C2v Geometry Research Articles

The K-shell spectra of tetrahydrofuran studied by electron energy loss spectroscopy and abinitio calculations

Ab initio calculations have been carried out in order to assign the bands observed in the carbon and oxygen K-shell spectra of gaseous tetrahydrofuran (THF), measured using inner-shell electron energy loss spectroscopy (ISEELS). The good agreement between the theoretical and the measured spectra allows us to re-assign precisely most of the peaks. The ionisation energies are calculated for the first time and found to be consistent with a quantum defect analysis of the core excitation energies. The calculated spectra for the C2v, C2 and Cs geometries of the molecule show very small differences. Thus, K-shell spectroscopy cannot be used to solve the controversy on the geometry of THF.

Molecular structures and molecular spectra for plutonium oxides

Employing hybrid HF/DFT functional in conjunction with the relativistic effective core potential for Pu atoms and all-electron basis set 6-311g（d） for O atoms, the equilibrium geometrical structures of PuO, PuO2 and Pu2O3 molecules are obtained in the geometry optimization. The infrared and Raman spectra are also calculated. The bond lengths and harmonic vibration frequencies of ground states of PuO and PuO2 molecules are all in agreement with available experimental data. In geometry optimization of Pu2O3 molecule, we have tested more than twenty initial structures with different spin multiplicities （1, 3, 5, 7, 9, 11 and 13）. A C2v geometry corresponding to electronic state of 11B2 is considered as the ground state of Pu2O3 molecule. The harmonic frequency, IR intensity, Raman scatting activity and depolarization ratio of Pu2O3 molecule are obtained for the first time in theory. The vibrational modes corresponding to the maximum peaks are assigned for PuO2 and Pu2O3 molecules. In all studied molecules, the charge transfers from Pu to O atoms are found from natural bonding orbital analysis （NBO）. Relative to PuO and PuO2 molecules corresponding to Pu-O single- bond, the interactions between Pu and O in Pu2O3 are much weaker. The spin magnetic moments of studied molecules stem mainly from the 5f atomic orbitals of Pu atoms, but for O atoms the antiparallel spins from 2p atomic orbital are exhibited.

Experimental Detection and Properties of H2O⋅⋅⋅AgCl and H2S⋅⋅⋅AgCl by Rotational Spectroscopy

