Cm-1 Mode Research Articles

Solid-Sm C* and Sm C*-Sm a phase transitions in ester ferroelectric liquid

Solid-Sm C* and Sm C*-Sm A phase transitions in ester ferroelectric liquid crystal D-4-(2-methylbu-toxy)phenyl 4-decyloxybenzoate (MBOPDOB) are examined by measurements of Raman spectroscopy and differential scanning calorimetry. The thermal hysteresis, with width about 4°C in temperature from solid to Sm C* phases, is recorded from the temperature-cycle measurements of the 15 and 49 cm-1 modes, manifesting first-order character of the solid-Sm C* transition. The overcooling of the Sm C* phase promotes the ordering of the molecular orientations. Continuously going through the Sm C*-Sm A point of the 93 cm-1 mode and the spontaneous polarization, and very small heat of the transition indicate that the Sm C*-Sm A transition is of a continuous second-order nature which is related to a small spontaneous polarization and a large temperature range of the Sm A phase. A model structure is proposed to discuss the small spontaneous polarization.

Thermally induced phase transitions in tridymite: an infrared spectroscopy study

The temperature dependence of the infrared active modes of meteoritic and synthetic tridymite have been investigated between 23 K and 1073 K in IR absorption and IR emission experiments. At room temperature both tridymite samples consist of a mixture of low temperature forms, in different proportions, due to the grinding. The sequence of phase transitions in Steinbach tridymite deduced from the IR data agrees well with recent X-ray and calorimetry studies using identical samples (Cellai et al. 1994). The previously suspected structural phase transition P6322⇔P63/mmc is confirmed by the disappearance of the 470 cm-1 mode and a temperature anomaly of the spectral shift of the 790 cm-1 mode. Changes in the infrared spectra of synthetic tridymite give a different sequence of phase transitions from those of the meteoritic sample, consistent with the structural phase transitions observed in a 29Si MAS NMR investigation using the same sample (Xiao et al. 1993).

Phonon Characterization of Raman Spectra in High Tc Superconductors Y1-xGdxBa2Cu3O7-δ

Concentration-dependent Raman spectra of Y1-xGdxBa2Cu3O7-δ (x = 0.4, 0.6, 0.8 and 1.0) show that the Raman mode from O(4) bridging shifts upward due to the increased symmetry of crystal potential. The linewidth and intensity of 508 cm-1 mode are decreased and increased with increasing x, respectively which is attributed to the charge transfer from the CuO basal planes to the CuO2 planes. Two second-order Raman modes at 798 and 896 cm-1 have been observed and confirmed.

Far-Infrared Study of the Vibrational Modes of 5′-GMP Gels and Crystals of Na+and K+

Five Far-Infrared (50-600 cm-1) spectra are presented: the sodium and potassium salts of 5' Guanosine Monophosphate (GMP), each salt in both the gel and crystal conformations, and poly(rG). Measurements were performed at a sample temperature of 10 K under vacuum with a liquid He-cooled bolometer. The spectra were fit with Lorentzians and assignments are suggested. There are noteworthy differences in oscillator strengths and frequencies of the bands between all spectra. We report the tentative observation of a 100 cm-1 mode which is in the neighborhood of a mode observed by Raman spectroscopy in solution (1) and dried gels (2).

Resolution of the reaction sequence during the reduction of O2 by cytochrome oxidase.

