C2v Point Group Research Articles

The electronic structure and stability of localised defects in semiconductors. I. Theory

In this the first in a series of two papers the authors provide a detailed exposition of a self-consistent symmetrised matrix method which is well suited to the study of localised defect systems in diamond-like and zincblende semiconductor crystals. The technique requires the full exploitation of the defect symmetry and they show how a group theoretical analysis can be used to great advantage for defects with Td, D2d and C3v point-group symmetries. When implemented, the technique is equivalent to a finite-cluster method employing many hundreds of atoms-typically between 300 and 1400.

Investigation of the possible pathways for magnetic exchange interactions in homobinuclear chelates of naphthazarin

Homobinuclear complexes of the binucleating naphthazarinato ligand of the general formula [Formula: see text] where M = Cu, Ni, and Zn, C10H4O4 = naphthazarinato ligand, and C10H8N2 = 2,2′-bipyridyl, have been prepared and studied. In these complexes the naphthazarinato ligand, acting as a bridging unit between the two metal centers, supports the propagation of magnetic exchange interactions through its extensive π-electron system. The spectroscopic and magnetic data of the compounds showed that each metal ion is surrounded by two oxygen and two nitrogen donor atoms in a nearly tetrahedral configuration (C2v point group) with the naphthazarinato ligand adopting a centrosymmetrical structure of C2h symmetry. The room-temperature magnetic data of the copper(II) and nickel(II) homobinuclear chelates (1.32 and 1.73 BM per metal ion at 8000 G, respectively), as well as the slight decrease of the magnetic moments as the magnetic field strength decreases are indicative of the operation of antiferromagnetism in these chelates. Quantum mechanical calculations of the Hückel LCAO-MO type improved by ω-technique have been used to provide a qualitative guide to the possible pathways for the superexchange processes observed in the tetrahedral copper(II) and nickel(II) chelates, as well as to explain qualitatively why there is no antiferromagnetic interactions propagated by the bridging naphthazarinato ligand in analogous homobinuclear chelates with other coordination geometries such as square planar, square-pyramidal, trigonal bipyramidal, and octahedral.

The weakly exothermic rearrangement of methoxy radical (CH3O⋅) to the hydroxymethyl radical (CH2OH⋅)

Although the CH3O⋅ and CH2OH⋅ radicals have long been considered critical intermediates in combustion and atmospheric processes, only very recently has the potential significance of the isomerization CH3O⋅→CH2OH⋅ been appreciated. This isomerization and related aspects of the CH3O⋅/CH2OH⋅ potential surface have been studied here using nonempirical molecular electronic structure theory with moderately large basis sets and with incorporation of electron correlation. The vibrational frequencies of CH3O⋅, CH2OH⋅ and seven other stationary points on the potential energy hypersurface have been predicted, both to compare with results from spectroscopy and to provide estimates of zero-point vibrational corrections. In general, there is reasonable agreement with those vibrational frequencies of CH3O⋅ and CH2OH⋅ which are known from experiment. Our ab initio calculations predict that CH3O⋅ lies 5.0 kcal mol−1 higher in energy than CH2OH⋅ with a barrier to rearrangement to CH2OH⋅ of 36.0 kcal mol−1. Rearrangement of CH3O⋅ to CH2OH⋅ via a dissociation–recombination mechanism is energetically more costly (by 6.1 kcal mol−1). The Jahn–Teller distortion of CH3O⋅ from point group C3v is described in some detail. Barriers to inversion and rotation in CH2OH⋅ are predicted and compared with the results of ESR experiments. Finally, the dissociation of CH3O⋅ and CH2OH⋅ to yield formaldehyde plus H⋅ are each predicted to involve modest reverse activation energies.

