reference, called CEP-scanning
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Ultrafast Dynamics of Adenine Derivatives Studied by Time-Resolved Photoelectron Spectroscopy in Water Microjets
Full text linkFemtosecond time-resolved photoelectron spectroscopy (TRPES) in liquid microjets is a powerful tool for elucidating the ultrafast photoinduced dynamics of species in the condensed phase. A pump pulse first excites the molecule of interest and is then followed by a probe pulse, which detaches the nascent electron distribution to vacuum at varying time-delays. The transient lifetimes, solvation timescales, and binding energies of the molecule can then be elucidated by tracking the time-evolving photoelectron distribution with a magnetic bottle time-of-flight spectrometer.Of particular interest to many fields of chemistry and biology is the process by which DNA and its nucleic acid (NA) constituents shed excess energy imparted by UV radiation. Beyond their intrinsic interest, study of UV-photoexcited NA constituents can also provide fundamental insights into the non-adiabatic processes of organic molecules generally. DNA components are known to undergo rapid de-excitation through a slew of conical intersections that involve ring-puckering modes of the nitrogenous base. Importantly, the local environment and small structural changes in the NA constituent are known to drastically affect these dynamics. For this reason, a bottom up approach to DNA photophysics is necessary.This dissertation explores the photodeactivation of the NA constituents adenosine and adenosine monophosphate in aqueous solution. In a series of pseudo-degenerate experiments, 4.69-4.97eV and 6.20eV photons were used as both the pump and probe pulses. The lowest ππ* excited state was populated by photons ranging in energy from 4.69-4.97eV, and this state was found to decay via internal conversion to vibrationally hot ground state on a sub-ps timescale. Another non-adiabatic channel was seen at an excitation energy of 6.20eV, and was tentatively assigned to the decay of a higher-lying ππ* excited state.These experiments mark the first reported use of a 6.20eV pulse to study the photoinduced dynamics in NA constituents with TRPES in liquid microjets. As a probe pulse, the 6.20eV pulse provides a fuller picture of the excited state relaxation dynamics. When used as a pump, this pulse is posited to interrogate different excited states than previously studied by others. Regardless, in both cases, information about the ground electronic state is energetically inaccessible.The lack of information regarding the ground state dynamics of NA constituents, and, in fact, many solvated species, remains an outstanding issue for TRPES in liquid microjets. The second half of this dissertation focuses on remedying this through the implementation of a new XUV source. High harmonic generation in a semi-infinite gas cell will be used to produce a femtosecond probe pulse ranging in energy from 20-100eV. With a more energetic probe, new regimes of fundamental physical chemistry in the condensed phase will be accessible
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Time Resolved Photoelectron Imaging of Electronic Relaxation Dynamics in Anionic Clusters
Full text linkElectronic relaxation dynamics are measured on a femtosecond timescale in three types of anionic clusters using time resolved photoelectron imaging. Auger relaxation timescales following interband excitation of electron-hole pairs in small Hgn− (n=9-20) are determined. Relaxation dynamics following charge transfer are investigated in I−(CH3CN)n (n=5-10). Internal conversion lifetimes of excited states of large anionic water clusters, (H2O)n− and the fully deuterated isotopolog (D2On− (n=25-200), as well as solvation dynamics in these clusters, are evaluated. A pronounced increase in the Auger lifetime of interband-excited states of Hgn − clusters with 13 or more constituent mercury atoms is revealed, indicating a shift from the van der Waals interactions typical of smaller clusters towards covalent bonding between mercury atoms in the cluster. This creates more delocalized electronic orbitals which reduce the coulomb interactions of the electron-hole pair, increasing the amount of time required for recombination and ejection of Auger electrons. Initial dynamics following charge transfer in I−(CH3CN)n clusters are associated with localization of an initially diffuse electron contained within the cluster. Later dynamics are assigned to rearrangement of the network of CH3CN molecules and ejection of neutral iodine from the cluster. Ultrafast internal conversion lifetimes of the first electronic excited state of anionic water clusters are measured at larger cluster sizes and with better time resolution than previous measurements. A marked reduction in the size dependence of the internal conversion lifetime at large sizes indicates a change in the electron water interaction for clusters larger than n≈70. Extrapolating internal conversion lifetimes of the larger clusters towards infinite cluster size predicts a condensed phase internal conversion lifetime of ~50 fs for the hydrated electron, supporting the nonadiabatic relaxation model. Solvation dynamics on both the ground and excited states are also observed