We report the first generation and characterization of two simple compounds formed by the interaction of either H2O or H2S with AgCl, namely H2O···Ag Cl and H2S···Ag Cl. They were observed in the gas phase by rotational spectroscopy. The AgCl is produced by laser ablation of metallic silver in the presence of CCl4 and then picks up an H2O or H2S molecule. AgCl is known, from interpretation of its Cl nuclear quadrupole coupling constant, to have a fractional ionic character of approximately 0.7, so that it has significant ionpair character. The interaction of AgCl with H2Omolecules, and in particular one H2O molecule, is of fundamental chemical interest because the H2O molecules have the opportunity to interact with an incipient Ag ion. How does this interaction differ from those of H2O with the less polar, covalent Lewis acids HCl and ClF (fractional ionic characters of 0.25 and 0.35)? The hydrogenand halogen-bonded complexes H2O···H Cl and H2O···Cl F have each been investigated in the gas phase by rotational spectroscopy as part of an extensive systematic program. H2O···H Cl and H2O···Cl F have equilibrium geometries of Cs symmetry, [2,3] with a pyramidal configuration at O when HCl or ClF forms either a hydrogen or halogen bond to that atom (see Figure 1). In each case, however, there is a low potential-energy barrier to the planar, C2v geometry so that even in the zero-point state the molecule is inverting and is effectively planar. On the other hand, in the analogous pair of complexes H2S···H Cl and H2S···Cl F the potential energy barrier is high enough to ensure that each has a permanently pyramidal configuration at S, with HCl or ClF forming a weak bond to S at approximately 908 to the H2S subunit, as shown in Figure 1. These angular geometries, and those of many other hydrogenand halogen-bonded complexes, can be rationalized by means of some simple empirical rules. For both H2O and H2S acting as Lewis bases, the electrophilic ends H and Cl of the weakly polar molecules HCl and ClF, respectively, are assumed to seek the axis of a nonbonding electron pair carried by the base. A further question is: Are the angular geometries of the resulting molecules H2Y···Ag Cl isomorphic with those of H2Y···H Cl and H2Y···Cl F (Y=O or S), indicating that the empirical rules are also obeyed when AgCl is the Lewis acid? All B···M X (B=CO, M=Cu, Ag, Au) have a linear arrangement similar to those in OC···H Cl and OC···Cl F. Thus, in all these systems, the Lewis acid attaches along the axis of the n-pair on C. A linear geometry was also found in N2···Cu F. Observed rotational transitions of both H2O···Ag Cl and H2S···Ag Cl were characteristic of a nearly prolate asymmetric rotor of large A value having only a-type transitions, which exhibit Cl nuclear quadrupole hyperfine structure. For H2O···Ag Cl, R-branch K 1= 1 transitions of the type (J+ 1)1,J+1 !J1,J and (J+ 1)1,J !J1,J 1 were observed in addition to the (J+ 1)0,J+1 !J0,J series and for a given J were more intense than those having K 1= 0. This observation confirms that the molecule has a pair of equivalent H nuclei exchanged by a rotationC2 about the a axis and therefore that the equilibrium geometry of H2O···Ag Cl is either C2V planar at equilibrium or Cs pyramidal but with a potential-energy barrier to planarity low enough that the v= 0 and 1 states associated with the motion that inverts the configuration at the O atom are well separated. For H2S···Ag Cl only the (J+ 1)0,J+1 !J0,J series could be detected despite a careful search, an observation consistent with a pyramidal configuration at the S atom and no inversion on the microwave timescale. The reason for the different behavior with respect to inversion is presumably that H2S···Ag Cl is more strongly bound than H2O···Ag Cl (see below) and that there is a much larger angle between the n-electron pairs on S than on O. The result is a higher and wider barrier to inversion in H2S···Ag Cl. The usual arguments show that for H2O···Ag Cl in the ground state the K 1= 1 levels occur in combination with the three symmetric proton spin functions while theK 1= 0 levels combine with the single antisymmetric function. Moreover, population transfer from K 1= 1 levels into K 1= 0 levels during the supersonic expansion is hindered by a collisional propensity rule which forbids triplet state (K 1= 1) to Figure 1. Angular geometries of several H2Y M X compounds; d indicates the local C2 axis of the H2O or H2S subunit.

Electronic structure of the Li2 [X 1Σ] Li [2p] excited 2A″ surface

AbstractPotential energy surface calculations are reported for the lowest 2A″ surface arising from the Li2 [X 1Σ] + Li* [2P] interaction. The 2A″ surface with Cs symmetry, which correlates to the 2B1 surface in C2v symmetry and to the 2Pi surface in C∞v, has been calculated using second order restricted open‐shell Møller–Plesset theory. Our calculated surface has a minimum in C2v symmetry that resembles the ground state surface but does not exhibit the Jahn–Teller splitting found for the ground state potential energy surface. Dipole transition moments are calculated in C2v geometry near the 2A″ minima using the internally contracted multireference singles and doubles configuration interaction theory. We have also analyzed the long range behavior of this 2A″ surface by fitting the ab initio calculations at long range with a functional series of the form ±Cn/Rn. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Static jahn-teller distortion in the tri-phenylene mono-negative ion

An MC-LCAO-MO method was employed to study a static Jahn-Teller distortion in the ground state of the triphenylene mono-negative ion. An SCF type iterative calculation with CI was carried out for the ground state of the anion in both D3h and C2v molecular geometries to obtain most stable conformations. It was found that the anion in the C2v geometry is more stable than that in the D3h geometry. The calculated lower transition energies are in good agreement with observed values.