Darstellung und spektroskopische Charakterisierung von Tetrachloro- und Tetrabromo-Oxalatoiridaten(IV) / Preparation and Spectroscopical Characterization of Tetrachloro- and Tetrabromoiridates(IV)

On treatment of [IrX6]2- with oxalate in aqueous solution at first [IrX4OX]3- (X = Cl, Br) is formed, which after extraction with pentylammonium ions into CH2Cl2 can be oxidised by X2 to give the corresponding pure Ir(IV) complexes [IrX4OX]2-. The IR and Raman spectra are assigned according to point group C2V- The UV/VIS absorption spectra show strong CT bands of transitions from "(π + σ)tlu"- and "πt2U"-ligand niveaus to t2g 5 (IrIV). These are split into three components by spin-orbit coupling and corresponding to the different groups of ligands: Xtr 2, Xc 2, ox. The spectrum of (TBA)2[IrBr4OX] recorded at 10 K is highly resolved, showing a splitting of the Brtr 2 → Ir(IV) and Bc 2 → Ir(IV) transitions by 1000-1400 cm-1. In the NIR-region two d-d-transitions are observed superimposed with a fine structure by coupling with vibration modes

Two-photon Excitation Spectra of 1-Azabicyclo[2.2.2]octane and Trimethylamine

Abstract The two-photon fluorescence excitation spectra of 1-azabicyclo[2.2.2]octane (ABCO) and trimethylamine were measured in the excitation wavelength range of 410–520 nm. The effect of the polarization (linear or circular) indicates that the symmetries of the upper states are \ ildeA1A1, \ ildeB1A1, and \ ildeC1E for ABCO while \ ildeA1A1 and \ ildeB1E for trimethylamine in C3v point group approximation. Rotational envelopes for the sequence structures are calculated forcircularly and linearly polarized light excitation and are in good agreement with experiment.

Darstellung und Schwingungsspektren von Chloro-Bromo-Platinaten(IV) einschließlich der Stereoisomeren / Preparation and Vibrational Spectra of Chloro-Bromo-Platinates(IV) Including Stereoisomers

The mixed chloro-bromo complexes [PtClnBr6-n]2-, n = 1-5, are separated by ion exchange chromatography on diethylaminoethylcellulose. The separation of corresponding stereoisomers for n = 2, 3, 4 is not possible. Due to the stronger trans-effect of Br compared with Cl, on treatment of [PtBrß]2- with Cl- in the presence of Br2 nearly pure cis-isomers, and by reaction of [PtClsBr]2- and cis-fPtC^Bro]2- with Br~/Br2 completely pure transisomers are formed. The stereoselectivity of the successive ligand exchange reactions is better than in corresponding series of Re, Os and Ir. The highly resolved vibrational spectra allow the distinction of the mixed ligand complexes as well as the estimation of purity of the isomers. All allowed stretching frequencies are observed and assigned according to point groups D4h, C4V, C3V and C2V. Especially in the ν(Pt-Br) region it is possible to distinguish bands arising either from symmetric Br-Pt-Br or asymmetric Cl-Pt-Br axes. The UV/VIS spectra exhibit systematic hypsochromic shifts on the successive exchange of Br-ligands by Cl. A critical discussion of the literature concerning chloro-bromo-platinates- (IV) shows the importance of effective separation processes for the isolation of pure mixed ligand complexes

The single crystal electronic spectra of cis-octahedral nickel(II) diamine complexes at 10 K

The single crystal polarised spectra, at 10 K, of a series of nickel(II) complexes containing the cis-chromophore NiN4O2 are reported. The four N ligands are provided by the diamines N,N′-diethylethylenediamine or meso-stilbenediamine, and the two O ligands by chelating nitrate or nitrite ion. The spectra are assigned in the point group C2v(III). The energies are calculated within the Normalised Spherical Harmonic Hamiltonian and the Orbital Angular Overlap formalisms. The parameters so derived are consistent with previous experience obtained with trans-analogs once the small bite of the chelating nitrite ligand is accounted for.

Identification and geometry of dimers of phosphine and the hydrogen halides HCl and HBr from their rotational spectra detected by pulsed-nozzle, fourier-transform microwave spectroscopy

The rotational spectra of dimers (PH3,HX) formed by phosphine with the hydrogen halides (X = Cl and Br) have been detected by pulsed-nozzle, Fourier-transform microwave spectroscopy and have been interpreted in favour of a dimer gemetry belonging to the C3v point group, with HX lying along the C3 axis of PH3 and oriented so that it forms a hydrogen bond to the phosphorus atom.

