Ground Vibrational Level Research Articles

Theoretical study of ClH2− electron detachment spectroscopy revisited

Electron detachment spectroscopy of ClH2− and ClD2− is revisited in this paper. Franck–Condon transition from the ground vibrational level of the electronic ground state of the anion to the coupled electronic manifold of the neutral species is investigated by a time-dependent wave packet (WP) approach. Rich vibronic structures due to Cl…H2 continuum states at higher energies appeared in the photodetachment band in our previous study [Chem. Phys. Lett. 394 (2004) 207] are eliminated on improving the representation of the anionic wavefunction and the WP propagation algorithm. The theoretical findings are compared with the available experimental and theoretical results.

Potential energy curves and vibrational levels of ground and excited states of LiAl

The potential energy curves (PECs) for ground electronic state (X1∑+) and seven excited electronic states (a3∏, A1∏, b3∑+, c3∑+, B1∏, C1∑+, d3∏) of LiAl are obtained using the multi-configuration reference single and double excited configuration interaction method. Equilibrium bond length Re, adiabatic excited energy Te and vertical excited energy Tv are obtained. It is shown that c3∑+ is an unstable repulsive state, A1∏ is a weak bound state and the others are all bound states. Predissociation can be found between b3∑+ and c3∑+ states. Eight electronic states are dissociated along two channels, Li(2S)+Al(2P0) and Li(2P0)+Al(2P0). And then PECs are fitted to analytical Murrell-Sorbie (MS) potential function to deduce the spectroscopic parameters:the Re is 0.2863 nm, ωe is 316 cm-1 and De is 1.03 eV for the ground state; the values of Tv of excited states are 0.27, 0.83, 1.18, 1.14, 1.62, 1.81 and 2.00 eV; the values of De are 1.03, 0.82 and 0.26, repulsive state, 1.54, 1.10, 0.93 eV, and the values of corresponding frequency ωe are 339, 237, 394, repulsive state, 429, 192, 178 cm-1. By solving the radial Schrödinger equation of nuclear motion, the vibration levels, inertial rotation constants (J=0) are reported for the first time.

Environmental ground borne noise and vibration protection of sensitive cultural receptors along the Athens Metro Extension to Piraeus

Attiko Metro S.A., the state company ensuring the development of the Athens Metro network, has recently initiated a new extension of 7.6km, has planned for line 3 of Athens Metro from Haidari to Piraeus “Dimotikon Theatre” towards “University of Piraeus” (forestation), connecting the major Piraeus Port with “Eleftherios Venizelos” International Airport. The Piraeus extension consists of a Tunnel Boring Machine, 2 tracks and, tunnel sections, as well as 6 stations and a forestation (New Austrian Tunnelling Method) at the end of the alignment. In order to avoid the degradation of the urban acoustic environment from ground borne noise and vibration during metro operation, the assessment of the required track types and possible noise mitigation measures was executed, and for each section and each sensitive building, the ground borne noise and vibration levels will be numerically predicted. The calculated levels were then compared with ground borne noise and vibration level criteria. The necessary mitigation measures were defined in order to guarantee, in each location along the extension, the allowable ground borne Noise and Vibration max. levels inside nearby sensitive buildings taking into account alternative Transfer Functions for ground borne noise diffusion inside the buildings. Ground borne noise levels were proven to be higher than the criterion where special track work is present and also in the case of the sensitive receptor: “Dimotikon Theatre”. In order to reduce the ground borne noise levels to allowable values in these sections, the installation of tracks and special track work on a floating slab was assessed and recommended.

