Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

Electronic structure of yttrium oxide.

Abstract: The electronic structure of stoichiometric Y{sub 2}O{sub 3} is studied both theoretically and experimentally. X-ray absorption, performed through total-yield measurements at the {ital K} and {ital L}{sub II} edges of yttrium atoms and the {ital K} edge of oxygen atoms, through total-yield measurements has given access to empty states of various orbital characters in the conduction band. The shape of the valence band was obtained by means of photoemission spectroscopy. These results are compared with self-consistent, semiempirical tight-binding calculations applied to clusters of increasing sizes, which lead to local densities of states. We show that the quasi-octahedral local environment of the yttrium atoms is responsible for the splitting of their {ital d} levels. However, this ligand-field approach is not sufficient to account for the yttrium and oxygen {ital K} thresholds, nor for the shape of the valence band for which band effects are important. The two-peak structure of the oxygen {ital K} edge results from the hybridization of the O {ital p} orbitals with the {ital e}{sub {ital g}} and {ital t}{sub 1{ital u}} states on the yttrium atoms. Three peaks are detected in the valence band: We show that they suggest the existence of direct-hopping terms between neighboring oxygenmore » atoms. Finally, the various calculations have given an estimate of the degree of covalency of the Y-O bond.« less

A Re-Investigation of the $\tilde{A}$ $^{2}\Sigma ^{+}$-$\tilde{X}$ $^{2}\Pi _{\text{i}}$ Band System of NCO

Abstract: The $\tilde{A}$ $^{2}\Sigma ^{+}$-$\tilde{X}$ $^{2}\Pi \_{\text{i}}$(a) absorption system of the NCO free radical has been re-investigated with higher resolving power than in the earlier work of Dixon (1960). Particular emphasis has been directed to the rotational analyses of bands involving the three vibronic levels, $\mu ^{2}\Sigma ^{(+)}$, $^{2}\Delta \_{i}$(a) and k$^{2}\Sigma ^{(-)}$,, associated with the first level of the bending vibration in the ground state. A misassignment in the earlier work has been corrected and a new value for the Renner parameter determined, namely $\epsilon $ = -0.144 $\pm $ 0.001. This revised value removes the discrepancy noted in the earlier electron resonance results.

Morphology dependence of the triplet excited state formation and absorption in polyfluorene

Abstract: Poly(9,9-dioctylfluorene) (PFO) is widely used as a highly efficient blue-emitting polymer for light-emitting diode applications. Films of PFO are known to contain a planar $\ensuremath{\beta}$-phase or a disordered glassy phase that affects the emission characteristics. We have studied the morphology dependence of the photoinduced absorption in such PFO films and find that the ${T}_{1}\text{\penalty1000-\hskip0pt}{T}_{\mathrm{n}}$ absorption signal differs between the two phases in energy, linewidth, and intensity. The lower intensity we observe in the $\ensuremath{\beta}$-phase as compared to the glassy phase is evidence for a lower ${T}_{1}$ population in the former. We attribute this to firstly, reduced intersystem crossing and secondly, increased charge generation due to both more extended conjugation along the chains and higher interchain interactions in the planar, well-ordered $\ensuremath{\beta}$-phase. The reduced energy and smaller linewidth of the triplet absorption in the $\ensuremath{\beta}$-phase as compared to the glassy phase are indicative of a more delocalized ${T}_{\mathrm{n}}$ state and a higher degree of order in the $\ensuremath{\beta}$-phase, respectively.

Self-steepening of the density profile of a CO/sub 2/-laser-produced plasma

Abstract: Interferometric measurements of plasmas produced by C${\mathrm{O}}_{2}$-laser pulses at intensities of ${10}^{14}$ W ${\mathrm{cm}}^{\ensuremath{-}2}$ provide direct evidence for density-profile modification due to radiation pressure

Direct Photodisintegration Processes in Nuclei

Abstract: The unexpectedly large ($\ensuremath{\gamma},p$) cross sections found in many moderately heavy nuclei are interpreted in terms of a direct photodisintegration process. The gamma-ray quantum is supposed to be absorbed by one proton in the nucleus, which is then emitted without the formation of an intermediate compound nucleus. The cross section for this process is small compared with that for the formation of a compound nucleus (which would almost always lead to the eventual emission of a neutron), but it has to be only a few millibarns to account for the experimental results. It is shown in this paper that if the nucleus is represented by a square well potential, the calculated cross sections turn out to be smaller than the experimental ones, but much larger than those obtained from the statistical theory.The angular distribution of the emitted protons should be of the form $A+B{sin}^{2}\ensuremath{\theta}$, where $\ensuremath{\theta}$ is the angle between the incoming photon and the proton, and the ratio $\frac{B}{A}$ depends on the angular momentum of the proton in the nucleus. This is confirmed by experimental results; from the experimental values of $\frac{B}{A}$ it appears that protons with $l=0$ in the nucleus contribute considerably to the effect in Rh and Ag. Feenberg's "wine bottle" potential can account for this more easily than the square well.The theory is applicable to fast photoneutron emission as well, and recent experiments by Poss show that fast photoneutrons are indeed emitted anisotropically.It is suggested that similar direct interaction mechanisms may account for the deviations of ($n,p$) cross sections from those predicted by the theory, as found recently by W\"affler.