FIR Spectra Research Articles

Structure and dynamics of crystal α-modification of potassium biiodate

FT-IR (4000-400 cm −1) and FIR (400-10 cm −1) spectra of α-modification of acid potassium iodate (α-KIO 3·HIO 3) were measured in the paraelectric (at 300-220 K) and ferroelectric (at 223-20 K) phases. FIR spectra of the ferroelectric phase were found to exhibit doublet structure of many bands while FT-IR spectra mainly remain invariable. The results are in good agreement with the order-disorder mechanism of ferroelectric phase transition connected with localization of the proton within a strong hydrogen bond.

IR induced isomerisation of HDO complexes: a method for the observation of FIR spectra of matrix isolated water complexes

The OD- and OH-stretching fundamentals of the HDO dimer and the HDO-formaldehyde complex have been irradiated with a monochromatic, tunable source. When the OD (OH) fundamental of HDO deuterium (hydrogen) bonded to water or formaldehyde in nitrogen matrices, is irradiated, HDO changes from D- to H-bonding (from H to D). By the irradiation, we can change most HDO complexes in a set of sites from D-bonding to H-bondingand reverse. This has been used to obtain infrared spectra in the region from 190 to 600 cm −1. The out-of-plane shear vibration of HDO, H- and D- bonded to another water molecule and to formaldehyde has been observed.

On the dynamical conductivity in icosahedral boron-rich solids

The FIR spectra of boron-rich solids measured down to exhibit strongly increasing reflectivities towards lower frequencies. These spectra are well described when a superposition of Drude-type and hopping-type dynamical conductivity is assumed. The corresponding fits were simultaneously made for the real and the imaginary part of the dielectric function to achieve unambiguous parameters. The results obtained can be described consistently, for example, with DC conductivity measurements, and moreover in the case of -rhombohedral boron, with the known energy band scheme. The bipolaron hopping model of the electronic transport in boron carbide is proved to be inappropriate.

G54.4–0.3 — Multi-Frequency Investigation of an SNR in Interaction with the ISM

G54.4–0.3 is an extended shell-type supernova remnant (SNR) in the Galactic plane. We selected this source as a candidate for the interaction of SNRs with the interstellar medium on the base of an investigation of cool IRAS point sources in the direction of SNRs. We found a statistical excess of IRAS sources with FIR spectra similar to young stellar objects (Td ≈ 25 − 45 K) in the vicinity of G54.4–0.3 and a number of other SNRs in the northern hemisphere (Junkes & Fürst 1992).

Radio Identifications of Extragalactic IRAS Sources

Extragalactic sources detected at λ= 60 microns were selected from the IRAS Faint Source Catalog, Version 2 by the criterion S_60 microns_ >= S_12_ microns. They were identified by position coincidence with radio sources stronger than 25 mJy at 4.85 GHz in the 6.0 sr declination band 0^deg^ < δ < +75^deg^ (excluding the 0.05 sr region 12^h^40^m^< α < 14^h^40^m^, 0^deg^< +5^deg^) and with radio sources stronger than 80 mJy in the 3.4 sr area o^h^ <α < 2o^h^, -40^deg^ < δ < 0^deg^ (plus the region 12^h^40^m^ < α < 14^h^40^m^, 0^deg^<δ <+5^deg^). Fields containing new candidate identifications were mapped by the VLA at 4.86 GHz with about 15" FWHM resolution. Difficult cases were confirmed or rejected with the aid of accurate (σ ~ 1") radio and optical positions. The final sample of 354 identifications in {OMEGA} = 9.4 sr is reliable and large enough to contain statistically useful numbers of radio-loud FIR galaxies and quasars. The logarithmic FIR radio flux ratio parameter q can be used to distinguish radio sources powered by "starbursts" from those powered by "monsters." Starbursts and normal spiral galaxies in a λ = 60 micron flux-limited sample have a narrow (σ_q_ = 0.14 +/- 0.01) q distribution with mean <q> = 2.74 +/- 0.01, and none have "warm" FIR spectra [α(25 microns, 60 microns) < 1.5]. The absence of radio- quiet (but not completely silent) blazars indicates that nearly all blazars become optically thin at frequencies v<~100 GHz. Nonthermal sources with steep FIR/optical spectra and dusty-embedded sources visible only at FIR and radio wavelengths must be very rare.