Time-resolved resonance Raman spectroscopy has been used to study the reduction of dioxygen by the mitochondrial enzyme, cytochrome oxidase. In agreement with earlier reports, Fe(2+)-O2 and Fe(3+)-OH- are detected in the initial and final stages of the reaction, respectively. Two additional intermediates, a peroxy [Fe(3+)-O(-)-O-(H)] and a ferryl (Fe4+ = O), occur transiently. The peroxy species shows an oxygen-isotope-sensitive mode at 358 cm-1 that is assigned as the nu(Fe(3+)-O-) stretching vibration. Our kinetic analysis indicates that the peroxy species we detect occurs upon proton uptake from bulk solution; whether this species bridges to Cu(B) remains uncertain. For the ferryl, nu(Fe(4+) = O) is at 790 cm-1. In our time-resolved spectra, the 358 cm-1 mode appears prior to the 790 cm-1 vibration. By using kinetic parameters deduced from the time-resolved Raman work and from a variety of time-resolved optical studies from other laboratories, we have assigned rate constants to several steps in the linear reaction sequence proposed by G. T. Babcock and M. Wikström [(1992) Nature (London) 356, 301-309]. Simulations of this kinetic scheme provide insight into the temporal behavior of key intermediates in the O2 reduction process. A striking aspect of the reaction time course is that rapid O2-binding and trapping chemistry is followed by a progressive slowing down of succeeding steps in the process, which allows the various transient species to build up to concentrations sufficient for their detection by our time-resolved techniques. Our analysis indicates that this behavior reflects a mechanism in which conditions that allow efficient dioxygen bond cleavage are not inherent to the active site but are only established as the reaction proceeds. This catalytic strategy provides an effective means by which to couple the free energy available in late intermediates in the reduction reaction to the proton-pumping function of the enzyme.

A Raman study of B203 through the liquid-glass transition range

The low frequency Raman spectrum of B203 and the boroxol ring vibrational mode at 808 cm-1 have been studied from room temperature to 1273 K as the glass transforms to a melt. Both the low frequeney "boson" peak and the boroxol mode are markedly influenced by the glass transition. Raising the temperature above Tg the strength of the 808 cm-1 mode decreases linearly indicating the Similar behavior of the boroxol ring concentration. The boson peak shows a different temperature behavior, which mirrors that of the sound velo city. The structural correlation length demostrates the same correlation range in the liquid and the glass. The results, when compared with neutron diffraction measurements contradict a recently proposed relation between the "boson correlation length" and the position of the first sharp diffraction peak of the structure factor.

Plasmon interpretation of 25 cm-1 mode in DNA.

An extension of the effective field approach for the normal mode dynamics of dissolved DNA polymers has been applied to study the vibrational modes of DNA-hydration sheath-counterion system, to include the effect of site bound counterions on the system dynamics. An alternative interpretation has been suggested for a 25 cm-1 mode recently observed in DNA samples and interpreted earlier as an interhelical mode. Analysing the eigenvectors this mode is found to possess a large electric dipole moment with longitudinal collective oscillations of the system. These characteristics identify this mode as a collective plasmon mode. Possible physical reasons for the existence of this character have been presented.

Sodalite from Vetralla (Roman potassic province) and Bancroft (Ontario, Canada): observed and simulated IR spectra

Infrared spectra of sodalites from Vetralla and Bancroft are compared to simulated spectra calculated from the available structural data and from empirical force constants applied to a simplified part-central-force potential-energy model. Calculation gives 18 vibrational modes including the 370 cm-1 mode observed by other authors in Raman spectra only. Increasing Si-O stretching constant implies variation of 3 high-frequency modes. The band group in the 750–650 cm-1 region comprises 3 modes strongly influenced by fal-o and subordinately by fsi-al. The 4 modes in the 500–350 cm-1 region are influenced by fo-si-o with weak contribution of O-oscillation, while the 295 cm-1 band is strongly influenced by fo-o, fNa-o and fal-o

ESR and Raman studies on Mn-substituted Y-Ba-Cu-O

ESR and Raman spectra were studied for YBa2(Cu1-xMnx)3O7-y. Among Raman active phonon modes, only the 440 cm-1 mode was found to depend on the Mn content. The two-magnon peak is shifted to the lower frequency side by the addition of Mn. These facts indicate that Mn ions preferentially occupy the site of Cu in the CuO2 plane. The ESR signal originating from antiferromagnetically interacting Mn ions in phase-separated clusters was obtained in all the Mn-doped samples. Both the Mn content dependences of the ESR intensity and the lattice constant show that the content of Mn ions in the CuO2 plane is saturated with an increase in the Mn content above x>0.05.