Photoelectron spectroscopic study of the E ⊗ e Jahn-Teller effect in the presence of a tunable spin-orbit interaction. III. Two-state excitonic model accounting for observed trends in the $\tilde{\rm X}^{\,2}{\rm {E}}$X̃2E ground state of $\rm {CH}_3\rm {X}^+\,(\rm {X}=\rm {F,\,Cl,\,Br,\,I})$ CH 3X+(X=F, Cl , Br ,I) and $\rm {CH}_3\rm {Y}\,(\rm {Y}=\rm {O,\,S})$ CH 3Y(Y=O,S)

Open-shell molecules in doubly degenerate (2)E electronic states are subject to the E ⊗ e Jahn-Teller effect and spin-orbit interactions. The rotational structure of the ground vibrational level of the X(+) (2)E ground state of CH(3)F(+) has been observed by high-resolution photoelectron spectroscopy. In contrast to what is observed in other members of the isoelectronic families CH(3)X(+) (X=Cl, Br, I) and CH(3)Y (Y=O, S), the spin-orbit interaction does not lead to a splitting of the ground state of CH(3)F(+). Observed trends in the spectra of the X (2)E ground states of these molecules are summarized. Whereas certain trends, such as the reduction of the observable effects of the Jahn-Teller interactions and the increase of the spin-orbit splitting with increasing nuclear charge of X and Y are easily understood, other trends are more difficult to explain, such as the much reduced spin-orbit splitting in CH(3)F(+) compared to CH(3)O. A simple two-state excitonic model is used to account for the trends observed within the series of the methyl-halide radical cations and also the similarities and differences between CH(3)F(+) and the isoelectronic CH(3)O radical. Within this model, the electron hole in the (2)E ground states of CH(3)X(+) and CH(3)Y is described in terms of contributions from the halogenic (or chalcogenic) p(x, y) orbitals and the pyramidal-methylic (e) orbitals. This model enables a global, semi-quantitative description of the combined effects of the Jahn-Teller and spin-orbit interactions in these molecules and also a simple interpretation of the spin-orbit-coupling reduction factor ζ(e).

Spectroscopy above the ionization threshold: Dissociative recombination of the ground vibrational level of ${\rm N}_{\rm 2}^{\rm + }$N2+

Comprehensive theoretical calculations are reported for the dissociative recombination of the lowest vibrational level of the N(2)(+) ground state. Fourteen dissociative channels, 21 electron capture channels, and 48 Rydberg series including Rydberg states having the first excited state of the ion as core are described for electron energies up to 1.0 eV. The calculation of potential curves, electron capture and predissociation widths, cross sections and rate constants are described. The cross sections and rate constants are calculated using Multichannel Quantum Defect Theory which allows for efficient handling of the Rydberg series. The most important dissociative channel is 2(3)Π(u) followed by 4(3)Π(u). Dissociative states that do not cross the ion within the ground vibrational level turning points play a significant role in determining the cross section structure and at isolated energies can be more important than states having a favorable crossing. By accounting for autoionization, the interactions between resonances, between dissociative states, and between resonances and dissociative states it is found that the cross section can be viewed as a complex dissociative recombination spectrum in which resonances overlap and interfere. The detailed cross section exhibits a rapid variation in atomic quantum yields for small changes in the electron energy. A study of this rapid variation by future high resolution storage ring experiments is suggested. A least squares fit to the calculated rate constant from the ground vibrational level is 2.2(+0.2)/(-0.4) × 10(-7) × (T(e)/300)(-0.40) cm(3)/sec for electron temperatures, T(e), between 100 and 3000 K and is in excellent agreement with experimentally derived values.

Evaluation of blast induced ground vibration for minimizing negative effects on surrounding structures

The present paper mainly deals with the prediction of blast-induced ground vibration level in Bakhtiary formation at intake of waterway system in Gotvand dam, Iran. For this research the ground vibration components were recorded carefully by means of 3 sets of vibration monitors for 32 blast events during the bench blasting in front of tunnels. Then, the data pairs of scaled distance and particle velocity were analyzed by using the USBM equation. At the end of statistical evaluations, a relationship between peak particle velocity and scaled distance for this site was established with good correlation. Again, other data measurements during tunnel excavation near concrete structures were used to validate the predicted PPV and optimize the blasting patterns to omit the effects of resonance and vibration in USBM (RI-8507) standard. Based on the vibration tests done in Bakhtiary conglomerate, constant dynamic factors of the rock mass related to vibration velocity are 159.07 and 1.077.

