Structure Of C2v Symmetry Research Articles

Accurate potential energy surfaces for the excited state of CF2 molecule

Multi-configurational self-consistent field and Multireference configuration interaction (MCSCF/MRCI) level have been carried out for the lowest two electronic potential energy surfaces (PESs) for excited state of CF2ã(3B1) in Jacobi coordinate. For getting the accurate global PESs, the authors used B-spline fitted method with 34816 potential energy points for each state. Four kinds of PESs in different angles and the significant avoided crossing point were discussed. We found that there are three important isomers and two transion states in the most possible isomerization process, which started from linear geometry to C2v symmetry structure. The needed additional reaction barrier energy is 0.813 eV for this process. In addition the electronic structures were discussed and the result was good agreement with experiment and former’s theoretical calculation works.

Theoretical study of Pu and Am tetracarbide molecules

The electronic structure and ground‐state molecular properties of Pu and Am tetracarbides have been investigated by relativistic multireference calculations using CASSCF/CASPT2 theory as well as by density functional theory in conjunction with relativistic pseudopotentials. The CASSCF/CASPT2 treatment has been extended by spin–orbit coupling effects for selected species using the CAS state‐interaction method. The five atoms can form various structural isomers, from which 12 ones have been identified in our study. The electronic ground state in both molecules corresponds to a planar fan‐type structure of C2v symmetry, in which the actinide atom is connected to a bent C4 moiety. The other structures are much higher in energy, the ones computed in this study appear between 250 and 1050 kJ/mol. The bonding characteristics in the most relevant structures have been analyzed on the basis of the valence molecular orbitals and natural bond orbital analysis. The most stable structures have been characterized by their spectroscopic (vibrational and electron) properties. © 2014 Wiley Periodicals, Inc.

Theoretical Study of Thorium and Uranium Tetracarbide Molecules

AbstractThe electronic structure and ground‐state molecular properties of neutral Th and U tetracarbides were investigated by relativistic multireference calculations using complete active space self‐consistent field/multiconfiguration second‐order perturbation theory (CASSCF/CASPT2) with an all‐electron basis set as well as by density functional theory (B3LYP) in conjunction with relativistic pseudopotentials. The former calculations were extended with complete active space state interaction (CASSI) calculations accounting for spin–orbit coupling. The four carbon atoms can be arranged in various forms around the actinide atom to result in ten structural isomers found altogether in our study. The electronic ground state in both molecules corresponds to a planar fan‐type structure of C2v symmetry, in which the actinide atom is connected to a bent C4 moiety. Three structures arise from various arrangements of C2 moieties around the Th and U, whereas six isomers contain a C3 moiety and a lone C bonded to the actinide. The latter CAnC3‐type structures are very high‐energy structures (over 200 kJ mol–1 with respect to the ground state). The bonding characteristics in the most relevant structures were analysed on the basis of the valence molecular orbitals and the natural bond orbital method. We evaluated and interpreted the vibrational and electronic spectra. The present computed data for UC4 suggest a revision of the assignment of a previously observed IR absorption band to a different isomer.

Concerted halogen bonding and orthogonal metal-halogen interactions in dimers of lithium formamidinate and halogenated formamidines: an ab initio study.

Dimers of lithium formamidinate, CH(NH)2Li, and halogenated formamidines, HN=CHNHX, (X=Cl, Br, or I) are used as model systems to investigate simultaneous N-X···N and N-Li···N interactions, in tandem with orthogonal Li···X interactions. Geometry optimizations and energy calculations for the dimers are examined with the MP2 method and the M06-2X hybrid functional and the aug-cc-pVTZ basis set (the aug-cc-pVTZ-PP basis set is used for the iodine atom). Both methods predict the formation of a planar structure of C2v symmetry, regardless of the identity of the halogen atom. In this structure, the identities of the constituent monomers are essentially lost. Accordingly, the N-X···N interactions emerge as a rather symmetric quasi-linear N···X···N, where the covalent N-X bond in the halogenated formamidine is replaced by a partly covalent N···X interaction. Formation of the C2v structure is also driven by a fairly linear N···Li···N interaction parallel to the N···X···N interaction, and a Li···X interaction orthogonal to both the N···X···N and N···Li···N interactions. The strength of the interactions increases with the size of the halogen. The robustness of the interactions suggests that the dimers studied here or suitable analogues may find diverse applications including their use as novel polymeric synthons.