A unimolecular reaction ABC→A+B+C involving three product molecules and a single transition state. Photodissociation of glyoxal: HCOHCO→H2+CO+CO

Following an earlier proposal [Y. Osamura and H. F. Schaefer, J. Chem. Phys. 74, 4576 (1981)], the unimolecular reaction HCOHCO→H2+CO+CO has been examined via nonempirical molecular electronic structure theory. Specifically, the constrained symmetric (point group C2v) transition state for this ABC→A+B+C reaction has been located at several levels of self-consistent-field (SCF) theory. Four different basis sets of contracted Gaussian functions were used: an STO-3G minimum basis, the small split valence 3-21G basis, the standard C(9s 5p/4s 2p) double zeta (DZ) set, and a double zeta plus polarization (DZ+P) basis. Vibrational analyses of the four stationary point structures (all of which are geometrically similar) yield a remarkable variety of results. The STO-3G stationary point has three imaginary vibrational frequencies, 3-21G has one imaginary frequency (and thus is a genuine transition state), while the DZ and DZ+P structures yield two imaginary vibrational frequencies. For the latter two cases, one of the two imaginary vibrations is a very small bending frequency, while the larger frequency clearly connects glyoxal with the three products H2+CO+CO. This suggests the existence of a slightly nonplanar true transition state. To our knowledge such a unimolecular transition state is without precedent. Configuration interaction (CI) suggests that the barrier for this ABC→A+B+C reaction is competitive with that for HCOHCO→H2CO+CO.

Dynamic nonlinear Jahn–Teller effect of the type E ⊗ ϵ

AbstractBy applying the projection operator method it is shown that the complicated Hamiltonian of a E ⊗ ϵ JT system with nonlinear coupling coefficients can be written in terms of two Hamiltonians which are simple to handle and transform according to irreducible representations E, A1, and A2 of C3v point group. A variational approach is then used to calculate the ground state energy, using the Hamiltonian that transforms according to E, as an explicit function of the linear and nonlinear coupling parameters. The energies calculated in the strong coupling limit are finally compared with the corresponding previously calculated energies.

Analytic configuration interaction gradient studies of SH4, sulfurane

The potential energy surface of SH4, the prototype sulfurane, has been examined in light of previous theoretical studies suggesting that there may be two distinct energy minima. The first of these has the four H atoms in roughly octahedral positions, as in the experimentally known SF4 molecule, and belongs to point group C2v. The second isomer is square pyramidal, point group C4v. Molecular electronic structure theory has been applied using basis sets of triple zeta (TZ) and triple zeta plus polarization (TZ+P) quality. Configuration interaction (CI) including in some cases all single and double excitations was carried out and geometries optimized via newly developed analytic CI gradient techniques. At the TZ SCF and TZ CI levels of theory there are both C2v and C4v relative minima, separated by +2.4 and −1.6 kcal, respectively. However, using the more complete TZ+P SCF and TZ+ P CI methods, the C2v minimum disappears, leaving only the C4v minimum. Geometries corresponding to the expected C2v minimum lie about 6 kcal above the square pyramid structure. The C4v mimimum lies 74.6 kcal above separated H2S+H2 at the TZ+ P CI level of theory, and this is reduced to 72.4 kcal when the effects of higher excitations (unlinked clusters) are considered. Harmonic vibrational frequencies have been predicted at the three simpler levels of theory to prove the proposed designations of the various stationary points. For the square pyramidal SH4, the predicted frequencies are quite sensitive to basis set, as might be expected for an extremely flat potential energy surface such as this. The square planar geometry lies only slightly above the square pyramid, which faces a barrier of 2.3 kcal to inversion. The transition state for dissociation via SH4→SH2+H2 was also located at several levels of theory and has an interesting structure. The barrier to dissociation is ∼46 kcal and the activation energy ∼42 kcal, suggesting that SH4 should be a ’’makable’’ molecule.

