Adiabatic Detachment Energies Research Articles

Flexible Acyclic Polyol-Chloride Anion Complexes and Their Characterization by Photoelectron Spectroscopy and Variable Temperature Binding Constant Determinations

Flexible acyclic alcohols with one to five hydroxyl groups were bound to a chloride anion and these complexes were interrogated by negative ion photoelectron spectroscopy and companion density functional theory computations. The resulting vertical detachment energies are reproduced on average to 0.10 eV by M06-2X/aug-cc-pVTZ predictions and range from 4.45-5.96 eV. These values are 0.84-2.35 eV larger than the adiabatic detachment energy of Cl(-) as a result of the larger hydrogen bond networks in the bigger polyols. Adiabatic detachment energies of the alcohol-Cl(-) clusters are more difficult to determine both experimentally and computationally. This is due to the large geometry changes that occur upon photodetachment and the large bond dissociation energy of H-Cl which enables the resulting chlorine atom to abstract a hydrogen from any of the methylene (CH2) or methine (CH) positions. Both ionic and nonionic hydrogen bonds (i.e., OH···Cl(-) and OH···OH···Cl(-)) form in the larger polyols complexes and are found to be energetically comparable. Subtle structural differences, consequently can lead to the formation of different types of hydrogen bonds, and maximizing the ionic ones is not always preferred. Solution equilibrium binding constants between the alcohols and tetrabutylammonium chloride (TBACl) in acetonitrile at -24.2, +22.0, and +53.6 °C were also determined. The free energies of association are nearly identical for all of the substrates (i.e., ΔG° = -2.8 ± 0.7 kcal mol(-1)). Compensating enthalpy and entropy values reveal, contrary to expectation and the intrinsic gas-phase preferences, that the bigger systems with more hydroxyl groups are entropically favored and enthalpically disfavored relative to the smaller species. This suggests that more solvent molecules are released upon binding TBACl to alcohols with more hydroxyl groups and is consistent with the measured negative heat capacities. These quantities increase with molecular complexity of the substrate, however, contrary to common interpretation of these values.

Structural Evolution and Electronic Properties of VnC2(0/-) and VnC4(0/-) (n = 1-6) Clusters: Insights from Photoelectron Spectroscopy and Theoretical Calculations.

The structural evolution and electronic properties of VnC2(-/0) and VnC4(-/0) (n = 1-6) clusters were investigated using photoelectron spectroscopy and density functional theory calculations. The adiabatic and vertical detachment energies of VnC2(-) and VnC4(-) (n = 1-6) clusters were obtained from their photoelectron spectra. The most stable structures were identified by comparing the results of our calculations with the experimental data. We found that the carbon atoms of VnC2(-/0) and VnC4(-/0) (n = 1-6) clusters were separated gradually with increasing number of vanadium atoms. For VnC2(-/0) (n = 3-6) and VnC4(-/0) (n = 4-6) clusters, the carbon atoms are separated by the vanadium atoms. The geometry of V4C4 is a cubic structure and the geometries of V5C4 and V6C4 are formed by one and two vanadium atoms capping the cubic V4C4 structure, respectively.

Investigation on the neutral and anionic BxAlyH2 (x + y = 7, 8, 9) clusters using density functional theory combined with photoelectron spectroscopy

The structure and bonding nature of neutral and negatively charged BxAlyH2 (x + y = 7, 8, 9) clusters are investigated with the aid of previously published experimental photoelectron spectra combined with the present density functional theory calculations. The comparison between the experimental photoelectron spectra and theoretical simulated spectra helps to identify the ground state structures. The accuracy of the obtained ground state structures is further verified by calculating their adiabatic electron affinities and vertical detachment energies and comparing them against available experimental data. The results show that the structures of BxAlyH2 transform from three-dimensional to planar structures as the number of boron atoms increases. Moreover, boron atoms tend to bind together forming Bn units. The hydrogen atoms prefer to bind with boron atoms rather than aluminum atoms. The analyses of the molecular orbital on the ground state structures further support the abovementioned results.

