Large Frequency Shift Research Articles

Study of complexes of water and ammonia molecules in He droplets

Spectra of the binary complexes of water and ammonia molecules in the OH stretching region have been studied in helium droplets. The infrared intensity in the hydrogen bond bridge stretching mode was found to be enhanced by a factor of 2.5 with respect to the ν 3 band of single water molecules. This enhancement factor is significantly smaller than that obtained in recent theoretical calculations. The observed large band frequency shifts are similar to those measured in other rare gas matrices indicating the strong hydrogen bonding in the complex.

Molecular resolution in dynamic force microscopy: topography and dissipation for weaklyinteracting systems

Dynamic force microscopy can be used to study the growth of organic molecules oninsulating substrates. The organic molecule 3,4,9,10-perylenetetracarboxylic-dianhydride(PTCDA) exhibits Volmer–Weber growth on KBr(001). While large areas are uncovered,some PTCDA crystallites of different heights, from two monolayers (ML) up to 20–30 ML,can be seen, even at low coverages. On the topmost layer of the crystallites, singlemolecules can be resolved. Such a molecular contrast does not only show in topography butalso in the dissipation signal. Here, the signal strongly depends on the frequency shift, i.e.,the minimum distance between tip and sample. At large frequency shifts, thedissipation is enhanced between the molecules, if the frequency shift is lower, a shiftof 0.2 nm between the peaks in topography and dissipation channel occurs. Wepropose a model that takes the crystalline growth of PTCDA into account, theshift between both signals being an effect of the two topmost layers of molecules.

High-Pressure Vibrational Spectroscopy of Energetic Materials: Hexahydro-1,3,5-trinitro-1,3,5-triazine

Vibrational spectroscopy has been used to investigate the room-temperature high-pressure phases of the energetic material hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The pressure-induced alterations in the spectral profiles were studied in a compression sequence to 30.2 GPa using Raman spectroscopy and to 26.6 GPa using far-infrared spectroscopy. At pressures near 4.0 GPa, several changes become immediately apparent in the Raman spectrum, such as large frequency shifts, mode splittings, and intensity changes, which are associated with a phase transition from alpha-RDX to gamma-RDX. Our study extends the kinetic stability of gamma-RDX to pressures near 18.0 GPa. Evidence for a new phase was found at pressures between 17.8 and 18.8 GPa and is based on the appearance of new vibrational bands and associated changes in intensity patterns. The new phase has vibrational characteristics that are similar to those of beta-RDX, suggesting the two polymorphs share a related crystal structure.

Explanation of the JET n = 0 chirping mode

Persistent rapid up and down frequency chirping modes with a toroidal mode number of zero (n = 0) are observed in the JET tokamak when energetic ions, in the range of several hundred keV, are created by high field side ion cyclotron resonance frequency heating. Fokker–Planck calculations demonstrate that the heating method enables the formation of an energetically inverted ion distribution which supplies the free energy for the ions to excite a mode related to the geodesic acoustic mode. The large frequency shifts of this mode are attributed to the formation of phase space structures whose frequencies, which are locked to an ion orbit bounce resonance frequency, are forced to continually shift so that energetic particle energy can be released to counterbalance the energy dissipation present in the background plasma.