Influence of some vehicle and track parameters on the environmental vibrations induced by railway traffic

A study is performed on the influence of some typical railway vehicle and track parameters on the level of ground vibrations induced in the neighbourhood. The results are obtained from a previously validated simulation framework considering in a first step the vehicle/track subsystem and, in a second step, the response of the soil to the forces resulting from the first analysis. The vehicle is reduced to a simple vertical 3-dof model, corresponding to the superposition of the wheelset, the bogie and the car body. The rail is modelled as a succession of beam elements elastically supported by the sleepers, lying themselves on a flexible foundation representing the ballast and the subgrade. The connection between the wheels and the rails is realised through a non-linear Hertzian contact. The soil motion is obtained from a finite/infinite element model. The investigated vehicle parameters are its type (urban, high speed, freight, etc.) and its speed. For the track, the rail flexural stiffness, the railpad stiffness, the spacing between sleepers and the rail and sleeper masses are considered. In all cases, the parameter value range is defined from a bibliographic browsing. At the end, the paper proposes a table summarising the influence of each studied parameter on three indicators: the vehicle acceleration, the rail velocity and the soil velocity. It namely turns out that the vehicle has a serious influence on the vibration level and should be considered in prediction models.

Kinetics of Isothermal Ethanol Adsorption onto a Carbon Molecular Sieve under Conventional and Microwave Heating

AbstractThe isothermal kinetics of ethanol adsorption from aqueous solution onto a zeolite type carbon molecular sieve (CMS‐3A) under conventional heating (CH) and microwave heating (MWH) was investigated. The adsorption kinetics is described by the model of a phase‐boundary controlled reaction for both heating modes. The activation energy (Ea) for the adsorption process under MWH is lower than under CH while the preexponential factor (lnA) is higher. Ethanol adsorption is a kinetically complex process whose complexity changes with the mode of heating. The established decrease in Ea and increase in lnA under MWH compared to CH is explained with the increase in the ground vibrational level of the – OH twisting vibrations in the ethanol molecule and with the decrease in its anharmonicity factor which is caused by the selective resonant transfer of energy from CMS‐3A to the OH oscillators.

Triplet-singlet conversion by broadband optical pumping

We demonstrate the conversion of cold Cs${}_{2}$ molecules initially distributed over several vibrational levels of the lowest triplet state ${a}^{3}\phantom{\rule{0.16em}{0ex}}{\ensuremath{\Sigma}}_{u}^{+}$ into the singlet ground state ${X}^{1}\phantom{\rule{0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{+}$. This conversion is realized by a broadband laser exciting the molecules to a well-chosen state from which they may decay to the singlet state through two sequential single-photon emission steps: The first photon populates levels with mixed triplet-singlet character, making possible a second spontaneous emission down to several vibrational levels of the ${X}^{1}\phantom{\rule{0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{+}$ states. By adding an optical scheme for vibrational cooling, a substantial fraction of molecules are transferred to the ground vibrational level of the singlet state. The efficiency of the conversion process, with and without vibrational cooling, is discussed at the end of the article. The presented conversion is general in scope and could be extended to other molecules.

A comparative kinetics study on the isothermal heterogeneous acid-catalyzed hydrolysis of sucrose under conventional and microwave heating

