Vibration-rotation bands in ethane

The absorption spectrum of ethane was recorded at 0.014 cm^?1 resolution in the range 4500–6500 cm^?1 using a Fourier transform spectrometer and at room temperature. Eighteen bands could be identified and their type assigned. Upper state rotational constants are provided for the band at 5948.338 cm^?1 and Coriolis constants are obtained for most perpendicular bands. Vibrational assignments are suggested for the bands at 5948 cm^?1 (v7 + v10), 5914 cm^?1(v8 + v ₁₀+ v ₁₁), and 5852cm^?1 (v ₅+v ₁₀). All vibrational bands reported in the literature are gathered.     

Density functional theory study of homologous organometallic molecules of the [RhXL2]2 (X = Cl,Br, or I; L = CO,PH3, or PF3) type

Density functional theory generalized gradient approximation calculations, which were tested in our previous detailed study of [RhCl(PF₃)₂]₂ (Seuret et al., 2003, Phys. Chem. chem. Phys., 5, 268–274), were applied for a series of homologous organometallic compounds of the [RhXL₂]₂ (X = Cl, Br, or I; L = CO, PH₃, or PF₃) type. Various properties of the studied compounds were obtained. Optimized geometries of [RhCl(PH₃)₂]₂ and [RhCl(CO)₂]₂ are in very good agreement with available experimental data. Geometries of other compounds as well as other properties (thermochemistry of selected fragmentation channels, barriers to structural changes, frontier orbitals) which are not available experimentally were predicted. All the considered compounds are not planar. Enforcing planarity of the central [RhX]₂ moiety requires only a small energetic cost ranging from 2.2 to 3.9 kcal mol^?1. The analysis of frontier orbitals indicates that the metals provide the most favourable site for the electrophilic attack in all considered compounds. The analysis of the shape of the lowest unoccupied molecular orbitals indicates that the halogens and ligands provide the most favourable site for the nucleophilic attack for [RhCl(CO)₂]₂ or [RhCl(PF₃)₂]. For [RhBr(PF₃)₂]₂, [RhI(PF₃)₂]₂ and [RhCl(PH₃)₂]₂, the nucleophilic attack on the halogen is less probable. Except for [RhCl(CO)₂]₂, the least energetically expensive decomposition channel involves initial separation of ligands. For [RhCl(CO)₂]₂, its decomposition into the RhCl(CO)₂ fragments was found to be the least energetically expensive fragmentation reaction which is probably one of the reasons for the known catalytic activity of this compound.     

Study of anharmonic effects in the IR spectrum of a solution of CF<Subscript>3</Subscript>Br in liquid argon

The vibrational spectrum of CF₃Br with the natural abundance ratio of isotopologues is studied in solutions in liquid Ar at T = 90 K in the frequency range 4000–400 cm^?1 with a resolution of 0.1 cm^?1 for the concentration range 3.1 × 10^?7?6.3 × 10^?3 mol %. The parameters of the vibrational spectrum of the molecule are determined: the frequencies are measured accurate to ± 0.1 cm^?1, and the transition probabilities are found up to the fourth order inclusive. One hundred fifty absorption bands of CF₃Br are interpreted, including the bands belonging to all the isotope modifications of this compound; the halfwidths of these bands are determined. For all the fundamental frequencies, the isotope shifts are obtained. Vibrational ?-resonance is studied. Using the experimental data obtained and taking into account this resonance, a complete set of parameters describing the experimental frequencies with the error δ ≈ 0.3 cm^?1 was found. This set consists of 6 harmonic frequencies and 30 anharmonicity constants, including the constants r _ik related to vibrational ?-resonances.     

The effect of resonance interactions on the absorption spectra of (SF6)2 dimers in low-temperature matrices: Calculations and experiment