Active site of bovine adrenocortical cytochrome P-45011.beta. studied by resonance Raman and electron paramagnetic resonance spectroscopies: distinction from cytochrome P-450/scc

Cytochrome P-45011 beta was purified as the 11-deoxycorticosterone-bound form from bovine adrenocortical mitochondria and its active site was investigated by resonance Raman and EPR spectroscopies. Resonance Raman spectra of the purified sample revealed that the heme iron adopts the pure pentacoordinated ferric high-spin state on the basis of the nu 10 (1629cm-1) and nu 3 (1490 cm-1) mode frequencies, which are higher than those of the hexacoordinated ferric high-spin cytochrome P-450scc-substrate complexes. In the ferrous-CO state, a Fe2(+)-CO stretching mode was identified at 481.5 cm-1 on the basis of an isotopic substitution technique; this frequency is very close to that of cytochrome P-450scc in the cholesterol-complexed state (483 cm-1). The EPR spectra of the purified sample at 4.2 K showed ferric high-spin signals (at g = 7.98, 3.65, and 1.71) that were clearly distinct from the cytochrome P-450scc ferric high-spin signals (g = 8.06, 3.55, and 1.68) and confirmed previous assignments of ferric high-spin signals in adrenocortical mitochondria. The EPR spectra of the nitric oxide (NO) complex of ferrous cytochrome P-45011 beta showed EPR signals with rhombic symmetry (gx = 2.068, gz = 2.001, and gy = 1.961) very similar to those of the ferrous cytochrome P-450scc-NO complex in the presence of 22(S)-hydroxycholesterol and 20(R),22-(R)-dihydroxycholesterol at 77 K.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct detection of a dioxygen adduct of cytochrome a3 in the mixed valence cytochrome oxidase/dioxygen reaction.

Time-resolved resonance Raman spectra have been recorded during the reaction of mixed valence (a3+ a2+(3)) cytochrome oxidase with dioxygen at room temperature. In the spectrum recorded at 10 microseconds subsequent to carbon monoxide photolysis, a mode is observed at 572 cm-1 that shifts to 548 cm-1 when the experiment is repeated with 18O2. The appearance of this mode is dependent upon the laser intensity used and disappears at higher incident energies. The high frequency data in conjunction with the mid-frequency data allow us to assign the 572 cm-1 mode to the Fe-O stretching vibration of the low-spin O2 adduct that forms in the mixed valence cytochrome oxidase/dioxygen reaction. The 572 cm-1 v(Fe2(+)-O2) frequency in the mixed valence enzyme/O2 adduct is essentially identical to the 571 cm-1 frequency we measured for this mode during the reduction of O2 by the fully reduced enzyme (Varotsis, C., Woodruff, W. H., and Babcock, G. T. (1989) J. Am. Chem. Soc. 111, 6439-6440; Varotsis, C., Woodruff, W. H., and Babcock, G. T. (1990) J. Am. Chem. Soc. 112, 1297), which indicates that the O2-bound cytochrome a3 site is independent of the redox state of the cytochrome a/CuA pair. The photolabile oxy intermediate is replaced by photostable low- or intermediate-spin cytochrome a3+(3), with t1/2 congruent to 200 microseconds.

Anharmonicity and frequency shift of the apex oxygen O(4) Raman mode in Y1Ba2Cu3O7−δ as a function of doping

We report the Raman spectra of Y1Ba2Cu3O7−δ with δ=0.1 and δ>0.9, as a function of temperature (up to 200 C). We suggest that the appearance of additional modes in the region of 580–600 cm-1 is due to anharmonicity of the crystal potential of the apex O(4) oxygen vibration in addition to disorder. The anomalous positive frequency shift of the 485 cm-1 mode with doping, as well as the anomalous frequency shift at high temperature are shown to be consistent with the reduction of anisotropy of the crystal potential of the O(4) oxygen caused by the gradual addition of charge in the CuO2 planes. Infrared active vibrational modes at this frequency seen in photoexcitation studies also support this conclusion.