The isothermal kinetics of sucrose hydrolysis at the acidic ion-exchange resin type IR-120 H under conventional (CH) and microwave heating (MWH) was investigated. Isothermal kinetics curves in the temperature range from 303 to 343K for both CH and MWH were determined. By application the model-fitting method, it was recognized that the kinetics of sucrose hydrolysis can be described by a first-order chemical reaction for both heating modes. The values of the activation energy (Ea) and pre-exponential factor (lnA) for sucrose hydrolysis were found to be lower under MWH than under CH. Application of the differential isoconversional method showed that sucrose hydrolysis was kinetically an elementary reaction. It is found that the increased rate of hydrolysis observed under MWH was not a consequence of overheating. A new explanation of the established effects of microwave heating based on a model of selective energy transfer during the chemical reaction is suggested. The established decreases in the activation energy and in the pre-exponential factor under MWH in comparison to CH is explained by an increase in the energy of the ground vibrational level of the –OH out-of-plane deformation in the sucrose molecule and with a decrease in the anharmonicity factor, which is caused by the selective resonant transfer of energy from the catalyst to the –OH oscillators in the sucrose molecules.

Prediction of blast-induced overbreak from uncontrolled burn-cut blasting in tunnels driven through medium rock class

Drilling and blasting is the predominant rock excavation technique in driving horizontal tunnels. This often results in large overbreak. One of the prime reasons for overbreak is the unacceptable levels of ground vibration generated in blasting. From the literature survey and practical experience, it was found that threshold levels of PPV for overbreak depends on rock properties, namely, rock strengths, P-wave velocity, specific gravity, Poisson’s ratio and rockmass parameters. Determination of threshold level of peak particle velocity (PPV) is crucial for controlling blast-induced overbreak and can be approximated by extrapolating the vibration predictor established from near-field vibration monitoring. This paper reports the experiments carried out in five horizontal tunnels for monitoring near-field ground vibration using accelerometer-based-seismograph planted in roof/sidewalls to establish ground vibration predictors. Blast-induced overbreak for each blast has been measured using a telescopic profiler. The threshold levels of PPV for overbreak have been estimated from the extrapolated vibration predictors to the overbreak zone and also using near field approximation technique. The estimated threshold levels of PPV for overbreak ranged between 590 and 1050mm/s in extrapolation model and 410–890mm/s in near-field HP model. Apart from these, a relationship between the percentage overbreak and rock/rockmass, charge and blast design parameters has been established through multivariate regression analysis of the data pertaining to five investigating sites. The result has been validated for four blasts within reasonable accuracy.

Laser cooling of the vibrational motion of Na2combining the effects of zero-width resonances and exceptional points

We propose various scenarios for molecular vibrational cooling combining the effects of two kinds of resonance states occurring during the photodissociation of Na${}_{2}$ taken as an illustrative example. Such resonances result from an appropriate sampling of laser parameters (wavelength and intensity): (a) For particular choices of intensity and wavelength, two resonance energies can be brought to complete coalescence, with their positions and widths becoming equal and leading to a so-called exceptional point (EP) in the parameter plane. Advantage can be taken from such points for very selective laser-controlled vibrational transfer strategies. (b) For specific intensities, far beyond the perturbation regime, some resonances can have a zero width (infinite lifetime). They are referred to as a zero-width resonance (ZWR) and may be used for vibrational purification purposes. We show how appropriately shaped, experimentally reachable laser pulses, encircling EPs or inducing ZWRs, may be used for a thorough and comprehensive control aiming at population transfer or purification schemes, which, starting from an initial field-free vibrational distribution, ends up in the ground vibrational level.

A two-step time simulation of ground vibrations induced by the railway traffic

Recent decades have been fertile in terms of development of vehicle dynamics simulations. But the usual applications dedicated to the train design rarely take into account ground vibrations. In order to assess the influence of vehicle dynamics on track deflection and therefore on ground wave propagation, the vehicle/track system must be studied globally. The track/soil coupling is first investigated, through various track/soil models. From there, a decoupled approach is proposed, which proves valid as far as the soil is sufficiently rigid with respect to the ballast. It works in two stages: the simulation of the vehicle/track subsystem provides in a first step the ground forces, considering the irregularities of the rail as the excitation mechanism. The resulting forces are then applied, in a second step, to the soil subsystem model. Two applications are presented, consisting of the passing of a tram over a local discontinuity and the passing of a high-speed train over a rough track. The results obtained show a good agreement with experimental measurements as well as the importance of the whole vehicle/track/soil dynamics on the level of ground vibration.