Anharmonicity in the V2O3 molecule and thermodynamic properties of V2O3 in the gas phase

A quantum-mechanical calculation of the relative stability, structural parameters, and vibrational frequencies of V2O3 molecule isomers for different spin states was carried out using the BPW91/6-311+G(d, p) method. It was shown that the isomer with the Cs structure (nonplanar VOVO rectangle with an O atom attached to it) in the X5A″ electronic state possesses the maximum stability. The energy of the C2v symmetry structure was higher than the lowest energy by just 23 cm−1. It definitely indicated the impossibility of usage of the harmonic model in order to calculate the thermodynamic functions of V2O3 (g). A model is proposed based on which the energy levels and vibrational sums of states for this type of motion were calculated for the Cs → C2v → Cs transition coordinate. These data, as well as results obtained from quantum-mechanical calculations, were used to calculate the thermodynamic functions of V2O3 (g) in the temperature range of T = 100–6000 K. The calculations were performed with the five excited electronic states with energies from 1000 to 9000 cm−1 taken into account. A comparison with the data calculated in the “rigid rotator-harmonic oscillator” approximation was performed.

Relaxed energy and structure of edge dislocation in iron

With modified analytical embedded-atom method and molecular dynamics simulation, this paper simulates the strain energy and the equilibrium core structure of a〈100〉 edge dislocation in BCC metal iron on atomistic scale. In addition, the trapping effect of dislocation on vacancy is investigated as well. The results show that the equilibrium dislocation core is quite narrow and has a C2v symmetry structure. Calculated strain energy Es of the dislocation is a linear function of ln(R/2b) while R ≥ 5.16 Å (1 Å = 0.1 nm), in excellent agreement with the elasticity theory prediction. Determined core radius and energy are 5.16 Å and 0.62 eV/Å, respectively. The closer the vacancy to the dislocation line is, the lower the vacancy formation energy is, this fact implies that the dislocation has a trend to trap the vacancy, especially for a separation distance of the vacancy from dislocation line being less than two lattice constants.

Structure, Stabilities, Thermodynamic Properties, and IR Spectra of Acetylene Clusters (C2H2)n=2-5.

There are no clear conclusions over the structures of the acetylene clusters. In this regard, we have carried out high-level calculations for acetylene clusters (C2H2)2-5 using dispersion-corrected density functional theory (DFT-D), Møller-Plesset second-order perturbation theory (MP2); and coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] at the complete basis set limit. The lowest energy structure of the acetylene dimer has a T-shaped structure of C2v symmetry, but it is nearly isoenergetic to the displaced stacked structure of C2h symmetry. We find that the structure shows the quantum statistical distribution for configurations between the T-shaped and displaced stacked structures for which the average angle (|θ̃|) between two acetylene molecules would be 53-78°, close to the T-shaped structure. The trimer has a triangular structure of C3h symmetry. The tetramer has two lowest energy isomers of S4 and C2h symmetry in zero-point energy (ZPE)-uncorrected energy (ΔEe), but one lowest energy isomer of C2v symmetry in ZPE-corrected energy (ΔE0). For the pentamer, the global minimum structure is C1 symmetry with eight sets of T-type π-H interactions and a set of π-π interactions. Our high-level ab initio calculations are consistent with available experimental data.

Bent-core molecules with lateral halogen atoms forming tilted, synclinic and anticlinic, lamellar phases

Four homologous series of symmetric bent-core molecules containing lateral fluorine or iodine substituents in the branches were synthesised and studied. Depending on the central ring and the lateral substituent the studied compounds exhibit a B7 phase or B2 type phases with anticlinic (SmCAPA) or synclinic (SmCSPA) interlayer structures. For the SmCSPA phase the C2v symmetry structure is proposed, with regularly spaced anticlinic–ferroelectric interlayer boundaries. In the SmCAPA phase strong optical activity was detected, chiral domain segregation could be induced by applying a weak electric field.

