Adiabatic Detachment Energies Research Articles

Photoelectron spectroscopy and ab initio calculations of small SinSm⁻ (n = 1,2; m = 1-4) clusters.

Binary cluster anions composed of silicon and sulfur elements, SinSm(-) (n = 1,2; m = 1-4), were investigated by using photoelectron spectroscopy and ab initio calculations. The vertical detachment energies and the adiabatic detachment energies of these clusters were obtained from their photoelectron spectra. The electron affinity of SiS molecule is determined to be 0.477 ± 0.040 eV. The results show that the most stable structures of the anionic and neutral SinSm (n = 1,2; m = 1-4) clusters prefer to adopt planar configurations except that the structures of Si2S4(-) and Si2S2 are slightly bent.

Theoretical Study on the Relationship between the Geometric Change and the s–p Hybridization Formation of LiAln− Clusters (n = 3–13)

Abstract The relationships between the geometric and electronic structures, and photoelectron spectra (PES) of LiAln− (n = 3–13) clusters were investigated. The ground and low-lying states geometries were optimized using B3LYP calculation. The assignment for large PES peaks was performed on the basis of calculated adiabatic detachment energies (ADE) and vertical detachment energies (VDE) values. PES peaks in Figure 2 of the clusters smaller than n = 6 are arose mostly from 3p of Al and those larger than n = 9 are 3s–3p (s–p) of Al. This peak pattern change occurs due to the s–p hybridization with the change in the geometric features. It was suggested that the high coordinated Al atom(s) in the Al framework and Li atom play an important role in forming the s–p hybridization at n ≥ 9.

Photoelectron spectroscopy of CoC2H2(-) and density functional study of Co(n)C2H2 (n = 1-3) anion and neutral clusters.

The anionic and neutral ConC2H2 (n = 1-3) clusters were investigated using anion photoelectron spectroscopy and density functional calculations. The adiabatic detachment energies and vertical detachment energies of ConC2H2(-) (n = 1-3) were determined. Our results show that the most stable geometries of anionic ConC2H2(-) (n = 1-2) and neutral ConC2H2 (n = 1-3) are composed of ConC2H clusters adsorbing a hydrogen atom on the top or bridge sites of Con, whereas Co3C2H2(-) consists of a five-member ring of Co3C2 carbide adsorbing two hydrogen atoms on two bridge sites of Co3. The reaction mechanisms show that the inserted isomer HCoC2H can convert into the vinylidene complex Co═C═CH2 via a side-on isomer M-η(2)-(C2H2).

Structural evolution and stabilities of negatively charged lead telluride clusters

The equilibrium geometric structures, relative stabilities and electronic properties of negatively charged lead telluride clusters are systematically investigated using density functional theory (DFT). The result offered both vertical and adiabatic detachment energies (VDEs and ADEs) for these clusters, divulging an outline of alternating values in which odd n clusters exhibited higher values than even n clusters. Simulations found the negatively charged lead telluride clusters with even n to be thermodynamically more stable than their immediate odd n neighbors, with a consistent pattern also being found in their HOMO–LUMO (HL) gaps. Analysis of the clusters dissociation energies found at [Formula: see text] cluster to be the preferred product of the queried fragmentation processes, consistent with our finding that [Formula: see text] cluster exhibits enhanced stability. Beyond n = 12, this study showed that the negatively charged ( PbTe )nclusters in the size range n = 13 – 20, prefer two-dimensional stacking of face-sharing lead telluride cubical units, where lead and tellurium atoms possess a maximum of five-fold coordination. The preference for six-fold coordination, which is observed in the bulk, was not observed at these cluster sizes.

A preorganized hydrogen bond network and its effect on anion stability.

Rigid tricyclic locked in all axial 1,3,5-cyclohexanetriol derivatives with 0-3 trifluoromethyl groups were synthesized and photoelectron spectra of their conjugate bases and chloride anion clusters are reported along with density functional computations. The resulting vertical and adiabatic detachment energies span 4.07-5.50 eV (VDE) and 3.75-5.00 (ADE) for the former ions and 5.60-6.23 eV (VDE) and 5.36-6.00 eV (ADE) for the latter species. These results provide measures of the anion stabilization due to the hydrogen bond network and inductive effects. The latter mechanism is found to be transmitted through space via hydrogen bonds, and the presence of three ring skeleton oxygen atoms and up to three trifluoromethyl groups enhance the ADEs by 1.61-2.88 eV for the conjugate bases and 1.01-1.60 eV for the chloride anion clusters. Computations indicate that the most favorable structures of the latter complexes have two hydrogen bonds to the chloride anion and one bifurcated interaction between the remote OH substituent and the two hydroxyl groups that directly bind to Cl(-).