The role of the Jahn-Teller coupling in dissociative recombination of H3O+ and H ions

We discuss the importance of the non Born-Oppenheimer Jahn-Teller coupling in the dissociative recombination of H3O+ and H ions with low energy electrons. The coupling is known to be important for dissociative recombination of H, for which detailed and simplified theoretical models have been previously developed. In this study we discuss how the detailed theoretical model reproduces individual resonances in the experimental spectrum of H. We present a simplified theoretical model of the dissociative recombination of H3O+. Similarly to H, we consider the Jahn-Teller coupling as a key factor responsible for the capture of the electron into a Rydberg state associated with excited vibrational levels of the ion. We use a simplified Jahn-Teller model for highly symmetrical ions (not only for H3O+ and H) and adopt the normal mode approximation for the vibrational states of H3O+. Using the multi-channel quantum defect formalism and accurate ab initio calculations, we derive the cross sections for electron capture by the ion that is initially in the ground vibrational level. In our approximation, once the electron is captured by the ion, the autoionization probability is neglected compared to the predissociation probability. This allows us to evaluate the cross section for the dissociative recombination of H3O+ using just a few parameters obtained from ab initio calculation. The total cross section obtained is in good agreement with data from storage ring experiments.

Isomerization reaction between linear AlNC and AlCN including the $\tilde X$X̃ 1Σ+ and $\tilde A$Ã 1Π states studied by three-dimensional wave packet propagation

Excitation transfers between linear AlNC and AlCN via the à (1)Π (1 (1)A", 2 (1)A')-X (1)Σ(+) transition were studied by a wave packet propagation method as applied to a simple system for an isomerization reaction. The photoabsorption and fluorescence spectra calculated in this work are in good agreement with Einstein's A and B coefficients reported in our previous paper [I. Tokue and S. Nanbu, J. Chem. Phys. 124, 224301 (2006)]. In the 2 (1)A'-X (1)Σ(+) excitation of linear AlNC, both isomerization to linear AlCN and dissociation to Al + CN can occur; the probability of both decay channels strongly depends on the vibrational modes of the initial wave packet. The 1 (1)A"-X (1)Σ(+) excitation of linear AlNC results primarily in dissociation with isomerization being found to be a relatively minor phenomenon. For the linear AlCN excitation, vibrational levels above 1000 cm(-1) occur for both isomerization and dissociation. The isomerization of AlNC ↔ AlCN was found to occur after the à (1)Π-X (1)Σ(+) fluorescence of AlNC and AlCN, with even the initial wave packet being made with the vibrational ground level of the à (1)Π state, whereas no dissociation was recognized for any of the cases calculated in this study using lower vibrational levels as initial wave packets. The procedure for wave packet propagation employed in this study is concluded to be very effective for analyzing in detail the reaction dynamics of isomerization for triatomic molecules.

Vibrationally quantum-state-specific dynamics of the reactions of CN radicals with organic molecules in solution

