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At least 1,387 records · Page 77Linked to original sources
PubMed2005

Ab initio studies on vibrational spectra of Ni(II), Pd(II), and Pt(II) complexes of M'X4(2-) and M'OS3(2-) (M' = Mo, W; X = O, S).

The vibrational spectra of MM'2X8(2-) and trans-MM'2S6O2(2-) (M = Ni(II), Pd(II), Pt(II); M' = Mo, W; X = O, S) are calculated using ab initio method at RHF/LanL2DZ level. The calculated vibrational frequencies of MM'2S8(2-) and trans-MM'2O2S6(2-) are evaluated via comparison with experimental data. The results obtained by this method have the deviation <5% for M'S and MS stretching vibrational frequencies, however, relatively higher deviation is obtained for M'O stretching vibrational frequencies. Some vibrational frequencies of these complexes that have not been experimentally reported are also predicted and some of the experimental values are assigned.

Models, Molecular↗
PubMed2006

Vibrational assignment of the normal modes of 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one via FTIR and Raman spectra, and ab inito calculations.

Raman and FTIR spectra of 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one were recorded in the regions, 100-3300 and 400-4000 cm(-1), respectively. Vibrational frequencies and intensities of the fundamental modes of this hetrocyclic organic molecule were computed using ab initio as well as AM1 semiempirical molecular orbital methods. Ab initio calculations were carried out with basis set up to RHF/6-311G. Conformational studies regarding the effect of moving the methoxy group in the 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one molecule to a different position on the ring was also carried out. Observed vibrational wavenumbers were found to be mostly consistent with ab initio values. The most intense mode of vibration observed at 1250 cm(-1) in Raman spectra, also observed as a strong band in FTIR, was assigned as C-O stretching vibration in the methoxy group. Asymmetric stretching vibrations between CC and CN bonds was predicted as most intense mode by our ab initio calculation.

Benzylidene Compounds↗
PubMed2006

Interatomic potential parameters of CdHe van der Waals complex derived from excitation spectrum of the C1 1(51P1)<--X10+(51S0) vibrational transition.

The first time observed excitation spectrum of the C(1)1(5(1)P(1))<--X(1)0+(5(1)S(0)) transition in CdHe van der Waals molecules is reported. Vibrational spectrum in the UV region (2286.0-2296 A) was excited in a continuous molecular-jet-expansion beam of CdHe seeded in helium using an in-house-built nitrogen-dye laser system. The excitation spectrum exhibits two vibrational components (v'<--v''=0) highly broadened by means of unresolved rotational structure and some additional contributions of "hot-bands" components (v'<--v''=1). The last effect is due to an extremely small separation of the vibrational levels in the ground X(1)0+ state of the CdHe molecule, where v'=0 vibrational level is separated from v''=0 by merely 6.0 cm(-1). It follows therefore that even in an extremely cold environment (T(v) approximately 10K) of a jet-expansion beam the population of v''=1 level is feasible, due to some residual collisions, and hence the v'<--v'=1 transitions are highly probable. The assignment of vibrational bands and numerical analysis of the spectrum was based and obtained with the aid of a rigorous computer simulation of the C(1)1<--X(1)0+ transition including the impact of rotational structure and hot-bands contributions. As a result we obtained optical potential parameters of the C(1)1(5(1)P(1)) state of CdHe molecule which are further discussed in terms of our recent (and only existing) experimental results regarding the X(1)0+, B1(5(3)P(1)) and A0+(5(3)P(1)) states of CdHe as well as in terms of ab initio calculations results.

Cadmium↗
PubMed2006

Piezoelectric linear motor concepts based on coupling of longitudinal vibrations.

Classically, rotary motors with gears and spindle mechanisms are used to achieve translatory motion. In means of miniaturization and weight reduction piezoelectric linear motors are of interest. Several ultrasonic linear motors found in literature base on the use of two different vibration modes. Most often flexural and longitudinal modes are combined to achieve an elliptic micro-motion of surface points. This micro-motion is converted to direct linear (or translatory) motion of a driven slider. To gain high amplitudes of the micro-motion and thus having a powerful motor, the ultrasonic vibrator should be driven near the eigenfrequency of its modes. Additionally, low mechanical and electrical losses lead to increased efficiency and large amplitude magnification in resonance. This demands a geometrical design that fits the eigenfrequencies of the two different modes. A frequency-deviation of only a few percent leads to non-acceptable disturbance of the elliptical motion. Thus, the mechanical design of the vibrators has to be done very carefully. Within this contribution we discuss different motor designs based on the coupling of two the same longitudinal vibrations within one structure to generate an elliptic motion of surface points. Different concepts based on piezoelectric plates and Langevin transducers are compared. Benefits and drawbacks against the combination of longitudinal and bending modes will be discussed. Numerical results of the stator vibration as well as motor characteristics are validated by measurements on different prototypes.