Vertical ionization energies of free radicals and electron detachment energies of their anions: a comparison of direct and indirect methods versus experiment.

The performance of several direct and indirect computational strategies for the calculation of the first ionization energies (IEs) of free radicals and adiabatic detachment energies of their anions has been tested using experimental data as references. The outer valence Green's function and the partial third-order approximations, which are based on electron propagator theory, have been identified as the most accurate. They were in turn used to estimate the IEs of a large set of free radicals for which these data have not been previously reported. The calculated data also have been used to assess the possible oxidation of nucleosides by these radicals, as well as the potential, antioxidant-protection effects of phenol, catechol, ascorbic acid, and Trolox in their neutral and deprotonated forms, via electron transfer.

Examining the amine functionalization in dicarboxylates: photoelectron spectroscopy and theoretical studies of aspartate and glutamate.

Aspartate (Asp(2-)) and glutamate (Glu(2-)), two doubly charged conjugate bases of the corresponding amino acids, were investigated using low-temperature negative ion photoelectron spectroscopy (NIPES) and ab initio calculations. The effect of amine functionalization was studied by a direct comparison to the parent dicarboxylate species ((-)CO2-(CH2)n-CO2(-), DCn(2-)), succinate (DC2(2-)) and propionate (DC3(2-)). Experimentally, the addition of the amine group for the n = 2 case (DC2(2-), Asp(2-)) significantly improves the stability of the resultant Asp(2-) dianionic species, albeit that NIPES shows only a small increase in adiabatic electron detachment energy (ADE) (+0.05 eV). In contrast, for n = 3 (DC3(2-), Glu(2-)), a much larger ADE increase is observed (+0.15 eV). Similar results are obtained through ab initio calculations. The latter indicates that increased stability of Asp(2-) can be attributed to the lowering of the energy of the singlet dianion state due to hydrogen bonding effects. The effect of the amino group on the doublet monoanion state is more complicated and results in the weakening of the binding of the adjacent carboxylate group due to electronic structure resonance effects. This conclusion is confirmed by the analysis of NIPES results that show enhanced production of near-zero kinetic energy electrons observed experimentally for amine-functionalized species.

Communication: Remarkable electrophilicity of the oxalic acid monomer: an anion photoelectron spectroscopy and theoretical study.

Our experimental and computational results demonstrate an unusual electrophilicity of oxalic acid, the simplest dicarboxylic acid. The monomer is characterized by an adiabatic electron affinity and electron vertical detachment energy of 0.72 and 1.08 eV (±0.05 eV), respectively. The electrophilicity results primarily from the bonding carbon-carbon interaction in the singly occupied molecular orbital of the anion, but it is further enhanced by intramolecular hydrogen bonds. The well-resolved structure in the photoelectron spectrum is reproduced theoretically, based on Franck-Condon factors for the vibronic anion → neutral transitions.

Vibrationally Resolved Photoelectron Spectroscopy of the Model GFP Chromophore Anion Revealing the Photoexcited S1 State Being Both Vertically and Adiabatically Bound against the Photodetached D0 Continuum

The first excited state of the model green fluorescence protein (GFP) chromophore anion (S1) and its energy level against the electron-detached neutral radical D0 state are crucial in determining the photophysics and the photoinduced dynamics of GFP. Extensive experimental and theoretical studies, particularly several very recent gas-phase investigations, concluded that S1 is a bound state in the Franck-Condon vertical region with respect to D0. However, what remains unknown and challenging is if S1 is bound adiabatically, primarily due to lack of accurate experimental measurements as well as due to the close proximity in energy for these two states that even sophisticated high-level ab initio calculations cannot reliably predict. Here, we report a negative ion photoelectron spectroscopy study on the model GFP chromophore anion, the deprotonated p-hydroxybenzylidene-2,3-dimethylimidazolinone anion (HBDI(-)) taken under low-temperature conditions with improved energy resolution. Despite the considerable size and low symmetry of the molecule, resolved vibrational structures were obtained with the 0-0 transition being the most intense peak. The adiabatic (ADE) and vertical detachment (VDE) energies therefore are determined both to be 2.73 ± 0.01 eV, indicating that the detached D0 state is 0.16 eV higher in energy than the photon excited S1 state. The accurate ADE and VDE values and the well-resolved photoelectron spectra reported here provide much needed robust benchmarks for future theoretical investigations.

