Overtone Resonance Research Articles

Protein Tuning of Excited-State Charge-Transfer Dynamics in Azurin

Resonance Raman spectra of azurin from Alcaligenes denitrificans have been measured at wavelengths throughout the S(Cys) → Cu charge-transfer absorption band to examine the effects of structure and environment on the excited-state charge-transfer dynamics. Measurement of the depolarization ratios suggest that the Raman scattering is enhanced by a single electronic transition. Self-consistent analysis of the absorption spectrum and the resonance Raman fundamental, overtone, and combination bands yields a total inner-sphere reorganization energy of 0.26 ± 0.02 eV, similar to that for Pseudomonas aeruginosa. The reorganization energy is distributed along similar vibrational modes in the two azurins, although the contribution from each mode is different. To understand these differences, molecular comparisons of the known structures and molecular modeling of the electrostatic field within the protein were performed. The results show that the two proteins have very similar structures, although the copper site itself has a slightly more tetrahedral geometry in A. denitrificans. The resonance Raman spectral differences between these two azurins are interpreted to arise from this copper site structural difference and a greater distribution of charges and/or dipoles near the coordinating histidines in A. denitrificans.

Ultrasensitive detections in atomic and molecular physics: demonstration in molecular overtone spectroscopy

We consider several highly sensitive techniques commonly used in detection of atomic and molecular absorptions. Their basic operating principles and corresponding performances are summarized and compared. We then present our latest results on the ultrasensitive detection of molecular overtone transitions to illustrate the principle and application of the cavity-enhanced frequency-modulation (FM) spectroscopy. An external cavity is used to enhance the molecular response to the light field, and an FM technique is applied for shot-noise-limited signal recovery. A perfect match between the FM sideband frequency and the cavity free spectral range makes the detection process insensitive to the laser-frequency noise relative to the cavity, and, at the same time, overcomes the cavity bandwidth limit. Working with a 1.064-μm Nd:YAG laser, we obtained sub-Doppler overtone resonances of C2HD,C2H2, and CO2 molecules. A detection sensitivity of 5×10-13 of integrated absorption (1×10-14/cm) over 1-s averaging time has been achieved.

Tunable YBCO resonators on YIG substrates

A tunable stripline resonator has been fabricated from YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films deposited on single-crystal Y/sub 3/Fe/sub 5/O/sub 12/ (YIG) substrates. The films were deposited by laser ablation and employ buffer layers for epitaxial growth. The surface resistance of the YBCO on YIG has been measured independently and is 5/spl times/10/sup -4/ /spl Omega/ at 10 GHz and 77 K. The resonator is tuned with an external field that changes the permeability of the YIG. At 77 K we have observed tunablity of the fundamental (approximately 1.7 GHz in zero applied field) and the overtone resonances of the stripline. A mode of resonance frequency of 12 GHz has demonstrated tuning of 500 MHz for 500 Oe external field without appreciable degradation of the Q which is about 1200. For 2 kOe the tuning range is approximately 1 GHz. For higher applied fields the Q of the resonance degrades significantly presumably because of degradation of the surface resistance of the YBCO due to the applied field. The measured Q in zero applied field is about a factor of two to four lower than expected from the surface resistance of the film indicating that losses in the YIG may be affecting the performance.

Femtosecond photodissociation dynamics of nitroethane and 1-nitropropane in the gas and solution phases from resonance Raman intensity analysis

We have obtained resonance Raman spectra of nitroethane and 1-nitropropane in the gas phase and in cyclohexane solution with excitation within the broad B-band absorption around 200 nm. The resonance Raman spectra are dominated by a long overtone progression in the nominal NO2 symmetric stretch vibrational mode. The initial short-time (femtosecond) photodissociation dynamics of the excitedelectronic state associated with the B-band absorption changes mainly in the two N–O bond lengths in the Franck–Condon region. Time-dependent wavepacket calculations have been carried out to simulate both the absorption spectra and the resonance Raman intensities. These calculations show that very fast predissociation competes with wavepacket motion out of the Franck–Condon region, and or there is a significant change in the transition dipole moment along the nominal NO2 symmetric stretch coordinate, that must be taken into account to correctly model the higher overtone resonance Raman intensities. Since the resonance Raman intensity patterns and calculation parameters are very similar for both gas and solution phase nitroethane and 1-nitropropane, electronic dephasing due tosolvent collisions does notappear tobe a significantfactor in determining the resonance Raman overtone intensities up to v = 9.