The dynamics of reactions of CN radicals with cyclohexane, d(12)-cyclohexane, and tetramethylsilane have been studied in solutions of chloroform, dichloromethane, and the deuterated variants of these solvents using ultraviolet photolysis of ICN to initiate a reaction. The H(D)-atom abstraction reactions produce HCN (DCN) that is probed in absorption with sub-picosecond time resolution using ∼500 cm(-1) bandwidth infrared (IR) pulses in the spectral regions corresponding to C-H (or C-D) and C≡N stretching mode fundamental and hot bands. Equivalent IR spectra were obtained for the reactions of CN radicals with the pure solvents. In all cases, the reaction products are formed at early times with a strong propensity for vibrational excitation of the C-H (or C-D) stretching (v(3)) and H-C-N (D-C-N) bending (v(2)) modes, and for DCN products there is also evidence of vibrational excitation of the v(1) mode, which involves stretching of the C≡N bond. The vibrationally excited products relax to the ground vibrational level of HCN (DCN) with time constants of ∼130-270 ps (depending on molecule and solvent), and the majority of the HCN (DCN) in this ground level is formed by vibrational relaxation, instead of directly from the chemical reaction. The time-dependence of reactive production of HCN (DCN) and vibrational relaxation is analysed using a vibrationally quantum-state specific kinetic model. The experimental outcomes are indicative of dynamics of exothermic reactions over an energy surface with an early transition state. Although the presence of the chlorinated solvent may reduce the extent of vibrational excitation of the nascent products, the early-time chemical reaction dynamics in these liquid solvents are deduced to be very similar to those for isolated collisions in the gas phase. The transient IR spectra show additional spectroscopic absorption features centered at 2037 cm(-1) and 2065 cm(-1) (in CHCl(3)) that are assigned, respectively, to CN-solvent complexes and recombination of I atoms with CN radicals to form INC molecules. These products build up rapidly, with respective time constants of 8-26 and 11-22 ps. A further, slower rise in the INC absorption signal (with time constant >500 ps) is attributed to diffusive recombination after escape from the initial solvent cage and accounts for more than 2/3 of the observed INC.

Prediction of ground vibration level induced by blasting at different rock units

Blasting is generally inevitable for hard rock excavation. Vibrations, induced from blasting affect adjacent and remote structures, as well as people in the neighborhood. This paper describes ground motions induced by blasting near underground and surface concrete structures during the construction of upper Gotvand dam. Effects of different rock formations, different detonators and explosives are analyzed. During underground and surface excavation, 498 ground motions, produces by 216 shots were measured with Vibraloc vibration monitors. Scaled distance and peak particle velocity data pairs were carefully recorded and analyzed statistically. This analysis allowed the document of empirical relationships between scale distance and peak particle velocity in different surface and underground regions. Finally, the particle and frequency values of further blast events were evaluated according to the USBM (RI 8507) to validate the relation and predict the influence level to the neighboring concrete structures.

The nascent OH detection in photodissociation of 2-(bromomethyl)hexafluoro-2-propanol at 193 nm: Laser-induced fluorescence study

Photodissociation of 2-(bromomethyl)hexafluoro-2-propanol (BMHFP) and 3-bromo-1-propanol (BP), involving σ C – Br * ← n Br transition at 193 nm, has been investigated by measuring laser-induced fluorescence spectra of the expected OH product. The OH channel is a minor dissociation pathway with a quantum yield of 0.17 ± 0.05 in BMHFP, whereas it was not observed in BP. Partitioning of the available energy into translation, rotation, and vibration of the photoproducts has been measured by state selective detection of the nascent OH product in BMHFP. OH is produced mostly in the ground vibrational level ( v″ = 0), with a rotational distribution being characterized by a temperature of 465 ± 25 K. But, a significant fraction of the available energy of 30.2 kcal mol −1 is partitioned into translation of OH (14.6 kcal mol −1). The OH( v″ = 0, J″) populations in the spin-orbit states as well as in the Λ-doublet states are statistical. A plausible mechanism of OH formation on excitation of BMHFP at 193 nm is suggested, with the primary reaction channel being elimination of Br atom by direct C–Br bond dissociation from a repulsive surface. The Br radical is detected using (2 + 1) resonance-enhanced multiphoton ionization (REMPI) at ∼234 nm. It is produced in both the ground ( 2P 3/2) and the excited ( 2P 1/2) spin-orbit states with the relative quantum yield of the latter to be 0.36. The co-fragment of Br undergoes secondary C–O bond dissociation to produce OH and F 3C–C( CH 2)–CF 3, with the reaction having a barrier located in the exit channel. In this two-step three-body dissociation process, a major fraction of the available energy is released into translation (〈 f T〉 ∼ 0.75), resulting from an impulsive C–Br bond dissociation in the primary step and presence of an exit barrier in the secondary process. Experimental results combined with theoretical calculations provide a clear picture of the dynamics of OH formation from BMHFP at 193 nm. In addition, the energetics of another channel, competing with OH, have been calculated from the primary product F 3C–C(CH 2)(OH)–CF 3. In contrast to BMHFP, the OH product could not be observed from the photolysis of 3-bromo-1-propanol (another saturated halogenated propanol) at 193 nm under the detection limit of the present experimental condition, although it has a higher absorption cross-section at 193 nm.

