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The molybdenum-sulfur bond plays an important role in many processes such as nitrogen-fixation, and it is found as a building block in layered materials such as MoS2, known for its various shapes and morphologies. Here, we present an accurate theoretical and experimental investigation of the chemical bonding and the electronic structure of 20 low-lying states of the MoS molecule. Multireference and coupled cluster methodologies, namely, MRCISD, MRCISD + Q, RCCSD(T), and RCCSD[T], were employed in conjunction with basis sets up to aug-cc-pwCV5Z-PP/aug-cc-pwCV5Z for the study of these states. We note the significance of including the inner 4s24p6electrons of Mo and 2s22p6of S in the correlated space to obtain accurate results. Experimentally, the predissociation threshold of MoS was measured using resonant two-photon ionization spectroscopy, allowing for a precise measurement of the bond dissociation energy. Our extrapolated computational D0value for the ground state is 3.936 eV, in excellent agreement with our experimental measurement of 3.932 ± 0.004 eV. The largest calculated adiabatic D0(5.74 eV) and the largest dipole moment (6.50 D) were found for the 5ς+state, where a triple bond is formed. Finally, the connection of the chemical bonding of the isolated MoS species to the relevant solid, MoS2, is emphasized. The low-lying septet states of the diatomic molecule are involved in the material as a building block, explaining the stability and the variety of the shapes and morphologies of the material. © 2022 American Chemical Society. All rights reserved.

The multiscaling quantum mechanics/molecular mechanics (QM/MM) approach was introduced in 1976, while the extensive acceptance of this methodology started in the 1990s. The combination of QM/MM approach with molecular dynamics (MD) simulation, otherwise known as the QM/MM/MD approach, is a powerful and promising tool for the investigation of chemical reactions’ mechanism of complex molecular systems, drug delivery, properties of molecular devices, organic electronics, etc. In the present review, the main methodologies in the multiscaling approaches, i.e., density functional theory (DFT), semiempirical methodologies (SE), MD simulations, MM, and their new advances are discussed in short. Then, a review on calculations and reactions on metalloproteins is presented, where particular attention is given to nitrogenase that catalyzes the conversion of atmospheric nitrogen molecules N₂ into NH₃ through the process known as nitrogen fixation and the FeMo-cofactor. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

The structure assignment and conformational analysis of thiosemicarbazone KKI15 and thiocarbohydrazone KKI18 were performed through homonuclear and heteronuclear 2D Nuclear Magnetic Resonance (NMR) spectroscopy (2D-COSY, 2D-NOESY, 2D-HSQC, and 2D-HMBC) and quantum mechanics (QM) calculations using Functional Density Theory (DFT). After the structure identification of the compounds, various conformations of the two compounds were calculated using DFT. The two molecules showed the most energy-favorable values when their two double bonds adopted the E configuration. These configurations were compatible with the spatial correlations observed in the 2D-NOESY spectrum. In addition, due to the various isomers that occurred, the energy of the transition states from one isomer to another was calculated. Finally, molecular binding experiments were performed to detect potential targets for KKI15 and KKI18 derived from Swis-sAdme. In silico molecular binding experiments showed favorable binding energy values for all four enzymes studied. The strongest binding energy was observed in the enzyme butyrylcholinesterase. ADMET calculations using the preADMET and pKCSm software showed that the two molecules appear as possible drug leads. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

Losartan potassium salt (LSR) is a well-known antihypertensive drug with proven beneficial effects on human health. Its formulation with the non-toxic 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) could improve its pharmacological profile. Thus, its molecular interactions are studied using a combination of Differential Scanning Calorimetry (DSC), Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD). First, its complexation is shown through Differential Scanning Calorimetry as lyophilization provided distinct thermal properties in comparison to the mixture. The complexation is further proved by utilizing the chemical shift changes in the complexation and T1 values. Furthermore, the reversible favorable complexation was shown by MD calculations. Such physical chemical properties provide evidence that this formulation must be further explored through biological experiments. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