Vibrational studies of the structural phase transition in caesium thiocyanate

The room-temperature Raman and infrared (IR) spectra of caesium thiocyanate (CsNCS) and the temperature (T) dependence of the various thermo-sensitive bands are presented. On the basis of these detailed experimental studies the orthorhombic-cubic transition in CsNCS at Tc approximately=470 K has been spectroscopically characterised as an order-disorder transition and to be first order in nature. Typical changes in the integrated intensity Inu (C-N) of the nu C-N-2042 cm-1 mode of the Raman spectrum below Tc are represented as Inu (C-N) varies as ( mod T-Tc mod )2 beta , with an order-parameter exponent beta approximately=0.35. These results are discussed in the context of a theory developed by Bruce et al. (1980) to describe the Raman activity of hard modes near a structural phase transition. A remarkably consistent value of beta approximately=0.35+or-0.02 is obtained by expressing the squares of the frequency shifts of the NCS- librational mode in the temperature range 300-453 K in terms of ( nu R2- nu 02) varies as mod T-Tc mod 2 beta , where nu 0= nu R(Tc)=125 cm-1 and nu R is the frequency of the in-plane rotatory mode. The anomalous increase in the band widths of many modes in the IR and Raman spectra closer to Tc may be attributed to increased anharmonicities as precursor effects to the transition. Above Tc the Raman spectrum due to the external modes is replaced by a broad-band spectrum and the fine structure ( nu C-N+or-external modes) in the nu C-N region of the IR spectrum is smeared off. These results have been related to the loss of translational invariance and the emergence of dynamic near Tc as both ions (Cs+, NCS-) are in motion.

Raman and Infrared Studies of Oxide Superconductors (La1-xMx)2CuO4

Raman and infrared studies of lattice vibrations in new superconductors (La1-xMx)2CuO4 are presented. The 664 cm-1 mode which shows resonant enhancement in La2CuO4 is assigned to the planar breathing mode which strongly interacts with electrons at EF. This resonant scattering is produced by the electronic transition spanning the quasi-square Fermi surface to the nesting directions. In the spectra of Im(ε) a strong peak appears at 246 cm-1 on substituting Sr for La. It is suggested that this mode is related to the electronic transition.

Temperature dependent low-frequency modes in the incommensurate phase of quartz

Simultaneous measurements of Raman and Brillouin scattering spectra were performed on the incommensurate (IC) phase of quartz near the alpha - beta transition at Tc=572 degrees C. In the low-frequency region there are two strongly temperature dependent modes. One is the 7 cm-1 mode observed in Raman spectra with considerable intensity only in the IC phase between Ti(=Tc+1.8K) and Tc. The other mode is the Rayleigh (elastic) component in Brillouin spectra which shows a sharp intensity maximum at about 1.0K above Tc, that is in the middle of the IC phase. This mode, coupled to the longitudinal acoustic mode, seems to separate the IC phase into two temperature regions. Raman activities of the amplitude and phase modes in the IC phase of quartz are studied and compared with the experimental results. In particular, possible differences between the '1-q state', for which the phonon condensation occurs in a single q-direction, and the '3-q state' are discussed. Then, assuming the existence of the '1-q state' in the IC phase, it is shown that the temperature dependences of the 7 cm-1 mode and the Rayleigh peak qualitatively agree with those of the A symmetry amplitude and A symmetry phase mode, respectively.

Effects of cholesterol and adrenodoxin binding on the heme moiety of cytochrome P-450scc: a resonance Raman study.

The effects of cholesterol and adrenodoxin binding on resonance Raman spectra of cytochrome P-450scc in both oxidized and CO-reduced states were examined. Upon cholesterol binding, oxidized cytochrome P-450scc showed a significant shift of spin equilibrium from low-spin to high-spin state. Addition of adrenodoxin caused a complete conversion of cholesterol-bound oxidized cytochrome P-450scc to a pure high-spin state that was considered to be in the hexacoordinated state judged by the v10 mode at 1620 cm-1 and v3 mode around 1485 cm-1. Cholesterol in substrate binding site may oppose a linear and perpendicular binding of carbon monoxide to the reduced heme iron, leading to the distorted Fe-C-O linkage. This is based on the following observations: (1) an increase of the Fe-CO stretching frequency to 483 from 477 cm-1 upon addition of cholesterol; (2) an enhanced photodissociability of bound carbon monoxide of CO complex of cytochrome P-450scc in the presence of cholesterol. As another aspect of the effect of cholesterol on the CO complex form of cytochrome P-450scc, the enhanced stability of the native form ("P-450" form) was observed. There was no additional effect of reduced adrenodoxin on the Raman spectra of the CO-reduced form of cytochrome P-450scc.

