Infrared spectra of hydrogen bonded crystals: Uracil

A theory of the infrared spectra of hydrogen bonds in molecular crystals of C$\text{5}\text{2}$h symmetry, containing, like uracil, four molecules and eight hydrogen bonds in the unit cell, is presented. The theoretical spectra are in good agreement in both the frequency and intensity distribution with experiment. The changes in the fine structure introduced by deuteration are quantitatively reproduced.     

The charge-charge flux-overlap model for the interpretation of atomic polar tensors and infrared intensities

The interpretation of infrared intensities using the concepts of atomic polar tensors divided according to contributions from charge-charge flux-overlap (CCFO) terms appears in general to be quite useful. Here we shall illustrate this analysis for the F and H atoms in chemically related molecules to show how their properties vary for CF, CH, OF and OH bonds as R varies in RCF, RCH and ROH molecules.     

Note on a theoretical interpretation of the isotopic ratio vOH/vOD versus vOH in isotopically diluted HDO molecules in solid hydrates

A simple intra- and inter-molecular potential for water molecules engaged in hydrogen bonding has been used in a one-dimensional approximation for a theoretical interpretation of the experimental correlation $\text{v}$_OH/$\text{v}$_OD versus $\text{v}$_OH in solid hydrates. The variation in the equilibrium OH(D) distance has also been considered.     

Computer plots of HOH normal modes depending on time

The combination of the antisymmetric and symmetric stretching vibrations of water is a decoupled OH vibration. It means the X₁₃ anharmonicity constant of HOH must be related with the X₃₃ anharmonicity constant of HOD. It is found that $\text{1}\text{2}$X₁₃(HOH)= X₃₃(DOH) = X(OH). Instead of the usual condition X_ik = 0 for i > k a new definition will be given for the anharmonicity constants: $\text{X}$_ik = $\text{X}$_ki. The X values of other molecules were compared with each other and it follows the general rule for a symmetric molecule m-M-m with m ? M: $\text{X}$₁₃ (mMm) = $\text{X}$₃₁ (mMm) = X (Mm).Computer plots of normal modes of the ν₁ + ν₃ combination depending on time show the rotation of the dipole moment derivatives vector. It is strongly different for H₂O and HOD and explains the different band intensities. We expect higher band intensities and X₁₃ values using IR light with rotating electric field vector.     

High-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d orbitals in the zinc and cadmium dihalides: Ligand field splittings and intensity variations

We have recorded the high-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d levels in gas-phase MX₂ molecules (M = Zn, Cd; X = Cl, Br, I). The d level spectra split into five peaks due to the combined effect of spin-orbit splitting and ligand field splitting on the d⁹ hole state, and the spectra have been fitted to a crystal field hamiltonian involving the cubic (C₄⁰) and non-cubic (C₂⁰) parts of the field from the halide ligands. Additional peaks in some spectra are due to vibrational splitting and configuration interaction. The ¦C₂⁰¦ value increases substantially from the chloride to the iodide for both Zn and Cd. Calculations of both the crystal field (C_{2 CF}⁰) and valence (C_{2 val}⁰) parts of C₂⁰ show that the increase in observed C₂⁰ is due to the C_{2 val}⁰ term attributed to the increase in covalency from the chlorides to the iodides. Shifts in the peak position due to the 2Σ_{$\text{1}\text{2 g}$} and 1Π_{$\text{3}\text{2 g}$} states from those expected on the ligand field basis. are attributed to slight bonding effects. These effecs cause a large discrepancy between calculated and observed C₄⁰ values. The intensities of the five Zn 3d peaks change markedly from HeI- to HeII-excited spectra. The Xα SW method has been used to calculate the intensities of the σ, π and δ 3d orbitals as a function of photon energy. These calculations show dramatic changes in intensity due. for example. to shape resonances. There is usually qualitative agreement between calculated and observed intensities.     

On the validity of level crossing calculations for 10B NQDR

The I=3 nuclear quadrupole resonance spectra (e.g. ¹⁰B) present peculiarities in comparison to I=1 or I=$\text{3}\text{2}$ spectra. Hence, the predictions of the simple level crossing theory with regard to the relative line intensities of I=3 DRLC spectra were checked by comparison with the experimental spectrum of borazine (B₃N₃H₆). If the experiment is properly conducted level crossing theory will be able to calculate the relative line intensities correctly in spite of the huge differences in the quantum-mechanical transition probabilities and other complications of the I=3 system. The relative line intensities should be fairly independent of the value of the asymmetry parameter.     