Negative ion photoelectron spectroscopy of P2N3-: electron affinity and electronic structures of P2N3˙.

We report here a negative ion photoelectron spectroscopy (NIPES) and ab initio study of the recently synthesized planar aromatic inorganic ion P2N3-, to investigate the electronic structures of P2N3- and its neutral P2N3˙ radical. The adiabatic detachment energy of P2N3- (electron affinity of P2N3˙) was determined to be 3.765 ± 0.010 eV, indicating high stability for the P2N3- anion. Ab initio electronic structure calculations reveal the existence of five, low-lying, electronic states in the neutral P2N3˙ radical. Calculation of the Franck-Condon factors (FCFs) for each anion-to-neutral electronic transition and comparison of the resulting simulated NIPE spectrum with the vibrational structure in the observed spectrum allows the first four excited states of P2N3˙ to be determined to lie 6.2, 6.7, 11.5, and 22.8 kcal mol-1 above the ground state of the radical, which is found to be a 6π-electron, 2A1, σ state.

Photoelectron imaging as a probe of the repulsive Coulomb barrier in the photodetachment of antimony tartrate dianions

A photoelectron imaging study of the text-book antimony tartrate dianion is presented. The vertical and adiabatic detachment energies are determined to be 2.5±0.1eV and 2.1±0.2eV, respectively. The photoelectron spectra exhibit a typical cut-off due to the presence of the repulsive Coulomb barrier (RCB) and the photoelectron images are highly anisotropic. Using a simple model for the RCB combined with classical molecular dynamics simulations, the photoelectron images were calculated and compared with experiment. Very good overall agreement between the simulations and experiments was achieved when the photodetachment occurs along a specific molecular axis.

Growth behavior and electronic structure of neutral and anion ZrGen (n = 1–21) clusters

The atomic and electronic structure of both neutral and negatively charged ZrGen (n=1–21) clusters have been studied using ab initio calculations. The atomic structures have been identified by comparing the calculated results of the electronic spectra of the anion clusters with the available photoelectron spectroscopy data. We find that the atomic structure of ZrGen cluster can be derived by adding one or more Ge atoms on smaller clusters. Our results show that in some cases a higher energy isomer of ZrGen anion cluster may be present in experiments, but the neutral of such an anion is often the lowest energy isomer. This shows the importance of the lowest energy isomer of neutral clusters in experiment. In some cases, it is found that two different isomers of the anion of a cluster converge to the identical isomer of the neutral. A large value of the highest occupied molecular orbital-lowest unoccupied molecular orbital gap as well as binding energy per atom has been calculated for ZrGe16 neutral cluster and hence, it is more stable and less reactive as compared to other clusters. This agrees with the high abundance of ZrGe16 cluster in experiments. The Zr atom is encapsulated in a cage-like structure at a size of thirteen or more Ge atoms. This also agrees with the experiments. Further, we have calculated vertical and adiabatic detachment energies and obtained a low value for ZrGe16 also in agreement with experiments. The addition of an electron to a neutral ZrGe11 cluster, however, changes its atomic structure drastically and thus, the calculated adiabatic and vertical detachment energies for ZrGe11 anion differ very significantly.

Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission.

We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine, and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.26-2.36 eV. The magnitudes of the repulsive Coulomb barriers (RCBs) of the complexes are all ∼1.7 eV, values that are lower than the RCB of the uncomplexed PtCl6 (2-) dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four clusters. The 266 nm spectra of the PtCl6 (2-) ⋅ thymine and PtCl6 (2-) ⋅ adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN)4 (2-) ⋅ nucleobase complexes [A. Sen et al., J. Phys. Chem. B 119, 11626 (2015)]. The observation of delayed electron emission bands in the PtCl6 (2-) ⋅ nucleobase spectra obtained in this work, as for the previously studied Pt(CN)4 (2-) ⋅ nucleobase complexes, is attributed to one-photon excitation of nucleobase-centred excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment. Moreover, the selective, strong excitation of the delayed emission bands in the 266 nm spectra is linked to fundamental differences in the individual nucleobase photophysics at this excitation energy. This strongly supports our previous suggestion that the dianion within these clusters can be viewed as a "dynamic tag" which has the propensity to emit electrons when the attached nucleobase decays over a time scale long enough to allow autodetachment.