Probing theSi(001)surface with a Si tip: Anab initiostudy

Topographic noncontact atomic force microscopy (NC-AFM) images of the $p(2\ifmmode\times\else\texttimes\fi{}1)$ and $c(4\ifmmode\times\else\texttimes\fi{}2)$ reconstructions of the $\mathrm{Si}(001)$ surface are simulated for the cases of weak and strong tip-surface interactions and various temperatures using ab initio density functional theory. In the simulations the surface is imaged by a sharp silicon tip with a single dangling bond at its apex. At a very close approach to the surface, the tip flips a surface dimer when positioned close to its lower atom. The energy barriers for an individual flipped surface dimer to regain its initial configuration are calculated to be $\ensuremath{\sim}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, implying that the surface should be able to ``heal'' itself at all but extremely low temperatures during one oscillation cycle of the cantilever. Thus, at small enough temperatures, $T\ensuremath{\leqslant}70\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and large frequency shifts, the imaging process is dominated by tip induced dimer flip events resulting in a permanent deformation of the surface and an apparent $p(2\ifmmode\times\else\texttimes\fi{}1)$ symmetric phase to be observed. No dissipation is expected as the tip oscillations are conservative at these conditions. At intermediate temperatures, $70\phantom{\rule{0.3em}{0ex}}\mathrm{K}\ensuremath{\leqslant}T\ensuremath{\leqslant}200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the flipped dimers are able to return to the ground state during each tip oscillation, resulting in continuous healing of the surface and thus large dissipation is expected. At $T\ensuremath{\geqslant}200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ dimers flip back and forth easily resulting in an apparent symmetric $p(2\ifmmode\times\else\texttimes\fi{}1)$ phase and noticeable dissipation. At small frequency shifts the dimers do not flip, still the upper dimer atoms are imaged as bright so that surface reconstruction can easily be determined. The possibility of manipulating the orientation of dimers at low temperatures and large frequency shifts by means of preprogrammed scan directions, is also discussed.

Angular and chromatic dispersion in Kerr-driven conical emission

We report measurements of ultrashort optical pulse filamentation in Kerr media with normal dispersion. We measure the angular dispersion of spontaneously generated colored conical emission and show that for large frequency shifts from the input pump frequency, it is well described by a relation between angle and frequency with slope determined solely by material chromatic dispersion. This measurement is in agreement with recent models that interpret filamentation dynamics in terms of the spontaneous formation of nonlinear X-waves. Finally, experimental results of filamentation in air show, for the first time, that the interpretation of CE in terms of X-waves may be also extended to gaseous media.

Orthorhombic α‐Ca(HCOO)2 and monoclinic LiH2C6H4SO3 · H2O crystals – new materials for Raman lasers with large frequency shifts

AbstractWe report on the first observation of χ(3)‐nonlinear lasing effects – efficient high‐order stimulated Raman scattering (SRS) in LiH2C6H4SO3 · H2O and α‐Ca(HCOO)2 single crys‐ tals. We classify these materials as promising SRS‐media for Raman laser converters with many large frequency shifts. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Newly-Developed Adaptive Noise Absorption Control Technology for High Speed Fan Noise Reduction

The paper describes about a newly-developed adaptive noise absorption control (AAC) technology I for fan noise reduction and about proof test results of the technology. The AAC technology adaptively controls the reactance part of acoustic impedance of duct liners with mobile reflective plates and large acoustic chambers, absorbs fan tones and broadband noise together, and achieves larger overall fan noise reduction over a wide fan speed range. For actual proof of the technology, adaptive duct liner I was made on trial basis and was examined. The test result clarifies that the duct liner I could reduce fan noise larger than O.A. SPL 10dB (A) at max fan speed of 6000rpm, including reduction of low frequency noise and fundamental BPF tone and harmonics of 18dB at maximum. In response to fan speed change, the reflective plate movement control could achieve the large peak frequency shift and peak level increase in the acoustic absorption spectra, and could reduce fan noise larger than O.A. SPL 9dB (A) over the fan speed range from 1000 to 6000rpm.

Effect of dispersion fluctuations on widely tunable optical parametric amplification in photonic crystal fibers

The effect of dispersion fluctuations on the conversion efficiency of large frequency shift parametric sidebands is studied by numerical simulation and experiment. Numerical results based on periodic and random dispersion models are used to fit the experimental results. The fitting parameters provide a measure of the uniformity of the photonic crystal fiber used in the experiment. This allows us to place limits on the required uniformity of a photonic crystal fiber for strong frequency conversion.