The development of artificial receptors for sensing and recognition of species, as well as for advanced logic functions, is a significant challenge in the field of molecular information technology. Here, we study theoretically, via DFT/TD-DFT calculations, the photophysical properties of a 3-input AND molecular logic gate which presents an enhanced fluorescence spectrum. It was found that the geometry conformation at an N atom of the piperazine group is the key factor for the correct calculation of the absorption spectra of the calculated structures. Its geometry is between tetrahedral and planar, while changes in the corresponding CNCC dihedral angle of about 10 degrees can cause significant shifts of the main peak of the absorption spectra up to 100 nm. Moreover, the unusually enhanced fluorescence of a molecular logic gate (MLG) is explained. Finally, we conclude that molecular systems having N atoms, whose geometry is between planar and tetrahedral, can be ideal molecules as sensors and molecular logic gates. Our calculated absorption and emission spectra are in excellent agreement with available experimental data. © 2022 American Chemical Society.

Iron-sulfur clusters play important roles in biology as parts of electron-transfer chains and catalytic cofactors. Here, we report a detailed computational analysis of a structural model of the simplest natural iron-sulfur cluster of rubredoxin and its cationic counterparts. Specifically, we investigated adiabatic reduction energies, dissociation energies, and bonding properties of the low-lying electronic states of the complexes [Fe(SCH3)4]2-/1-/2+/3+ using multireference (CASSCF, MRCISD), and coupled cluster [CCSD(T)] methodologies. We show that the nature of the Fe-S chemical bond and the magnitude of the ionization potentials in the anionic and cationic [Fe(SCH3)4] complexes offer a physical rationale for the relative stabilization, structure, and speciation of these complexes. Anionic and cationic complexes present different types of chemical bonds: prevalently ionic in [Fe(SCH3)4]2-/1- complexes and covalent in [Fe(SCH3)4]2+/3+ complexes. The ionic bonds result in an energy gain for the transition [Fe(SCH3)4]2- → [Fe(SCH3)4]- (i.e., FeII → FeIII) of 1.5 eV, while the covalent bonds result in an energy loss for the transition [Fe(SCH3)4]2+ → [Fe(SCH3)4]3+ of 16.6 eV, almost half of the ionization potential of Fe2+. The ionic versus covalent bond character influences the Fe-S bond strength and length, that is, ionic Fe-S bonds are longer than covalent ones by about 0.2 Å (for FeII) and 0.04 Å (for FeII). Finally, the average Fe-S heterolytic bond strength is 6.7 eV (FeII) and 14.6 eV (FeIII) at the RCCSD(T) level of theory. © 2021 American Chemical Society. All rights reserved.

The effect of peri-fusion on the aromaticity of 6-membered N−, O−, N,N−, N,N,N− and N,O-doped naphthalene derivatives has been studied via NICS-z, -xz, -xy, and -xyz scans employing DFT and MP2 calculations. The relative aromaticity of these structures was found to vary with the type of heteroring and the distance from the plane. Their corresponding ordering depends on the scan approaches. Accordingly, i) along the z axis at the center of the naphthalene B and C constituent rings, it is 1,8>2>7,9≫4>6, 5>3 (the most aromatic members are naphthalene and the N,O-derivative 8), ii) along the x symmetry axis of naphthalene, it is 3>8,7>5>4>9>6>2>1 (the most aromatic one is a N-derivative 3) and iii) along the z axis, on the xy plane, it is 6>1>8>9>2>5>7>3>4 at z=0.8 Å and 1>2>8>9>6>7>5>3>4 at 2.4 Å (the most aromatic ones are the N,N,N-derivative 6 at 0.8 Å and naphthalene at 2.4 Å). Their relative magnetic anisotropy ordering remains virtually unaltered in all different approaches (z-, xz-, xy-, and xyz-scans), as does their aromaticity at z=2.4 Å. The σ component of the total density is dominant close to the plane while the π component picks up in significance with increasing distance from the plane. The peri-fused ring appears to be a heteroring not just a heterobridge. © 2021 Wiley-VCH GmbH