The IR absorption spectra of (SF₆)₂ dimers in Ar and N₂ matrices are investigated at 11 K. As a result of the resonance dipole-dipole interaction, the band of the triply degenerate vibration v ₃ is split into two components v _{X, Y} and v _Z. In comparison with the gaseous state, the splitting Δv = v _{X, Y} ? v _Z in the argon matrix decreases to 18.45 cm^?1, whereas, in the nitrogen matrix, the band v _{X, Y} is split into components v _X and v _Y, with the splitting being equal to δ ≈ 0.9 cm^?1. A model that takes into account the influence of the matrix on the spectra of dimers is developed. The model makes it possible to successively (i) calculate the resonance spectrum of an isolated dimer in terms of the model of local modes taking into account resonance interactions, (ii) determine with the help of the Monte Carlo method the structure of a matrix consisting of 512–1440 Ar (or N₂) atoms and a rigid (SF₆)₂ dimer, and (iii) take into account interactions of local dipole moments of a dimer with particles of the matrix in the approximation of dipole-induced dipole interactions. The model developed satisfactorily describes the experimental results. The calculated frequencies v _Z, v _X, and v _Y of a dimer in the matrix are shifted toward smaller frequencies as compared to the gaseous state, while the resonance splitting decreases virtually by 2 cm^?1. It is shown that, in an argon matrix with a symmetric arrangement of argon atoms nearest to a dimer, the splitting of v _{X, Y} proves to be smaller than 0.05 cm^?1. In a nitrogen matrix, this splitting increases virtually to 0.4 cm^?1.     

Computational studies of the halooxyhalocarbenes XOCX (X = F,Cl)

Ab initio calculations at the B3LYP, MP2, MP4 and CCSD(T) levels of theory were performed to predict the stability of the halooxyhalocarbenes, XOCX (X = F, Cl). The calculations indicate that the nonlinear FOCF molecule is stable with an energy 16 kJ mol^?1 below the energy of possible reacting fragments F₂ and CO. However, a nonlinear equilibrium structure for ClOCCl was located, but it was found to be about 192 kJ mol^?1 higher in energy than the energy of Cl₂ and CO. The charge distribution in these molecules was analysed using the atoms in molecules (AIM) method.     

Conformational equilibria in dihaloheptasilanes X2Si[SiMe(SiMe3)2]2 with X = F,Cl, Br,I: A Raman spectroscopic and quantum chemical DFT study

Equilibrium geometries, stabilities and vibrational wavenumbers for conformers of the dihaloheptasilanes X₂Si[SiMe(SiMe₃)₂]₂ with X = F, Cl, Br and I were calculated at the density functional B3LYP level employing 6‐311G(d) basis sets and SDD pseudopotentials for Br and I. Two spectroscopically distinct low‐energy conformers were located for all four heptasilanes with energy differences of 5.5, 4.7, 1.9 and 1.2 kJ mol⁻¹ for X = F, Cl, Br and I, respectively. Five more conformers were found for difluoroheptasilane and four for X = Cl, Br and I. They all have relative energies larger than 7.5 and up to 17 kJ mol⁻¹ and are negligibly populated at room temperature. Variable temperature solution Raman spectra (−70 to + 100 °C) in a wavenumber range typical for Si Si stretching vibrations (280‐350 cm⁻¹) confirm these results. For X = Br and I, no temperature effects at all could be observed as a very rapid inter‐conversion between the two low‐energy conformers, which is fast even on the time scale of Raman spectroscopy, occurs. For X = Cl, rapid inter‐conversion also occurs, and a third conformer could be detected at higher temperatures (50–100 °C). For X = F, intensity changes with temperature are consistent with the presence of two low‐energy conformers. Copyright © 2007 John Wiley & Sons, Ltd.     

Vibrational Spectra of Benzylidene Aniline,O-Hydroxybenzylidene O-Hydroxyaniline and its Complexes with Cu(II) and NI(II) Metal Ions

Abstract

The FTIR and FT Raman spectra of benzylidene aniline, and o-hydroxybenzylidene o-hydroxyaniline compounds in the solid state in the wavenumber (1800-200 cm^?1) are recorded. An assignment for nearly all fundamentals are proposed. Comparison of the spectra of trans stilbene and benzylidene aniline reveals that v N-Ph stretch for the latter compound is situated at 1368 cm^?1 in the IR spectra with medium intensity. for o-hydroxybenzylidene o-hydroxyaniline, the stretching modes v N-Ph, and v C-Ph are observed at 1356 and 1226 cm^?1 respectively. the two v O-Ph are observed as intense bands in the IR spectra at 1245 and 1278 cm^?1, respectively. the FTIR spectra of the o-hydroxybenzylidene o-hydroxyaniline complexes with Cu(II) and Ni(II) metal ions are also recorded and assigned.     