Multimode guided-wave non-3omega third-harmonic generation by ultrashort laser pulses

Unlike third-harmonic generation in a monochromatic field, which gives rise to a signal at the frequency 3omega0, with omega0 being the frequency of the pump field, a broadband ultrashort pump pulse can generate isolated spectral peaks that are substantially shifted from the frequency 3omega0. In the multimode guided-wave regime, this non-3omega third-harmonic generation maps adjacent guided modes of the third harmonic onto a manifold of spectral peaks around 3omega0. The spectral shifts and the widths of these peaks are controlled by the phase and group-velocity mismatch between the pump field and third-harmonic modes, as well as the length of nonlinear-optical interaction, allowing the spectral contents of the third-harmonic signal to be engineered by tailoring the dispersion of the pump and third-harmonic modes involved in the nonlinear-optical process. Photonic-crystal fibers possess a unique combination of properties required to achieve large frequency shifts in non-3omega third-harmonic generation, allowing efficient tunable frequency upconversion based on this phenomenon.

A study of the acoustic behavior of a plastic, blast-hardened, antitank landmine

Mechanical resonances in landmines are often exploited by some acoustic-to-seismic detection schemes. As such, a study of an acoustically active landmine has been performed. Measurements of the mechanical resonances of the pressure plate reveal seven modes below 1.6 kHz and a large frequency shift of the first symmetric mode of the pressure plate, such that it occurs higher in frequency than the first asymmetric mode. The pressure plate is considered to act as an elastically supported thin plate, and the observed perturbation of the first symmetric mode is believed to be caused by the landmine’s blast-hardening mechanism. This is confirmed by a lumped acoustic element model of the system of pressure plate and blast-hardening mechanism. Mass-loading experiments in water show a decrease in resonance frequency with increasing depth that saturates at shallow depths as predicted by Velea et al. [J. Acoust. Soc. Am. 115, 1993 (2004)]. Similar mass-loading measurements in sand reveal an interesting phenomenon; flush burial of the landmine effectively removes the effect of the blast-hardening mechanism on the pressure plate. A qualitative theoretical model of this phenomenon will be presented.

Time-Domain Theoretical Analysis of the Noncoincidence Effect, Diagonal Frequency Shift, and the Extent of Delocalization of the CO Stretching Mode of Acetone/Dimethyl Sulfoxide Binary Liquid Mixtures

A time-domain method for simulating vibrational band profiles that simultaneously takes into account both the diagonal and off-diagonal effects is developed and applied to the C=O stretching bands of neat liquid acetone and the acetone/dimethyl sulfoxide (DMSO) binary liquid mixtures. By using this method, it is possible to examine the influence of liquid dynamics on the noncoincidence effect (NCE), which arises from the off-diagonal vibrational interactions, as well as the frequency shifts and band broadening, which are related to both the diagonal and off-diagonal effects. It is shown that the simulations for the C=O stretching bands of acetone in acetone/DMSO binary liquid mixtures on the basis of this method can reproduce the experimentally observed concave curvature of the concentration dependence of the NCE and the unusually large frequency shift of the anisotropic Raman band. The widths of the infrared, isotropic Raman, and anisotropic Raman bands calculated for neat liquid acetone are also in good agreement with those observed. Based on these calculations, the extent of delocalization of the C=O stretching vibrational motions is examined by referring to two quantitative measures of this property, one calculated in the frequency domain and the other in the time domain. It is shown that the extent of delocalization gets larger as the mole fraction of acetone increases, the C=O stretching vibrations being delocalized over a few tens of molecules in neat liquid acetone. It is also shown that the extent of delocalization is related to the quantity called NCE detectability, which is the ratio between the magnitude of NCE and the bandwidth. It is therefore suggested that the extent of delocalization of vibrational motions may be estimated from observable features of Raman band profiles.

Four-wave mixing with large Stokes shifts in heavily Ge-doped silica fibers

Four-wave mixing (FWM) in nonlinear germanosilicate fibers with GeO2 concentrations as high as 67 mol.% in the core is studied theoretically and experimentally. Large frequency shifts of 1875-3829 cm(-1) are observed in the mixed-mode pump parametric process. The dependence of FWM phase matching on the GeO2 concentration, core diameter, and index profile is demonstrated. The 2.5% conversion efficiency of an 887 nm signal to a 1.3 microm communication band is obtained at a 2 W cw pump power inside the fiber.