Synthesis and characterization of triarylphosphine complexes of zinc(II) halides

AbstractBoth 1:1 and 1:2 complexes are formed by zinc(II) halides and triarylphosphines unless electronic and/or steric factors intervene. Tri‐p‐chlorophosphine (a weaker base than PPh3) forms only a 1:1 complex, whereas bulky tri‐(ortho‐substituted phenyl)phosphines do not react. The complexes ZnX2PR3 and ZnX2(PR3)2 have been characterized by elemental analyses, conductance, far‐IR and (in a few cases) Raman spectral studies. The Zn–X and Zn–P stretching and Zn–X bending vibrational frequencies have been assigned in the complexes with a pseudo‐tetrahedral structure of C2v symmetry. Copyright © 2003 John Wiley & Sons, Ltd.

Ab initio and Density Functional Study of Structure and Bonding of Cage Compounds Containing Boron, Phosphorus and Group 14 Atoms.

Ab initio and density functional calculations for five vertex cage compounds of the type P2(YB)2EH2, (E=C, Si, Ge, Sn, Y=H, H2N) using 6-311G++(d,p) and 3-21G++(d,p) basis sets, showed that they adopt a trigonal bipyramidal structure of C2v symmetry with the two phosphorus atoms occupying the apical position, the HB or NB groups residing in the trigonal basal plane. The theoretical results agree well with the experimental data for E=Si, Ge and Sn. For the carbon cage P2(HB)2CH2 this structure is a transition state and the minimum is a cage of Cs symmetry with a distorted B–B–C ring in the equatorial plane. Key structural parameters within the cages show a linear dependence on the covalent radii and the diffuseness of the orbitals of the heteroatom E. The results of the natural population analysis (NPA) and the values of nucleus independent chemical shifts (NICS) calculated reveal a bonding description very close to the idealized localized Lewis structure, in contrast to the parent P2(HB)3 cage. This is more pronounced in the case of the NH2 substituted cages.

Theoretical Analysis of Structures of Ga4N4 Clusters

The structures and energies of a Ga4N4 cluster have beencalculated using a full-potential linear-muffin-tin-orbitalmolecular-dynamics (FP-LMTO MD) method. We obtained twenty-fourstructures for a Ga4N4 cluster. The most stable structure weobtained is a Cs three-dimensional structure, the energy of which islower than that of the C2v symmetry structure proposed by Kandalamet al. [J. Phys. Chem. B 106 (2002) 1945] The calculated results showthat the isomer with an N3 subunit is preferred, supporting theprevious result made by Kandalam et al. We found that the moststable structure of Ga4N4 clusters presented semiconductor-likeproperties through the calculation of the density of states.

Ab initio and density functional study of structure and bonding of cage compounds containing boron, phosphorus and group 14 atomsElectronic supplementary information (ESI) available: optimized bond lengths and angles. See http://www.rsc.org/suppdata/nj/b3/b301191g/

Ab initio and density functional calculations for five vertex cage compounds of the type P2(YB)2EH2, (E=C, Si, Ge, Sn, Y=H, H2N) using 6-311G++(d,p) and 3-21G++(d,p) basis sets, showed that they adopt a trigonal bipyramidal structure of C2v symmetry with the two phosphorus atoms occupying the apical position, the HB or NB groups residing in the trigonal basal plane. The theoretical results agree well with the experimental data for E=Si, Ge and Sn. For the carbon cage P2(HB)2CH2 this structure is a transition state and the minimum is a cage of Cs symmetry with a distorted B–B–C ring in the equatorial plane. Key structural parameters within the cages show a linear dependence on the covalent radii and the diffuseness of the orbitals of the heteroatom E. The results of the natural population analysis (NPA) and the values of nucleus independent chemical shifts (NICS) calculated reveal a bonding description very close to the idealized localized Lewis structure, in contrast to the parent P2(HB)3 cage. This is more pronounced in the case of the NH2 substituted cages.