Untersuchung der Flammenemission von Metallhalogeniden und deren Nutzung zur Analytik der Halogene

Departing from the until now well known A and B systems of the indium and gallium halide emissions the authors tried to find further spectra of molecule bands in flames. The following band systems were observed: InF¹ (A, B and C systems), GaF¹ (A, B and C systems), A1F¹ (A system), T1C1¹, TlBr¹, TII¹ and the C systems of the GaCl, GaBr, InCl and InBr molecules.From the behaviour of the intensities of excited and nonexcited MeX species and the existence of InF-C bands (excitation energy 5.30 eV) in the hydrogen-nitrogen diffusion flame it could be derived that the excited state results from the reaction of metal and halogen atoms. Furthermore the experimental results of MeX intensity measurements indicate reactions of excited molecules with particles of flame gases. This is especially valid for the A and B systems of the indium and gallium halides (triplet states) which have as a result of the forbidden transitions a relatively long life time. Using other gas mixtures (Hr-air, propane-air) and observation of CuX and alkaline earth halide bands as well gave the possibility to set up a block diagram of optimum conditions for measuring the different MeX emissions.Examination of the analytical performance gave detection limits of 0.7 $\text{mg}\text{l}$ for F^?1 and about 4 $\text{mg}\text{l}$ for Cl^?, Br^? and I^? by means of InX emissions. The limits of the concentration ratios for the determination of traces were 1:640 (Cl^? in HBr) up to 1:60,000 (I^? in HF). The best determinations of other halogens are possible in HC1 and HF matrices.     

Magnesium ion mediated protonation of imines in acetonitrile

Addition of magnesium perchlorate to a solution of imine PhCHN-C₄H₉ ($\text{1}$) and diimine PhCHN(CH₂)₃NCHPh ($\text{4}$), in acetonitrile, results in the formation of the corresponding iminium salts due to traces of water present in the solvent. This conclusion is based upon infrared spectra of solutions of imines, iminium salts, deuterated iminium salts and mixtures of imines and magnesium perchlorate in acetonitrile, containing varying amounts of water. The results suggest that magnesium ion catalyzed reactions of imines in CH₃CN involve iminium intermediates.     

Excited triplet state spectroscopy in the infrared

A new method for the investigation of the infrared spectra of metastable $\text{excited}$$\text{electronic}$ states is presented. With a Fourier Transform infrared spectrometer as the probe and a CW Xe lamp source as the pump, the infrared spectrum of the lowest triplet state of triphenylene isolated in a N₂ matrix at 15K has been examined. CH out-of-plane wagging modes are prominent and shifted from their ground state frequencies. It is expected that when fully developed this method will provide important information on excited state force constants and potential energy surfaces.     

The observation of fine-structure transitions in the LMR spectrum of the SeD radical at 5.6 μm

Magnetic and electric dipole transitions between the ²Π_{$\text{1}\text{2}$} and ²Π_{$\text{3}\text{2}$} components of the ground state of SeD have been observed at 1770 cm^?1 in an LMR experiment using a CO laser. The measurements have been combined with other data from the EPR and far-infrared LMR spectra to determine parameters in the effective hamiltonian. A combination of these results with the analogous ones for SeH provides a determination of fundamental parameters relating to the spin-orbit and spin-rotation interactions.     

The magnetic circular dichroism spectrum of matrix-isolated TaO

TaO has been matrix-isolated in an argon matrix at 14 K and 24 K and studied spectroscopically in the visible region (300–850 nm). Both adsorption and magnetic circular dichroism (MCD) spectra have been recorded and analyzed. A determination of the total angular momentum quantum numbers (ω) for fourteen excited electronic states has been made. The g factors for the ground ²Δ_{$\text{3}\text{2}$} and excited ²φ_{$\text{5}\text{2}$} states have been determined from a moment analysis of the MCD and absorption spectra of the 450.3 nm band. The present study indicates the power of the combination of magnetic circular dichroism and matrix isolation for the assignment of excited electronic states of high temperature molecules.     

Synthesis and conformational analysis of 68,11-dihalo[5]metacyclophanes

The synthesis of the 8,ll-dihalo[5]metacyclophanes $\text{1b-1d}$ (halogen = chlorine or bromine) from 1,2-dimethylenecycloheptane ($\text{2}$) is described. Spin saturation transfer and line shape analysis of the temperature dependent ¹H NMR spectra showed $\text{1b-1d}$ to occur in two conformations A (85-89%) and B (15-11%, respectively). The conformation of the pentamethylene bridge was fully analyzed from vicinal proton coupling constants which obey the Karplus relation inspite of severe distortions of the carbon valence angles. The thermodynamic parameters of the ground and transition state were determined for the equilibrium between the conformers A and B and are discussed in terms of steric interactions in these highly strained molecules.     

The optical absorption and emission spectra of Cs2NaSmCl6

Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs₂NaSmCl₆. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, ⁶H_{$\text{5}\text{2}$} to cystal fi levels of ⁶H_{$\text{7}\text{2}$-$\text{15}\text{2}$}, ⁶F_{$\text{1}\text{2}$-$\text{11}\text{2}$}, ⁴G_{$\text{5}\text{2}$-$\text{9}\text{2}$}, ⁴F_{$\text{3}\text{2}$,$\text{5}\text{2}$}, ⁴I_{$\text{9}\text{2}$}, and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in ⁶H_{$\text{5}\text{2}$}→⁶F _{$\text{1}\text{2}$-$\text{9}\text{2}$} and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm³⁺)-ligand (Cl^?) interaction mechanisms. The E_u″(⁶H_{$\text{5}\text{2}$})→E′(⁶H_{$\text{1}\text{2}$}) E_u′(⁶F_{$\text{1}\text{2}$}) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs₂NaSmCl₆. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling O_h wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state.     