UV-Cross-Linked Poly(vinylpyridine) Thin Films as Reversibly Responsive Surfaces

We report that UV-cross-linked poly(4-vinylpyridine) (P4VP) films acted as reversibly responsive coatings that controlled surface wettability and swelling toward external stimuli: solvent and pH. The polymer films were prepared simply by spin-coating a solution of P4VP followed by UV irradiation. These cross-linked films, when treated with chloroform, showed ∼31% increase in film thickness whereas films extracted with methylene chloride or n-butanol exhibited a slight decrease. The increase in film thickness was due to the protonation of pyridyl groups by hydrogen chloride resulting from the photodegeneration of chloroform. The film expanded to minimize repulsion around the charged centers. This hypothesis was further confirmed by exposing the cross-linked film to hydrogen chloride vapor. The film expanded ∼37% whereas no thickness increase was observed for films exposed to ammonia or methanol vapors. The extent of swelling was monitored in situ using a quartz crystal microbalance sensor. Large oscillation frequency shifts were detected when the UV-cross-linked P4VP film was exposed to acidic buffer solutions. The changes were rapid, and the effect was reversible.

Vapor phase detection of a narcotic using surface acoustic wave immunoassay sensors

Currently, the narcotic sniffing dog remains the most accurate, reliable, and widely used sensing technology in the war on drugs. However, recent studies done at the Institute for Biological Detection Systems at Auburn University, Auburn, AL, have shown that in the presence of extraneous odors (nontarget odors), these animals show a higher propensity for so-called false alarms. For this reason, there have been an increasing demand for a portable, highly specific vapor-sensing device capable of distinguishing a target vapor signature in a complex odor. In this paper, we present the results of a series of experiments demonstrating real-time vapor phase detection of cocaine molecules. A distinctive response or signature was observed under laboratory conditions, where the cocaine vapors were presented using an INEL vapor generator and under "field" conditions facilitated by the Georgia Bureau of Investigation Crime Lab. For these experiments, the sensor component was an ST-X quartz resonator with a center frequency of approximately 250-MHz. Anti-benzoylecgonine (anti-BZE) antibodies are attached to the electrodes on the device surface via a protein-A cross linker. We observed a large transient frequency shift accompanied by baseline shift with the anti-BZE coated sensor. After repeated experiments and the use of numerous controls, we believe that we have achieved real-time molecular recognition of cocaine molecules.

Spectroscopic identification of adsorption properties of Zn2+ ions at cationic positions of high-silica zeolites with distant placing of aluminium ions

For Zn2+ cations in ZnZSM-5 zeolite unusual type of cationic positions, formed by two distantly placed framework aluminium atoms, is considered. Some extent of structural destabilization of cations in these cationic positions in comparison with traditional localization should result in promoted Lewis activity and adsorption activity of these sites. The last ones are manifested in the significantly increased IR low frequency shifts for adsorbed molecules and in their ability for heterolytic dissociation at elevating temperature. DFT cluster quantum chemical modeling of light alkane adsorption on Zn2+ in ZnZSM-5 zeolites confirms these conjectures in full agreement with recent experiments. Similar to the previously considered dihydrogen and methane molecule adsorption, we present here the calculations of ethane molecular and dissociative adsorption on these sites. It is shown that the unusually large ethane IR frequency shift recently observed in ZnZSM-5 zeolite can result from adsorptive interaction of C2H6 with Zn2+ stabilized in a cationic position with distantly placed aluminium ions. The dissociative adsorption of ethane molecules with the formation of bridged hydroxyl group and Zn–C2H5 structure is considered and an activation energy of ethylene formation from the alkyl fragment is evaluated.

Nanomechanical hydrogen sensing

A nanomechanical beam resonator is used as a sensitive, specific hydrogen sensor. The beam is fabricated from AuPd alloy and tested by magnetomotive transduction at room temperature. The fundamental resonance frequency decreases significantly and reversibly at hydrogen pressures above 10−5Torr, whereas the frequency shifts observed for other gases are significantly smaller. The large frequency shift is likely due to the formation of interstitial hydrogen in the metal alloy lattice, which relieves the built-in tensile stress in the resonator beam. The uptake of hydrogen as measured by frequency shift is consistent with previous studies.