Electron detachment and fragmentation of laser-excited rotationally hotAl4−

Absolute photoabsorption cross sections of negatively charged tetra-atomic aluminum clusters have been measured for photon energies between 1.8 and 2.7 eV. The experiment used the depletion technique in combination with an electrostatic ion-beam trap, in which ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ ions produced in a sputter ion source were stored for 90 ms before being subjected to a short laser pulse. Moreover, the competition between one-atom fragmentation and electron emission of the laser-excited ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ has been measured. These measurements show that fragmentation dominates electron emission at all photon energies below the electron attachment energy of $\ensuremath{\sim}2.2$ eV, even though the fragmentation energy is expected to be 10%--20% higher than the electron attachment energy. These findings, when taken together with the delayed-electron and fragmentation yields observed in a previous measurement [O. Aviv et al., Phys. Rev. A 83, 023201 (2011)], can be well explained within the statistical phase-space theory for unimolecular decays assuming the ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ ions to be rotationally hot. The analysis permits the determination of the adiabatic electron detachment energy of ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ to be ${E}_{\text{ad}}=(2.18\ifmmode\pm\else\textpm\fi{}0.02)$ eV and the one-atom fragmentation energy to be ${D}_{0}=(2.34\ifmmode\pm\else\textpm\fi{}0.05)$ eV. Moreover, two direct $s$-wave ionization channels are observed with threshold energies of $(2.18\ifmmode\pm\else\textpm\fi{}0.02)$ eV and $(2.45\ifmmode\pm\else\textpm\fi{}0.02)$ eV.

Structures and Electronic Properties of (KI)n(-/0) (n = 1-4) and K(KI)n(-/0) (n = 1-3) Clusters: Photoelectron Spectroscopy, Isomer-Depletion, and ab Initio Calculations.

The (KI)n(-) (n = 1-4) and K(KI)n(-) (n = 1-3) clusters were studied by negative ion photoelectron spectroscopy and ab initio calculations. Comparison between the theoretical vertical detachment energies and the experimental values revealed that multiple isomers may coexist in the experiments. The existence of two isomers for K(KI)(-) and K(KI)2(-) were confirmed directly by isomer-depletion experiments, in which the low adiabatic detachment energy isomers were depleted by a 1064 nm laser beam before the anions were photodetached by a 532 nm laser beam. Our results show that the most stable structures of the K(KI)(-), (KI)2(-), and K(KI)2(-) anions are chain structures, while those of their neutral counterparts are planar. Three-dimensional structures start to appear at n = 3 for (KI)n(-/0) and K(KI)n(-/0). In the K(KI)n(-) cluster anions, the excess electron is localized on the extra K atom and forms an electron pair with the existing s electron of the K atom; the resulting negatively charged K prefers to interact with the other positively charged K atoms rather than with the I atoms. Both the anionic and neutral (KI)4 clusters have cuboid structures, which may be regarded as the smallest structural motif of KI crystal.

Electron Detachment as a Probe of Intrinsic Nucleobase Dynamics in Dianion-Nucleobase Clusters: Photoelectron Spectroscopy of the Platinum II Cyanide Dianion Bound to Uracil, Thymine, Cytosine, and Adenine.