Norcembrene diterpenoids from pacific soft-corals of the genus sinularia (Alcyonacea; octocorallia)

Four new norcembrene diterpenoids, 2–5, have been isolated from several species of the soft-coral $\text{Sinularia}$ collected in Palau, Western Caroline Islands. These new compounds are closely related to a unique norcembrenolide, 1, previously reported from the Australian soft-coral $\text{Sinularia}$$\text{leotoclados}$. The structure assignments of these new compounds were provided by interpretation of spectral data, and the structures of norcembrenes 2 and 3 were confirmed by single crystal X-ray analysis.     

The chemistry of phenalenium systems XXXIII. The Dibenzo[de;thi]naphthacenyl dication and the dianon

The dibenzo[de;hi]naphthacenyl dication ($\text{4}$) and dianion ($\text{5}$) have been generated from a mixture of the corresponding precursor hydrocarbons. The pmr spectra of $\text{4}$ and $\text{5}$ indicated that the positive and the negative charges were found to be fully delocalized over the molecules, respectively, consistent with the C_2v-symmetry structures. The pmr chemical shifts of $\text{4}$ correlate well with the Hückel charge densities.     

The conformation of 4-t-butylcycloheptanone

The 400 MHz ¹H NMR spectra of two deuterated derivatives of 4-t-butylcycloheptanone ($\text{2}$ and $\text{3}$) provided ²J_HH values for the α-methylene protons on each side of the carbonyl group. The interpretation of their magnitude shows clearly that the carbonyl group is located at position 1 of the twist-chair conformation while the t-butyl group is located at position 4e.     

The infrared carbonyl band of ethyl haloacetates and rotational isomerism

The integrated intensities of the carbonyl band components of the following ethyl haloacetates, R-COOFt (R = CH₂Cl, CH₂Br, CHCl₂ and CHBr₂), have been measured at different temperatures. From these intensities, values of ΔH° for the equilibrium between the $\text{cis}$ and $\text{gauche}$ rotamers have been estimated. Ethyl haloacetates have been studied in both CCl₄ solution and in gas phase. The absolute values of ΔH° in solution are lower than in gas phase. Results obtained in gas phase indicate that the stability of the $\text{gauche}$ rotamer increases with the size of the halogen atom.     

Temperature effects in x-ray photoelectron spectra of paramagnetic cupric and iron complexes with anomalous magnetic properties

The temperature dependence of the XPS spectra of paramagnetic cupric and iron complexes with anomalous magnetic properties is studied. It was found that the XPS spectra of polynuclear complexes with antiferromagnetic interaction, such as cupric acetate, do not change with temperature, although their magnetic moments diminish essentially. The Fe 2p spectra of mononuclear iron (III) complexes with the spin multiplicity transitions S = $\text{1}\text{2}$ ? S = $\text{5}\text{2}$ exhibit temperature-dependent reversible alterations of shake-up satellite intensity which correlate with the spin state of the paramagnetic Fe(III) ion. The results obtained prove the mechanism of appearance of intensive shake-up satellites in XPS spectra of paramagnetic 3d element complexes, which relates shake-up excitations with the interaction of the photoelectron with unpaired valence 3d electrons during photoionization.     

Determination of atomic parameters from powder diffraction intensity ratios

The basis for a systematic use of intensity ratios is given in order to determine positional and occupational parameters. Given a series of N powder diffraction intensities, the matrix of intensity ratios is defined. Expressing them as vectors, it is shown that they form a subset of $\text{1}\text{2}\text{(N}{}^2\text{? N)}$ elements in a vectorial space with dimension N ? 1. Since any intensity ratio may be obtained from the product or division of other ratios, their vectorial representation is used to define a criterion for independence for a set of ratios, transforming the product in a sum of the corresponding vectors. Any set of N ? 1 independent ratios may be used in the determination of atomic parameters. In order to find the most suitable set, it is proposed to assign an index to each intensity ratio, which depends upon the difference between observed and calculated values and their derivatives with respect to the parameters to be determined. Then, an independent set of intensity ratios is chosen among those with higher indices, for each point of a convenient grid in the space of the parameters, finding the best set at each point. Finally, the best absolute set is defined as that with the minimum value of an agreement indicator between observed and calculated values. An illustrative example of the procedure indicated above is shown, and the results are compared with those obtained by other powder integrated intensity methods. In this work, comparison with the Rietveld profile refinement method is not considered.