Analysis of the influence of the surface wettability on the quartz sensor response

Abstract Acoustic impedances of water and Brij-58 (a nonionic detergent) in contact with hydrophilic and hydrophobic electrodes of thickness shear mode resonators were studied. Measurements were performed at the fundamental, third and fifth overtone resonances of the AT quartz. Discrepancies were observed between the real and imaginary parts of the acoustic impedance, Re( Z L ) and Im( Z L ), for the hydrophilic quartz as well as the chemically modified quartz (hydrophobic surface). Moreover for this latter surface, the imaginary component of the acoustic impedance was lower than for the native resonator. This difference is especially due to the surface wettability. The extent of liquid rigidly coupled to the quartz surface was thus quantified, and it was shown that it was lower for a hydrophobic quartz than for a hydrophilic one. Furthermore it has been observed that for both components of the acoustic impedances, a significant transient signal appears before equilibrium whatever the liquid used.

Overtone resonance Raman scattering beyond the Condon approximation: Transform theory and vibronic properties

The time correlator formalism is used to develop the expression for nth order (overtone) resonance Raman scattering (RRS) to include both Raman frequency shifts upon electronic excitation as well as non-Condon vibronic coupling. In particular the compact operator formalism recently introduced by Hizhnyakov and Tehver [J. Raman Spectrosc. 19, 383 (1988)] to obtain several RRS correlators (including overtone scattering with frequency shift, but in the Condon approximation) is used to extend the theory. At the same time a formal advantage is achieved by the limited introduction of the Born–Oppenheimer approximation. Also transform relationships including non-Condon effects are given that link the Raman excitation profile of nth order scattering to the absorption spectrum. Finally, it is emphasized how all three vibronic parameters—potential energy surface displacement, Raman mode frequency changes, and the linear non-Condon coupling parameter—can be quantitatively determined without the need for absolute Raman cross-section measurements. The relative scattering intensity of the fundamental and three (or more) overtones suffices to fix the three. By way of application, the vibronic parameters are determined from published single wavelength overtone RRS in six molecules.

Intramolecular Hydrogen Bonds and Fermi Resonance in N-Substituted N'-(2-Fluorobenzoyl)thiourea Derivatives

The presence of intramolecular NH...O=C bonds was proved in N-substituted N'-(2-fluorobenzoyl)thiourea derivatives by analysis of their infrared spectra. The intramolecular vibrational effects bring about a shift of the ν(NH) vibrational band to lower frequencies to the extent that the band gets into a vicinity to the δ(NH) overtone and Fermi resonance occurs between them. In addition, the ν(NH) vibration is also affected by Fermi resonance with the ν(CO) + δ(NH) combination. Double absorption bands were observed in the ν(CO) region for some of the derivatives. Based on perturbation theory applied to three-level interactions and using the Langseth and Lord equations, the band frequencies corrected for Fermi resonance were calculated and the hydrogen bond strength was examined in the compounds studied.

High overtone resonance Raman spectra of photodissociating nitromethane in solution

High overtone resonance Raman spectra of photodissociating nitromethane in solution

Time-resoled coherent Raman spectroscopy of low temperature molecular solids in a high pressure diamond anvil cell

We present time-resolved Raman measurements of vibrational relaxation in a high pressure diamond anvil cell at low temperature. Pressure dependent vibrational relaxation measurements are presented for the symmetric stretch and Fermi resonant overtone modes in crystalline CS 2 and for the totally symmetric CC stretching mode of benzene. Pressure-induced changes in the picosecond coherent Raman decays are correlated with pressure-induced anharmonicities in the intermolecular potential energy function.