Effect of crystallization, poling and ageing conditions on the FIR, dielectric and pyroelectric properties of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02)

AbstractWe studied the influence of hot‐pressing temperature as well as poling and ageing conditions on the amount of polar phase of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02) foil. FIR transmission spectra of hot‐pressed homopolymer and copolymer films were measured in the 30‐450 cm—1 range as a function of hot‐pressing temperature Thp and poling temperature Tp. The FIR studies show that homopolymer and copolymer consist of both polar and nonpolar modifications of PVDF. The content of the polar phase tends to decrease with Thp and increase after poling. The FIR spectra of our samples exhibit a strong absorption peak near 100 cm—1 absent in the biaxially oriented Solef samples, which is believed to be due to the amorphous phase in our samples. Four thermally stimulated current (TSC) maxima are attributed to the relaxation in the amorphous region (∼40°C), to the dipolar relaxation in the nonpolar (∼60°C) and polar (∼80°C) phase, and the space charge relaxation (dependent on the poling temperature). The pyroelectric coefficient of the homopolymer and copolymer thermoelectret foil prepared by hot‐pressing is of the same order as that of the PVDF thermoelectret foil produced by Solvay and can be influenced by the hot‐pressing conditions. The dielectric response of the hot‐pressed PVDF‐type foils can be described by the Kohlrausch‐–Williams‐Watts function and is characteristic of a heterogeneous system.

Methyl tunnelling in pure and matrix isolated halogenomesitylenes

The trihalogenomesitylenes, C 6(CH 3) 3X 3, where X = Cl, Br, I crystallise in the triclinic P 1 space- group, such that the three methyl groups in one molecule see different environments. Indeed, we have detected three tunnelling and three torsional transitions in the pure compounds. In the case of a 3.7% mixture of protonated tribromomesitylene in a matrix of hexabromobenzene, we have detected only one tunnelling transition at 102μeV; from this, we conclude that the three methyl groups of the TBM molecule in the dilute mixture are equivalent in what is a relatively symmetrical environment and as a consequence also in the isolated molecule. A solid solution of 6% fully protonated trichloromesitylene in a matrix of fully deuterated TCM gives three transitions similar to those in the pure compound, indicating that there is no strong coupling between the different methyl groups. We also present Raman and FIR spectra of pure TBM giving the phonon frequencies at the Γ point. Some IR absorption maxima fall near maxima of the neutron spectra, indicating coupling between some phonons and the torsional transitions. So as to give us a model of the tribromomesitylene system we have optimised atom-atom Buckingham-type coefficients so as to reproduce the experimental phonon frequencies. The coefficients were used to calculate the intermolecular contribution V ex(θ) to V s(θ), the potential hindering the methyl groups. The intramolecular contribution V in(θ) was found using the quantum chemistry program AM1. The total hindering potential V s(θ) so obtained allowed us to calculate the principal dynamic features of the methyl rotors in reasonable agreement with the experiments.

A far infrared study of benzene-fluorinated benzene binary mixtures

The experimental FIR spectra of liquid equimolar binary mixtures formed with benzene, 1,3,5-trifluorobenzene and hexafluorobenzene have been compared with the spectra calculated as a weighted sum of the corresponding spectra of the neat liquids. In contrast to the other binary mixtures, for C 6H 6/C 6F 6 a marked deviation from the additivity is observed. These results are interpreted as providing evidence for the existence of a different and stronger local ordering which might be ascribed as the “signature” of a very short-lived “complex”.