Structural isomers of Ti₂O₄ and Zr₂O₄ anions identified by slow photoelectron velocity-map imaging spectroscopy.

High-resolution anion photoelectron spectra are reported for the group 4 metal dioxide clusters Ti2O4(-) and Zr2O4(-). Slow photoelectron velocity-map imaging (SEVI) spectroscopy of cryogenically cooled, mass-selected anions yields photoelectron spectra with submillielectronvolt resolution, revealing extensive and well-resolved vibrational progressions. By comparison of the spectra with Franck-Condon simulations, we have identified the C(2v) and C(3v) isomers as the ground states of Ti2O4(-) and Zr2O4(-) anions, respectively. Minor contributions from the C(2h) isomer of Ti2O4(-) and the C(2v) isomer of Zr2O4(-) are also seen. The SEVI spectra yield upper bounds for the adiabatic detachment energies, as well as vibrational frequencies for various modes of the neutral Ti2O4 and Zr2O4 species.

Investigation of ternary ConCN−1/0 (n = 1–5) clusters by density functional calculations

The neutral and anionic Co(n)CN (n = 1-5) clusters were investigated using density functional calculations. The most stable structures of neutral and anionic Co(n)CN (n = 1-5) clusters have been identified. In these structures, the CN radical retains its integrity as a structural unit. For anionic Co(n)CN(-) (n = 1-5) and neutral Co(n)CN (n = 1-2) clusters, the CN prefers to be adsorbed on the top sites of Co(n) clusters via the C terminal, forming a linear or quasi-linear N-C-Co structure. For neutral Co(n)CN (n = 3-5) clusters, the CN is adsorbed on the bridge sites of Co(n) (n = 3-5) by both C and N atoms. Compared to the free CN radical calculated at the same level, the C-N stretching frequencies of neutral Co(n)CN (n = 3-5) are red-shifted while they are blue-shifted for neutral Co(n)CN (n = 1-2). The adiabatic and vertical detachment energies of anionic Co(n)CN(-) (n = 1-5) clusters are calculated based on density functional calculations. In addition, the most favored dissociation channels of neutral and anionic Co(n)CN (n = 1-5) clusters are determined by calculating the dissociation energies of various possible dissociation pathways.

Photoelectron spectroscopy and density functional study of ConC2− (n = 1–5) clusters

ConC2(-) (n = 1-5) cluster anions were investigated using anion photoelectron spectroscopy. The adiabatic detachment energies (ADEs) and the vertical detachment energies (VDEs) of the ConC2(-) (n = 1-5) cluster anions were determined from their photoelectron spectra. Density functional calculations were performed for the ConC2 (n = 1-5) cluster anions and neutrals. Our studies show that the structures of ConC2(-) (n = 1-5) can be described as attaching C2 to the top sites, bridge sites, or hollow sites of the Con clusters. The C2 retains an integral structure unit in the ConC2 (n = 1-5) cluster anions and neutrals, rather than being separated by the Con clusters. The C2 unit in the ConC2 (n = 1-5) cluster anions and neutrals has the characteristics of a double-bond.

Bottom-up substitution assembly of AuF4−n0,−+nPO3 (n = 1–4): a theoretical study of novel oxyfluoride hyperhalogen molecules and anions AuF4−n(PO3)n0,−

Compounds with high electron affinity, i.e. superhalogens, have continued to attract chemists’ attention, due to their potential importance in fundamental chemistry and materials science. It has now proven very effective to build up novel superhalogens with multi-positively charged centres, which are usually called ‘hyperhalogens’. Herein, using AuF4− and PO3 as the model building blocks, we made the first attempt to design the Au,P-based hyperhalogen anions AuF4−n(PO3)n− (n = 1–4) at the B3LYP/6-311+G(d)&SDD and CCSD(T)/6-311+G(d)&SDD (single-point) levels (6-311+G(d) for O, F, P and SDD for Au). Notably, for all the considered Au,P systems, the ground state bears a dioxo-bonded structure with n ≤ 3, which is significantly more stable than the usually presumed mono-oxo-bonded one. Moreover, the clustering of the –PO3 moieties becomes energetically favoured for n ≥ 3. The ground states of AuP4O120,− are the first reported cage-like oxide hyperhalogens. Thus, the −PO3 moiety cannot be retained during the ‘bottom-up’ assembly. The vertical detachment energy (VDE) value of the most stable AuF4−n(PO3)n− (n = 1–4) ranges from 7.16 to 8.20 eV, higher than the VDE values of the corresponding building blocks AuF4− (7.08 eV) and PO3− (4.69 eV). The adiabatic detachment energy values of these four hyperhalogens exceed 6.00 eV. Possible generation routes for AuF4−n(PO3)n− (n = 1–4) were discussed. The presently designed oxyfluorides not only enriches the family of hyperhalogens, but also demonstrates the great importance of considering the structural transformation during the superhalogen → hyperhalogen design such as for the present Au–P based systems.