The vibrational overtone spectrum of a thin polymer film

Using photothermal deflection spectroscopy (PDS), vibrational overtone spectra have been obtained in organic thin films for the first time. Overtone and combination resonances for several orders above the fundamental are observed. The frequencies, relative intensities, and linewidths can be precisely determined. Assignments to specific CH bond resonances are made using the theory of anharmonic vibrations based on a Morse potential for local modes. Details of the molecular potential can be studied, as can be transition from normal to local made behavior.

High pressure raman studies of GaAs/A1As superlattices: folded-acoustic phonons and resonant second-order scattering

Abstract We have used Raman scattering to study the vibrational and electronic properties of GaAs/AlAs superlattices. In the first-order Raman spectra we obtain the pressure dependence of the confined-optic and folded-acoustic phonon frequencies. A mode Gruneisen parameter of 1.2±0.1 is found in all cases. In the second-order Raman spectra we see resonant overtone and combination scattering of GaAs-like longitudinal-optic (LO) phonons and GaAs-like and AlAs-like interface vibrations. The resonance is with the lowest-energy P-like valence-to-conduction subband transition (E1h ), when the energy gap is pressure tuned into out-going resonance with the laser light. This technique permits the measurement of E1h well above the direct-indirect crossover pressure.

Suppression of anharmonic spurious modes in quartz resonators by modified electrode design using charge cancellation

AbstractOne of the most important problems in the design of the thickness vibration resonator is how to suppress the anharmonic higher‐order spurious mode which is generated near the main resonant frequency. It is easy to realize a single resonant characteristic by the design based on the trapped energy theory, but the area of the electrode and, consequently, the inductance, are limited. This paper proposes a method which improves this point and increases the degrees of freedom in the design, suppressing the anharmonic spurious mode by adding a mass to the edge of the electrode and by cancelling the charge. In other words, a modified circular electrode structure is proposed in which the peripheral part (ring) of the electrode has a larger thickness. The third overtone resonator is analyzed in detail, and it is shown theoretically that the dominant (3, 3, 1) spurious mode is suppressed by the charge cancellation, thereby realizing a resonator with an essentially single resonant characteristic over a wide frequency range. It is noted that the charge cancellation characteristics for the spurious mode are strongly dependent on the platebacking of the ring electrode. The data for the optimum design are summarized in a table which will be utilized in the future design.

Acoustic dimensional resonance tomography: Some examples in one-dimensional systems

A spatial map of the variation of acoustic impedance within a material structure can be made using only its resonance frequencies. We demonstrate this for a 1-D rod having a diameter D which varies along its length l by determining D(l) from fundamental and overtone resonances. We also show how the technique can locate material/processing inhomogeneities in the elastic modulus and/or density on a scale of several parts per thousand for ‘‘stock’’ rods of an aluminum alloy using nondestructive and noncontact testing. And finally, we apply dimensional resonance tomography in new measurement methods to obtain the thermal diffusivity along a rod and the heat transfer coefficient of the rod to its ambient. The latter technique provides quantitative data while allowing an arbitrary and unknown initial temperature distribution, requiring no temperature measurement or Fourier analysis, and can be done in noncontact fashion with the measurement of frequency and time, only.

Vibrational overtone intensities of the isolated CH and CD chromophores in fluoroform and chloroform

Absolute integrated band strengths are reported for the Fermi resonance overtone polyads ( N = 1 to 4) of the isolated CH chromophore in CHF 3, CDF 3, CHCl 3, CDCl 3. The CH data are evaluated with the Mecke function for the local dipole moment μ( r)α rexp(-α r) and the resulting first predictions for CD agree with experiment. The results are discussed in relation to electronic structure calculations, IR multiphoton excitation, and IR photochemistry.