We report the first low-temperature photoelectron spectra of isolated gas-phase complexes of the platinum II cyanide dianion bound to nucleobases. These systems are models for understanding platinum-complex photodynamic therapies, and a knowledge of the intrinsic photodetachment properties is crucial for characterizing their broader photophysical properties. Well-resolved, distinct peaks are observed in the spectra, consistent with complexes where the Pt(CN)4(2-) moiety is largely intact. Adiabatic electron detachment energies for the dianion-nucleobase complexes are measured to be 2.39-2.46 eV. The magnitudes of the repulsive Coulomb barriers of the complexes are estimated to be between 1.9 and 2.1 eV, values that are lower than for the bare Pt(CN)4(2-) dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four dianion-nucleobase complexes and also in the 266 nm spectra of the Pt(CN)4(2-)·thymine and Pt(CN)4(2-)·adenine complexes. The selective excitation of these features in the 266 nm spectra is attributed to one-photon excitation of [Pt(CN)4(2-)·thymine]* and [Pt(CN)4(2-)·adenine]* long-lived excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment signals. We attribute the delayed electron detachment bands observed here for Pt(CN)4(2-)·thymine and Pt(CN)4(2-)·adenine but not for Pt(CN)4(2-)·uracil and Pt(CN)4(2-)·cytosine to fundamental differences in the individual nucleobase photophysics following 266 nm excitation. This indicates that the Pt(CN)4(2-) dianion in the clusters can be viewed as a "dynamic tag" which has the propensity to emit electrons when the attached nucleobase displays a long-lived excited state.

Structures and electronic properties of neutral and anionic Can (n = 2–22) clusters

We perform a first-principles based genetic algorithm global research to obtain the stable structures of neutral and anionic Can (n=2–22) clusters. To examine the stabilities of neutral and anionic calcium clusters, we investigate the binding energies and second differences of total energy of all these clusters. We further discuss the trend of size-induced transition from non-metal to metal by means of natural bonding orbital analysis, bond length and angle distribution. The vertical detachment energies and adiabatic detachment energies of anionic calcium clusters are also computed and compared well with the experimental data.

Photoelectron spectroscopy and theoretical studies of gaseous uranium hexachlorides in different oxidation states: UCl6 (q-) (q = 0-2).

Uranium chlorides are important in actinide chemistry and nuclear industries, but their chemical bonding and many physical and chemical properties are not well understood yet. Here, we report the first experimental observation of two gaseous uranium hexachloride anions, UCl6 (-) and UCl6 (2-), which are probed by photoelectron spectroscopy in conjunction with quantum chemistry calculations. The electron affinity of UCl6 is measured for the first time as +5.3 eV; its second electron affinity is measured to be +0.60 eV from the photoelectron spectra of UCl6 (2-). We observe that the detachment cross sections of the 5f electrons are extremely weak in the visible and UV energy ranges. It is found that the one-electron one-determinental molecular orbital picture and Koopmans' theorem break down for the strongly internally correlated U-5f(2) valence shell of tetravalent U(+4) in UCl6 (2-). The calculated adiabatic and vertical electron detachment energies from ab initio calculations agree well with the experimental observations. Electronic structure and chemical bonding in the uranium hexachloride species UCl6 (2-) to UCl6 are discussed as a function of the oxidation state of U.

Photoelectron spectroscopy of B4O4 (-): Dual 3c-4e π hyperbonds and rhombic 4c-4e o-bond in boron oxide clusters.

Gas-phase anion photoelectron spectroscopy (PES) is combined with global structural searches and electronic structure calculations at the hybrid Becke 3-parameter exchange functional and Lee-Yang-Parr correlation functional (B3LYP) and single-point coupled-cluster with single, double, and perturbative triple excitations (CCSD(T)) levels to probe the structural and electronic properties and chemical bonding of the B4O4 (0/-) clusters. The measured PES spectra of B4O4 (-) exhibit a major band with the adiabatic and vertical detachment energies (ADE and VDE) of 2.64 ± 0.10 and 2.81 ± 0.10 eV, respectively, as well as a weak peak with the ADE and VDE of 1.42 ± 0.08 and 1.48 ± 0.08 eV. The former band proves to correspond to the Y-shaped global minimum of Cs B4O4 (-) ((2)A″), with the calculated ADE/VDE of 2.57/2.84 eV at the CCSD(T) level, whereas the weak band is associated with the second lowest-energy, rhombic isomer of D2h B4O4 (-) ((2)B2g) with the predicted ADE/VDE of 1.43/1.49 eV. Both anion structures are planar, featuring a B atom or a B2O2 core bonded with terminal BO and/or BO2 groups. The same Y-shaped and rhombic structures are also located for the B4O4 neutral cluster, albeit with a reversed energy order. Bonding analyses reveal dual three-center four-electron (3c-4e) π hyperbonds in the Y-shaped B4O4 (0/-) clusters and a four-center four-electron (4c-4e) π bond, that is, the so-called o-bond in the rhombic B4O4 (0/-) clusters. This work is the first experimental study on a molecular system with an o-bond.