Slow electron velocity-map imaging spectroscopy of the 1-propynyl radical

High resolution photoelectron spectra of the 1-propynyl and 1-propynyl-d(3) anions acquired with slow electron velocity-map imaging are presented. The electron affinity is determined to be 2.7355+/-0.0010 eV for the 1-propynyl radical and 2.7300+/-0.0010 eV for 1-propynyl-d(3). Several vibronic transitions are observed and assigned using the isotopic shifts and results from ab initio calculations. Good agreement between experimental spectra and calculations suggests a C(3v) geometry for the 1-propynyl radical. No evidence is found for strong vibronic coupling between the ground electronic state and the low-lying first excited state.

Low-energy electron scattering by deoxyribose and related molecules

We apply first-principles computational methods to study elastic scattering of low-energy electrons by 2-deoxyribose and 2-deoxyribose monophosphate, which are of interest as components of the DNA backbone, and to tetrahydrofuran (THF), which has been studied as a deoxyribose analog. To investigate the dependence of the scattering process on the molecular conformation, we examine Cs and C2 conformers of THF as well as the planar C(2v) geometry imposed in earlier calculations. There is little difference between the elastic cross sections determined at the nonplanar geometries, but there are noticeable differences between those results and the cross sections computed using the planar ring. By comparing results for tetrahydrofuran obtained with and without inclusion of polarization effects, we obtain energy shifts that are applied to the computed resonance positions for deoxyribose and deoxyribose monophosphate.

High-Spin Stability of Triiminiummethane Ion -A Comparative Study with Trimethylenemethane-

High-spin stability of non-Kekule-type molecule triiminiummethane ion (TIM3+) is discussed using the semiempirical molecular orbital method. The triplet ground state A2’ with a D3h geometry is predicted to lie below the Jahn-Teller distorted singlet states similar to trimethylenemethane (TMM). The lowest singlet states B1, B2 and A1 with C2v geometries are nearly degenerate. The spin-density distribution of the A2’ state is calculated and the origin of the spin alignment is discussed relating to the spin-polarization rule characteristic of high-spin organic molecules. The valence bond analysis on the spin states of TIM3+ is also carried out.

Revisiting the geometry of nd10 (n+1)s0 [M(H2O)]p+ complexes using four‐component relativistic DFT calculations and scalar relativistic correlated CSOV energy decompositions (Mp+ = Cu+, Zn2+, Ag+, Cd2+, Au+, Hg2+)

Hartree-Fock and DFT (B3LYP) nonrelativistic (scalar relativistic pseudopotentials for the metallic cation) and relativistic (molecular four-component approach coupled to an all-electron basis set) calculations are performed on a series of six nd10 (n+1)s0 [M(H2O)]p+ complexes to investigate their geometry, either planar C2v or nonplanar C(s). These complexes are, formally, entities originating from the complexation of a water molecule to a metallic cation: in the present study, no internal reorganization has been found, which ensures that the complexes can be regarded as a water molecule interacting with a metallic cation. For [Au(H2O)]+ and [Hg(H2O)]2+, it is observed that both electronic correlation and relativistic effects are required to recover the C(s) structures predicted by the four-component relativistic all-electron DFT calculations. However, including the zero-point energy corrections makes these shallow C(s) minima vanish and the systems become floppy. In all other systems, namely [Cu(H2O)]+, [Zn(H2O)]2+, [Ag(H2O)]+, and [Cd(H2O)]2+, all calculations predict a C2v geometry arising from especially flat potential energy surfaces related to the out-of-plane wagging vibration mode. In all cases, our computations point to the quasi-perfect transferability of the atomic pseudopotentials considered toward the molecular species investigated. A rationalization of the shape of the wagging potential energy surfaces (i.e., single well vs. double well) is proposed based on the Constrained Space Orbital Variation decompositions of the complexation energies. Any way of stabilizing the lowest unoccupied orbital of the metallic cation is expected to favor charge-transfer (from the highest occupied orbital(s) of the water ligand), covalence, and, consequently, C(s) structures. The CSOV complexation energy decompositions unambiguously reveal that such stabilizations are achieved by means of relativistic effects for [Au(H2O)]+, and, to a lesser extent, for [Hg(H2O)]2+. Such analyses allow to numerically quantify the rule of thumb known for Au+ which, once again, appears as a better archetype of a relativistic cation than Hg2+. This observation is reinforced due to the especially high contribution of the nonadditive correlation/relativity terms to the total complexation energy of [Au(H2O)]+.