Conformer-selective photoelectron spectroscopy of α-lactalbumin derived multianions in the gas phase

We have recorded conformer-selective, gas-phase photoelectron spectra of α-lactalbumin derived multianions generated by electrospraying solutions of both the native protein and its denatured form (as prepared by breaking the sulfur-sulfur bonds by chemical reduction). Three different groups of gas-phase multianion conformers have been observed and characterized. Highly-folded and partially-unfolded structures are obtained from solutions of the native protein. Only highly-elongated conformers are observed upon electrospraying the denatured protein. Adiabatic detachment energies were determined at several negative charge states for each conformer group. In comparison to highly-elongated conformations, highly-folded structures show a steeper decrease of electron binding energy with increasing negative charge. By comparing experimental detachment energies for highly-elongated structures with the predictions of a simple electrostatic model calculation, we have determined the effective dielectric shielding constant.

Theoretical and experimental studies of the interactions between Au2− and nucleobases

Combined anion photoelectron spectroscopy and relativistic quantum chemical studies are conducted on nucleobase-Au2(-) cluster anions. The vertical detachment energies of uracil-Au2(-) (UAu2(-)), thymine-Au2(-) (TAu2(-)), cytosine-Au2(-) (CAu2(-)), adenine-Au2(-) (AAu2(-)), guanine-Au2(-) (GAu2(-)) are determined to be 2.71 ± 0.08 eV, 2.74 ± 0.08 eV, 2.67 ± 0.08 eV, 2.65 ± 0.08 eV and 2.73 ± 0.08 eV, respectively, based on the measured photoelectron spectra. Through computational geometry optimizations we have identified the lowest-energy structures of these nucleobase-Au2(-) cluster anions. The structures are further confirmed by comparison of theoretically calculated vertical and adiabatic electron detachment energies with experimental measurements. The results reveal that the Au2(-) anion remains as an intact unit and interacts with the nucleobases through N-HAu or C-HAu nonconventional hydrogen bonds. The nucleobase-Au2(-) cluster anions have relatively weak N-HAu hydrogen bonds and strong C-HAu hydrogen bonds compared to those of nucleobase-Au(-) anions.

Hydrogen-Bond Networks: Strengths of Different Types of Hydrogen Bonds and An Alternative to the Low Barrier Hydrogen-Bond Proposal

We report quantifying the strengths of different types of hydrogen bonds in hydrogen-bond networks (HBNs) via measurement of the adiabatic electron detachment energy of the conjugate base of a small covalent polyol model compound (i.e., (HOCH2CH2CH(OH)CH2)2CHOH) in the gas phase and the pKa of the corresponding acid in DMSO. The latter result reveals that the hydrogen bonds to the charged center and those that are one solvation shell further away (i.e., primary and secondary) provide 5.3 and 2.5 pKa units of stabilization per hydrogen bond in DMSO. Computations indicate that these energies increase to 8.4 and 3.9 pKa units in benzene and that the total stabilizations are 16 (DMSO) and 25 (benzene) pKa units. Calculations on a larger linear heptaol (i.e., (HOCH2CH2CH(OH)CH2CH(OH)CH2)2CHOH) reveal that the terminal hydroxyl groups each contribute 0.6 pKa units of stabilization in DMSO and 1.1 pKa units in benzene. All of these results taken together indicate that the presence of a charged center can provide a powerful energetic driving force for enzyme catalysis and conformational changes such as in protein folding due to multiple hydrogen bonds in a HBN.

