Showing papers on "Resonance published in 1973"

Effects of Resonance Bonding on the Properties of Crystalline and Amorphous Semiconductors

Abstract: The resonance aspect of chemical bonding is extended to solids with particular emphasis on its consequences for structural and vibrational properties. It is shown, for example, that the square of the infrared effective charge is proportional to the high-frequency dielectric constant in resonance-bonded systems. The IV-VI compounds and the group-VI elements are shown to exhibit the features of such resonance bonding. The dependence of resonance bonding on long-range order is discussed with respect to differences in the properties of the amorphous and crystalline phases of these materials.

Fourier synthesized excitation of nuclear magnetic resonance with application to homonuclear decoupling and solvent line suppression

Abstract: A method is described for exciting a nuclear magnetic resonance spectrum with a radio frequency source having any desired frequency spectrum. The frequency spectrum of the source is first specified and then Fourier synthesized to define a function which is used to modulate a radio frequency carrier. The NMR spectrum is obtained by Fourier transforming the response of the spin system to this excitation. The technique is applied to the problem of suppressing a strong solvent line while simultaneously observing all other resonance lines in a spectrum and to homonuclear decoupling while observing a complete spectrum.

Dielectric parameterization of raman lineshapes for GaP with a plasma of charge carriers

Abstract: We have studied the Raman lineshapes of several samples of GaP with appreciable carrier concentrations. There is no feature identifiable as a plasma resonance, but there are pronounced effects of interaction with the LO phonon resonance. For analysis we have developed a model along lines laid down by Barker and Loudon, employing Nyquist relations to calculate infrared fluctuations which scatter light. We introduce a response matrix α(ω) withseveral resonances; and we uncover some points which seem to be new, for coupled-mode scattering systems in general. In the GaP-plasma problem the data do not necessitate inclusion of the scattering amplitude from the plasma; we ascribe this to large plasma damping rates (ωτ≲1). This provides an account for the lack of any apparent plasma resonance in the scattering and for the modified appearance of the LO phonon, relative to the pure crystal. We emphasize that the following parameters suffice: Lorentz parameters measured in linear infrared experiments, the nonlinear parameterC from a visible-infrared mixing experiment, and the plasma frequency and damping fit to each sample. Beyond treatment of the plasma problem, the theory bears more generally on the conditions under which an LO Raman lineshape measures locally the shape of 〈E 2〉ω. Also it bears upon the analysis of polariton linewidths to infer the variation of the phonon damping Γ(ω).

Low energy magnetic and electric dipole transitions of the biphenyl crystal

Abstract: The absorption and fluorescence spectra of biphenyl‐h10 and biphenyl‐d10 neat crystals, and of lightly and heavily doped isotopically mixed crystals have been studied at 4.2 °K. The first singlet excited state of biphenyl is assigned as 1B3g (33128.2 cm−1 in biphenyl‐h10, 33270.4 cm−1 in biphenyl‐d10) and transitions to it are found to be consistent with a magnetic dipole mechanism by polarization measurements and calculations. The bulk of the intensity in the 1B3g ⇄1Ag(X) transitions is electric dipole arising from Herzberg‐Teller coupling through a mode b2u (9) at 626 cm−1 (h10) and ≈ 593 cm−1 (d10). The next excited state is assigned as 1B2u (M‐polarized) and the splitting of the 1B3g and 1B2u states of 746.8 ± 3 cm−1 provides the inter‐ring resonance interaction corresponding to the splitting of the 1B2u (D6h) state of benzene through excitation exchange interactions and second‐order shifts. The isotopic mixed crystal spectra provide evidence that the width of the biphenyl crystal exciton band (from 1...

Microwave optical double resonance spectroscopy with a cw dye laser: BaO X1Σ and A1Σ

Abstract: A tunable, single frequency, continuous wave, dye laser has been used to optically pump various lines of the BaO A 1Σ‐X 1Σ electronic transition. Microwave optical double resonance (MODR) spectra are recorded as changes in the intensity of dye laser induced photoluminescence. Fourteen microwave rotational transitions in the X 1Σ (ν = 0,1) and A 1Σ (ν = 0–5) states of 138Ba16O and one transition in the A 1Σ (ν = 1) state of 137Ba16O have been observed. Partially deperturbed rotational constants obtained for BaO A 1Σ are B(ν) = 0.25832(2) − 0.001070(5) (ν + 1/2) cm−1. Two physical models are described which account for microwave optical double resonance effects in the strong (nonlinear) and weak (linear) optical pumping limits. Observed changes in photoluminescence polarization caused by excited state microwave transitions are predicted by a semiclassical transition dipole model. A three level steady state kinetic treatment of microwave optical double resonance indicates that the BaO MODR transitions reported in this paper are observed near the strong optical pumping limit. It is shown that for most allowed transitions in diatomic molecules a 100 mW single frequency, dye laser is sufficiently intense to significantly deplete rotational levels of the electronic ground state with respect to neighboring rotational levels and to cause the populations of the depleted ground state and optically pumped excited state levels to become comparable.