Oxygen-Assisted Water Dissociation on Metal Surfaces: Kinetics and Quantum Effects

A model of oxygen-assisted water dissociation reaction (OWD, H2O + O → 2OH), based on a tunnel mechanism of H transfer, is presented and analyzed to show that the corresponding activation energies are much lower than those of water dissociation on a clean surface. The Morse and the Pőschl–Teller potentials are used to describe the initial and final energy wells. The reaction probability is analyzed in the framework of the nonadiabatic theory that also allows considering the hydrogen transfer in the case of a strong electron coupling. It is shown that the main contribution to the rate constant is due to quantum transition between the ground vibrational levels of the H atom in the initial and final potential wells. Numerical analysis of the rate constants and kinetic isotope effects is performed for the OWD proceeding on platinum, copper, nickel, and rhodium metal surfaces.

Photoelectron Spectroscopic Study of the Oxyallyl Diradical

The photoelectron spectrum of the oxyallyl (OXA) radical anion has been measured. The radical anion has been generated in the reaction of the atomic oxygen radical anion (O(•-)) with acetone. Three low-lying electronic states of OXA have been observed in the spectrum. Electronic structure calculations have been performed for the triplet states ((3)B(2) and (3)B(1)) of OXA and the ground doublet state ((2)A(2)) of the radical anion using density functional theory (DFT). Spectral simulations have been carried out for the triplet states based on the results of the DFT calculations. The simulation identifies a vibrational progression of the CCC bending mode of the (3)B(2) state of OXA in the lower electron binding energy (eBE) portion of the spectrum. On top of the (3)B(2) feature, however, the experimental spectrum exhibits additional photoelectron peaks whose angular distribution is distinct from that for the vibronic peaks of the (3)B(2) state. Complete active space self-consistent field (CASSCF) method and second-order perturbation theory based on the CASSCF wave function (CASPT2) have been employed to study the lowest singlet state ((1)A(1)) of OXA. The simulation based on the results of these electronic structure calculations establishes that the overlapping peaks represent the vibrational ground level of the (1)A(1) state and its vibrational progression of the CO stretching mode. The (1)A(1) state is the lowest electronic state of OXA, and the electron affinity (EA) of OXA is 1.940 ± 0.010 eV. The (3)B(2) state is the first excited state with an electronic term energy of 55 ± 2 meV. The widths of the vibronic peaks of the X̃ (1)A(1) state are much broader than those of the ã (3)B(2) state, implying that the (1)A(1) state is indeed a transition state. The CASSCF and CASPT2 calculations suggest that the (1)A(1) state is at a potential maximum along the nuclear coordinate representing disrotatory motion of the two methylene groups, which leads to three-membered-ring formation, i.e., cyclopropanone. The simulation of b̃ (3)B(1) OXA reproduces the higher eBE portion of the spectrum very well. The term energy of the (3)B(1) state is 0.883 ± 0.012 eV. Photoelectron spectroscopic measurements have also been conducted for the other ion products of the O(•-) reaction with acetone. The photoelectron imaging spectrum of the acetylcarbene (AC) radical anion exhibits a broad, structureless feature, which is assigned to the X̃ (3)A'' state of AC. The ground ((2)A'') and first excited ((2)A') states of the 1-methylvinoxy (1-MVO) radical have been observed in the photoelectron spectrum of the 1-MVO ion, and their vibronic structure has been analyzed.