Journal Article↗
PubMed2000

The development of reactor coolant pump vibration monitoring and a diagnostic system in the nuclear power plant.

Monitoring abnormalities within reactor coolant pumps due to vibration, we introduce a Wigner distribution (WD) to a vibration monitoring system for analyzing vibration signals, and develop an on-line diagnostic method using the neural network employing back propagation algorithm. A rotor kit is used to simulate the abnormal conditions in the pump such as bearing rubbing, shaft bending, misalignment, etc. The data collected from the kit are analyzed using both a conventional system based on the Fourier transform (FT) and the software developed with the WD in this study, and they are compared. The study shows that spectrum represented by WD makes it easy to analyze the vibration signals of a rotating machine and the developed diagnostic method will help the operators grasp the cause of vibrations.

Journal Article↗
PubMed2002

Enhanced vibration performance of ultrasonic block horns.

Block horns are tuned components designed to vibrate in a longitudinal mode at a low ultrasonic frequency. Reliable performance of such horns is normally associated with the amplitude of vibration, uniformity of vibration amplitude at the working surface and the avoidance of modal participation by non-tuned modes at the operating frequency. In order to maximise vibration amplitude uniformity, standard slotting configurations are included in the horn design. However, defining a slotted block geometry which guarantees sufficient tuned frequency isolation from nearby modes as well as high amplitude and amplitude uniformity, is not straightforward. This paper discusses horn configurations which satisfy these criteria and investigates the design requirements of block horns which operate as intermediate components in ultrasonic systems, where the block horn dominates the vibration behaviour of the system. The importance of mode shape characterisation is discussed and modes are classified using experimental data from 3D laser Doppler vibrometer measurements and finite element analysis. In particular, the role of additional fine slots and castellations are studied with reference to two distinct ultrasonic applications involving a similar block horn.

Journal Article↗
PubMed2003

Open-circuit test of a PZT vibrator and its applications.

This study investigates a terminal transient response of a Langevin-type PZT vibrator theoretically and experimentally to quantify an electrical shock and refine an equivalent circuit of the vibrator. The shock is induced immediately after an AC sinusoidal voltage of the vibrator is switched off. Then, the transient response involves a DC part and an AC part, which approach zero at the DC and AC times, respectively, and the vibrator is placed on a sponge in air. To do so, we should propose an open-circuit test to find the AC and DC times in addition to the maximum amplitude of the transient response. Thus the DC times exceeds the AC time, and the AC and DC times are used to estimate the resistances in the equivalent circuit presenting the real mechanical and dielectric losses, respectively. Therefore, the resistances in the equivalent circuit are sensitive to the vibration amplitude, but the inductance and capacitances are not. Furthermore, the maximum amplitude is required to cause the shock, and depends on the frequency of the source and the open-circuited time, and is about 65 times the amplitude of the source.

Journal Article↗
PubMed2000

Functional imaging of vocal fold vibration: digital multislice high-speed kymography.

For the diagnosis of voice disorders, and especially for the classification of hoarseness, direct observation of vocal fold vibration is essential. Furthermore, a quantitative description of the movement of the vocal fold becomes increasingly necessary to document and compare findings as well as the progression of speech therapy. On the base of digital high-speed sequences of vocal fold vibration, multiple "functional images"-also called digital kymograms-are obtained using image- and signal-processing algorithms. Digital kymograms can serve as a powerful aid for visualization, description, and classification of vocal fold vibration and as an intermediate step for image interpretation by biomechanical modeling. This visualization technique will be discussed and compared to other techniques currently available: videokymography and videostroboscopy. The technique is applied to several clinical examples: aperiodic processes (phonation onset), irregular vocal fold vibration (paralysis of the recurrent nerve), particular vibration modes (anterior-posterior modes), and running speech.

Humans↗
PubMed2001

Fragment mode analysis and its application to the vibrational normal modes of boron trichloride-ammonia and boron trichloride-pyridine complexes.