The chalcogen-bonded homo-cavitand and hetero-cavitandAY+AY′capsules (Y, Y′ = Se, Te), as well as their encapsulated complexes with one or two guest molecules have been studied theoreticallyviadensity functional theory (DFT), while the1H NMR spectra of the homo-cavitand encapsulated complexes (inASe+ASe) have been measured experimentally. There is excellent agreement between theoretical and experimental spectra. In all cases, we found significant1H upfield shifts which are more intense in theASe+ASecage compared to theATe+ATeandASe+ATecages. The non-uniform electron distribution which gives rise to an inherent electric field and a non-zero electric dipole moment of the encapsulated complexes, the induced electric field effects, the magnetic anisotropy which is enhanced due to the polarizability of chalcogen atoms, and the peripheral chains, which are responsible for the solubility of the cages, increase the upfield shifts of1H of the encapsulated molecules; the peripheral chains lead to an increase of the upfield shifts by up to 1.8 ppm for H of the rim and up to 1.2 ppm for the terminal H in the interior of the cage. Hence, substantial1H upfield chemical shifts of the guests in these capsules are consequences of (i) the enhanced aromaticity of the walls of the capsules due to the polarizability of chalcogen atoms, (ii) the induced and inherent electric field effects, and (iii) the peripheral chains. © the Owner Societies 2021.

We present a theoretical study of chalcogen bonded container capsules (AX+AX) where X=O, S, Se, and Te, and their encapsulation complexes with n-C9H20 (n-C9H20@AX+AX). Both Se and Te encapsulation complexes have significant experimental and computed binding energies, analogous to the hydrogen bonded counterparts, while the S and O capsules and their encapsulation complexes show only weak binding energies, which are attributed to different types of bonding: chalcogen S⋅⋅⋅N bonds for S-capsules and π–π stacking and weak hydrogen bonds for the O case. All AX+AX and C9H20@AX+AX present unusually high magnetic anisotropies in their interiors. The 1H NMR spectra of the encapsulation complexes display the proton signals of the encapsulated n-nonane highly upfield shifted, in agreement with the available experimental data for the Se capsule. We found that different factors contribute to the observed magnetic anisotropy of the capsule's interior: for the Te capsule the most important factor is Te's large polarizability; for the O analogue the inductive effects produced by the electronegative nature of the O and N heteroatoms; and for the S and Se capsules, the polarizability of the heteroatoms combines with electric field effects. © 2020 Wiley-VCH GmbH

The tetrahedral copper(I) diimine complex [Cu(pq)2]BF4 displays high photocatalytic activity for the H2 evolution reaction with a turnover number of 3564, thus representing the first type of a Cu(I) quinoxaline complex capable of catalyzing proton reduction. Electrochemical experiments indicate that molecular mechanisms prevail and DFT calculations provide in-depth insight into the catalytic pathway, suggesting that the coordinating nitrogens play crucial roles in proton exchange and hydrogen formation. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Multiple bonds between atoms are one of the most fundamental aspects of chemistry. Double and triple bonds are quite common, while quadruple bonds are a true oddity and very rare for the main group elements. Identifying molecules containing quadruple bonds is very important and, even more so, determining the necessary requirements for the existence of such bonds. Here we present high-level theoretical calculations on the isoelectronic MX molecules, i.e., TcN, RuC, RhB, and PdBe, showing that such a quadruple bond with main group elements is not that uncommon. We found that quadruple bonds are formed in their ground states X3Δ(TcN) and χ1ς+ (RuC, RhB, and PdBe) and in the two lowest excited states of TcN (1ς+, 1Δ), RuC (1,3Δ), and RhB (1,3Δ). The quadruple bonds consist of two πand two σ bonds: (4dxz-2px)2, (4dyz-2py)2, (4dz2-2pz)2, and 5s0 → 2s2 (1ς+) or 5pz0→2s2 (1,3Δ). Bond lengths, dissociation energies, dipole moments, spectroscopic parameters, and relative energy ordering of the states were calculated via multireference and coupled cluster methodology using the aug-cc-pV5ZX(-PP)M basis sets. We study how the atomic states involved and how the gradual transition from covalent to dative bond, from TcN to PdBe, influence all of the calculated data, such as bond dissociation energies, bond lengths, and relative energy ordering of the states. Finally, we report the requirements for the occurrence of such bonds in molecular systems. All Be, B, C, and N atoms combining with the appropriate second-row transition metal can form quadruple bonds, while they cannot form such bonds with the first-row transition metals. © 2020 American Chemical Society.