High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in axially symmetric coordination complexes

High-frequency and -field electron paramagnetic resonance (HFEPR) has been used to study several complexes of high-spin manganese(III) (3d⁴,S = 2): [Mn(Me₂dbm)X] and [Mn(OEP)X] (X = Cl^?, Br^?), where Me₂dbm^? is the anion of 4,4′-dimethyldibenzoylmethane and OEP^2? is the dianion of 2,3,7,8,12,13,17,18-octaethylporphine. These non-Kramers (integer spin) systems are not EPR-active with conventional magnetic fields and microwave frequencies. However, use of fields up to 15 T in combination with multiple frequencies in the range of 95–550 GHz allows observation of richly detailed EPR spectra. Analysis of the field- and frequency-dependent HFEPR data allows accurate determination of the following spin Hamiltonian parameters for these complexes: [Mn(Me₂dbm)Cl],D = ?2.45(3) cm^?1; [Mn(Me₂dbm)Br],D = ?1.40(2) cm^?1; [Mn(OEP)Cl],D = ?2.40(1) cm^?1; [Mn(OEP)Br],D = ?1.07(1) cm^?1 (E ≈ 0, andg ≈ 2.0 in all cases). Comparison of structural data with the electronic parameters for these and related complexes shows quantitatively the effects of axial and equatorial ligation on the electronic structure of Mn(III). These high-spin complexes can be employed as building blocks in the construction of single-molecule magnets. Thus the accurate determination and understanding of the electronic properties, best obtainable by HFEPR, of these monomeric units is important in understanding and improving the properties of the polynuclear single-molecule magnets which can be formed from them.     

High-resolution FTIR spectra of CH2 = CClF in the 930-1050 cm−1 region

The gas-phase infrared spectra of natural CH₂ = CClF have been measured in the v ₆ and 2v ₁₂ band regions (930–1050 cm^?1) by high-resolution Fourier transform spectroscopy at room temperature. 1-Chloro-1-fluoroethylene is a planar asymmetric rotor (κ = ?0.54) belonging to the symmetry point group C_s and the vibrations investigated of symmetry species A′ give rise to a/b-hybrid bands with contributions of comparable intensity from both the components.

The rovibrational analysis of the fine structure led to the identification of 1894 (J ? 73, K_a ? 20) and 718 (J ? 53, K_a ? 8) transitions for the v ₆ and 2v ₁₂ bands of the ³⁵Cl isotopic species, respectively. Using the Watson's A-reduction Hamiltonian in the I^r representation a set of accurate spectroscopic parameters for both the excited states u ₆ = 1 and u12 = 2 of ³⁵Cl has been obtained for the first time. Transitions of ³⁷Cl isotopomer could also be assigned in the Q branch region of the 2v ₁₂ overtone; the determined band origin shift of 0.782 cm^?1 towards the lower wavenumbers led to describing the v ₁₂ fundamental as a vibration mainly involving the CFCl bending motion.     

High-resolution FTIR spectrum of vinyl chloride: rovibrational analysis of the v 10 and v 11 fundamental bands

The Fourier transform gas-phase infrared spectra of the v ₁₀ and v ₁₁ bands of natural CH₂=CHCl have been measured with a resolution of 0.005 cm^?1 in the frequency range 820–1010 cm^?1. These vibrations of symmetry species A″ give rise to c-type bands and the transitions observed are characterized by δK _a = ±1 and δK _c = 0, ±2. Both J and K structures have been resolved in different subbranches and about 1800 (J ≤ 64, K _a ≤ 13) and 2800 (J ≤ 72, K _a ≤ 14) transitions for the v ₁₀ and v ₁₁ fundamentals, respectively, have been identified for the ³⁵Cl isotopomer. Combined analysis of the assigned data with the available ground state constants allowed the determination of the band origins, rotational and centrifugal distortion parameters for the v ₁₀ = 1 and v ₁₁ = 1 excited states of CH₂=CH³⁵Cl isotopic species. The molecular constants obtained account for slight perturbations in the v ₁₀ vibrational level.     

The ro-vibrational analysis of the v4 fundamental band of CF3Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

The v₄ fundamental band of CF₃⁷⁹Br and CF₃⁸¹Br, present in natural isotopic abundance, was investigated in the 8.3-μm region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5–1205.0 cm^?1, 1208.0–1210.1 cm^?1 and 1212.5–1214.5 cm^?1. The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm^?1. A Fourier transform infrared spectrum covering the entire spectral region of the v₄ band, between 1190 and 1220 cm^?1, was recorded at 298 K with a resolution of 0.004 cm^?1. The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v₄. In total, 4651 transitions were assigned to CF₃⁷⁹Br, 4047 to CF₃⁸¹Br, with J″_max? = K″_max?=80; of these, 3171 for CF₃⁷⁹Br and 2755 for CF₃⁸¹Br are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C_3v symmetry. The v₄ band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v₄ = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v₄ = 1 for CF₃⁷⁹Br and CF₃⁸¹Br were obtained. The bromine isotopic splitting amounts to 6.9 × 10^?3 cm^?1. In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.     

