The electron spin resonance spectra of the toluene,p-xylene and m-xylene anions

The electron spin resonance (e.s.r.) spectra of the anions of toluene, p-xylene and m-xylene have been studied and the proton hyperfine coupling constants determined. These are in excellent agreement with the predictions of Hückel molecular orbital theory.     

Thermalization of photoexcited molecules in solution

Analysis of the steady-state absorption/fluorescence spectra of several laser dyes in room temperature solution suggests that the fluorescing molecules, if initially formed in a vibrationally excited state, lose their excess energy surprisingly slowly, remaining significantly warm on a nanosecond time scale. A similar analysis of the steady-state absorption/fluorescence spectra of GaAs confirms that in this case the carriers are fully thermalized, possessing no excess energy when they recombine on a microsecond time scale. A classical model which accounts qualitatively for slow molecular cooling is presented. We conclude that rapid molecular photoconversion processes are likely to involve incompletely cooled (thermalized) excited states.     

Noise power spectra of the inductively coupled plasma

Noise power spectra for the ICP were determined under various conditions, by Fast Fourier Transform (FFT) digital techniques. The major noise types observed were white noise, low frequency noise, and high frequency proportional noise. The high frequency proportional noise increased with concentration of analyte and radio frequency input power. The high frequency proportional noise decreased with increasing nebulizer flow rate and coolant gas flow rate.. The low frequency noise components extended to higher frequencies as the resonance wavelengths of the measured transitions increased. Changing the observation height in the plasma determined which noise types were present in the noise power spectrum. At observation heights near the power coils, all three noise types were present, whereas, low frequency noise predominated at significantly greater heights. Changing the torch design changed the relative amplitudes of the different high frequency proportional noise components, but did not greatly change their respective peak frequencies.     

Search for nu(mu)-->nu(e) and nu(mu)-->nu(e) oscillations at NuTeV

Limits on nu(mu)-->nu(e) and nu(mu)-->nu(e) oscillations are extracted using the NuTeV detector with sign-selected nu(mu) and nu(mu) beams. In nu(mu) mode, for the case of sin(2)2alpha = 1, Delta(m)(2)>2.6 eV(2) is excluded, and for Delta(m)(2)>1000 eV(2), sin(2)2alpha>1.1 x 10(-3). The NuTeV data exclude the high Delta(m)(2) end of nu(mu)-->nu(e) oscillation parameters favored by the LSND experiment without the need to assume that the oscillation parameters for nu and nu are the same. We present the most stringent experimental limits for nu(mu)(nu(mu))-->nu(e)(nu(e)) oscillations in the large Delta(m)(2) region.     

Precise determination of electroweak parameters in neutrino-nucleon scattering

The NuTeV Collaboration has extracted the electroweak parameter sin(2)theta(W) from the measurement of the ratios of neutral current to charged current nu and (-)nu cross sections. Our value, sin(2)theta((on-shell))(W) = 0.2277 +/- 0.0013(stat) +/- 0.0009(syst), is 3 standard deviations above the standard model prediction. We also present a model independent analysis of the same data in terms of neutral-current quark couplings.     

Ice-catalyzed ionization of hydrochloric acid

Ionization of hydrochloric acid (HCl) on stratospheric ice particles is believed to be a key step in the depletion of stratospheric ozone. Ab initio calculations based on a model HCl-water cluster show that HCl ionization on ice surfaces is a barrierless process. Since this mechanism is rapid and produces chloride anions that are exposed to ambient stratospheric chlorine reservoir molecules, it is likely to be important for stratospheric chemistry. It complements a previously suggested mechanism where HCl forms part of the ice lattice before ionizing. The mechanism proposed here is also consistent with experimentally observed ionization of HCl on ice at low temperatures and under vacuum, where the HCl is not expected to be encapsulated in the ice lattice.     

Application of cylindrical near-field acoustical holography to the visualization of aeroacoustic sources

The purpose of this study was to develop methods for visualizing the sound radiation from aeroacoustic sources in order to identify their source strength distribution, radiation patterns, and to quantify the performance of noise control solutions. Here, cylindrical Near-field Acoustical Holography was used for that purpose. In a practical holographic measurement of sources comprising either partially correlated or uncorrelated subsources, it is necessary to use a number of reference microphones so that the sound field on the hologram surface can be decomposed into mutually incoherent partial fields before holographic projection. In this article, procedures are described for determining the number of reference microphones required when visualizing partially correlated aeroacoustic sources; performing source nonstationarity compensation; and applying regularization. The procedures have been demonstrated by application to a ducted fan. Holographic tests were performed to visualize the sound radiation from that source in its original form. The system was then altered to investigate the effect of two modifications on the fan's sound radiation pattern: first, leaks were created in the fan and duct assembly, and second, sound absorbing material was used to line the downstream duct section. Results in all three cases are shown at the blade passing frequency and for a broadband noise component. In the absence of leakage, both components were found to exhibit a dipole-like radiation pattern. Leakage was found to have a strong influence on the directivity of the blade passing tone. The increase of the flow resistance caused by adding the acoustical lining resulted in a nearly symmetric reduction of sound radiation.     

Polariton-biexciton transitions in a semiconductor microcavity

The influence of four-particle correlations on the nonlinear optics of a semiconductor microcavity is determined by a pump-and-probe investigation. Experiments are performed on a nonmonolithic microcavity which contains a ZnSe quantum well. In this system the biexciton binding energy exceeds both the normal-mode splitting between exciton and cavity mode and all damping constants. Oscillatory spectral features below the excitonic resonance are observed in the response for counterpolarized beams. Comparison with model calculations shows that in this case the coherent nonlinearity is dominated by biexciton-exciton interactions beyond the Hartree-Fock approximation.