Electronic excited-state mixing in NeCl2

Ab initio calculations that explicitly include spin-orbit interactions are reported for the NeCl2 system of electronic states. A surprising curve crossing is observed for the C2v, T-shaped geometry. Away from the C2v geometry, the states mix, as expected. On the basis of these new results we propose a new mechanism for electronic energy transfer from highly vibrationally excited levels of the B electronic state of the chlorine molecule. It is proposed that as long as vibrational predissociation of NeCl2 proceeds by direct coupling of the initial state to the continuum states the Ne atom does not sample geometries that efficiently quench the Cl2 B electronic state. However, when the vibrational dynamics changes to the intramolecular vibrational relaxation regime the Ne atom becomes quite effective at coupling the Cl2 B3Pi0u+ state with a 3Pi2g state.

Ab initio molecular orbital study of conformational properties of cyclohexyne, cycloheptyne, and cyclooctyne

AbstractThe structures and relative energies for the basic conformations of cyclohexyne (1), cycloheptyne (2), and cyclooctyne (3) have been calculated by the HF/6‐31G*, MP2/6‐31G*, and B3LYP/6‐31G* methods. The C2 symmetric twist conformer of 1 is calculated to be more stable than the planar C2v geometry. Ring inversion of the envelope conformation of 2 takes place via C2 symmetric twist transition state, which is 34.0 kJ mol−1 higher than the envelope form. The C2 symmetric chair conformation of 3 is calculated to be 11.7 kJ mol−1 more stable than the unsymmetrical twist‐boat (3‐TB) geometry. Interconversion of the chair conformation and 3‐TB takes place via an unsymmetrical transition state, which is 37.6 kJ mol−1 less stable than the chair form. Conformational racemization of the chiral 3‐TB takes place via the boat transition state. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Theoretical Study on the Small Clusters of LiH, NaH, BeH2, and MgH2

High-level ab initio molecular orbital theory is used to calculate the geometries, vibrational frequencies, atomic charges, and binding energies of the small clusters (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) (n = 1-4). For (LiH)(n) and (NaH)(n), there are planar cyclic structures when n = 2, 3. We have found the cubic structure T(d) in addition to the planar cyclic D(4)(h) when n = 4. The D(4)(h) is less stable than the T(d) geometry. For (BeH(2))(n) and (MgH(2))(n), when n = 3, there are three kinds of structures: chain C(2)(v), planar cyclic D(3)(h), and hat-like C(2)(v). The C(2)(v) geometry is more stable than the others. When n = 4, there are four kinds of structures: chain D(2)(h), cubic T(d), string-like C(2), and cubic transformation C(1). The most stable compounds in the families of (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) are cubic T(d), cubic T(d), chain D(2)(h), and string-like C(2) geometries, respectively, when n = 4. Calculated binding energies range from -24 to -37 kcal/mol for (LiH)(n) and --19 to -30 kcal/mol for (NaH)(n), (BeH(2))(n), and (MgH(2))(n). The hydrogen atoms in hydride clusters always have negative charges. The atomic charges of planar cyclic structures are weaker than those of cubic structures, and there is a tendency of reducing along with the increase of the cluster size. The vibrational frequencies of planar cyclic structures have consistent tendency, too. It indicates that the bond distance increases with the ionic character of the bond.

Structure of the Dimethyl Ether−CO2 van der Waals Complex from Microwave Spectroscopy

The rotational spectrum of the 1:1 weakly bound complex formed between dimethyl ether (DME) and CO2 has been assigned by Fourier transform microwave spectroscopy, leading to rotational constants of A = 5401.24(11) MHz, B = 2010.8637(17) MHz, and C = 1493.4844(15) MHz for the normal isotopic species. Measurement of rotational spectra for an additional four isotopomers has allowed a structure determination for this complex, giving a C2v geometry in which the CO2 lies in the heavy atom plane of the DME and is aligned perpendicular to its C2 axis. This orientation is supported by second moment data and a dipole moment of μa = μtotal = 1.661(6) D. The C···O distance has been determined to be 2.711(1) A. Ab initio optimizations at the MP2/6-311++G(2d,2p) level predict a C2v geometry with a C···O bond length of 2.685 A, slightly shorter than, but still in very good agreement with, the experimental value. Predicted rotational constants and dipole moment at this level of theory are A = 5379 MHz, B = 2018 MHz, C = ...

