Dependence Of Frequency Shift Research Articles

Vibration, rotation, and parity specific predissociation dynamics in asymmetric OH stretch excited ArH2O: A half collision study of resonant V–V energy transfer in a weakly bound complex

Para ArH2O complexes are detected via slit jet direct absorption spectroscopy using continuous wave difference frequency generation of high resolution tunable IR in the 3780 cm−1 v3=1←0 asymmetric OH stretch region. P/R and Q branch transitions on the Π(101,v3=1)←Σ(000,v3=0) band are observed, which derive oscillator strength from the 101←000 v3=1←0 transition in free H2O and access upper states of e and f parity, respectively. Frequency shifts in the f parity levels (Q branch), and both frequency shifts and predissociation broadened linewidths in the e parity levels (P/R branch) are evidenced in the spectrum, unambiguously characteristic of an avoided crossing in the vicinity of J′=6 with a second, near resonant vibration–internal rotation state in ArH2O. From detailed analysis of the avoided crossing, this perturbing state is assigned to a symmetric (v1=1) OH stretch+internal rotor state in ArH2O, which resonantly mixes with the IR laser prepared asymmetric (v3=1) OH stretch by resonant ‘‘half collisional’’ V→V transfer with the Ar atom. The striking parity dependence of the observed predissociation linewidths results from energy conservation and the symmetries of the asymptotic Ar+H2O (v1=1) states; the e parity levels can dissociate to the ground 000 rotor level of H2O (v1=1), whereas the f parity levels can access at lowest the 111 rotor level, therefore releasing insufficient energy to rupture the van der Waals bond. The data establishes a clear upper limit on the dissociation bond strength for para ArH2O, and place spectroscopic constraints on the promoting internal rotor state in ArH2O (v1=1). A simple local mode theory of half collision induced mixing between symmetric and asymmetric stretch excitation in H2O is presented. The model predicts a coupling which is proportional to three factors, (i) a ‘‘steric’’ term which describes the overlap of initial/final internal rotor wave functions in the ArH2O angular geometry conductive to energy transfer, (ii) a ‘‘collisional’’ term which depends on the van der Waals stretching frequency and reduced mass, and (iii) an intramolecular V→V term to describe the ‘‘rephasing’’ of the OH local modes that characterizes the collisional transformation between asymmetric and symmetric stretch vibrations. All the parameters in the model are accessible from the high resolution van der Waals spectra, and the resulting predictions are in surprisingly good agreement with the coupling spectroscopically determined from the perturbation analysis. The high efficiency of the predissociation dynamics is also qualitatively consistent with the near gas kinetic v3↔v1 energy transfer observed by Finzi et al. [J. Chem. Phys. 63, 2285 (1975)] in thermally averaged H2O(v1,v3)+Ar collisions. In summary, analysis of the J and parity dependent predissociation linewidths and frequency shifts in a van der Waals near-IR spectrum of ArH2O offers an unusually detailed glimpse at collision induced intramolecular V–V transfer in vibrationally excited H2O from a half collision perspective.

Morphology dependent anomalous frequency shifts of infrared absorption bands of polymer crystals: Interpretation in terms of transition dipole–dipole coupling theory

For such crystalline linear polymers as trigonal poly(oxymethylene) (t-POM), orthorhombic poly(oxymethylene) (o-POM), and poly(ethylene oxide) (PEO), it has been found that the infrared bands polarized parallel to the chain axis exhibit anomalously large high-frequency shifts as the crystal morphology of the sample goes from the extended-chain crystal (ECC) to the folded-chain crystal (FCC). The common features of the remarkable spectral change were investigated systematically and summarized as follows: (1) the anomalous bandshifts were observed only for the infrared-active parallel bands, (2) the magnitude of the shift was proportional to the oscillator strength of the band, (3) the overtones corresponding to the parallel fundamental bands did not show such a remarkable shift, and (4) the appearance of the high-frequency bands in FCC was ascribed not to the folded molecular structure, but to the lamellar-type crystal morphology. The morphology-dependent bandshifts were interpreted quantitatively in terms of the transition dipole–dipole coupling theory. By integrating the interacting energy over cylindrical crystal having various radius/height ratios, it was demonstrated that the energy due to the dipole interaction vanished for the idealized ECC and became maximum for the infinitely thin lamellar crystal. The magnitudes of the bandshifts between the two extreme cases were calculated on the basis of the absolute values of the oscillator strengths of the bands measured on highly crystalline samples of t-POM, o-POM and PEO and their crystal structures. The results agreed well with the observed band gaps between the ECC and FCC samples. The change in the absorption profiles of the parallel bands with change in crystal morphology was simulated. The result reproduced well the observed spectral change.