Theoretical Interpretation of the Photoelectron Spectra of Al3O2-and Al3O3-

Hartree−Fock (HF) and density functional theory (DFT) calculations have been used to determine the equilibrium geometries of the ground electronic state of Al3O2, Al3O3, and their corresponding negative ions. The calculated global minimum for Al3O2 has a “vee” shape of C2v symmetry with a (a1)1 2A1 configuration. A kite-shaped structure of C2v symmetry has been obtained as a local minimum with a (b2)1 2B2 configuration. The corresponding negative ions have also been found to be global and local minima, respectively, with (a1)2 1A1 and (b2)2 1A1 electron configurations. A higher energy trigonal bipyramidal D3h structure has been found with a 1A1‘ (e‘)4 electron configuration. For Al3O3-, the calculated global minimum has a bicyclic rectangular shape of C2v symmetry with a (b2)2 1A1 configuration, whereas the corresponding neutral Al3O3 with a (b2)1 2B2 configuration has been found to be a local minimum. On the other hand, a kite shape of C2v symmetry with a (a1)1 2A1 configuration has been found to be the global minimum of neutral Al3O3. The lowest triplet state of Al3O3- had a hexagonal shape of D3h symmetry with a (e‘)2 configuration. This triplet minimum has slightly higher energy than either of the singlet minima. Configuration interaction (CI) calculations have been performed using the DFT optimized geometries for the two lowest energy structures of Al3O2- and the two lowest energy structures of Al3O3- to determine the low lying vertical excited states of Al3O2 and Al3O3. Those results have been utilized to interpret the recently reported experimental photoelectron spectra of Al3O2- and Al3O3-. On the basis of the present CI results, the symmetry of the states involved in the photoelectron peaks have been assigned for both spectra.

An ab initio Hartree-Fock Investigation of Endohedral Sc@C82

Abstract The electronic structure of endohedral Sc@C82 with a C82 cage of C2v symmetry has been studied by ab initio Hartree-Fock (HF) calculations. The optimized position of Sc in the configuration of minimum energy is predicted to be on the two-fold axis of the fullerene cage. In the corresponding configuration Sc is above the center of a hexagon of site symmetry C2 . This structure of C2v symmetry is nearly degenerate with Cs and Ct structures with Sc slightly displaced from the center of the coordinated hexagon. The binding energy of the endohedral complex is larger than 3.55 eV. The ab initio HF data of the C2v topoisomer of the fullerene unit are compared with new experimental findings and HF results derived for the 3(C2) topoisomer of the C82 cage.

Rotational spectrum, H, F nuclear spin–nuclear spin coupling and structure of the furan–HF dimer

The rotational spectrum of the ground vibrational state of the hydrogen-bonded dimer furan–HF has been observed in the frequency region 6–18 GHz using molecular beam Fourier transform microwave spectroscopy (MB-FTMW). Accurate rotational and all quartic centrifugal distortion constants except ΔK have been obtained for this complex. Additionally, the Daa element of the 1HF nuclear spin–nuclear spin coupling tensor has been determined from the hyperfine structure present in all the observed transitions. The rotational parameters are consistent with a planar equilibrium structure of C2v symmetry for the dimer, with the HF subunit lying along the C2 axis of the complex.

Molecular and Electronic Structures of the Short-Lived Excited Triplet State of Tropone

Time-resolved electron paramagnetic resonance experiments on the short-lived T1 state of nonphosphorescent tropone were carried out using mixed crystals. Well-resolved hyperfine splittings due to allowed and forbidden transitions were observed at principal axes of the zero-field tensor. The spin density distribution, C−H bond angles, and the sign of the D value were deduced from the hyperfine spectra. It has been concluded that the T1 state of tropone mainly has a 3ππ* configuration and holds its molecular structure of C2v symmetry. The experiments and molecular orbital calculations indicate that the large Franck−Condon factor between the T1 and the S0 states arises from the change of the potential surfaces due to the antibonding character of the π* orbital at the C4−C5 bond in the T1 state.

