G. Paliani

Vibrational spectrum of sodium nitroprusside. Normal coordinateanalysis for the Fe(CN)5NO2− ion

Abstract The analysis of the infrared and Raman spectra of Na 2 [Fe(CN) 5 NO] · 2H 2 O has led to an assignment of the fundamental vibrations of the Fe(CN) 5 NO 2− ion which is supported by studies of the infrared spectra of Na 2 [Fe(CN) 5 15 NO] · 2H 2 O, Na 2 [Fe(CN) 5 NO] · 2(H,D) 2 O and Na 2 [Fe(CN) 5 NO]. A normal coordinate treatment (using a diagonal symmetry force field) has been carried out on the basis of a C 4v symmetry model for the anion. The significance of the resulting valence force constants is briefly discussed.

BRILLOUIN SPECTRA AND VIBRATIONAL-TRANSLATIONAL ENERGY EXCHANGE IN LIQUID ACETONITRILE

Polarized light scattering experiments in the GHz frequency range (Rayleigh–Brillouin spectra) are reported for liquid acetonitrile. Hypersonic velocities and absorption coefficients have been measured as a function of temperature and of transferred wave vector. The plots of these quantities versus frequency show characteristic dispersion which is indicative of relaxation phenomena. The occurring relaxation has been interpreted as due to a thermal process in which the translational energy of molecules is transferred, during the collisions or through dipolar interactions, into internal degrees of freedom of low quanta vibrational motions. The quite strange behavior of the relaxation time with the temperature has been interpreted and compared with the behavior of the relaxation time in liquid chloroform.

Infrared crystal spectra of heterocyclic compounds. 1 . IR spectra of solid modifications of thiophene

Abstract The infrared spectra of the four solid modifications of thiophene have been studied. Absence of appreciable band shifts and solid state splitting, in going from the liquid to the solid phases, seems to indicate that the crystals of thiophene are disordered at least until the 4th solid modification becomes stable. Polarization measurements, carried out on the 4th phase, allow a tentative determination of the crystal structure at 100°K.

Non-coincidence effect of aromatic ring vibrations

The non-coincidence of the maxima of the isotropic and the anisotropic profiles in Raman spectra has always been considered an efficacious probe of the structure and dynamics of polar liquids. An anomalous, negative non-coincidence effect has been observed in ring breathing modes of aromatic molecules, without dipole moment (p -xylene, mesitylene) or with a weak permanent dipole (toluene, o -xylene, m -xylene). Temperature effects and isotopic dilution have also been performed in toluene and o -xylene, confirming the presence of a resonant coupling mechanism. Previous analogous results of other aromatic non-polar liquids (benzene, hexafluorobenzene) have been confirmed. It has been hypothesized that quadrupolar intermolecular forces and steric repulsive interactions balance each other giving final negative values of non-coincidence effect.

Molecular dynamics and vibrational relaxations in liquid nitromethane. II. Raman, coherent anti‐Stokes Raman spectroscopy, and transient optical Kerr effects in the totally symmetric ν4 mode in CH3NO2

The vibrational relaxation of the ν4 mode of CH3NO2 liquid and its molecular dynamics are investigated. Temperature and solvent effects on vibrational dephasing and correlation times are discussed in terms of the adiabatic impact theory to infer that, in the molecular collision, the attractive part of intermolecular potential is explored. The statistical uncorrelation of rotational and vibrational relaxations is experimentally demonstrated.

Vibrational analysis of tellurophene and its deuterated derivatives

Abstract The i.r. and Raman spectra of tellurophene, tellurophene-2- d 1 , tellurophene-2-5- d 2 , tellurophene-3-4- d 2 , tellurophene-2-3-4- d 3 and tellurophene-2-3-4-5- d 4 have been studied. A vibrational assignment of the fundamental frequencies of all these molecules has been carried out on the basis of i.r. vapor band contours and depolarization states of Raman lines. Such an assignment conveniently fits the isotopic “sum” and “product” rules. A comparison of the vibrational behaviour of tellurophene and that of the other congeners is made and a rationalization of some frequency shifts is attempted.

Resonant Raman spectra of soluble trans polyacetylenea)

Resonant Raman spectra of a soluble form of trans polyacetylene are here reported. Accurate excitation profiles have been obtained by using the 1196 and the 1370 cm−1 bands of toluene as an internal standard. Both the integrated and sliced excitation profiles exhibit a resolved vibronic structure, whose shape is interpreted in terms of the magnitude of the electron–phonon coupling and of the inhomogenous distribution of the electronic energies due to the interaction with the solvent. The present data are compared with those obtained from solid samples.

Vibrational spectra of π-allyl-and π-allyl-d5-dicarbonyl-nitrosyliron

Abstract Vibrational spectra of π-C3H5Fe(CO)2NO and π-C3D5Fe(CO)2NO have been studied in the liquid and solid states. The spectra have been interpreted on the basis of a C3 molecular symmetry. A reassignment of some bands is proposed for the allylic fragment based on vH/vD isotopic shifts. Examination of spectra of deuteriated derivatives has also allowed a reasonable assignment of all modes involving the FeCO and FeNO groups.

Isotopic and chemical dilution effects on the vibrational relaxation rate of some totally symmetric motions of liquid acetonitrile

Abstract The vibrational dephasing of the ν 1 (C–H, C–D stretching) and ν 3 (C–H, C–D bending) symmetric motions of liquid acetonitrile in its light and fully deuterated forms has been studied in the frame of the vibrational time correlation functions obtained as Fourier transforms of the isotropic Raman spectral distributions and interpreted within the Kubo theory. In addition, the experimental isotropic profiles have been analysed within the bandshape approach formulated by analytical Fourier transformation of the Kubo vibrational time correlation functions in order to derive the relaxation parameters in the frequency domain. The effects of the isotopic (CH 3 CN/CD 3 CN and vice versa) and chemical (CCl 4 ) dilution on the bandshapes and on the vibrational relaxation parameters have been studied. It was observed that the decay rate of ν 1 mode is insensitive to the isotopic dilution but varies appreciably with chemical (CCl 4 ) dilution. The vibrational dephasing of ν 3 mode is qualitatively, but not quantitatively, affected in the same way by chemical dilution and shows a slower modulation regime than that exhibited by the stretching mode. Unlikely from the latter, the ν 3 mode results are slightly affected by the isotopic dilution. Phase relaxation mechanisms of these two motions of acetonitrile in the liquid state are proposed on the basis of these data, and a comparison is made with the results earlier published.

Infrared crystal spectra of heterocyclic compounds. II. IR spectrum of selenophene in the solid state

Abstract Infrared spectra of solid selenophene at different temperatures, have been measured using polarized radiation. Just below the freezing point the selenophene molecule has a noticeable degree of ring-rigidity, allowing for a definite location in sites of lower symmetry than the molecular one. Dichroic behaviour of IR lines in the solid state enables us to attribute the bands to the relative symmetry species and give a tentative hypothesis for the space group of the crystalline selenophene.