Structures and Electronic Properties of V3Sin– (n = 3–14) Clusters: A Combined Ab Initio and Experimental Study

Vanadium-doped silicon cluster anions, V3Sin– (n = 3–14), have been generated by laser vaporization and investigated by anion photoelectron spectroscopy. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these clusters were obtained. Meanwhile, genetic algorithm (GA) combined with density functional theory (DFT) calculations are employed to determine their ground-state structures systematically. Excellent agreement is found between theory and experiment. Among the V3Sin– clusters, V3Si5–, V3Si9–, and V3Si12– are relatively more stable. Generally speaking, three V atoms prefer to stay close with others and form strong V–V bonds. Starting from V3Si11–, cage configurations with one interior V atom emerge.

Ab initio and anion photoelectron study of AunRhm (n = 1-7, m = 1-2) clusters.

Anion photoelectron spectroscopy (PES) and ab initio calculations have been used to identify the unique structural, electronic, and magnetic properties of both neutral and anionic binary AunRhm (n = 1-7 and m = 1-2) clusters in vacuo. Negative ion photoelectron spectra are presented with electron binding energies measured up to 3.493 eV. We discuss our computational results in the context of the PES experiment, in which the calculated electron affinities and vertical detachment energies are in good agreement with the measured values. Theoretically, we investigate the low-lying energy structures and the spin isomers of each neutral, anionic and cationic species. The PES spectra, binding energies, fragmentation energy, electron affinities, vertical and adiabatic detached energies, HOMO-LUMO (H-L) gaps and vibrational spectra are presented and discussed. Our results show that the characteristic planarity for gold clusters is preserved for many of the bimetallic clusters. This study is therefore compared with the case of pure gold for which ample experimental and theoretical data are available. Both experimental and theoretical results obtained here are compared and discussed with previous theoretical studies on the same systems.

SF6(-) photodetachment near the adiabatic limit.

High sensitivity photodetachment cross-section measurements of SF6(-) are performed near the adiabatic threshold limit. The extraction of adiabatic detachment energy (ADE) from the high sensitivity measurement of the cross-section change as a function of photon energy is discussed. Below the vertical detachment energy a steep 4 orders of magnitude cross-section drop is observed, with cross sections as low as 2 × 10(-6) Å(2) measured for photon energies below 2 eV. The cross-section is fitted with both the expected spectral shape based on recently calculated Frank-Condon overlaps and a phenomenological threshold function. The resulting 1.7 ± 0.02 eV ADE values are significantly higher than previously recommended experimental ADE values obtained based on kinetics modeling, and possible differences between the experimental approaches are discussed.

Ab Initio Theoretical Investigation on the Geometrical and Electronic Structures of Gallium Aurides: Ga Aun0/- and Ga2Aun0/- (n = 1–4)

This study presents a systematic investigation of the geometric and electronic properties of GaA and Ga2A (n = 1–4) clusters based on density functional theory and wave function theory. Detailed orbital analyses, adaptive natural density partitioning, and electron localization function analyses are performed and relevant results are discussed. GaA (n = 1–4) clusters with n‐Au terminals and Ga2A (n = 1–4) clusters with bridged Au atoms possess geometric structures and bonding patterns similar to those of the corresponding gallium hydrides Ga and Ga2. Ga–Au interaction is predicted to occur through highly polar covalent bonds in monogallium aurides. In contrast to the highly symmetric ground states of C2v Ga2Au, C2v Ga2Au2, and D3h Ga2Au3, C3v Ga2Au4 is composed of strong interactions between a Ga+ cation and the face of a tetrahedral GaA anion. The adiabatic and vertical detachment energies of the anions under study are calculated to facilitate their experimental characterization. Geometric and electronic structural comparisons with the corresponding gallium hydrides are conducted to establish an isolobal analogy between gold and hydrogen atoms.