Photoelectron spectroscopy of the doubly-charged anions [MIVO(mnt)2]2- (M = Mo, W; mnt = S2C2(CN)2(2-): access to the ground and excited states of the [MVO(mnt)2]- anion.

Photodetachment photoelectron spectroscopy was used to investigate the electronic structure of the doubly charged complexes [MIVO(mnt)2]2- (M = Mo, W; mnt = 1,2-dicyanoethenedithiolato). These dianions are stable in the gas phase and are minimal models for the active sites of the dimethyl sulfoxide reductase family of molybdenum enzymes and of related tungsten enzymes. Adiabatic and vertical electron binding energies for both species were measured, providing detailed information about molecular orbital energy levels of the parent dianions as well as the ground and excited states of the product anions [MVO(mnt)2]-. Density functional theory calculations were used to assist assignment of the detachment features. Differences in energy between these features provided the energies of ligand-to-metal charge-transfer transitions from S(pi) and S(sigma) molecular orbitals to the singly occupied metal-based orbital of the products [MVO(mnt)2]-. These unique data for the M(V) species were obtained at the C(2)(v)() geometry of the parent M(IV) dianions. However, theoretical calculations and available condensed phase data suggested that a geometry featuring differentially folded dithiolene ligands (Cs point symmetry) was slightly lower in energy. The driving force for ligand folding is a favorable covalent interaction between the singly occupied metal-based molecular orbital (a1 in C2v) point symmetry; highest occupied molecular orbital (HOMO)) and the least stable of the occupied sulfur-based molecular orbitals (b1 in C2v point symmetry, HOMO-1) that is only possible upon reduction to the lower symmetry. This ligand folding induces a large increase in the intensity predicted for the a' S(pi) --> a' dx2 - y2 charge-transfer transition originating from the HOMO-2 of [MVO(mnt)2](-) under Cs point symmetry. Electronic absorption spectra are available for the related species [MoVO(bdt)2]- (bdt = 1,2-benzenedithiolato) and for the oxidized form of dimethyl sulfoxide reductase. The intense absorptions at approximately 1.7 eV have been assigned previously to S(sigma) --> Mo transitions, assuming C2v geometry. The present work indicates that the alternative a' S(pi) --> a' dx2 - y2 of Cs geometry must be considered. Overall, this study confirms that the electronic structure of the M-dithiolene units are exquisitely sensitive to dithiolene ligand folding, reinforcing the proposal that these units are tunable conduits for electron transfer in enzyme systems.

Electron-intramolecular-vibration interactions in positively charged phenanthrene-edge-type hydrocarbons.

Electron-phonon interactions in positively charged phenanthrene-edge-type hydrocarbons such as phenanthrene, chrysene, and picene are studied. The C-C stretching modes around 1500 cm(-1) and the low-frequency modes around 500 cm(-1) strongly couple to the highest occupied molecular orbitals (HOMO) in phenanthrene-edge-type hydrocarbons. The total electron-phonon coupling constants for the monocations (lHOMO) of 0.251, 0.135, and 0.149 eV for phenanthrene, chrysene, and picene, respectively, are estimated to be larger than those of 0.130, 0.107, and 0.094 eV for anthracene, tetracene, and pentacene, respectively. The phase patterns difference between the HOMO localized on carbon atoms which are located at the molecular edge in acene-edge-type hydrocarbons and the delocalized HOMO in phenanthrene-edge-type hydrocarbons is the main reason for the result. Strengths of orbital interactions between two neighboring carbon atoms in the HOMO become weaker with an increase in molecular size because the electron density on each carbon atom in the HOMO becomes smaller with an increase in molecular size in phenanthrene-edge-type hydrocarbons. On the other hand, the frontier orbitals of acene-edge-type hydrocarbons have somewhat nonbonding characters and thus cannot strongly couple to the totally symmetric vibrational modes compared with the frontier orbitals of phenanthrene-edge-type hydrocarbons. This is the reason why the lHOMO value for phenanthrene-edge-type hydrocarbons decreases with an increase in molecular size more significantly than that for acene-edge-type hydrocarbons, and the reason why the lHOMO value for polyphenanthrene with C2v geometry (0.033 eV) is estimated to be similar to that for polyacene (0.036 eV). The reorganization energies between the neutral molecules and the corresponding monocations for phenanthrene-edge-type hydrocarbons with large molecular size are estimated to be larger than those for acene-edge-type hydrocarbons with large molecular size.

