Spectrochimica Acta最新文献

The infra-red spectra (4000-400 cm⁻¹) of methyl-, ethyl- and n-propylmercapturic acids, and of the corresponding sulphoxides and sulphones are reported. Characteristic vibrations are identified, and some differences between the spectra of the compounds as solids and in solution are interpreted in terms of different conformations.

We have analysed the ultra-violet absorption spectrum of azoxybenzene into component bands. This analysis has enabled us to propose a new interpretation of the electronic transitions of azoxybenzene, which partially differs from those of earlier authors.

The infrared absorption spectra of monoglycine nitrate, diglycine nitrate, triglycine sulphate, their deuterated and ¹⁵N (glycine and HNO₃) substituted analogs have been investigated at room temperature and at liquid N₂ temperature. These data have been utilized to suggest the nature of the binding between the polyatomic units in the respective crystal lattices. Based on these studies a plausible switching mechanism in the ferroelectric phase of diglycine nitrate is proposed. The data on triglycine sulphate are consistent with the reported crystal structure and the proposed switching mechanism. There is no indication of any phase transition in monoglycine nitrate between room temperature and liquid N₂ temperature.

Methods are explored for separating areas of overlapping bands into parts useful for enthalpy calculations. These methods consist of arbitrary procedures wherein lines of demarcation are drawn vertically at peak maxima or at the minimum between the peaks. Possible errors in the enthalpies thus obtained are examined by using Lorentzian or Gaussian band profiles as models. It is shown that, in general, the errors for these two profiles are in opposite directions and that they tend to cancel for real bands.

The infrared absorption spectra of glycine, mono- and di-glycine hydrochlorides and hydrobromides, their deuterated analogs and the ones containing ¹⁵N substituted glycine have been investigated from 3500 to 250 cm⁻¹ at room temperature as well as at liquid N₂ temperature. The spectra of the equilibrium mixtures containing the species (i) NH₃⁺CH₂COO⁻, (ii) NH₂⁺DCH₂COO⁻, (iii) NHD₂⁺CH₂COO⁻ and (iv) ND₃⁺CH₂COO have been discussed in terms of the vibrational modes of the groups NH₃⁺ (NH₂D⁺, NHD₂⁺, ND₃⁺), CH₂, COO⁻ and the skeleton CCN⁺ in the light of the effect of the coupling of vibrations on the absorption characteristics. The region 3200-1800 cm⁻¹ shows bands which seem to represent characteristic N⁺H⋯O/N⁺D⋯O bond properties and the Fermi resonance between N⁺H(N⁺D) stretch and the overtones/combinations (believed to be the cause of the complexity of this region) does not appear probable as revealed by our deuteration studies.

The spectra of monoglycine hydrochloride and hydrobromide indicate a dimer formation between two glycinium units (NH₃⁺CH₂COOH) through very strong hydrogen bonds (OH⋯O). The spectral data on diglycine hydrochloride and hydrobromide are consistent with the reported crystal structure.

The infra-red active metal-chlorine vibrational modes of compounds containing the (Mo₆Cl₈)⁴⁺ and (W₆Cl₈)⁴⁺ cores have been studied above 200 cm⁻¹. Two bands associated with vibrations of the cage are observed in all cases, and the correlation between their energies and the presence of other ligands is discussed.

It has been found that pentafluorophenol (PFP) forms hydrogen-bonded complexes with triphenylphosphine oxide (TPPO) of the type 1:1, 2:1 and 1:2. The K_ass, ΔF, ΔH and ΔS values for the various complexes have been determined.

The infra-red spectra in the OH stretching vibration region for mixtures of various proton acceptors with PFP in carbon tetrachloride have been compared with the corresponding spectra using respectively phenol, pentabromophenol or pentachlorophenol as proton donor.

The infrared intensifies of the two low-frequency fundamentals of hexafluorobenzene have been measured in the vapor phase, and the value of the intensity of the Fermi doublet at 1000 cm⁻¹ has been checked. The intensity of the 317 cm⁻¹ band is very low, contrary to the estimate made by STEELE and WHIFFEN. Although both the low-frequency bands show the PQR structure of a parallel vibration, estimation of the PQR spacing expected for this molecule confirms the assignment of the 317 cm⁻¹ band to the e_1u fundamental, ν₂₀, made by STEELE and WHIFFEN. The CF bond moments are presented, together with a discussion of the nature of the bond moment hypothesis and an estimate of the vibronic effects to be expected in this molecule.

The Bilot and Kawski [1] equation, relating Stokes shift to solvent parameters, was applied to the electronic spectra of aromatic amines in various solvents. The equation was found to be in good agreement with the experimental data. In addition, the effect of hydrogen-bonding between solvent and solute was studied. The deviations of these systems from the theoretical equation provided an estimate of the energy of the specific interactions, which were found to be consistent with hydrogen-bond energy values. The theoretical significance of these results is discussed.

Infrared liquid and solution spectra were recorded over the range 400–3800 cm⁻¹ at temperatures ranging from 25°C to −100°C for CH₃OP(S)Cl₂, CD₃OP(S)Cl₂, and CH₃OP(O)Cl₂. This study of infrared spectra at several temperatures adds support to a previous conclusion that the absorption bands of ν_PO and ν_PS appear as doublets due to the existence of rotational isomers. In addition, it is shown that the absorption bands of several fundamentals also appear as doublets in the infrared spectrum due to the presence of rotational isomers. Also, the study of the infrared spectrum of CD₃OP(S)Cl₂ has enabled a definite assignment for the fundamentals due to CH₃ and CD₃ groups and the fundamentals for the COPCl₂ skeleton, which occur in the 400–3800 cm⁻¹ region of the spectrum.