High-resolution rovibrational analysis of vibrational states of A2 symmetry of the dideuterated methane CH2D2: the levels ν 5 and ν 7 + ν 9

The infrared spectrum of the CH₂D₂ molecule has been measured in the region 900–1500?cm^?1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.0024?cm^?1 (FWHM, unapodized). Transitions belonging to the hot bands ν ₇?+?ν₉?ν ₇, ν₇?+?ν₉? ν ₉, ν₅?+?ν₇?ν₅, and ν₅?+?ν₉?ν₅ were extracted from the recorded spectra to determine the rovibrational energies of the A₂ symmetry vibrational states (v ₇?=?v ₉?=?1) at 2329.698?cm^?1 and (v ₅ ?=?1) at 1331.409?cm^?1. Vibrational energies as well as rotational and centrifugal distortion parameters of the (v ₇?=?v ₉=1) and (v ₅?=?1) states were determined that reproduce the experimental rovibrational energy levels of the (v ₇?=?v ₉?=?1) and (v ₅?=?1) vibrational states with a d _rms deviation of 0.0017 and 0.0006?cm^?1, respectively. The results are discussed in relation to the equilibrium structure of methane, which is redetermined here from the experimental data, and in relation to its potential hypersurface and anharmonic vibrational dynamics.     

Infrared spectrum of boron chloride (BCl)

The spectrum of the Δv = 1 band of BCl was measured between 828 and 870 cm^?1 with a tunable diode laser. The absorptions of the v = 1-0, 2-1, 3-2, and 4-3 transitions of BCl were observed in both a microwave discharge and a dc discharge through BCl₃. Spectra of ¹¹B³⁵Cl, ¹¹B³⁷Cl, ¹⁰B³⁵Cl, and ¹⁰B³⁷Cl were observed in natural abundance. A set of eight Dunham coefficients was determined by fitting the data for all observed isotopic species with the appropriate reduced mass factors. A BCl bond distance, r_e = 0.1715283(31) nm, was determined which agrees with the value derived from the electronic spectrum of BCl. The band center for the v = 1-0 transition of ¹¹B³⁵Cl is ν₀ = 829.4087(8) cm^?1.     

Franck-Condon Factors and r-Centroids for the (B [sbnd] X) and (C [sbnd] X) Bands of the 107Ag 109Ag Molecule

Arrays of Franck-Condon factors q(v′, v″) and r-centroids r(v′, v″) were computed using Morse potentials for C¹Π [sbnd] X¹Σ⁺ _g and B O⁺ _u [sbnd] X¹Σ⁺ _g bands of the ¹⁰⁷Ag ¹⁰⁹Ag molecule.     

High-resolution infrared spectrum of CHD279Br: ro-vibrational analysis of the ν5 and ν9 fundamentals

ABSTRACT

The high-resolution infrared spectrum of CHD₂⁷⁹Br has been investigated by Fourier transform spectroscopy in the range 700–900?cm^?1 at an unapodized resolution of 0.0035?cm^?1. This spectral region is characterised by the absorptions of the ν₅ (814.5185?cm^?1) and ν₉ (716.9649?cm^?1) fundamental bands, corresponding to H–C–Br deformation and CD₂ rocking modes, respectively. The ν₅ vibration of symmetry species A^′ gives rise to an a-/c-hybrid band with a predominant a-type component, while the ν₉ mode of A^′′ symmetry produces a b-type envelope. The spectral analysis resulted in the identification of 5290 (J^′?≤?63 and K_a^′?≤?13) and 1657 (J^′?≤?53 and K_a^′?≤?12) transitions for ν₅ and ν₉ bands, respectively. The assigned data were fitted using the Watson’s S-reduced Hamiltonian in the I^r representation and the v₅?=?1 and v₉?=?1 state parameters up to the quartic centrifugal distortion terms have been obtained. From spectral simulations the dipole moment ratio |Δμ_a/Δμ_c| of the ν₅ band has been determined to be 1.4?±?0.1 while the intensity ratio between ν₅ and ν₉ fundamentals has been estimated to have a value of 4.3?±?0.5.     

