Vibrational excitation by electron impact in thin solid films of cyclopropane

Vibrational electron-energy-loss spectra of solid films of cyclopropane have been recorded at different incident energies, scattering angles, and upon changing the sample crystallinity. The intensity variations are exploited for the assignment of the observed vibrational modes. A simple model is used to explain the intensity distribution in the multiple scattering spectral region dominated by twofold loss processes. This model demonstrates that dipole scattering processes may be distinguished from excitation through impact scattering even in completely disordered samples by comparing the intensities of the multiple scattering bands to those of the fundamental vibrations.     

Angular distribution of the photoelectron spectrum of CO2, COS,CS2, N2O,H2O,and H2S

The photoelectron spectra of the triatomic molecules CO₂, COS, CS₂, N₂O, H₂O, and H₂S have been measured as a function of the angle θ between the direction of the incoming photon and outgoing photoelectron. The photoelectron spectra have been measured with a double-focusing electrostatic electron spectrometer to which has been attached a chamber containing a gas discharge lamp that can be freely rotated. (The photon source used was the 21.22 eV He I resonance line). From the dependence of intensity as a function of θ the angular parameter β was determined for each ionization band observed in the photoelectron spectra. A correlation was noted between the values of β and the molecular orbitals relative to the contributions of oxygen and sulfur atomic orbitals. Individual β values were also obtained for most of the vibrational bands seen in the photoelectron spectra. In most cases the vibrational structure showed little or no change in the angular parameter for a given electronic state. In certain cases, however, such as the fourth ionization band in CS₂, CO₂, and COS, rather sizeable changes in β were observed for the different vibrational bands.     

Unravelling overlaps and torsion-facilitated coupling using two-dimensional laser-induced fluorescence

Two-dimensional laser-induced fluorescence (2D-LIF) spectroscopy is employed to identify contributions to fluorescence excitation spectra that arise from both overlapping bands and coupling between zero-order states (ZOSs). Evidence is found for the role of torsional motion in facilitating the coupling between vibrations that particularly involves the lowest-wavenumber out-of-plane vibrational modes. The experiments are carried out on jet-cooled p-fluorotoluene, where the molecules are initially in the lowest two torsional levels. Here we concentrate on the 390–420?cm^?1 features in the S₁?←?S₀ excitation spectrum, assigning the features seen in the 2D-LIF spectrum, aided by separate dispersed fluorescence spectra. The 2D-LIF spectra allow the overlapping contributions to be cleanly separated, including some that arise from vibrational-torsional coupling. Various coupling routes open up because of the different symmetries of the lowest two torsional modes; these combine with the vibrational symmetry to provide new symmetry-allowed vibration-torsion (‘vibtor’) interactions, and the role of the excited m?=?1 torsional level is found to be significant.     

Vibrational structure in the valence electron spectra of pyridine and pyridine—d5

The He(I) electron spectra of pyridine and pyridine-d₅ have been recorded. Distinct vibrational progressions are observed in the first and fourth electronic bands and a vibrational analysis is made. The isotopic effect on the vibrational energies is found to be helpful in the assignment of the vibrational peaks.By consideration of highly resolved spectra the vibrational interpretation of certain bands in the photoelectron spectra of pyridine and pyridine-d₅ has been accomplished. The spectra of the two species display differences due to isotope exchange but are nevertheless similar in structure. This is of great help in the vibrational assignment.     

Ab initio calculations of the vibrational spectra of AgInSe2 and AgInTe2

The phonon spectra and densities of states of AgInSe₂ and AgInTe₂ semiconductor crystals with a chalcopyrite structure have been calculated from first principles by the linear response method. The frequencies calculated at the center of the Brillouin zone are in agreement with the experimental data obtained using IR and Raman spectroscopy. According to the atomic contributions to the vibrational modes, the spectra of the AgInSe₂ and AgInTe₂ crystals exhibit three groups of bands: the vibrations in the low- and medium-frequency ranges are mixed in character with approximately identical contributions of all sublattices, and the bands at higher frequencies are associated with the contributions of Ag, C ^VI and In, C ^VI (C ^VI = Se, Te) atoms. The position of these bands allows us to make the inference that, in the crystals under investigation, the In-C ^VI bonding is stronger than the Ag-C ^VI bonding.     

Formation of electronically excited states in ultrathin Alq3 films during electron bombardment

Electronic and vibrational electron energy loss spectra are studied on ultrathin Alq₃ films for different electron energies, thicknesses, and temperatures of the film. The shape of the spectrum and the position of the lines are very weakly dependent on the film thickness, indicating weak interaction between the adsorbed molecules and the platinum substrate. The temperature dependence of the vibrational bands is weak. The positions of the triplet and singlet maxima are close to gas-phase and thin-film data obtained for high electron energy. Interference of electrons is observed in measuring the energy loss spectra. The effect of dipole and collisional excitation mechanisms is shown. From the similarity between the energy loss spectra it follows that the nature of the interaction between low-energy electrons and organic materials is the same in gas and thin-film phases, and likewise for the characteristics of the motion of the electrons. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 786–791, November–December, 2006.     