Improved quartz crystal microbalance technique

The importance of using the most pertinent mathematical description of the mass load versus frequency relation for quartz crystal thin-film thickness monitors is reviewed. The different usable crystal load ranges of the so-called frequency- and period-measurement techniques in comparison with the Z-Match technique are calculated for most of the commonly used deposition materials. A new thin-film thickness monitoring procedure is described, which takes the influence of the acoustic film properties on the mass load versus frequency slope into consideration without need for the explicit knowledge of the acoustic impedance ratio z of the deposited film and the quartz crystal. It is shown how the effective z value in the composite resonator built by the quartz crystal and the deposited foreign layer can be derived from a measurement of a quasiharmonic overtone resonance frequency in addition to the commonly practiced exclusive measurement of the fundamental resonance frequency. The presently established relation between the mass load or the deposited film thickness and the corresponding resonance frequency of the loaded crystal is enhanced by a more rigorous one-dimensional composite resonator description. The introduced so-called series resonance relation is of significance for the accurate determination of the specific acoustic impedance ratio z of the deposited film and the crystal. Furthermore, the deviations of the frequency spectra of plano-convex shaped crystals from that of the one-dimensional (infinite plate) geometry are investigated and taken into account. The achieved accuracy in the z determination from the first and third quasiharmonic frequencies justifies the applicability of the two-frequency or auto slope accommodation technique introduced in this paper.

A semiclassical study of forced anharmonic oscillators

In this paper we develop semiclassical equations of motion for the forced anharmonic oscillator. Both the main and the overtone resonances were explicitly considered. The general formalism was applied to the Duffing oscillator, whose periodic solutions for the main and the third overtone resonances were calculated. The classical and the semiclassical solutions are very similar, the only qualitative difference being the disappearance of the unstable classical solutions.

Theory of intramolecular energy relaxation and vibrational overtone resonance absorption lineshapes of isolated polyatomic molecules

The vibrational dynamics of an isolated polyatomic molecule in interaction with a laser field is treated by using a graphical analysis of the molecular operators. The lineshape arises from any order of the perturbing intramolecular interaction leading to an integral equation for the local mode scattering operator. Explicit calculation indicates that the identity of the local mode and the normal mode quanta can no longer be retained over hopping times which are comparable to mean free times. The renormalization method introduced here is quite capable of probing short time intra-molecular dynamics and improves on the strict Born approximation utilized by Heller and Mukamel earlier. Essential features of the lineshape remain the same except for the generalization to higher order effects and the inclusion of the interference processes.

Subharmonic non-linear acoustic resonances in open tubes—Part I, theory

An open tube is considered, driven at one-half of the fundamental frequency. The interesting fact appears that acoustic theory breaks down in the inviscid case. At a sufficient intensity of a resonant overtone, the distortion effects become too strong to use an expansion scheme.

Subharmonic non-linear acoustic resonances in closed tubes

A closed tube is considered driven at one-half of the fundamental frequency. The interesting fact appears that acoustic theory breaks down in the inviscid case. At a sufficient intensity of a first resonant overtone, the theory of Chester applies.

Electromechanical coupling factors and fundamental material constants of thickness vibrating piezoelectric plates

The vibrations of piezoelectric plates are governed by the linear piezoelectric equations which may contain a rather large number of elastic, piezoelectric and dielectric constants. But under certain very restrictive but practically important circumstances, piezoelectric coupling coefficients occur naturally in the solutions of the equations, a different coefficient arising in each particular case. Under more general circumstances many of the material constants remain in the solution, and the utility or significance of any of the coupling coefficients appears questionable. The solution of the problem of the thickness vibrations of an arbitrarily anisotropic plate is used in demonstrating the significance and limitations of the coupling coefficient for various types of anisotropy. In many of the instances when the coupling coefficient turns out to be useful, the frequency equation shows that the overtone resonances are not integral multiples of the fundamental. The departure from an integral multiple relationship depends on the coupling coefficient only, and consequently, the coupling coefficient can be determined from simple resonance measurements.