Darstellung und spektroskopische Charakterisierung von Tetrakis (chloro -iodo ) oxalato -osmaten (IV )/Preparation and Spectroscopical Characterisation of Tetrakis(chloro-iodo)oxalato-osmates(IV)

Abstract On treatment of [OsI4ox]2- with Cl- the mixed complexes [OsClnI4-nox]2-, n = 1, 2, 3, are formed. The isolation and complete separation of the differently coloured geometric isomers is achieved by ion exchange chromatography on diethylaminoethyl cellulose. The IR and Ra spectra are assigned according to point groups C2v, Cs, C1. The mutual influence of ligands, especially by the high trans effect of I, is indicated by shifts of the distinct vibrational and electronic bands. The observed splittings of I→Os transitions are attributed to the different groupings I-Os-I, I-Os-Cl, and I-Os-O, important for the distinction of stereoisomers. The CT-bands as well as the d-d-transitions show batho-chromic shifts with increasing number of I-ligands. Up to five spin-orbit components in the NIR region are well resolved. The assignment is improved by the electronic Ra spectra. The fine structure of some d-d-bands originates from coupling with symmetric vibrational modes.

Study on ferrous phosphites from the point of view of hydrogen bonding

Ferrous phosphites FeHPO3·3 H2O, FeH2P2O5, FeH4P2O6·1/2 H2O and FeH10P4O12·4 H2O were studied using X-ray powder patterns, thermography, electron reflectance spectroscopy, magnetic susceptibility measurements andRaman and infrared molecular spectra. The results obtained indicate that all the phosphites studied contain an approximately octahedral coordination sphere consisting of oxygen atoms, which produces a weak crystal field around the iron atom. Phosphite FeHPO3·3 H2O contains an HPO32− anion with the symmetry decreased from point groupC3v toCs. Ferrous diphosphite FeH2P2O5 contains a non-linear P−O−P bond with a valence angle of 159°. The hydrogen bonds between the water molecule and the HPO32− anion indicate a positive hydratation of the phosphite anion. Medium-strong or strong hydrogen bonds, 258–270 pm long, correspond to mutual interactions of the anions in the crystal lattice of hydrogenphosphites. Hydrogen bonding in hydrogenphosphites causes a decrease in theDq values.

Infrared absorption spectra of 2,3- and 3,5-dichloroaniline

The infrared absorption spectra of 2,3- and 3,5-dichloroanilines have been recorded in the region 250–4000 cm−1. The spectra of the latter are recorded in solid phase (KBr and Nujol mull) and in CS2/CCl4 and CHCl3 solutions while that of the former in thin film only. The spectra have been analysed assuming C 3 and C2v point group symmetry respectively and a tentative assignment of the observed bands to different fundamental modes has been made.

The fluorescence excitation spectrum of chromyl chloride (CrO2Cl2) cooled in a free jet expansion

The fluorescence excitation spectrum of CrO2Cl2 in a free jet has been studied using a single mode tunable CW dye laser. Spectra were recorded for the A4 (origin), A5, and D5 bands. Sequence congestion has been entirely eliminated and detailed rotational structure of the bands observed for the first time. Assignment of the A4 origin band indicates the excited state to be B1 in vibronic symmetry under the C2v point group. The best least squares fit rotational constants are: A″=0.1073±0.0002 (cm−1); A′=0.0910±0.0003 (cm−1), B″=0.0620±0.0004 (cm−1); B′=0.0659+0.0003 (cm−1); C″=0.0521±0.0010 (cm−1); C′=0.0524±0.0010 (cm−1). Assignment of the D5 band indicates it is based on the same electronic transition but involves a symmetric vibration in the excited state. Possible geometries for the ground and excited states are also reported.