Face-Capping μ3-BO in B6(BO)7–: Boron Oxide Analogue of B6H7– with Rhombic 4c–2e Bonds

Using the first-principle approaches, we predict a B6(BO)7(-) cluster with a face-capping μ(3)-BO, which is the boron oxide analogue of closo-B6H7(-) with a face-capping μ(3)-H. Detailed topological analysis of electron density clearly reveals the existence of three rhombic 4c-2e bonds around the B/H apex in both C3v B6(BO)7(-) and C3v B6H7(-), which possesses similar electron densities at their bond and ring critical points. The adaptive natural density partitioning (AdNDP) analysis provides a direct and visual picture of the B-B-B-B/H 4c-2e bonds for the first time. Adiabatic and vertical electron detachment energies of the concerned monoanions are calculated to facilitate their future photoelectron spectroscopy measurements and characterizations. The presence of the B6(BO)7(-) and B6H7(-) clusters extends the BO/H isolobal analogy to the whole μ(n)-BO/H series (n = 1, 2, and 3) and enriches the chemistry of boronyl.

Theoretical studies of sulfite – sulfur dioxide clusters, SO32−(SO2)n: structure and stability of SnO2n+1 anions, n = 1–5

Density functional calculations using the B3PW91 functional with the 6-311+G(3df) basis set were performed on the addition of n = 1–4 SO2 molecules to SO3− and SO32−. Geometry optimizations were performed for a large number of possible structures. At n = 4, the dianionic cluster becomes adiabatically more stable than the monoanionic one, with an adiabatic electron detachment energy of 0.30 eV. Monoanionic clusters are characterized by the O–S–O–SO3 moiety having long O–S bonds to SO2 molecules. Dianionic clusters, however, prefer S–S bonding of O3S–O–S(O) with SO2.

First principles gas phase study of the structures, energetics and spectroscopic parameters of aluminium antimonide, Al x Sb y (x + y = 3, 5), clusters

Theoretical methods (DFT/B3LYP and MP2) have been used to optimize the geometries of the Al x Sb y (x + y = 3, 5) clusters and their anions. Single point energy computations at CCSD(T) level have also been performed using the optimized B3LYP and MP2 structures. The basis sets used for Al and Sb atoms are 6-311+G(2d) and LANL2DZdp ECP, respectively. Harmonic vibrational frequency computations were carried out to confirm the nature of the stationary points. We report the structural and spectroscopic parameters of the named clusters. We also report the relative energy of the clusters, the vertical electron detachment energy, the adiabatic electron detachment energy and the adiabatic electron affinity. The most stable structures at the CCSD(T)//MP2 level are, the D ∞h linear structure (AlSb2) and the C 2v V-bent structure (AlSb 2 − ), the C 2v V-bent structure (Al2Sb and its anion), the C 2v edge-capped tetrahedron (Al2Sb3 and its anion), the C 2v trigonal bipyramidal structure (Al3Sb2 and its anion), the C 4v square pyramidal (AlSb4) and a C 2v ground structure for its anion, the C 2v planar trapezoidal structure (Al4Sb) and the C 2v edge-capped tetrahedron (Al4Sb−). The adiabatic electron affinities calculated at the CCSD(T)//MP2 level are 2.17 eV (AlSb2), 2.17 eV (Al2Sb), 2.38 eV (Al2Sb3), 2.76 eV (Al3Sb2), 2.21 eV (AlSb4) and 2.03 eV (Al4Sb). The findings of this research are analysed, discussed and compared with the analogous picnogenides clusters.

Theoretical study of hydrogen adsorption on Co clusters

We present results of a systematic study of the adsorption of one to five hydrogen atoms on Conn=1–5 neutral clusters. The density functional (DFT) formalism has been adopted to perform this study with the use of the hybrid functional B3LYP. We present results for their binding, vertical and adiabatic detachment energies, magnetic moments, HOMO–LUMO gaps and their infra red spectra. The results show that by the use of an hybrid functional we obtain different ground state geometries as well as magnetic moments than some of the previous theoretical studies. We test the methodology comparing the calculated Infra Red (IR) spectra for the cationic clusters: Co4Ar+, Co5Ar+, Co4H2+ and Co5H6+ with the available Far Infra Red Multiple Adsorbed Photon (FIR-MPD) experimental spectra, and we obtained a good agreement. We found the adsorption of H2 exclusively dissociative for all neutral ConHmn=1–5, m=1–5 clusters. The twofold bridge site is identified to be the most favorable for adsorption on neutral Con (n>2). Therefore hydrogen adsorption in clusters is different than it is on surfaces, where it is known that hydrogen adsorbs in high coordination sites. We found that as we add H atoms: first, a structural transition from three to two dimensions occur in the cluster geometry, second an enhanced but non-monotonic change in their magnetic moments is observed, and finally the stability of the system is greatly increased.