Regium bonds formed by MX (M═Cu,Ag, Au; X═F,Cl, Br) with phosphine-oxide/phosphinous acid: comparisons between oxygen-shared and phosphine-shared complexes

ABSTRACT

Regium bonds interaction between phosphine oxide (H₃PO), the trans phosphinuous acid (T-PH₂OH), the cis phosphinuous acid (C-PH₂OH) and MX (M═Cu, Ag, Au; X═F, Cl, Br) complexes were investigated by means of ab initio MP2/aug-cc-pVTZ method. For phosphinuous acid and MX complexes, two types of regium bonded interaction (trans and cis complexes) are observed and the two types of structures are very easily transformed from one type to another due to a low energy barrier. The molecular interaction energies are in the order of Au?>?Cu?>?Ag, F?>?Cl?>?Br and increase with the decrease of intermolecular distance R_int. Two resonance-type structures of P:M-X (ωI) ? P–M:X (ωII), O:M-X (ωI) ? O–M:X (ωII) are recognised by the natural resonance theory (NRT) and the natural bond orbitals (NBOs) analysis. The competition between ωI ? ωII resonance structures mainly arises from hyperconjugation interactions, in all phosphor-shared complexes, P–M:X resonance accounts for a larger proportion which leads to the covalent characters. All of complexes have been described in terms of their electron density properties.     

High resolution study of the v 7 + v 8 band of ethylene (C2H4) at 1889 cm-1

The v ₇ + v ₈ A-type band of C₂H₄ has been recorded between 1932 and 1847 cm^-1 with a resolution of 0·06 cm^-1. The transitions with K _-1 ? 8> and J ? 2>5 have been assigned. Although slight Coriolis resonances perturb the band, the analysis has been made easy through the use of an elaborate set of asymmetric top computer programmes. The band centre and a set of upper state constants have been obtained. With these constants, 288 observed upper state energy levels have been fitted with a standard deviation of 0·021 cm^-1.

Using very simple expressions, we have predicted all the resonance effects perturbing the levels of ethylene near 2000 cm^-1. This led us to the identification of the v ₄ + v ₈ and v ₈ + v ₁₀ combination bands in low resolution spectra.     

Electronic states and transitions of the TeX (X = C1, Br,I) radicals

Ab initio multireference configuration interaction calculations including spin-orbit coupling have been carried out for the first time for valence electronic states of the TeX (X = Cl, Br, I) radicals and compared with the results for the isovalent TeF and IO systems obtained earlier at a similar level of theoretical treatment. The calculated spectroscopic constants are in good agreement with experimental data in the rare cases when the latter are available. It is shown that the X² II(σ²π⁴π?³) ground state bonding becomes consistently weaker down the TeX group (calc. D_e, = 25480cm^?1 for TeF, 12 100cm^?1 for Tel) due to the more covalent character of bonding in the heavier radicals. The first excited state, A ⁴Σ^? (π?→ σ?), is calculated to be bound in all systems. It is split into Ω 1/2 and 3/2 components, with regular ordering in the Franck-Condon region, opposite to that of the ground X²II state. For larger internuclear distances, the A₁ ⁴Σ^? _1/2 state undergoes an avoided crossing with X₂ ²II_1/2, which causes a shoulder in the X₂ potential curve and also leads to a crossing between the A₁, and A₂ curves and large distinctions in their vibrational frequencies. The π? → σ? B²Σ^?, C²δ, and 1 ²Σ⁺ states are calculated to lie next in energy. They are all bound in the lightest of the TeX radicals, TeF, but successively lose their bonding character down the group. In contrast to oxygen monohalides, the 2²II(σ²π³ π?⁴) state has a repulsive potential curve. Electric dipole transition moments and radiative lifetimes have also been calculated for the low lying bound states in all systems. Most of them are found to be quite weak. The A^1,2 → X^1,2 spectra are dominated by parallel contributions, with the A₂ → X₁ being the strongest one. The T values for this transition are quite similar and lie in the 17–30 μs range. Radiative lifetime values for the B → X^1,2 transitions demonstrate very irregular behaviour for various, TeX radicals, due to strong admixture of A⁴Σ^? character to the X^1,2 states near the B²Σ^? potential minimum. The A^{1,2 4}Σ^? _1/2,3/2 and B²Σ^? _1/2 states of TeX (X = Cl, Br, I) still await their experimental observation.