The Structure of the Free MnF3 MoleculeA Beautiful Example of the Jahn−Teller Effect

A new high-temperature gas-phase electron diffraction analysis of manganese trifluoride, combined with high-level quantum chemical calculations, provides direct geometrical evidence of a Jahn−Teller distortion in a free molecule. The potential energy surface of the molecule was scanned extensively by computation at the SCF level. CASSCF and CASPT2 calculations established that of the many C2v symmetry stationary points on the potential energy surface the lowest energy ones are quintets. The global minimum is a quintet state of 5A1 symmetry. In this planar C2v symmetry structure there are two longer and one somewhat shorter Mn−F bonds, with two bond angles close to 106° and one bond angle of about 148°. The second lowest energy state was of 5B2 symmetry, which turned out to be a transition state with an imaginary b2 (in plane) bending frequency. A constrained planar structure of D3h molecular symmetry has appreciably higher energy than the 5B2 symmetry structure. The experimental data are in complete agree...

The ClO4 radical: Experiment versus theory

The chlorine tetroxide radical and its anion have been investigated with unrestricted Hartree–Fock, density functional and hybrid Hartree–Fock/density functional methods, perturbation theory, and coupled cluster methods. It is predicted that the minimum on the ClO4 radical potential energy surface corresponds to the 2B2 ground electronic state, a C2v-symmetry structure. The C3v structure identified experimentally lies a few kcal mol−1 higher energetically. A Cs symmetry structure lies very close energetically to the C2v minimum at some levels of theory. Adiabatic electron affinities, equilibrium geometries, harmonic vibrational frequencies, infrared intensities, isotopic shifts, and dipole moments are presented for all methods. Comparisons with recent experimental vibrational data for the radical are made. It is predicted that the C2v equilibrium geometry of the ground state is Re(Cl–O1)=1.502 Å, Re(Cl–O2)=1.424 Å, θe1=93.6° and θe2=114.2°. The adiabatic electron affinity of the ClO4 radical is predicted to lie near 5.2 eV.

Infrared absorption of cyclic- and trans-NaNO2 and KNO2 in solid argon

Sodium nitrite dispersed in solid argon exhibited infrared absorption at 1293.0, 1222.8, and 825.6 cm−1, corresponding, respectively, to symmetric and asymmetric stretching, and bending, modes of the NO−2 moiety in a bidentate planar cyclic structure of C2v symmetry (designated cyclic-NaNO2). After irradiation of the matrix sample with emission from the KrF laser at 248 nm, new lines at 1446.2, 1159.1, and 787.1 cm−1 were recorded. A sample containing Na15NO2 absorbed at 1272.1, 1198.2, and 821.7 cm−1 before irradiation; new lines at 1419.6, 1136.9, and 782.8 cm−1 were observed after irradiation. New lines observed after irradiation are assigned to sodium nitrite with a monodentate planar trans structure (designated trans-NaNO2). Ab initio calculations according to density functional theory at Becke3LYP/6-311+G* level predicted line positions, isotopic shifts, and relative IR intensities similar to those observed experimentally for both isomers. Similar results were obtained for cyclic-KNO2 at (1313.4, 1310.8), (1217.3, 1207.9), and (807.2, 809.5) cm−1 before irradiation, and for trans-KNO2 at (1412.4, 1413.2), (1171.0, 1178.2, 1176.4), and 783.1 cm−1 after irradiation at 248 nm; the numbers grouped in parentheses reflect line splitting.

Hydrogen bonding between the water molecule and the hydroxyl radical (H2O⋅HO): The global minimum

Ab initio quantum mechanical self-consistent-field (SCF) and single and double excitation configuration interaction (CISD) methods have been used in a new study of hydrogen bonding between the water molecule and the hydroxyl radical. The basis sets used are double-zeta plus polarization (DZP) and triple-zeta plus double polarization (TZ2P). The two energetically low-lying minima are 2A′ and 2A″ states, with hydrogen bonding occurring between the oxygen atom in the water molecule and the hydrogen atom in the hydroxyl radical; the 2A′ state has a slightly (∼0.3 kcal/mol) lower energy. The comparable planar C2v symmetry structure lies <0.1 kcal/mol higher in energy. The hydrogen bond distance H...O of the 2A′ is ∼1.94 Å, which is close to that of the water dimer. The ground state dissociation energy is 5.6 kcal/mol, which is larger than that of the water dimer. The predicted infrared spectra for these structures are also reported.