On the absorption saturation in the vibrational-rotational bands of molecules

Analytical expressions describing saturation of the stationary absorption coefficient in a vibrational-rotational band in the spectrum of a molecular gas are obtained taking into account that many other bands are involved in the absorption process as well. The formulas are derived for an arbitrary spectral composition of the pumping radiation with an allowance for a difference between the rotational and vibrational relaxation rates and between the relaxation rates of the lower and upper vibrational levels. The influence of saturation on the appearance of the partial inversion and the negative absorption effects is considered. The general formulas are simplified and the vibrational and rotational contributions to the saturation are separated within the frame-work of the local Elsasser model for the rotational band structure. Explicit relationships between the dimensionless parameters describing the vibrational and rotational saturation mechanisms are obtained and analyzed, and conditions under which one of these mechanisms is dominating are determined. Particular calculations were performed for the (000)–(010) and (000)–(001) absorption bands of the O₃ molecule and features of the saturation effect in these bands were established.     

Fine band structure of the vibrational spectra of fullerite C<Subscript>60</Subscript> and enhancement of intermolecular interaction in high-temperature phase

The fine structure of the fundamental vibrational bands and some combination tones of fullerite C₆₀ in its IR absorption and reflection spectra, as well as in Raman spectra, has been studied. This structure is due to the overlapping components of Davydov and isotopic splittings and the removal of vibrational degeneracy with symmetry lowering. It is shown that for IR F _u (i) bands (i = 1–4) and low-frequency H _g (1) and A _g (1) bands in the Raman spectrum the splittings at room temperature exceed those for the low-temperature phase. The enhancement of intermolecular interaction at elevated temperatures is explained by the nonequilibrium vibrational excitation of the medium as a result of nonlinear interaction of vibrational modes and by the change in the electronic states.     

A simple empirical model for the collisional spectral shift of air-broadened CO2 lines

A simple empirical model is proposed for the pressure-induced shifts of air-broadened CO₂ absorption lines. It is based on the introduction of components symmetric and antisymmetric with respect to the rotational quantum number m, and on a separation of vibrational and rotational contributions. These components are modelled though empirical analytical laws with parameters that are obtained from fits of the measured shifts in only two different bands. It is then shown that the model leads to satisfactory results for a number of other vibrational transitions in which the shifts take significantly different values. This provides a simple way to generate values for unmeasured transitions and this tool can thus be used to complement spectroscopic databases.     

Raman scattering in the Bi2TeO5 single crystal

Polarized Raman spectra of the Bi₂TeO₅ single crystal have been investigated for the first time. The group-theoretic analysis of the first-order vibrational spectra is performed. The number of the experimentally observed bands is less than the predicted number of normal modes. The spectral ranges with similar bands are revealed. Some ranges in the spectra of Bi₂TeO₅ are identified from the spectral data for the materials containing bismuth-oxygen and tellurium-oxygen complexes.     

The absorption spectrum of 12C2H2 IV. The regions 7600–9200 cm−1 and 10600–11500 cm−1

The absorption spectrum of ¹²C₂H₂ has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10600–11 500 cm^?1 spectral region, where no absorption bands were previously reported. Fifteen bands starting from the vibrational ground state are observed and rotationally analysed. All corresponding excited vibrational levels were assigned using the polyad model, the so-called cluster model (El Idrissi, M.I., Liévin, J., Campargue, A., and Herman, M., 1999, J. chem. Phys., 110, 2074) which allows vibrational energies, rotational B_v constants and, to some respect, relative band intensities to be predicted. Additional data and constants are also provided in the range 7600–9200cm^?1, whenever improving the literature results, from spectra recorded previously at ULB using Fourier transform spectroscopy. The assignment procedure in the range recorded by ICLAS is detailed, leading to a deeper understanding of vibration-rotation and intensity features of the absorption bands within the frame of the cluster model.     

Vibrational spectra of 2-cyclooctylamino-5-nitropyridine and its mixtures with C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerenes

The vibrational spectra of 2-cyclooctylamino-5-nitropyridine (COANP) solutions and the evolution of the spectra upon changing over from the solutions to solid-phase COANP are investigated. The bands observed in the spectra are assigned to the corresponding vibrational modes. The nature of the interaction of COANP with C₆₀ and C₇₀ fullerenes is elucidated by analyzing the transmission spectra of these compounds. No interaction of the COANP compound with C₆₀ and C₇₀ fullerenes is revealed under the studied conditions. It is assumed that the physical nature of this phenomenon can be associated with the formation of liquid-crystal clusters consisting of fullerene molecules.     