Synthesis, crystal structure, magnetism and vibrational spectrum of Dipotassium Iron(II) Hexathiodiphosphate(IV), K2Fe[P2S6

AbstractK2Fe[P2S6] was synthesized from the elements at 1173 K in sealed quartz tubes. The compound forms transparent orange crystals, stable against air and moisture. K2Fe[P2S6] crystallizes in the monoclinic system, space group P21/n (No. 14), with cell dimensions (T = 298.5 K) a = 6.0622(4), b = 12.172(1) and c = 7.3787(8) Å, β = 101.113(7)°, Z = 2. The novel structure type (mP22) is characterized by columns of alternating face‐sharing S6 octahedra and trigonal antiprisms (both distorted) parallel to the a axis, which are interconnected by inserted K+ (CN 10; {2,6,2}‐polyhedra; d(KS) = 3.231 − 3.845 Å). The S6 polyhedra of the columns are centered alternately by Fe (d̄(FeS) = 2.577 Å) and P2 pairs which are inclined to the a axis by 73.4°. The bond lengths in the hexathiodiphosphate(IV) anions, [P2S6]4−, with approximate 3 2/m – D3d symmetry, are d̄(PP) = 2.20 and d̄(PS) = 2.02 Å. The compound is paramagnetic above TN = 28 K with μ = 4.69 B.M. and orders antiferromagnetically below TN. The internal modes of the observed Raman and FIR spectra of K2Fe[P2S6] are in accord with the factor group analysis, and the spectra are assigned on the basis of [P2S6]4− units, taking into account the deviation from D3d symmetry.

The Rotational Spectrum of CHF 3 in the Submillimeter-Wave and Far-Infrared Region: Observation of the K = 3 Line Splitting

The milimeter-wave, submillimeter-wave. and FIR spectra of the ground state of CHF 3 have been observed and analyzed up to J = 78. The resulting spectroscopic constants are: B 0/MHz = 10 348.8706(2), D J /kHz= 11.34482(13), D JK /kHz = −18.11765(50), H JJJ /Hz= 0.020069(24), H JJK /Hz = −0.08598(10), H KKJ /Hz 0.11372(27), L J /mHz = −0.669(16) × 10 −4, L JJK /mHz = 0.4953(80) × 10 −3, L JK /mHz = −0.1189(17) × 10 −2, and L JKK /mHz = −0.1115(31) × 10 −2. The splitting of the K = 3 ground state lines has been observed starting from the J = 29 ← 28 transition and the determined values of the splitting constants are h 3/Hz = 0.29689(45) ×10 −2 and δ h 3/Hz = −0.2054(52) × 10 −7.

Darstellung, Eigenschaften und elektronische Raman-Spektren von Di(bromo)phthalocyaninatometallaten(III) der Eisengruppe / Synthesis, Properties and Electronic Raman Spectra of Di(bromo)phthalocyaninatometalates(III) of the Iron Group Elements

Abstract Low spin di(bromo)phthalocyaninatometalates of tervalent iron, ruthenium and osmium ([MBr2Pc2-]-) are formed by the reaction of [FeBrPc2-] or H[MBr2Pc2-] (M = Ru, Os) with excess bromide in DMF or THF and isolated as (nBu4N)+ salts. The electronic spectra show the typical π- π*- transitions (B, Q, N region) of the Pc2- ligand together with a number of extra bands due to trip-multiplett and (Pc, Br → M)CT transitions. νs(MBr) is observed in the resonance Raman (RR) spectrum (RR enhanced for M = Fe, Ru) at 161 cm-1 (Fe), 183 cm-1 (Ru) and 192 cm-1 (Os), νas(MBr) at 251 cm-1 (Fe), 234 cm-1 (Ru) and 218 cm-1 (Os) in the FIR spectra. The RR spectra obtained by excitation at low absorbance between the B and Q region are dominated by the intraconfigurational " Γ7 →Γ 8" transition due to spin orbit splitting of the 2T2g ground state for Fe at 583 cm-1, Ru at 1026/1050 cm-1 and Os at 3131 cm-1 . In the MIR resp. NIR spectra vibronically induced transitions are observed for the Ru or Os complex.