Diode lasers in external cavities with frequency-shifted feedback

We have investigated the spectral broadening of diode lasers in an external linear cavity with frequency-shifted feedback. With an 850 nm infrared diode of 30 MHz free running bandwidth, we observe a feedback level dependent frequency shift and continuous line broadening up to 5 GHz. A 660 nm visible laser diode exhibits a symmetric broadening enhanced by relaxation oscillations and, at large feedback levels, multimode operation over a bandwidth up to 1 THz, tunable over 3.1 THz (44 Å). In each case, the acousto-optic frequency shifter prevents constructive interference of successive roundtrips inside the external cavity and thus the build-up of a discrete axial mode spectrum.

The effective velocity distribution of atoms and the improvement of the accuracy for an optically pumped cesium beam frequency standard with sharp angle incidence of probing laser beam

The effective velocity distribution of atoms which make contributions to the fluorescence signal in an atomic beam in an optically pumped cesium beam frequency standard with a sharp angle incidence of probing laser light has been calculated. It shows a narrow velocity distribution. With a narrow effective velocity distribution the accuracy of the evaluation of the cavity phase dependent frequency shift and second order Doppler shift can be improved.

The sensitivity of chromospherically induced p- and f-mode frequency shifts to the height of the magnetic canopy

Previous investigations of the effect of a magnetic canopy on the solar p- and f-modes are extended to allow for variations in height of the magnetic canopy. Analytical solutions in the limit of long horizontal wavelength are obtained; the solutions exhibit explicitly the dependence of frequency shifts on magnetic field strength, wavenumber, and canopy height. Frequency shifts are principally due to changes in canopy height. Full numerical solutions are also presented. It is argued that changes in chromospheric magnetism will be manifest in p- and f-mode data sets gathered at different phases of the solar cycle. A comparison of theoretical results obtained here with the recent data obtained by Libbrecht and Woodard (1990) is made. 24 refs.

Pressure and temperature dependence of laser-induced fluorescence of Sm:YAG to 100 kbar and 700 °C and an empirical model

The inability to measure pressure with accuracy at high temperature has been a hindrance to the development of simultaneous high-temperature, high-pressure experimental techniques. The results of recent laser-induced fluorescence studies at high temperature and high pressure indicate that Sm:YAG is a promising pressure calibrant with very low-temperature sensitivity. The most intense feature in the fluorescence spectrum is a doublet at 16186.5 cm−1. The Sm:YAG doublet exhibits a pressure-induced peak shift comparable to the R1 shift of ruby. However, the temperature-induced shift of the doublet is almost two orders of magnitude less than that observed for the R1 peak. Simultaneous high-pressure-temperature experiments indicate that the pressure and temperature effects on the frequency and line shape can be added linearly. An empirical model based on the linear combination of pressure dependent frequency shift and temperature dependent linewidth and intensity ratio successfully predicts the doublet line shape at simultaneous pressure and temperature. Use of the model facilitates measurement of peak position at high temperature resulting in improved accuracy and repeatability of the pressure determination. Pressure measurements at 400 °C and 40 kbar based on the Sm:YAG doublet peak position agree with the temperature-corrected ruby R1 pressure measurement to within 3 kbar. At 15 kbar and 900 °C the uncertainty in the Sm:YAG fluorescence peak wavelength is 5 cm−1 due to temperature-induced line broadening; this corresponds to an uncertainty in the pressure determination of ±2.5 kbar. The high thermal and chemical stability of YAG materials make Sm:YAG an ideal pressure calibrant for high-temperature applications. In addition the frequency and intensity of the Sm:YAG fluorescence allow simple conversion from experimental setups designed for ruby fluorescence measurement.

Oxygen atom detection using third harmonic generation

Atomic oxygen has been detected using the four-wave mixing technique of third harmonic generation (THG). Ground state O((3)P(j)) atoms, generated using a microwave discharge, were monitored by focusing a 391-nm dye laser beam into the post-discharge region and observing radiation at 130 nm, near resonant with the 3s (3)S(0)(1)? 2p(4)(3)P(j) transition, produced along the laser propagation direction. The observed concentration dependent frequency shifts of the laser excitation spectrum verified the assignment of THG. Oxygen atoms were also detected in the same manner following photodissociation of NO(2). An important point for diagnostic purposes is that both the VUV intensity and peak frequency shift are dependent on O atom concentration. The relationship between these variables was explored by employing chemical titrations to establish absolute concentration. The demonstrated sensitivity is 5 x 10(13) cm(-3), but this could be significantly improved. Implications for three-photon resonant multiphoton ionization detection as well as in situ monitoring of atomic oxygen metastable states ((1)D(2) and (1)S(0)) are discussed. Third harmonic generation provides state selective and low aperture detection with sensitivity comparable to other optical methods and shows promise as a general detection technique. Third harmonic generation, optical detection, four-wave mixing, oxygen, atomic detection, atomic spectroscopy, VUV radiation.