Novel Properties of a-SI:H Prepared by Dual Ion Beam Sputtering

ABSTRACTFilms of a-Si:H were deposited by dual ion beam sputtering using a new configuration in which both the argon and hydrogen beam sources are directed at the silicon target. This geometry also permits independent control of the hydrogen and argon energy and particle flux. Infrared absorption mealurents show that even for high hydrogen concentrations, the 2000 cm-1 Si-H stretching band is dominant. This result is in contrast with the more conventional configuration in which the H soyrce is directed at the substrate, resulting in films with dominant 2100 cm-1 mode. This suggests that the precursors resulting in H-incorporation are different for the two configurations. In fact, IR reflectance and SIMS analysis of the silicon sputtering target reveal hydrogen is incorporated, peaking at about 30 Å below the target surface. A strong increase in the photo and dark dc conductivity occurs as the hydrogen ion enery is reduced below 30 eV, suggesting the importance of preventing high energy back-scattered H ion bombardment of thS film. At a H ion energy of 8eV, the values are 2x10-5 (AM1) and 2x10-9 (ohm-cm-1), respectively. Spectroscopic ellipsometry measurements of films reveal a Si-Si bond packing greater than that of low Hcontent a-Si prepared by LPCVD even up to H contents as high as 24%. Above 25% a microstructural transition is observed, verified by SEM, resulting in an increase in the density of voids, (which appears to be responsible for a sudden drop in the hydrogen-induced compressive stress) and accompanied by a shift in the dominant stretching mode energy.

Photo-selection and Zeeman experiments on the phosphorescence of platinum porphin between 1·3 K and 77 K

We report phosphorescence and polarization spectra of the lowest 3 Eu state of platinum porphin in an EPA glass at 1·3 and 77 K. From the results the relative polarizations of the different components of the 0-0 multiplet are determined and vibronic bands involving degenerate modes are identified. The conspicuous 238 cm-1 eg vibronic doublet is studied in more detail by Zeeman experiments on PtP in an n-octane single crystal at 1·3 and 4·2 K, and the relative radiative decay rates of the lower spin components of the 3 Eu state to the two components of the 238 cm-1 ground state vibration are determined. Finally, we account for the decay rates of the 238 cm-1 mode by a mechanism of spin-orbit and vibronic coupling, in which the intensity is stolen from transitions between triplet states.

Raman and infrared spectra of CdIn 2S 4 and ZnIn 2S 4

Four one-phonon Raman lines have been found in CdIn 2S 4 (ZnIn 2S 4) spinels at 92 (72) cm -1, 186 (184) cm -1, 246 (253) cm -1, and 367 (372) cm -1 for incident photon energies well below the energy gap E G ∼ 2.4 (2.2) eV at 300 K. For photon energies close to E G , the 367 cm -1 mode underwent a resonant enhancement in CdIn 2S 4 and four infrared active but Raman forbidden F 1 u modes appeared in the CdIn 2S 4 and ZnIn 2S 4 Raman spectra: TO modes at 226 (221) cm -1 and 309 (312) cm -1, and LO modes at 274 (272) cm -1 and 340 (342) cm -1.

On the phonon spectra of polysulphurnitride, (SN)x

A four-parameter valence force model is presented on the basis of a simplified three-dimensional (SN)x structure. It describes reasonably the gross features of the phonon data known up to now. Evidence for non-central interchain forces is found. The model favours a high-frequency cut-off of the optic spectra at 1004 cm-1. Thus it further suggests that only two lines (1004 cm-1, 660 cm-1) out of all experimental Ag frequencies larger than 600 cm-1 are associated with a first-order Raman process. It explains why the intensity of the peak at 660 cm-1 is expected to be much stronger than that of the 1004 cm-1 mode. The importance of internal strain effects in (SN)x is manifested. The phonon dispersion curves calculated along (010) are presented.