A method for expressing quantitatively the vibrational normal modes of a molecule in a basis set consisting of the normal vibrations (plus translations and rotations) of its constituent fragments is presented. The method is illustrated by describing the vibrational modes of BCl3-NH3 and BCl3-pyridine electron donor-acceptor complexes in terms of motions of BCl3 and either NH3 or pyridine. These complexes show examples of mixing between modes located on different fragments, mixing between modes of one fragment due to symmetry lowering, and the transformation of six fragment translations/rotations into vibrations of the complex. Although perturbation theory has been proposed to explain such examples of mode mixing, calculations imply that interactions between fragments of both complexes are too strong for perturbation theory to be generally applicable. In addition, the transformation of fragment rotations and/or translations into vibrations of the composite molecule will always occur and cannot be understood in detail by using perturbation theory. For the BCl3-pyridine complex, a band observed at 1107 cm(-1) is re-assigned as a combination of C-H in-plane bending and a ring-breathing mode of the pyridine fragment.

Ammonia↗
PubMed2002

Structural and vibrational study of the Ci(1) conformation of 18-crown-6.

Optimized geometry, vibrational frequencies and IR absorption intensities were calculated for the Ci(1) conformation of 18c6. Optimized geometry was compared with the experimental geometry and that of the Ci(2) conformation of 18c6. The Ci(1) conformation is more planer than the Ci(2) conformation of 18c6, which provides an explanation that free 18c6 in the crystal phase has a Ci(1) conformation. Vibrational frequencies were scaled using an unvaried one-scale-factor scaling of 0.928. Calculated vibrational frequencies were compared with the experimental vibrational frequencies. The root-mean-square deviation of the difference between the calculated and experimental frequencies was only 15 cm(-1). This excellent agreement between the calculated and experimental frequencies is an indication of the proper assignment of the fundamental vibrational frequencies of the Ci(1) conformation of 18c6.

Crown Ethers↗
PubMed2002

The anomalous solvent effect in the vibrational spectrum of 2,3-diphenyl-cycloprop-2-enone: an experimental and theoretical investigation.

2,3-Diphenyl-cycloprop-2-enone (DPC) was investigated aiming to understand the origins of the anomalous solvatochromism in its vibrational spectrum. Its Raman and IR spectra in several solvents were obtained revealing that the v(C=C) mode is much more sensitive to the solvent than the v(C=O) mode. Hartree-Fock and density functional theory calculations were undertaken for obtaining the structure and the vibrational spectra of DPC and 2,3-dimethylcycloprop-2-enone (DMC), revealing that both in terms of structure as well as of vibrational spectrum, DPC and DMC are very similar. Such results indicated that DMC could be used as a model system to simulate the solvent effect in DPC, what was done using three different methods: the first takes into account the dielectric effect via the self-consistent reaction field (SCRF); the second is the supermolecular approach that considers explicity the formation of solute-solvent clusters and the third is a combined approach, SCRF + supermolecule. The anomalous solvatochromism in the vibrational spectrum of DPC can be understood on basis of the significant participation of the v(C=O) mode in the one assigned to the v(C=C) vibration, as well as by the presence of a Fermi resonance involving the former. In addition, the v(C=O) mode involves a significant participation of the (C-C) mode (C(cyclopropene)-C(phenyl)) and the two interatomic distances, C=O and C-C, show opposite trends with increasing solvent polarity. Summing up, the anomalous solvatochromic effect of DPC can be understood by the complex composition of its v(C=O) mode that, in addition, is affected by the presence of a Fermi resonance.

Cyclopropanes↗
PubMed2003

Theoretical studies on vibrational spectra of mixed cyanide-halide complexes of platinum(IV) and palladium(IV).

The vibrational spectra of mixed cyanide-halide complexes, M(CN)4X 2 2- and M(CN)5X2- (M=Pt and Pd; X=F, Cl, Br and I), have been systematically investigated by ab initio RHF, B3LYP and MP2 methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of platinum complexes are evaluated via comparison with the experimental values. In the infrared frequency region, the C--N stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations, -16-4 cm(-1) for Pt(CN)4X 2 2- and -18 to -2 cm(-1) for Pt(CN)5X2-. However, in far-infrared region, the results obtained at RHF level are better than those calculated at B3LYP and MP2 levels. For RHF/SDD method, the deviations for Ptz.sbnd;X and Ptz.sbnd;C stretching vibrational frequencies are -14-1 and -12 to -2 cm(-1) in the complex Pt(CN)4X2 2-, -19 to -11 and -15-14 cm(-1) in the Pt(CN)5X2- complex, respectively. The vibrational frequencies of palladium(IV) and some platinum(IV) complexes that have not been experimentally reported are predicted.