Layer rigidity effects on dynamical properties of mixed ion pillared clays

We have discussed a peculiar composition dependent torsional mode frequency shift for mixed ion pillared vermiculite compounds in terms of the phenomenological contact interaction. We have also constructed a plot of the normalized basal spacing versus normalized torsional mode frequency for two vermiculite intercalation compounds, Cs x Rb 1- x - Vm and [( CH 3) 4 N +] x [( CH 3) 3 NH +] 1- x - Vm. This plot shows a striking “scaling-like” behavior for the two different mixed-ion systems. An attempt to understand this behavior based on the virtual crystal approximation has been made. This model calculation reveals a very close relationship between the basal spacing and the gallery ion-oxygen interaction.

Temperature Dependent Frequency Shifts in the Resonance Absorption and Resonance Fluorescence Scattering of Mössbauer γ‐Quanta

AbstractThe relativistic Doppler effect in the resonance absorption and resonance fluorescence scattering of Mössbauer γ‐quanta of a 57Co source is investigated in the temperature range 295 K ≦ T ≦ ≦ 585 K. The temperature shift of the resonance is d(ln ω)/dT = − (2.38 ± 0.07) × 10−15 K−1 in absorption and − (2.67 ± 0.10) × 10−15 K−1 in backscattering. The data are compared with Bragg scattered Mössbauer γ‐quanta from the (200) reflection of NaCl in the same temperature range. A limit d(ln ω)/dT ≦ 7.5 × 10−17 K−1 is obtained.

The behavior of the infrared spectrum of carbon monoxide adsorbed at platinum electrodes from non-aqueous solvents

Electrochemical oxidation of vanadium hexacarbonyl anion, V(Co) 6 in aprotic solvents results in formation of the V(0) complex which decomposes to form CO in high concentrations next to the electrode surface. As a result, CO is more rapidly adsorbed on the surface than by conventional methods. Surface reflection infrared spectroscopy shows that the potential dependent frequency shift for the infrared active bands due to CO adsorbed on platinum is 19 cm −1/V in 1,2-dichloroethane and 22 cm −1/V in acetonitrile, which are considerably less than the 30 cm −1/V observed in aqueous systems.

Time dependent upward frequency shifts in the Orbitron MASER

In our experiments with the pulsed Oribtron MASER, we have noted that there is an upward chirp in frequency even though the anode voltage is decreasing. We have found theoretically that this is a natural consequence of the negative-mass instability and the chirp rate can be predicted from this theory. Experimental data we have obtained is also in good agreement with these predictions.

Raman scattering of amorphous carbon/semiconductor interface layers

Using Raman spectroscopy we have studied the film/substrate interface of hard hydrogenated amorphous carbon (a-C:H) films deposited on crystalline silicon and germanium. For film thicknesses below ∼ 100 Å a frequency down shift of the main a-C:H Raman peak is observed. This substrate dependent frequency shift provides evidence for the formation of an amorphous SiC interfacial layer for a-C:H deposited on silicon. This assignment is supported by the comparative study of thick (∼ 1 μm) a-Si 1−xC x:H films. The Raman data for a-C:H deposited on germanium and for a-Ge 1−xC x:H, respectively, are also compatible with the concept of an amorphous carbide interface layer.

Pair of local vibration mode absorption bands related to EL2 defects in semi-insulating GaAs

A pair of correlated bands, which show the same fine structure at low temperature, is discovered in infrared absorption spectra of semi-insulating GaAs crystals. At 80 K the bands peak at 730 cm−1 and 714 cm−1, respectively. According to the fine structures, the spectral linewidths, and the temperature dependence of frequency shifts, the two absorption bands are identified to be induced by local vibration modes of the same defect. As the interconversion of the two bands under some conditions of illumination and temperature variation is very similar to the transformation between the ground state and the metastable state of the EL2 level, these absorptions are ascribed to be related to the EL2 defect.

An infra-red study of CO adsorption on potassium-doped pt(110)-(1 × 2); the long range potassium-CO interaction

The co-adsorption of CO with very low coverages of potassium on Pt(110)-(1 × 2) has been studied using RAIRS, LEED and TPD. Low coverages of potassium (q K < 0.1) very slightly increase the CO desorption temperature but lowers the vibrational frequency of the linear CO species by 100 cm −1 . The v(CO) peak on the potassium doped surface is also significantly broader (FWHM of 40 cm −1 ) than that of the clean surface (FWHM of 18 cm −1). The perturbed CO species on the potassium doped surface exhibits a coverage dependent frequency shift identical in magnitude to that of CO on the clean Pt(110) surface. Isotope mixture experiments indicate that the upward frequency shift with CO coverage is due solely to dipole-dipole interactions. No additional chemical contribution to the coverage dependent frequency shift is induced by the presence of potassium, despite the, downward shift in the singleton frequency for the linear CO species of 100 cm −1.