Vibrational modes activated by structural disorder in FIR transmission of Hg1-x-yCdxMnyTe

FIR transmission spectra of HgCdMnTe are investigated over a wide spectral range (from 40 cm-1 up to 400 cm-1) at different temperatures (from 5 K up to 300 K). It is shown that different transverse and longitudinal acoustic, local and resonant modes are activated by disordering and manganese impurities in the range of low values of single-phonon state densities of HgCdTe. FIR spectra seem to be a good probe for characterization of the quality of semimagnetic crystals.

Normal coordinate analysis of the vibrational spectrum of benzil molecule

Normal coordinate analysis is performed for the benzil molecule. Force constants of phenyl rings are transferred from earlier studies on binuclear aromatic molecules. The existance of some low-frequency internal modes have been proved, thus eliminating the earlier explanations of the excess of the bands observed in the low-frequency Raman and FIR spectra of benzil crystal.

Normal coordinate analysis of the vibrational transitions in benzil

Normal coordinate analysis is performed for the benzil molecule. Force constants of phenyl rings are transferred from earlier studies on binuclear aromatic molecules. The existence of some low-frequency internal modes has been proved, thus eliminating the earlier explanations of the excess of the bands observed in the low-frequency Raman and FIR spectra of the benzil crystal

Dust temperature distributions in star-forming condensations

The FIR spectra of the central IR condensations in the dense cores of molecular clouds AFGL 2591. B335, L1551, Mon R2, and Sgr B2 are reanalyzed here in terms of the distribution of dust mass as a function of temperature. FIR spectra of these objects can be characterized reasonably well by a given functional form. The general shapes of the dust temperature distributions of these objects are similar and closely resemble the theoretical computations of de Muizon and Rouan (1985) for a sample of 'hot centered' clouds with active star formation. Specifically, the model yields a 'cutoff' temperature below which essentially no dust is needed to interpret the dust emission spectra, and most of the dust mass is distributed in a broad temperature range of a few tens of degrees above the cutoff temperature. Mass, luminosity, average temperature, and column density are obtained, and it is found that the physical quantities differ considerably from source to source in a meaningful way.

Colour-selected IRAS galaxies - a comparative investigation of their radio properties

We report the results of VLA observations of two complete samples of IRAS galaxies, one ‘normal’ and the other selected to have warm FIR spectra similar to those of Arp 220 and other ultraluminous infrared galaxies. We find that these samples are indeed significantly different in the sense that the color-selected galaxies have more centrally condensed, higher surface brightness, and flatter spectrum radio emission in common with high-luminosity IRAS galaxies. Their FIR/radio ratios are consistent with a star formation origin for the radio emission.

The quaternary systems MS[sbnd]Cr 2S 3[sbnd]In 2S 3( M =Mn, Fe, Co)

The phase diagrams of the quaternary systems MCr 2S 4 MIn 2S 4 Cr 2S 3 In 2S 3) (M =Mn, Fe, Co, (Cd, Hg)) have been studied by X-ray phase analyses and FIR spectra of quenched samples. At temperatures above 1200, 1200, and 1330 K, spinel-type solid solutions(1 − y)Cr 2−2 x In 2 x S 3− yMS are formed in a large range of compositions. Two-phase regions are only the regions near Cr 2S 3 and between MS and M(Cr, In) 2S 4. At lower temperatures, the spinel-type solid solutions (except M =Cd and Hg) decompose to Cr-rich and In-rich compounds. The sections with constant y show more or less nonquasibinary behavior. Thus, cobalt is enriched in the Cr-rich solid solutions. The phase width of Cr 2S 3 with respect to M content is 2.5 mole% for M =Co, but it is negligible for M =Mn and Fe.

