Absorption (logic)

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

X-ray resonance exchange scattering in UAs.

Abstract: Resonant enhancement of the magnetic x-ray scattering cross section in UAs has been investigated by tuning the incident x-ray energy through the uranium ${\mathrm{M}}_{\mathrm{IV}}$ and ${\mathrm{M}}_{\mathrm{V}}$ absorption edges. At the ${\mathrm{M}}_{\mathrm{IV}}$ edge the intensity for the (0,0,(5/2) magnetic reflection is enhanced by ${10}^{7}$ relative to the nonresonant component far above the edge, and is a remarkable 1% of the intensity of the (0,0,2) charge peak. At the ${\mathrm{M}}_{\mathrm{V}}$ edge the enhancement is ${10}^{5}$. The dramatic enhancement at M edges has been predicted by Hannon et al., and arises from strong electric multipole transitions between atomic core states and the exchange-split Fermi edge states.

Photo-excitation from dia- to ferri-magnetism in a Rb-Co-hexacyanoferrate Prussian blue analogue

Abstract: We studied the photo-excitation process, the relaxation of the photo-excited state towards the stable state, and the photo-induced magnetic properties of the Prussian blue analogue Rb0.52Co [Fe(CN)6]0.84, 2.3 H2O. Magnetic, Mossbauer and reflectivity measurements have been performed during and after illumination. The efficiency of the photo-excitation device is maximum at \(\lambda \cong 700 - 750\) nm. The process, however, is severely hindered by bulk absorption of the light; it is rapidly completed at the surface of the sample and then proceeds slowly in the bulk. Under the effect of photo-excitation the system turns from a dia- to a ferri- magnet, with a Tc value ≥21 K, indicative of the transformation of the material due to the following optical electron transfer: \(F{e^{II}}(LS) + C{o^{III}}(LS) \to F{e^{III}}(LS) + C{o^{II}}(HS)\) Thermal relaxation towards the stable electronic state is observed in the 95-110 K temperature interval, obeying a self-accelerated kinetics. At low temperature, a weak, non-exponential, relaxation is detected. These features are discussed in terms of co-operative effects in the frontal process of photo- excitation. The peculiarities of a photo-excited state created below the magnetic ordering temperature are discussed. A metastable magnetic state has been observed in low fields, denoted “Raw Photo-Induced State" (RPI), with a magnetization curve in-between the field-cooled and zero-field-cooled curves.

S1 and T1 species of .beta.-carotene generated by direct photoexcitation from the all-trans, 9-cis, 13-cis, and 15-cis isomers as revealed by picosecond transient absorption and transient Raman spectroscopies

Abstract: Time-resolved absorption spectra, upon excitation of the all-trans, 9-cis, 13-cis, and 15-cis isomers of {beta}-carotene, were recorded by using 20-25-ps, 355-nm pump and white-continuum interrogating pulses. The isomers showed the S{sub n} {l arrow} S{sub 1} absorption at 556 (all-trans), 565 (9-cis), 560 (13-cis), and 562 (15-cis) nm; no time-dependent changes of the absorptions were detected. (The S{sub 1} lifetimes for the all-trans and 15-cis isomers were determined precisely, by using 0.5-ps pump and interrogating pulses, to be 12.4 {plus minus} 0.5 and 14.0 {plus minus} 0.5 ps, respectively.) After the decay of the S{sub n} {l arrow} S{sub 1} absorption, a weak absorption ascribable to the T{sub n} {l arrow} T{sub 1} transition remained in the 510-520-nm region, from which the quantum yield of intersystem crossing was estimated to be on the order of 10{sup {minus}3}. Transient Raman spectra were recorded by using 355-nm pump and 532-nm probe mode-locked (76 MHz), Q-switched (800 Hz) pulse trains (pulse duration {approximately} 100 ps). An S{sub 1} Raman spectrum was extracted by subtraction between a pair of pump-and-probe spectra with different delay times, i.e. 0 and 500 ps. A T{sub 1} Raman spectrum was extracted by subtracting a probe-only spectrum from amore » pump-and-probe spectrum with the delay time 500 ps. Each isomer showed a unique S{sub 1} Raman spectrum, which was interpreted by assuming the configuration of the particular isomer. On the other hand, the 13-cis and 15-cis isomers showed T{sub 1} Raman spectra that are essentially the same as that shown by the all-trans isomer, the 9-cis isomer showed a unique T{sub 1} Raman spectrum. The above results indicate (1) that no isomerization takes place in the S{sub 1} state and (2) that the T{sub 1} state is generated through intersystem crossing.« less

High signal-to-noise ratio laser technique for accurate measurements of spectral line parameters

Abstract: An experiment enabling extremely high signal-to-noise ratios in the measurement of spectral line shapes is described. This approach, which combines high-bandwidth locking of a continuous wave probe laser and the frequency-stabilized cavity ring-down spectroscopy technique, enables long-term signal averaging and yields high-resolution spectra with a relatively wide dynamic range and low detection limit. By probing rovibronic transitions of the ${}^{16}$O${}_{2}$ $B$ band near $\ensuremath{\lambda}=689$ nm, exceptionally precise measurements of absorption line shape and line position are demonstrated. A signal-to-noise ratio of $220\phantom{\rule{0.16em}{0ex}}000$ and a minimum detectable absorption coefficient of $2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ is reported, which corresponds to the lowest line intensity measurable by this setup of approximately $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}30}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}/(\mathrm{molecule}$ ${\mathrm{cm}}^{\ensuremath{-}2})$. Careful analysis of the data revealed a subtle line-shape asymmetry that could be explained by the speed dependence of the collisional shift. The demonstrated measurement precision enables the quantification of systematic line-shape deviations, which were approximately 1 part in 80 000 of the peak absorption. The influence of slowly drifting etaloning effects on the precision of the line-shape analysis is discussed. How this method can enable experiments that address a number of fundamental physical problems including the accurate optical measurement of the Boltzmann constant and tests of the symmetrization postulate is also discussed.

Identification of H$_2$CCC as a diffuse interstellar band carrier

Abstract: We present strong evidence that the broad, diffuse interstellar bands (DIBs) at 4881 and 5450\,\AA are caused by the $B\,^1$B$_1$\,$\leftarrow$\,$X\,^1$A$_1$ transition of H$_2$CCC (l-C$_3$H$_2$). The large widths of the bands are due to the short lifetime of the $B\,^1$B$_1$ electronic state. The bands are predicted from absorption measurements in a neon matrix and observed by cavity ring-down in the gas phase and show exact matches to the profiles and wavelengths of the two broad DIBs. The strength of the 5450\,\AA DIB leads to a l-C$_3$H$_2$ column density of $\sim5\times10^{14}$ cm$^{-2}$ towards HD\,183143 and $\sim2\times10^{14}$\,cm$^{-2}$ to HD\,206267. Despite similar values of $E$($B-V$), the 4881 and 5450\,\AA DIBs in HD\,204827 are less than one third their strength in HD\,183143, while the column density of interstellar C$_3$ is unusually high for HD\,204827 but undetectable for HD\,183143. This can be understood if C$_3$ has been depleted by hydrogenation to species such as l-C$_3$H$_2$ towards HD\,183143. There are also three rotationally resolved sets of triplets of l-C$_3$H$_2$ in the 6150$-$6330\,\AA region. Simulations, based on the derived spectroscopic constants and convolved with the expected instrumental and interstellar line broadening, show credible coincidences with sharp, weak DIBs for the two observable sets of triplets. The region of the third set is too obscured by the $\alpha$-band of telluric O$_2$.