For the ground states of the diatomic carbide FeC (X 3Δ) and its ions, FeC+ (X 2Δ) and FeC- (X 2Δ), we report on accurate multireference variational ab initio results employing augmented correlation consistent basis sets of quintuple cardinality. The dissociation energies and bond lengths are found to be D00 =87±1, 95.2, and 84±1 kcal/mol at re =1.581, 1.556, and 1.660 Å for FeC, FeC+, and FeC-, respectively. All our final numbers are in agreement with the available experimental data. © 2010 American Institute of Physics.

We have examined the electronic structure and bonding of the Mn2 molecule through multireference variational calculations coupled with augmented quadruple correlation consistent basis sets. The Mn atom has a 6S (4s23d5) ground state with its first excited state, 6D (4 s1 3 6D), located 2.145 eV higher. For all six molecular states 1∑g+, 3 u+, 5∑g+, 7∑u +, 9∑g+, and 11IIu+ (1) correlating to Mn (6S) +Mn (6S), and for six undecets, i.e., 11Πu, 11∑g+, 11Δg, 11Δu, 11IIu+ (2), and 11Πg with end fragments Mn (6S) +Mn (6D), complete potential energy curves have been constructed for the first time. We prove that the bonding in Mn2 dimer is of van der Waals type. The interaction of two Mn 6S atoms is hardly influenced by the total spin, as a result the six states, singlet (1∑ g+) to undecet (11IIu+ (1)), are in essence degenerate packed within an energy interval of about 70 cm-1. Their ordering follows the spin multiplicity, the ground state being a singlet, X 1∑g+, with binding energy De (D0) ≈600 (550) cm-1 at re ≈3.60 Å. The six undecet states related to the Mn (6S) +Mn (6D) manifold, are chemically bound with binding energies ranging from 3 (11Π g) to 25 (11Πu) kcal/mol and bond distances about 1 Å shorter than the states of the lower manifold, Mn ( 6S) +Mn (6S). The lowest of the undecets is of Πu symmetry located 30 kcal/mol above the X 1∑g + state. © 2008 American Institute of Physics.

The electronic structure and bonding of 19 states of the diatomic nickel carbide (NiC) has been studied by multireference methods. Potential energy curves have been constructed for all states, whereas for the three lowest states of symmetries X +1, a Π3, and A Π1 well separated from the rest of the states, special attention was paid through the use of very large basis sets and the calculation of core-valence correlation and scalar relativistic effects. The recommended binding energies for these states are 91, 67, and 54 kcalmol with respect to the ground state atoms. Our results in general can be considered in fair agreement with the limited experimental findings. © 2007 American Institute of Physics.