Adsorption Behavior of Metal Ions onto a Bovine Serum Albumin (BSA) Membrane Monitored by Means of an Electrode-Separated Piezoelectric Quartz Crystal

The interaction between metal ions and bovine serum albumin (BSA) was studied by using a piezoelectric quartz crystal (PQC) arranged in the electrode-separated configuration. A silanized surface of the PQC was coated with a BSA membrane via a coupling reaction with glutaraldehyde. The frequency shifts obtained from PQC coated with a BSA membrane suggested that various kinds of metal ions could be adsorbed onto the BSA membrane from aqueous solutions containing a low concentration of metal ions (2 or 10 micromol dm(-3)), only when the BSA was denatured with an alkaline solution. Anionic species of Pt(IV) and Au(III) were adsorbed onto the denatured BSA membrane from an acetic acid solution at pH 2.2, and cationic species of Cd(II), Zn(II), Co(II), Ni(II), Cu(II), and Ag(I), and cations, such as Ca2+, Ba2+, and Mg2+, were adsorbed from ammonia buffer at pH 9.5, whereas Al(III), Cr(III), Fe(III), Hg(II), and Pb(II) were hardly adsorbed. The adsorption mechanisms of these metal ions are discussed, based on the electrostatic interaction between the metal ions and the denatured BSA membrane, and complex formation between the metal ions and amino acid residues of the denatured BSA. Further, the PQC coated with a denatured BSA membrane was applied to the determination of Pt and Cd, using large frequency shifts for Pt(IV) and Cd(II).

Decoherence in strongly coupled quantum oscillators

In this paper, we present a comprehensive analysis of the coherence phenomenon of two coupled dissipative oscillators. The action of a classical driving field on one of the oscillators is also analyzed. Master equations are derived for both regimes of weakly and strongly interacting oscillators from which interesting results arise concerning the coherence properties of the joint and the reduced system states. The strong coupling regime is required to achieve a large frequency shift of the oscillator normal modes, making it possible to explore the whole profile of the spectral density of the reservoirs. We show how the decoherence process may be controlled by shifting the normal mode frequencies to regions of small spectral density of the reservoirs. Different spectral densities of the reservoirs are considered and their effects on the decoherence process are analyzed. For oscillators with different damping rates, we show that the worse-quality system is improved and vice versa, a result which could be useful for quantum state protection. State recurrence and swap dynamics are analyzed as well as their roles in delaying the decoherence process.

Contrast effect of hydrogen bonding on the acceptor and donor OH groups of intramolecularly hydrogen-bonded OH pairs in diols

We studied the influence of hydrogen bonding on the fundamental and overtone bands of the OH-stretching vibration of each OH group in the intramolecularly hydrogen-bonded OH(I)::OH(II) pair in 1,2-, 1,3- and 1,4-diols. The hydrogen bonding between the two OH groups significantly increases in strength from the five-membered ring of a 1,2-diol to the seven-membered ring of a 1,4-diol. Although the hydrogen bonding does not affect the vibrational property of the OH(II) (or acceptor), it significantly influences the OH(I) (or donor). As the hydrogen bonding becomes stronger from a 1,2- to a 1,4-diol, the fundamental band of the OH-stretching shifts downwards by from about 50 to 140 cm −1, and the overtone band markedly decreases in intensity, although the effect on the intensity and bandwidth of the fundamental band varies among 1,2-, 1,3- and 1,4-diols. The quantum-mechanically calculated normal frequencies of the acceptor and donor OH groups in the hydrogen-bonded ring are in good agreement with the observed frequencies. The calculated interatomic distance between the O of an acceptor OH and the H of a donor OH is the shortest for a 1,4-diol, which is consistent with the largest frequency shift caused by the hydrogen bonding.