Infrared Spectroscopy of the ν1 Band of Sulfur Tetrafluoride, SF4

Infrared absorption spectra of the ν₁ axial S-F stretching vibrational bands of sulfur tetrafluoride, SF₄, have been recorded and analyzed. A diode-laser jet spectrometer was used to record high-resolution spectra of ³²SF₄, with 87 vibration-rotation lines of the ν₁ fundamental being assigned. Least-squares fitting of the data yielded a precise vibrational band origin, as well as rotational parameters for the upper state. In addition, lower-resolution spectra of a static sample of SF₄ held at room temperature were recorded using a Fourier transform (FTIR) spectrometer. The progressions of prominent features observed in the room-temperature FTIR spectra are attributed to summation bands arising from ν₁ transitions from excited vibrational levels of the low-frequency ν₄ manifold of both ³²SF₄ and ³⁴SF₄.     

The Rotational Analysis of the Three New Virbrational Bands of NO2 in the Range 5680–5720 Å

The three new vibrational bands in the range 5680–5720 Å of the fluorescence excitation spectra of NO₂ were measured at the normal temperature and were assigned with the rotational quantum numbers. In these bands there are strong spin and rotational forbidden transitions which express the complexity of NO₂ spectra.     

Vibrational spectra of crystalline Bi1−xSbx alloys

Second order Raman scattering is reported at 300 K in crystalline Bi_1?x Sb_x alloys. The spectra, which are interpreted in terms of dominant overtone processes, indicate variations in the phonon density of states for the optical bands with composition. The form of the spectra, which include contributions from Bi-Bi, Bi-Sb and Sb-Sb bonds, implies microscopic statistical clustering effects analogous to those in Ge_1?xSi_x alloys. A comparison of the spectra with inelastic tunneling results in superconducting amorphous Bi_1?xSb_x indicates covalent bonding contributions in the latter.     

An Infrared Spectroscopic Study of Crystalline Copper (II) Propionate and Butyrate

Abstract

Abstract: The vibrational spectra of crystalline anhydrous copper (II) propionate and butyrate were studied by FT-IR spectroscopy. A detailed assignment of the spectra of both compounds is presented and discussed. It is shown that the presence of two non-equivalent sets of carboxylate ligands within the crystals gives rise to several band splittings, which are particularly evident in those bands ascribable to normal modes involving predominantly the -C_βH₃ or -C_βH₂-fragments. In addition, the vibrational assignments made for the studied molecules are shown to be very useful to help understanding the much more complex spectra of long chain copper carboxylates.     

The Infrared and Raman Spectra of β-and α-Tricalcium Phosphate (Ca3(Po4)2)

Factor group analysis was applied to interpret the vibrational spectra of β-and α-tricalcium phosphate (Ca₃(PO₄)₂). The analysis predicts the number of bands formed due to the splitting of the fundamental vibrational modes of the PO₄ ^3-ion. The number of the infrared and Raman bands predicted by this analysis for the two phases are drastically different and can be ascribed to the difference in atomic arrangements in the two phases resulting in greater shielding of the PO₄ ^3-ions in the β-phase than in the α-phase. Discrepancies in the number of predicted and experimentally-observed bands can be attributed to the weak intensities of some vibrational modes or the convolution of vibrations and limited spectral resolution.     

Pre-resonant enhancement of the Raman scattering from KI:Tl+

E_g and T_2g spectra at room and nitrogen temperature at several laser wavelengths are reported for KI:Tl⁺. As resonance with Tl⁺ -absorption bands is approached the optic phonon parts of the spectra are enhanced relative to the acoustic phonon parts, and distortions occur within the acoustic and optic parts of the spectra. A model for the scattering is employed which involves electron-phonon coupling to nearest and nn neighbors. Exchange and crystal field contributions to the electron-phonon coupling are distinguished.     

Reflectivity spectra of new organic metal (BEDO-TTF)5[CsHg(SCN)4]2

The polarized reflectivity and optical conductivity spectra of microcrystals of the new organic conductor (BEDO-TTF)₅[CsHg(SCN)₄]₂ based on the donor molecule bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) have been studied in the spectral ranges 600–6500 and 9000–40000 cm^?1 at 300 K for three principal lattice directions. The optical evidence for the quasi-two-dimensional character of the conducting electronic system is obtained. The conclusion is made that the studied crystal is the quasi-two-dimensional semimetal with overlapping electron energy bands. The basic parameters of the electronic system of the crystal are determined in the framework of the Drude model. It is found that the allowed electron energy bands of the crystal are somewhat narrower than those of the previously studied structurally allied superconductor based on the same molecule. The features of vibrational structure are identified in the σ(ω) spectra for the specified three polarizations.