Anion A(-) • HX clusters with reduced electron binding energies: proton vs hydrogen atom relocation upon electron detachment.

Clustering an anion with one or more neutral molecules is a stabilizing process that enhances the oxidation potential of the complex relative to the free ion. Several hydrogen bond clusters (i.e., A(-) • HX, where A(-) = H2PO4(-) and CF3CO2(-) and HX = MeOH, PhOH, and Me2NOH or Et2NOH) are examined by photoelectron spectroscopy and M06-2X and CCSD(T) computations. Remarkably, these species are experimentally found to have adiabatic detachment energies that are smaller than those for the free ion and reductions of 0.47 to 1.87 eV are predicted computationally. Hydrogen atom and proton transfers upon vertical photodetachment are two limiting extremes on the neutral surface in a continuum of mechanistic pathways that account for these results, and the whole gamut of possibilities are predicted to occur.

Structures and electron affinity of XO30,−, XOF40,− and XO2F20,− (X = P, As, Sb, Bi): a theoretical study of novel superhalogen formulae and exceptions of superhalogen formulae

Most superhalogen species are in the form of oxides or halides. To enrich the family of superhalogen species, herein, we investigated the structures and electron affinity (EA) values of higher group 15 elements (X = P, As, Sb, Bi) oxyfluoride species XO30,−, XOF40,− and XO2F20,−, at the CCSD(T)/aug-cc-pVTZ-pp & aug-cc-pVTZ //B3LYP/aug-cc-pVTZ-pp & aug-cc-pVTZ levels (aug-cc-pVTZ-pp for X = Sb and Bi). Some oxyfluoride species, i.e., PO2F20,−, AsO2F20,−, SbO2F20,−, POF40,−, AsOF40,−, SbOF40,− and BiOF40,−, were found to possess higher EA (VDE: 5.0–6.2 eV; ADE: 4.5–5.5 eV) than halogens (F: 3.4 eV; Cl: 3.6 eV). Thus, we recommended that the oxyfluorides in the form of XO2F20,− and XOF40,− should be considered as potential superhalogens, which have not been considered previously. Surprisingly, we showed that BiO3 and BiO2F2, in superhalogen formulae, possess a high vertical detachment energy (VDE) yet a low adiabatic detachment energy (ADE). This is in marked contrast to the previously reported superhalogens, which generally contain both the high VDE and high ADE values. It is the first report about exceptions of superhalogen formulae. These findings revealed that for the analogous main-group compounds with the same structural formula, the difference in the metallic property of the core element could lead to the significant difference in the ground structures of either the anionic or neutral structures, which would result in the much differed superhalogen features.

Tin content effect on the structural and energetic properties of lead telluride clusters

Density functional theory calculations are performed to investigate tin content effect on the structural and energetic properties of lead telluride clusters. Tin atoms prefer to be doped on the exterior sites rather than the interior sites of lead telluride clusters. The geometry of the clusters is not affected due to the amount of tin content except for a slight distortion observed by changes in bond length. A considerable change has been observed in the HOMO–LUMO gap of the clusters with increasing number of tin atoms for corresponding size, but the band inversion which is observed in the bulk is not observed on the clusters in these size ranges. The change in binding energy between doped clusters is almost negligible for the same number of tellurium atoms, it is observed to be constant or there is a change of up to 0.02 eV with each successive doping of tin atoms. Both adiabatic and vertical detachment energies are observed to increase with increasing number of doping tin atoms. The fragmentation energy of losing PbTe dimer changes with an even–odd alternation, clusters with even number of Te atoms are more stable because they need higher energy to dissociate as compared to the other clusters. Some clusters are found to be magic (more stable) because of their enhanced binding, HOMO–LUMO gap, and fragmentation energies, typical examples are Pb4−mSnmTe4 (m = 1–4) clusters.