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High-Resolution Photoelectron Imaging and Infrared Photodissociation Spectroscopy of Cold Negative Ions
Full text linkSlow electron velocity-map imaging of cryogenically-cooled anions (cryo-SEVI) is a versatile spectroscopic technique that provides high-resolution detachment spectra of molecular ions, yielding insight into the vibrational and electronic properties of neutral species. This method provides orders-of-magnitude improvement in resolution over earlier measurements, and invariably reveals new subtleties in the resultant spectra. The cryo-SEVI apparatus has multiple ion-generation and photodetachment modes of operation which enable application to a vast range of molecular species, including organic radicals, reactive intermediates, and metal-oxide clusters.While free radicals are generally highly reactive and difficult to isolate in a laboratory experiment, their corresponding anions are closed-shell, and thus cryo-SEVI is particularly well-suited for characterization of the vibronic structure of neutral radicals with relevance to combustion and atmospheric chemistry. In this thesis, several free radicals were probed by photodetachment of the corresponding anions. The cryo-SEVI spectrum of the tert-butyl peroxide anion showed detachment to two electronic states of the corresponding peroxy radical, giving a number of vibrational and electronic quantities regarding this atmospherically-relevant species. In addition to the peroxy radical, the heterocyclic aromatic radicals derived from hydrogen abstraction from furan and pyridine have been studied. These isomer-specific spectra showed interesting isomeric trends in their photoelectron angular distributions, providing insight into the charge distribution resulting from deprotonation of the parent heterocycle.In a similar vein, the vinylidene anion (H2CC-) is used to obtain spectroscopic access to neutral vinylidene, a high-energy isomer of acetylene. The isomerization of vinylidene to acetylene on the neutral ground state surface has a remarkably low barrier, resulting in the potential for coupling between vinylidene vibrational states and highly excited levels of acetylene. The extent to which this coupling occurs, and the resultant lifetime of neutral vinylidene, has been the subject of some debate in the physical chemistry community. By performing cryo-SEVI experiments on the vinylidene anion and relating these results to a highly accurate ab initio potential energy surface, the state-specificity of coupling to acetylene was clearly established. The detachment spectra of vinylidene anions also showed other interesting spectroscopic effects, such as vibronic coupling between excited neutral states as well as resonant autodetachment from vibrationally excited anions.Finally, cryo-SEVI has also been used to investigate gas-phase clusters which serve as models for the defect sites that constitute reactive centers on catalytic surfaces. These defect sites have geometries, stoichiometries, and charge distributions which differ from that of the rest of the surface, and can be challenging to probe in bulk experiments. Gas-phase metal oxide cluster anions thus provide model systems whose properties can be monitored as a function of cluster size and stoichiometry. To this end, two bare aluminum oxide clusters, Al2O2- and Al3O3-, have been characterized using cryo-SEVI. This work revealed electronically-mediated autodetachment from Al2O2-, and established the energy ordering of the close-lying Al3O3- isomers.Following characterization of the bare cluster anions, it is of interest to characterize the products formed by reaction of metal oxide clusters with molecules of interest to catalysis, providing spectroscopic access to other parts of the potential energy surfaces of model catalytic reactions. To this end, cryo-SEVI was used to interrogate the product formed by reaction of TiO2- with a single H2O molecule, and comparison of these results to the cryo-SEVI spectra of bare TiO2- showed a similar energetic dependence of charge state as is observed for bulk water splitting on titania surfaces.While cryo-SEVI provides invaluable information regarding neutral species via photodetachment of the corresponding anion, infrared photodissociation (IRPD) experiments may be used to structurally characterize the anions themselves, which can be particularly useful in cases where multiple low-lying isomers are expected. In an IRPD experiment, an ion of interest is complexed with a weakly interacting tagging species (such as Ar or D2) in a cryogenic ion trap, and the resultant cluster is irradiated with tunable infrared light. When the incident light is resonant with a vibrational transition of the ion, the tagging molecule is lost, and so monitoring the mass spectrum following irradiation provides a measurement of the vibrational spectrum of the bare ion. In this thesis, IRPD is used to observe the loss of a D2 tag from microhydrated acetate anions, CH3CO2(H2O)n D2, to determine the first steps in the structural evolution of the first solvation shell for this carboxylate anion
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