Frequency shift and relaxation of muon-spin-precession in Cd1−xMnxTe

Transverse-field muon spin roation (μSR) is studied in Cd1−xMnxTe, x=0.4 and 0.6 mixed crystals. A large temperature dependent frequency shift and a strong relaxation of the μSR-signal are observed. In the vicinity of the spinglass transition, the relaxation rate becomes so large that the signal disappears. The rate of Mn spin fluctuations causing the μ+-line narrowing at high temperatures is estimated to be of the order of 109 S−1.

Self-interaction of compressional hydromagnetic waves in a cylindrical plasma-filled waveguide

Nonlinear behaviour of azimuthally symmetric compressional hydromagnetic waves propagating along a cylindrical cold magnetized plasma-filled waveguide is investigated. A nonlinear Schrödinger equation describing the nonlinear evolution of such waves is derived. Numerical evaluation of the dispersive and nonlinear terms reveals that such waves are modulationally stable in the fundamental radial mode of propagation. Calculations are presented for the amplitude dependent frequency and wavenumber shifts.

Absorber speed dependence of the coherence relaxation rate of the J=0–1 transition of N2O

The coherence relaxation rate (T2) of the J=0 –1 transition of 15N2O has been examined using microwave transient techniques. The transient decays were analyzed by a model which considers the absorber speed dependence of the collisional relaxation process [S. L. Coy, J. Chem. Phys. 73, 5531 (1980)]. The decays were also analyzed by the standard speed independent model. In the speed dependent analysis, a linear absorber speed dependence of the form k(v)=k0+k1(v−v̄), where v̄ is the Boltzmann average speed, was assumed. Values of k0=0.0300(1) μs−1 mTorr−1 and k1v̄=0.0099(4) μs−1 mTorr−1 were determined. In the speed independent analysis a relaxation rate, k=0.029 22(6) μs−1 mTorr−1, was found. This corresponds to a pressure broadening parameter 1/2πT2 of 4.65(1) MHz/Torr. A zero pressure transition frequency and pressure dependent frequency shift parameter were also determined. They are 24 274.7865(1) MHz and +30(4) kHz/Torr, respectively. The experimental uncertainties reported above are two standard errors from linear least squares fits of k, k0, k1v̄, and transition frequency, vs sample pressure. The most significant systematic error is a 1% uncertainty in the pressure calibration which contributes an additional 1% error to the slopes determined from the linear least squares fits.

Temperature dependence of Raman spectra in the mixed system KNO2-NaNO2

The temperature dependence of Raman bands due to internal nodes has been observed on samples with various mixture ratios of NaNO2 and KNO2. The band assigned to the bending mode of NaNO2 shifts to a lower frequency and decreases in intensity as temperature increases. The temperature dependence of frequency shift of the bending mode of KNO2 becomes noticeable with increasing mole fraction of NaNO2. The half-width of the stretching mode increases when the ferroelectric phase transition is approached.

4f-electron-phonon-interaction in PrF 3

Raman and infrared spectroscopic data of the Davydov-splitting of two crystal field levels, temperature dependent frequency shifts and a magnetic field dependent splitting of a doubly degenerate optical phonon are reported for PrF 3. The results are due to the magneto-elastic interaction (m.e.i.) between optical phonons and 4f-states.

Temperature and hydrogen-concentration dependence of hydrogen optic vibrational frequencies inα- andα′-phase niobium hydride: Static lattice strain and anharmonicity effects

We calculate the shift and broadening of hydrogen optic vibrational frequencies in the $\ensuremath{\alpha}$ (lattice-gas) and ${\ensuremath{\alpha}}^{\ensuremath{'}}$ (lattice-liquid) phases of $\mathrm{Nb}{\mathrm{H}}_{c}$ as a function of temperature $T$ and hydrogen concentration $c$ (H-Nb ratio). We assume the H's vibrate in local modes and linearly relate their vibrational frequencies to the static local lattice dilation through an anharmonicity parameter $\ensuremath{\gamma}$ estimated from inelastic neutron scattering data. The static local lattice dilations are obtained from a grand-canonical Monte Carlo calculation. The H lattice-gas or lattice-liquid model used in the Monte Carlo calculation is an approximation of that of Horner and Wagner, which involves a lattice-mediated H-H strain interaction and H-H hard core. Our calculatins are done in that part of the region described by $0.1&lt;c&lt;0.5$ and $400 &lt;T&lt;600$ K which lies outside the $\ensuremath{\alpha}\ensuremath{-}{\ensuremath{\alpha}}^{\ensuremath{'}}$ coexistence region. Our calculated $c$- and $T$-dependent frequency shifts are roughly consistent with the available data. The calculated broadenings are too small. We estimate that the addition of thermal lattice fluctuations to the model would yield realistic broadenings.