The ground and 18 low lying excited states of the diatomic molecule cobalt carbide, CoC, have been examined by multireference variational methods (MRCI) combined with quantitative basis sets. All calculated states are bound and correlate adiabatically to the ground-state atoms, Co(a4F) + C( 3P). We report complete potential energy curves, equilibrium bond distances, dissociation energies (De), spectroscopic constants, electric dipole moments and spin-orbit splittings. The bonding character of certain states is also discussed with the help of Mulliken distributions and valence-bond-Lewis diagrams. We are practically certain that the ground state is of 2Σ+ symmetry with a state of 2Δ symmetry lying less than 3 kcal/mol higher, in agreement with the relevant experimental findings. Our best estimate of the X2Σ+ dissociation energy is De(D0) = 83(82) kcal/mol at r e = 1.541 Å, 0.02 Å shorter than the experimental bond length. © 2006 American Chemical Society.

We have studied 40 states of the diatomic iron carbide cation FeC + by multireference methods coupled with relatively large basis sets. For most of the states, we have constructed complete potential energy curves, reporting dissociation energies, usual spectroscopic parameters, and bonding mechanisms for the lowest of the studied states. The ground state is of 2Δ symmetry, with the first excited state (a 4Σ-) lying 18 kcal/mol higher. The X 2Δ state displays a triple-bond character, with an estimated D0 value of 104 kcal/mol with respect to the adiabatic products or 87 kcal/mol with respect to the ground-state fragments. © 2005 American Chemical Society.

We have investigated the interaction of the methylidene, CH(X 2Π, a4Σ-) and methylene, CH 2(X̃3B1, ã1A1) with H2O, employing the (P)MPn (n = 2, 4) techniques in conjunction with the sequence of correlation consistent basis sets aug-cc-pVxZ, x = 2, 3, and 4. For the CH⋯OH2 system, we have located four minima (m) and three transition states (ts) and for the CH2⋯OH 2, five minima and four transition states. All our results have been corrected for zero-point energy (ZPE) and basis set superposition errors (BSSE), while for the most important m_ structures, we report complete basis set (CBS) interaction limits. We also report fully optimized geometries, harmonic frequencies, dipole moments, Mulliken charges, and potential energy curves. The highest CH(X2Π)⋯OH2 (ml_2Π) and CH2(ã1A 1)⋯OH2 (m1_1A1) interactions are the result of electron transfer from the oxygen atom to the empty p π orbitals of CH(X2Π) and CH2(ã 1A1), respectively (ylide-like structures). At the (P)MP4/AQZ//MP2/ATZ level, including ZPE, BSSE, and CBS extrapolation, we obtain ΔE0(BSSE)+CBS = -9.36 kcal/mol at rC⋯O = 1.752 Å, and -9.73 kcal/mol at rC⋯O = 1.741 Å for the m1_2Π and m1_1A1, respectively. © 2005 Wiley Periodicals, Inc.

Employing multireference variational (MRCI) and coupled cluster (CC) methods combined with quadruple-ζ quality correlation-consistent basis set, we have studied 36 states of the magnesium diboride (MgB2) molecule as well as 17 states of the experimentally unknown diatomic MgB. For all states of MgB2, we report geometries, atomization energies, and dipole moments, while for the first 5 states, potential energy profiles have been also constructed. The ground state is formally of 1A1 V-shaped symmetry with an atomization energy of 108.1(109) kcal/mol at the MRCI(MRCI + Davidson correction) level. The first excited state (3B1) is less than 1 kcal/mol above the X̃1A1 state, with the next state of linear Mg - B - B geometry (b̃3Σ -) located 10 kcal/mol higher. In all states, bent or linear, the bonding is complicated and unconventional because of the extraordinary bonding agility of the boron atom(s). © 2005 American Chemical Society.

With the purpose of comparing expectation dipole moment values 〈μ〉 with finite-field obtained dipole moments μ FF, we recalculated by the finite-field method previously reported 〈μ〉 values of 38 excited states of FeC. In most of the cases μ FF is significantly larger than 〈μ〉.© 2005 American Institute of Physics.