Accurate potential energy surfaces for the study of lithium–hydrogen ionic reactions

Three-dimensional potential energy surfaces (PESs) have been computed, and numerically fitted, for the two lowest electronic states of the LiH2+ system, which are of importance for the astrophysically relevant LiH++H→Li++H2 and LiH+H+→Li+H2+ exoergic reactions. We extend the recently computed 11 000 multi reference valence bond ab initio energy values [Martinazzo et al., Chem. Phys. 287, 335 (2003)] with 600 multireference configuration interaction calculations with complete active self-consistent field reference functions and a large Li(12s10p4d1f)/H(8s6p3d1f) basis set. We have fitted the full set of energy values with a modified Aguado–Paniagua ansatz that correctly takes into account in this ionic system the important long-range contributions to the potential. Calibration calculations on the three-body potential term and the use of essentially exact results for the two-body contributions allow us to estimate the overall accuracy of the analytic PESs to be within that required for accurate quantum scattering calculations. The above reactions can be treated adiabatically because of the large energy gap separating the two electronic states. The relevant potential energy surfaces have a very different shape. On the one hand, the ground-state PES shows a simple structure, with a downhill route to the products and a shallow well at the C2v geometry which lies 0.286 eV below the Li++H2 asymptote. On the other hand, the first excited state is characterized by one deep, dipole-charge well which lies 1.315 eV below the LiH+H+ asymptote, one charge-induced dipole well 0.586 eV below the Li+H2+ asymptote, and a saddle point between them which lies 0.227 eV below the LiH+H+ asymptote. A conical intersection with the second excited state has been found but not yet studied in detail, since we deemed it to be of no direct relevance for the above reactions.

Infrared spectroscopy of V+(H2O) and V+(D2O) complexes: Solvent deformation and an incipient reaction

V + ( H 2 O ) Ar n and V+(D2O)Arn complexes are studied with mass-selected infrared photodissociation spectroscopy in the O–H (O–D) stretch region. Two vibrational bands are measured 50–80 cm−1 to the red from the symmetric and asymmetric stretches in free water. Rotational analysis for V+(H2O)Ar indicates a C2v geometry with argon opposite water and significant expansion of the H–O–H angle. The v=1 level in the asymmetric stretch undergoes distortion consistent with selective excitation into the coordinate of an insertion reaction.

Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH3) and boron trifluoride (BF3) as a function of angles of reorganization from planar (D3h) to pyramidal (C3v) shape