ChemInform Abstract: FIR Spectra, Two‐Dimensional Vibrational Potential Energy Surface, and Conformation of Cyclohexene and Its Isotopomers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Linear anions [CuAs 2] 5−, [AuP 2] 5− and [AuAs 2] 5− in potassium compounds

K 5[AuP 2], K 5[AuAs 2] and K 5[CuAs 2] were prepared from molten mixtures of the elements under an argon atmosphere in sealed niobium ampoules. The compounds form shiny black plates which are sensitive to moisture. The crystal structures of the three isotypic compounds were refined from X-ray single-crystal data. The characteristic units are linear anions [As-Cu-As] 5-, [P-Au-P] 5- and [As-Au-As] 5- with bond lengths CuAs = 230.7(2) pm, AuP = 236.8(9) pm and AuAs = 246.0(3) pm respectively, enclosed in a distorted hexagonal close packing of the potassium cations. The structural relationship to the K 5[CuSb 2] and Na 4[HgP 2] types is discussed concerning the cation polyhedra. The FIR spectra of the compounds are measured, the assignment of the observed frequencies being based on the D ∞h symmetry of the isolated [X-T-X] 5− units. The crystallographic data are as follows: space group P6 3/ mmc (no. 194), Z = 2; K 5[CuAs 2] − a = 537.7(2) pm, c = 1877.1(4) pm, c/ a = 3.49; K 5[AuP 2] − a = 563.6(2) pm, c = 1871.6(4) pm, c a = 3.32 ; K 5[AuAs 2] − a = 573.0(2) pm, c = 1921.6(4) pm, c a = 3.35 .

Structural and spectroscopic studies of halogenocuprate(I) complexes

Reaction of tetraalkylammonium halides, PPh3 and copper(I) halides in a 1 : 1 : 1 mole ratio in dichloromethane yields complexes [NR4][Cu(PPh3)X2](R = Et, X = Cl or Br; R = Pr, X = Br, I; R = Bu, X = Br) and [NEt4]2[Cu2(PPh3)2I4]. These have been characterized by infrared and cross polarization magic angle spinning (CP MAS)31P NMR spectroscopy, and the structures of most have been determined by single-crystal X-ray diffraction. The compounds [NR4][Cu(PPh3)X2] in the first group above contain mononuclear anions [Cu(PPh3)X2]– with essentially trigonal planar PCuX2 co-ordination. The P–Cu–X and X–Cu–X angles are all within 5 ° of the ideal trigonal angle of 120 °. The compound [NEt4]2[Cu2(PPh3)2I4] contains the centrosymmetric binuclear anion [Cu2(PPh3)2I4]2–{a dimer of [Cu(PPh3)I2]–} in which the two copper atoms are bridged by two iodine atoms, and each copper atom is also bound to a terminal iodine atom and PPh3 molecule. The FIR spectra of the mononuclear complexes [Cu(PPh3)X2]– show strong bands at 264, 195 and 175 cm–1 for X = Cl, Br and I respectively, which are assigned to the asymmetric v(CuX) stretching mode of the bent X–Cu–X units, and weak bands at 194, 150 and 128 cm–1 due to the symmetric v(CuX) mode. In addition, the X = Cl complex shows a strong band at 126 cm–1 which is assigned as the δ(CuCl2) bending mode. The dimer [Cu2(PPh3)2I4]2– shows a remarkably simple spectrum in the v(CuI) region: a partially resolved doublet at 113 and 126 cm–1. The above vibrational frequencies are compared with those of the species [CuX2]– and [Cu2I4]2–, from which the present species can be considered to be derived by addition of one PPh3 molecule per copper atom. The solid state CP MAS 31P NMR spectra generally consist of asymmetric quartets due to coupling of the 31P nucleus to the quadrupolar copper nucleus, and the splitting patterns are interpreted in terms of the copper co-ordination environment.