Resonance, Auger, and autoionization processes involving He$sup +$(2s) and He$sup ++$ near solid surfaces

Abstract: Electronic transition processes of a resonance and of an Auger type which can occur at a solid surface were studied for incident metastably excited He/sup +/ (2s) and doubly charged He/sup ++/ ions. Atomically clean Ni(100) and Ni(110) surfaces were used as well as those surfaces with a c(2 x 2)Se structure adsorbed upon them. It is shown that the principal process of deexcitation of the He/sup +/(2s) ion involves resonance tunneling to a doubly excited He/sup o**/ state of the He atom followed by its autoionization to the ground-state ion He/ sup +/(ls) with the ejection of a fast electron. Autoionized electrons produced near the surface are 0.7 to 0.9 eV faster than those produced in free space. The change in the work function from 4.7 eV for Ni(110) to 5.1 eV for Ni(100) reduces the number of peaks of ejected electrons from two to one. These experimental facts are shown to be self-consistent and to arise from energy-level shifts near the solid surface. Several aspects of the kinetics of the two-stage processes in competition with possible single-stage processes are discussed. It is also demonstrated that He/sup ++/ is first resonance neutralized by one electronic charge to the He/supmore » +/(2s) state, which process is then followed, closer to the surface, by those observed for incident He/sup +/(2s). (auth)« less

Resonance Raman spectroscopic study on iodine in various organic solvents: Spectroscopic constants and halfband widths of the I2 vibration

Abstract: Resonance Raman spectra have been obained from various iodine solutions. High intensity overtone progressions of the stretching vibration were observed, allowing the determination of the spectroscopy constants ωe and ωexe and estimation of ωeye for the stretching vibration for the ground state in various environments. The values are compared to those obtained for the gas phase. The overtone progression shows a large increase in half-bandwidth with increasing vibrational quantum number.

Interference structure near the resonance cone

Abstract: The interference structure near the resonance cone of an oscillating point charge in a warm magnetized plasma is investigated theoretically, using the quasistatic approximation and neglecting ion motion. Depending on the frequency and plasma parameters, the interference structure appears inside, outside, or on both sides of the resonance cone. For frequencies less than both the plasma and cyclotron frequencies, the structure lies inside the resonance cone except for frequencies near the cyclotron frequency where the amplitude is small because of cyclotron damping. For frequencies between the upper‐hybrid frequency and the larger of the cyclotron and plasma frequencies, the structure lies outside the resonance cone provided the frequency and angle are sufficiently removed from the upper‐hybrid frequency and 90°, respectively. A simple expression for the angular interference spacing is derived.

Studies of tellurium shielding by heteronuclear magnetic double resonance in a representative series of compounds

Abstract: Tellurium-125 chemical shifts determined by heteronuclear double resonance in a range of organotellurium compounds are found to parallel closely the 77Se chemical shifts in analogous compounds. The tellurium shielding decreases as the electronegativity of substituents increases and this is attributed to dominance by the paramagnetic term. Variations in ΔE do not appear to be important.

Density effect on the Fermi resonance in gaseous CO2 by Raman scattering

Abstract: Raman scattering was used to study the Fermi resonance of ν1 and 2 ν2 bands in gaseous CO2 over the density interval of 15–534 amagat Both vibrations were found to shift to lower frequency as density was increased The resonance repulsion of the two bands was also found to increase with increasing density

Rate equations and transient phenomena in semiconductor lasers

Abstract: This contribution attempts to review certain resonance effects which occur in the dynamic behaviour of semiconductor lasers. To study these effects theoretically, a rate equation approach is used for single-mode operation in the region of lasing threshold. The two basic rate equations are given and their transient solutions discussed. The existence of two time constants in these equations, viz. the electron lifetimeτ e and the photon lifetimeτ e; gives rise to a characteristic resonance frequency in the GHz region. This resonance manifests itself in transient ‘spiking’ effects, in quantum noise phenomena, and in high-frequency modulation experiments. In a modified form the resonance frequency may also be studied in lasers with external cavities and in double-diode configurations (or, equivalently, conventional devices with non-uniform excitation along the cavity length). In the latter two examples mentioned above, the resonance is excited by optical feedback of the laser radiation into the active medium via a ‘lossy’ or insufficiently inverted region. In the ‘spiking’ oscillations commonly observed at the commencement of laser operation, the initial ‘population overshoot’ is the cause of the resonance. For the case of quantum noise it is the requirement that the photon and electron populations have integer values which supplies the driving force-a true quantum effect. High-frequency modulation experiments directly reveal the same resonance frequency where a strong maximum in modulation intensity occurs.

Resonant Raman scattering from cytochrome c: Frequency dependence of the depolarization ratio

Abstract: The depolarization ratio has been measured for several peaks in the resonant Raman spectrum of horse heart ferrocytochrome c (reduced) using six argon and krypton ion laser lines near resonance with the β absorption band. The depolarization ratio is observed to be a strong function of laser frequency so that previous mode symmetry assignments for heme proteins based on data at a single frequency are unreliable. For the anomalously polarized peaks (ρl > 3/4), the depolarization ratio increases to a maximum when the laser frequency is midway between the α and β absorption bands. These data are compared with a theoretical expression for the dispersion derived using perturbation theory to treat mixing of the D4h basis states. Quantitative estimates of the relative contributions of the different symmetry representatives are obtained.

Resonance Raman spectrum and vibrational analysis of the ozonide ion in the argon matrix‐isolated M+O3− species

Abstract: Beams of alkali metal atoms and ozone molecules at high dilution in argon were condensed on a tilted copper wedge at 16°K and were examined by argon and krypton plasma laser excitation. Very intense bands shifted 1010 cm−1 below the exciting lines showed small alkali metal effects and appropriate oxygen‐18 shifts for assignment to the v1 symmetric oxygen‐oxygen mode of the ozonide ion in the M+O3− species. The intense fundamental and a regular progression of overtones out to 4v1 suggest that these spectra are probably due to the resonance Raman effect. Vibrational analysis for six isotopic ozonide species produced the oxygen‐oxygen force constant 4.18 ± 0.11 mdyn/A. The spectroscopic value for the heat of atomization of the ozonide ion calculated from the vibrational constants ω1 = 1028.2 cm−1 and X11 = 4.95 cm−1 for Cs+O3− is 153 kcal/mole, which agrees well with the thermodynamic value.