The ground state symmetry of the titanium phosphide molecule, TiP, was discussed using multireference and coupled cluster methods and very large basis sets was discussed. The ground state of TiP was of 2σ+ symmetry with the first excited state A 2δ no more than 3.5 kcal/mol higher. Coupled cluster singles and doubles with perturbative triples calculations were also performed. Potential energy curves, dissociation energies, bond lengths, dipole moments, and the usual spectroscopic constants were also reported.

A study was conducted on the calculations of the dipole moment of the X3Δ state of FeC by increasing the basis set size, and using also the finite field method for obtaining the dipole moment (μFF). As a result, a dramatic improvement was observed using the finite field method: the μFF increases by approximately 0.6 D as compared to the value in both MRCI and C-MRCI levels of theory, while it seems to be independent of the basis set size, at least within these particular series of basis sets.

The acetylene-water (A-W) interactions have been investigated by examining the van der Waals clusters AWx, x = 2, 3, and 4, at the second order (MP2) perturbation theory using the correlation-consistent basis sets, aug-cc-pVnZ, n = D (AW2, AW3, and AW4), T (AW2). We located 4 minima (m) and 2 saddle points (sp), 10 m and 3 sp, and 30 m and 3 sp on the potential energy surfaces of the AW2, AW3, and AW4 clusters, respectively. We report the fully optimized geometries and interaction energies ΔEe, including corrections for basis set superposition error, ΔEe(BSSE), as well as zero-point energies, ΔE0(BSSE), for the various stationary points. The global minima of the AW2 and AW3 clusters are cyclic configurations in which the acetylene molecule inserts into the water hydrogen bonding network. The corresponding interaction energies ΔEe(BSSE)[ΔE0(BSSE)] are AW2, - 10.37 [-6.70] kcal/mol (MP2/aug-cc-pVTZ) and AW3, - 17.80 [-11.46] kcal/mol (MP2/aug-cc-pVDZ). The global minimum of AW4 corresponds to a van der Waals complex between a cyclic water tetramer W4 and A with an interaction energy of -28.01 [-18.67] kcal/mol (MP2/aug-cc-pVDZ). The 4 and 10 local minima for the x = 2 and 3 clusters span an energy range of 4.3 and 6.1 kcal/mol above the respective global minima. For AW4, the energy range for the 30 minima is 14.1 kcal/mol; however, the first 28 lie within 8.4 kcal/mol above the global minimum. The analysis of the many-body interaction energy terms suggests that the global and low-lying ring networks are stabilized by the maximization of the many-body (mainly the 3-body) terms, whereas the higher lying minima are mainly described by 2-body interactions.

Continuing our study on the electronic structure of the carbides BC and AlC (Tzeli, D.; Mavridis, A. J. Phys. Chem. A 2001, 105, 1175), we have investigated the electronic structure of 29 and 30 excited states of the BC and AlC molecules, respectively, by ab initio quantum mechanical multireference methods and quantitative basis sets. For both diatomic species we report complete potential energy curves, total energies, interatomic distances, dissociation energies, dipole moments, Mulliken charges, energy gaps, and usual spectroscopic constants. Our results are, in general, in good to very good agreement with the existing experimental values.

Using ab initio multireference methods and large correlation consistent basis sets, we have investigated the ground electronic structure of the carbides BC and AlC, the ground and the first two excited states of the corresponding anions, BC- and AlC-, and the ground (linear) structures of the hydrides H-BC and H-AlC. By employing a series of increasing size basis sets for the BC molecule, i.e., cc-pV/iZ, aug-cc-pVnZ, cc-pCVnZ, and aug-cc-pCVnZ, n = 2, 3, 4, and 5, we have examined the convergence of its properties as a function of n. For both the neutral diatomic species and their anions we have obtained full potential energy curves, bond distances (re), dissociation energies (De), and the usual spectroscopic constants. For the BC molecule, our best re and De values are re = 1.4911 Å and De = 102.2 kcal/mol in excellent agreement with experimental results. In the AlC case the calculated De = 77.13 kcal/mol is at least 12 kcal/mol higher than the experimental number. No experimental or theoretical data exist in the literature for the anion BC-. For this system we obtain re = 1.4445 Å and De = 118.67 kcal/mol; the corresponding values of the AlC- species are re = 1.8945 Å and De = 77.16 kcal/mol. © 2001 American Chemical Society.