Theoretical study of the electronic structure of diazomethane

The least-energy dissociation path of the ground state of CH2N2 was determined from ab initio calculations using in a complementary way basis sets of minimal size (STO-3G) and double-zeta (DZ) quality. The results indicate that the least-energy point of attack of the N2 molecule on CH2 (1A1) is roughly perpendicular to the molecular plane (93 °), the C and N atoms being almost co-linear (angle C-N-N:203 ° with outermost N atom pointing away from CH2). The potential barrier of ∼ 1.2 eV found previously on the C2v dissociation path, disappears completely along the least-energy dissociation path (point group Cs (out-of-plane)). These findings corroborate the Woodward-Hoffman rules for this process since the outermost orbitals of the two intersecting states found in point group C2v (...2 b1 and ...8 a1) both correlate to the same irreducible representation (10 a) in point group Cs (out-of-plane). Larger basis set calculations (DZ + polarization functions on all centers, 3 dc and 3 dN developed here), were also carried out on CH2N2 (1A1,3A2 and1A2) at the1A1 equilibrium geometry and on CH2 (3B1) and N2 (1Σg+) at their respective equilibrium geometries. These calculations, together with consideration of correlation energy differences, yield D00 (CH2N2,1A1) = 19 kcal/mole and vertical excitation energies of 67 and 73 kcal/mole for the3A2 and1A2 states respectively. The latter value is in good agreement with the measured experimental value: 72.4 kcal/mole corresponding to the maximum of intensity in the1A2←1A1 absorption band. © 1977 Springer-Verlag.

The Vibrational Spectra of Tetracyanothiophene

Abstract The polarized infrared and far-infrared spectra of the tetracyanothiophene (TCNT) crystals were recorded by means of the normal and oblique incidence of radiation upon the (001) and (20\bar1) sample planes. The Raman spectra of the powdered sample and of a saturated solution in acetonitrile or 1,2-dichloroethane were also obtained. The observed bands were experimentally classified into the symmetry species of the free molecule (the point group C2v) under the assumption of an oriented gas model. Assignments of the observed bands to individual fundamental vibrations were carried out with the aid of the spectral data of the analogous molecules and the normal coordinate analysis of the in-plane vibrations, which was made with a modified Urey-Bradley force field.

Komplexchemie polyfunktioneller Liganden, XXXVIII. Präparative und schwingungsspektroskopische Untersuchungen zum Reaktionsverhalten von Mn2(CO)10 gegenüber dem tritertiären Phosphin 1.1.1-Tris(diphenylphosphinomethyl)äthan.

Decacarbonyldimanganese reacts with the tritertiary phosphine 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) to give the ionic complex [Mn(CO)3triphos][Mn(CO)5]. Treatment of [Mn(CO)3triphos][Mn(CO)5] with Na[B(C6H5)4], HClO4 and NH4PF6 yields the manganese(I) salts [Mn(CO)3triphos]Y (Y = B(C6H5)4, ClO4, PF6). The IR (2100-300 cm-1) and FIR spectra (350-200 cm-1) of all compounds are reported. Based on Raman polarization data the assignment of the v(CO) (A1 + E), δ(MnCO) (A1 + 2 E), v(MnC) (A1 + E) and v(MnP) (A1) modes was possible for the coordination polyhedra cis-Mn(CO)3P3(point group C3v). The v(MnP) (E) mode was unobserved due to its very low frequency.

Vibrational Assignments of Some Monosubstituted Pyridines

Abstract The infrared spectra of 2-(ortho) and 4-(para) vinyl- and ethyl-pyridines have been analysed in the region 400–4000 cm−1 in liquid phase. The bands obtained are discussed assuming the molecules under Cs and C2v point groups. The group sensitive fundamentals are compared with those of similar molecules reported in the literature.

Theoretical study of the electronic structure of diazomethane

Ab initio calculations of the dissociation process CH2N2 → CH2 + N2 are presented. Calculations were made on the ground 1A1 state as well as on the first few excited states (3B1, 1B1, 1A1*) necessary to the description of the dissociation mechanism in point group C2v symmetry. The variation of energy was determined as a function of the parameters RCH-RNN and θHCH at several RCN values. Most results were obtained by using a basis set of Gaussian lobe functions contracted to “double-zeta” accuracy. A few calculations were made with the addition of polarization functions on all centers. The equilibrium geometry of the ground state, determined from coupled quadratic equations in the molecular parameters, is in satisfactory agreement with experimental values. The dissociation paths on the potential energy surfaces were determined. The locus of intersection points of the two 1A1 states is described; the avoided crossing of the two potential surfaces was determined from CI calculations based on an “intermediate” Hamiltonian. The geometric and electronic rearrangements due to dissociation as well as the bonding characteristics of the orbitals are discussed.