Cyanides↗
PubMed2003

Ab initio prediction of the vibrational spectrum of the hydrogen bonded complex O2N...HONO2.

The changes in the structural parameters and vibrational characteristics (vibrational frequencies, infrared intensities and Raman activities) arising from the hydrogen bonding between NO(2) and HONO(2) have been studied employing ab initio 6-31G(d, p)/UHF and 6-31+G(d, p)/UHF, and B3LYP/6-31G(d, p) calculations. The charge rearrangement upon hydrogen bonding have been, estimated using the Mulliken population analyses. It was established that the complexation between NO(2) and HONO(2) leads to changes in the structural parameters and the vibrational characteristics of the monomers. The most sensitive to the hydrogen bond formation are the vibrational characteristics of the normal modes of the monomer bonds participating in the hydrogen bonding. The predicted shifts in the vibrational frequencies by ab initio and B3LYP/6-31G(d, p) calculations are in very good agreement with the experimentally observed, which is an evidence for the reliance of the studied structure.

Hydrogen Bonding↗
PubMed1999

A vibrational spectroscopic assignment of the disulfide bridges in recombinant bovine growth hormone and growth hormone analogs.

Disulfide stretching vibrations for bovine growth hormone (bGH) occur in a vibrational envelope centered at 540 cm-1 which spans 480-580 cm-1. A multitude of vibrational bands present in this envelope, that are not related to disulfide stretching, emphasize the need for model compounds when assigning S-S stretching modes. Raman spectroscopic data for bGH analogs, in which one or both of the two disulfide bridges have been selectively cleaved, have been used to characterize the S-S stretching envelope for the two cystine links in bGH. The Raman data for the r-bGH analogs indicate that the number of disulfide bonds present in r-bGH is determined, not by the observance of the presence or absence of a single spectral peak, but by the relative intensity of vibrational envelope from 520-560 cm-1. Cleavage of disulfide bridges in bGH results in a general decrease in vibrational spectral intensity in the 520-560 cm-1 range. This decrease in intensity is proportional to the number of cystine links severed.

Animals↗
PubMed2000

Density functional theory study on fundamental vibrational spectra of disilyl iodide and its isotopomer.

Density function theory calculations using B3' exchange functional and LYP' correlation functionals (B3LYP) with the 3-21G** basis set were carried out to study the molecular structure and fundamental vibrational frequencies of Si2H5Br, Si2H5I and their isotopomers. One scale factor used to scale Si-H(D) force constants for Si2H5Br is transferred from Si2H5Br to Si2H5I. Other scale factors of force constants for Si2H5I and Si2D5I are determined by a least-squares fitting to experimental vibrational frequencies. The predictions of fundamental vibrational frequencies for Si2H5I and its isotopomer are given. The scaled DFT force fields using B3LYP/3-21G** reproduced the observed fundamental vibrational frequencies of Si2H5I and its deuterium isotopomer with a mean absolute deviation of 6 cm(-1). Reassignment of some fundamental vibrational modes of Si2H5I and its isotopomer is discussed.

Silanes↗
PubMed1995

Binding sites of quinones in photosynthetic bacterial reaction centers investigated by light-induced FTIR difference spectroscopy: symmetry of the carbonyl interactions and close equivalence of the QB vibrations in Rhodobacter sphaeroides and Rhodopseudomonas viridis probed by isotope labeling.