We present an extensive study of the stationary points on the acetylene-water (AW) ground-state potential energy surface (PES) aimed in establishing accurate energetics for the two different bonding scenarios that are considered. Those include arrangements in which water acts either as a proton acceptor from one of the acetylene hydrogen atoms or a proton donor to the triple bond. We used a hierarchy of theoretical methods to account for electron correlation [MP2 (second-order Moller-Plesset), MP4 (fourth-order Moller-Plesset), and CCSD(T) (coupled-cluster single double triple)] coupled with a series of increasing size augmented correlation consistent basis sets (aug-cc-pVnZ, n = 2,3,4). We furthermore examined the effect of corrections due to basis set superposition error (BSSE). We found that those have a large effect in altering the qualitative features of the PES of the complex. They are responsible for producing a structure of higher (C2v) symmetry for the global minimum. Zero-point energy (ZPE) corrections were found to increase the stability of the C2v arrangement. For the global (water acceptor) minimum of C2v symmetry our best estimates are ΔEe = -2.87 kcal/mol (ΔE0= -2.04 kcal/mol) and a van der Waals distance of Re= 2.190 Å. The water donor arrangement lies 0.3 kcal/mol (0.5 kcal/mol including ZPE corrections) above the global minimum. The barrier for its isomerization to the global minimum is Ee = 0.18 kcal/mol; however, inclusion of BSSE- and ZPE-corrections destabilize the water donor arrangement suggesting that it can readily convert to the global minimum. We therefore conclude that there exists only one minimum on the PES in accordance with previous experimental observations. To this end, vibrational averaging and to a lesser extend proper description of intermolecular interactions (BSSE) were found to have a large effect in altering the qualitative features of the ground-state PES of the acetylene-water complex. © 2000 American Institute of Physics.

Using semiquantitative basis sets and ab initio multireference methods, we have investigated the electronic structure of scandium aluminide cation, ScAl+. In addition to the ground state (X2Δ), we have constructed potential energy curves for 20 more states spanning an energy range of no more than 1.5 eV. The first three states, X2Δ, 12∏, and 22∑+, are practically degenerate within the accuracy of our calculations. They have similar binding modes and a binding energy of about 30 kcal/mol with respect to their adiabatic fragments Sc(2D) + A1+(1S). The rest of the states correlate to Sc+(3D or 3F) + Al(2P). For all states we report bond lengths, dissociation energies, harmonic frequencies, Mulliken charges, and energy gaps. © 2000 American Chemical Society.

The ground states of the isovalent molecules NLi2 (X̄2Π0) and PLi2 (X̄2B1), along with some low-lying excited states (2B2,4Σg-, 2Σg-, 4Σu-, 2Σu-, and 2A1) have been examined using ab initio CISD, CASSCF, and MRCI methods in conjunction with relatively large correlation consistent basis sets. We report total energies, geometries, binding energies, Mulliken charges, energy gaps, and for certain states, potential energy curves. All states examined are bound with respect to the ground-state atoms N or P(4S) + 2Li(2S), while the mean binding energies N-Li and P-Li of NLi2 and PLi2 are 42.5 and 40.2 kcal/mol, respectively.

The electronic structure of the isovalent P-Li and P-Na species in their ground X3Σ- state and low-lying excited states, A3Π, a1Δ, b1Σ+ and B3Σ-, has been studied employing CISD, CASSCF and multireference CI techniques. For both molecules and all states studied, we report full potential energy curves, dissociation energies, bond lengths, and spectroscopic constants. © 1997 Elsevier Science B.V.