AbstractIn chemical response the BH3 and BF3 molecules undergo the physical process of planar (D3h) to pyramidal (C3v) reorganization in shape as the condition precedent to the event of chemical reaction under the requirement of symmetry. A frontier orbital and density functional study of the variation of the stability of electronic structures and chemical reactivity of associated with the physical process of D3h to C3v geometry reorganization has been performed. The theoretical parameters viz. eigenvalues of HOMO and LUMO, the HOMO and LUMO energy gap, the global hardness and global softness, the chemical potential, the condensed Fukui function, and local softness of B atom, the reaction site, have been computed over a wide range of ∠XBX angles. The nature of variation in the intrinsic chemical reactivity, global and local, of the molecules associated with their geometry reorganization during the chemical event of charge transfer interaction involving their frontier molecular orbitals has been quantitatively explored. The hardness profiles as a function of reaction coordinates are consistent with the principle of maximum hardness (PMH). Results demonstrate that the hardness and softness are not a static and invariable property of molecules but a dynamic and variable function of molecular structure. The hardness parameters and the HOMO–LUMO gap of the molecules are so modified with the distortion of molecular geometry that, after a certain stage of molecular deformation, the profiles of such parameters of the molecules intersect and cross each other, signifying that the relative order of the intrinsic hardness of their equilibrium geometry is reversed. The intrinsically hard molecule BF3 becomes softer than the intrinsically soft molecule BH3 as a consequence of structural distortion. The increase in chemical reactivity computed in terms of density functional parameters are transparent and justified in terms of the profiles of the eigenvalues of the frontier orbitals. The profiles of chemical potential reveal the inherent difference in the tendency of backdonation from two molecules. The computed values of Fukui functions and local softness parameters of the B atom site demonstrate that the concept of local softness can be exploited for a theoretical analysis and understanding of the characteristic chemical events of the molecules under consideration. The profiles of the Fukui functions and local softness parameters of the two molecules seem to reflect and reveal their intrinsic difference in the tendency of receiving donation in the LUMO (electrophilicity) and that of backdonation from the HOMO (nucleophilicity) and the inherent difference of overall reactivity of the two molecules by a simultaneous operation of two opposing processes of charge transfer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Rotational spectrum of jet-cooled HfO2 and HfO

The rotational spectrum of jet-cooled hafnium dioxide obtained by laser ablation of a solid ceramic rod has been investigated by Fourier-transform microwave spectroscopy in the 8 to 28 GHz frequency range. Rotational transitions within the ground and several excited vibrational states of the lowest vibrational mode of the molecule have been assigned. The resulting spectra have been fit, yielding rotational parameters for the five most abundant isotopomers of HfO2. Centrifugal distortion effects are noticeable even for the lowest-J transitions. Very large quadrupole coupling effects for the isotopomers with nuclear quadrupole moments (179Hf (I=9/2) and Hf177 (I=7/2)) have been accounted for using the diagonal elements of the nuclear quadrupole coupling tensor. A ground-state effective C2v geometry has been obtained for HfO2, yielding ro(Hf–O)=1.7764(4) Å and ∠(O–Hf–O)=107.51(1)°. The electric dipole moment has been determined for HfO2180 from Stark-effect measurements, giving μ=26.42(3)×10-30C⋅m [7.92(1) D]. Ab initio calculations using density functional theory and relativistic core potentials are in satisfactory agreement with the experimental results. Finally, in the course of this investigation, the rotational spectrum of the diatomic molecule, HfO, has also been reexamined, and new results for vibrational satellites (up to v=18 in some cases) of the J=1←0 rotational transition are reported. A vibrational analysis using Le Roy’s form of the Dunham expansion has allowed the determination of atomic mass-dependent Born–Oppenheimer breakdown parameters for both atoms of HfO.

An ab Initio and Density Functional Study of Al3As, Al3As-, AlAs3, and AlAs3-

The low-lying electronic states of Al3As, AlAs3, and the corresponding anions have been studied at the B3LYP and CCSD(T) levels using the 6-311+G(2df) one-particle basis set. The ground electronic states of Al3As- and Al3As have a cyclic planar C2v geometry. A 1A1-(C3v) state is located 0.2 eV above the 1A1-(C2v) ground state of Al3As. For AlAs3, a near degeneracy is found between the 1A1 (C2v) and the 1A‘ (Cs) lowest states while the anion, AlAs-, has a 2A‘ (Cs) ground state. The adiabatic electron affinities of Al3As and AlAs3 are calculated to be 1.8 and 1.9 eV, respectively. Electron detachment energies computed for the anions and the harmonic vibrational frequencies of both the anions and the neutral molecules are presented and discussed. It is anticipated that the computed data will aid future analysis and the interpretation of experimental photoelectron photodetachment spectra of these systems.