The photoreduction of the secondary quinone acceptor QB in reaction centers (RCs) of the photosynthetic bacteria Rhodobacter sphaeroides and Rhodopseudomonas viridis has been investigated by light-induced FTIR difference spectroscopy of RCs reconstituted with several isotopically labeled ubiquinones. The labels used were 18O on both carbonyls and 13C either uniformly or selectively at the 1- or the 4-position, i.e., on either one of the two carbonyls. The QB-/QB spectra of RCs reconstituted with the isotopically labeled and unlabeled quinones as well as the double differences calculated from these spectra exhibit distinct isotopic shifts for a number of bands attributed to vibrations of QB and QB-. The vibrational modes of the quinone in the QB site are compared to those of ubiquinone in vitro, leading to band assignments for the C = O and C = C vibrations of the neutral QB and for the C***O and C***C of the semiquinone. The C = O frequency of each of the carbonyls of the unlabeled quinone is revealed at 1641 cm-1 for both species. This demonstrates symmetrical and weak hydrogen bonding of the two C = O groups to the protein at the QB site. In contrast, the C = C vibrations are not equivalent for selective labeling at C1 or at C4, although they both contribute to the approximately 1617-cm-1 band in the QB-/QB spectra of the two species. Compared to the vibrations of isolated ubiquinone, the C = C mode of QB does not involve displacement of the C4 carbon atom, while the motion of C1 is not hindered. Further analysis of the the spectra suggests that the protein at the binding site imposes a specific constraint on the methoxy and/or the methyl group proximal to the C4 carbonyl. The FTIR observations provide compelling evidence for almost identical conformation and identical interactions of the ubiquinone in the QB binding site of Rb. sphaeroides and Rp. viridis in contrast to the X-ray structures, which yield different descriptions for the hydrogen-bonding pattern of QB binding. In the semiquinone state, the bonding interactions of the C***O groups are also symmetrical and the C***C are inequivalent at C1 and C4. However, the interactions are almost the same in the RCs of both species.

Binding Sites↗
PubMed1990

Metal-ligand vibrations of cyanoferric myeloperoxidase and cyanoferric horseradish peroxidase: evidence for a constrained heme pocket in myeloperoxidase.

The low-frequency FeCN vibrations of cyanoferric myeloperoxidase (MPO) and horseradish peroxidase (HRP) have been measured by resonance Raman spectroscopy. The ordering of the frequencies of the predominantly FeC stretching and FeCN bending normal vibrational modes in the two peroxidases differs. These normal mode vibrations are identified by their wavenumber shifts upon isotopic substitution of the cyanide ligand. For MPO, the stretching mode nu 1 (361 cm-1) occurs at a lower frequency than the bending mode delta 2 (454 cm-1). For HRP, the order is reversed as nu 1 (456 cm-1) is at a higher frequency than delta 2 (404 cm-1). Normal coordinate analyses and model complexes have been used to address the origin of this behavior. The nu 1 stretching frequencies in cyanide complexes of iron porphyrin and iron chlorin model compounds are similar to one another and to that of HRP. Thus, the inverted order and altered frequencies of the nu 1 and delta 2 vibrations in MPO, relative to those in HRP and the model compounds, are not inherent to the proposed iron chlorin prosthetic group in MPO but, rather, are attributed to distinct distal environmental effects in the MPO active site. The normal coordinate analyses for MPO and HRP showed that the nu 1 and delta 2 vibrational frequencies are not pure; the potential energy distributions for these modes respond not only to the geometry but also to the force constants of the nu(FeC) and delta(FeCN) internal coordinates.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed2005

Vibrational distributions of the CO(v) products of the C2H2 + O(3P) and HCCO + O(3P) reactions studied by FTIR emission.

The C2H2 + O(3P) and HCCO + O(3P) reactions are investigated using Fourier transform infrared (FTIR) emission spectroscopy. The O(3P) radicals are produced by 193 nm photolysis of an SO2 precursor or microwave discharge in O2. The HCCO radical is either formed in the first step of the C2H2 + O(3P) reaction or by 193 nm photodissociation of ethyl ethynyl ether. Vibrationally excited CO and CO2 products are observed. The microwave discharge experiment [C2H2 + O(3P)] shows a bimodal distribution of the CO(v) product, which is due to the sequential C2H2 + O(3P) and HCCO + O(3P) reactions. The vibrational distribution of CO(v) from the HCCO + O(3P) reaction also shows its own bimodal shape. The vibrational distribution of CO(v) from C2H2 + O(3P) can be characterized by a Boltzmann plot with a vibrational temperature of approximately 2400 +/- 100 K, in agreement with previous results. The CO distribution from the HCCO + O(3P) reaction, when studied under conditions to minimize other processes, shows very little contamination from other reactions, and the distribution can be characterized by a linear combination of Boltzmann plots with two vibrational temperatures: 2320 +/- 40 and 10 300 +/- 600 K. From the experimental results and previous theoretical work, the bimodal CO(v) distribution for the HCCO + O(3P) reaction suggests a sequential dissociation process of the HC(O)CO++ --> CO + HCO; HCO --> H + CO.

Journal Article↗