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Absorption (logic)
About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.
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TL;DR: In this paper, an f-f transition intensity model was proposed to analyze the crystal-field splittings of several anomalous multiplets, and the resulting 144-level data set was analyzed in terms of a model Hamiltonian that assumes site symmetry for the ions in Nd:YAG.
Abstract: Results obtained from optical absorption measurements on ${\mathrm{Nd}}^{3+}$:${\mathrm{Y}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$ (Nd:YAG) at 10 and 29 K are reported and analyzed. The low-temperature (10 K) absorption spectrum shows transitions from the lowest Stark component of the $^{4}$${\mathit{I}}_{9/2}$ (ground) multiplet to 133 of the 155 crystal-field (Stark) levels predicted to be located between 3900 and 40 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, spanning 35 excited multiplet manifolds of ${\mathrm{Nd}}^{3+}$(4${\mathit{f}}^{3}$). Among the 133 transitions observed in the 10-K absorption spectrum, 97 are sufficiently well resolved to permit quantitative determination of transition line strengths. Energy levels for the $^{4}$${\mathit{I}}_{9/2}$ and $^{4}$${\mathit{I}}_{11/2}$ multiplets are taken from previously obtained optical emission measurements, and the resulting 144-level data set is analyzed in terms of a model Hamiltonian that assumes ${\mathrm{D}}_{2}$ site symmetry for the ${\mathrm{Nd}}^{3+}$ ions in Nd:YAG. Inclusion of two-electron correlation crystal-field (CCF) interaction terms in the model Hamiltonian explains the crystal-field splittings of several anomalous multiplets, and reduces the rms deviation between calculated and observed energies (for 144 levels) from 28 to 14 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The optical line-strength data obtained in this study are analyzed in terms of an f-f transition intensity model developed by us in previous work. This model has broad applicability in analyses of f-f intensity data for transitions between Stark levels. Emission branching ratios for transitions from the $^{4}$${\mathit{F}}_{3/2}$ multiplet are calculated and compared with literature values.
72 citations
TL;DR: In this article, a variety of results are reported for the ground state of the hydrogen molecule, including improved Born-Oppenheimer calculations, a study of the convergence of energies with basis set size, adiabatic calculations, and the first successful ab initio nonadiabatic calculation.
Abstract: A variety of results are reported for the ground state ($X^{1}\ensuremath{\Sigma}_{g}^{+}$) of the hydrogen molecule. They include improved Born-Oppenheimer calculations, a study of the convergence of energies with basis-set size, adiabatic calculations, and the first successful ab initio nonadiabatic calculation. The latter, which treats ${\mathrm{H}}_{2}$ as a four-body problem, leads us to predict that the dissociation energy of ${\mathrm{H}}_{2}$ is 36117.92 ${\mathrm{cm}}^{\ensuremath{-}1}$. This value may be compared with 36 117.8\ifmmode\pm\else\textpm\fi{}0.4 ${\mathrm{cm}}^{\ensuremath{-}1}$ (the value derived from the experimental ionization potential), with 36118.6\ifmmode\pm\else\textpm\fi{}0.5 ${\mathrm{cm}}^{\ensuremath{-}1}$ (the value derived from the experimental vibrational levels of the $B^{1}\ensuremath{\Sigma}_{u}^{+}$ state), or with 36118.3 ${\mathrm{cm}}^{\ensuremath{-}1}$ (the upper-bound value derived from the experimental absorption limit).
72 citations
TL;DR: Two-photon absorption cross sections for transitions from the O and 3p ground electronic state to the 3p, 4p and 4p states have been calculated by explicit evaluation of the perturbation-theory summation using matrix elements calculated from configuration-interaction wave functions and sum rules to correct for truncation.
Abstract: Two-photon absorption cross sections for transitions from the O${(\mathrm{}}^{3}$P) ground electronic state to the 3p ${}^{3}$P, 4p ${}^{3}$P, and the autoionizing ${\mathrm{O}}^{+}$(${\mathrm{}}^{2}$D)3p' and ${\mathrm{O}}^{+}$(${\mathrm{}}^{2}$P)3p'' states have been calculated by explicit evaluation of the perturbation-theory summation using matrix elements calculated from configuration-interaction wave functions and sum rules to correct for truncation. The role of different contributions in the summation has been analyzed. For the 3p ${}^{3}$P state, a cross section of ${\mathcal{J}}_{J\mathcal{'}}$${\ensuremath{\sigma}}_{0}^{(2)}$(J'\ensuremath{\leftarrow}J) of (1.319\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}35}$ ${\mathrm{cm}}^{4}$ has been obtained, which is in excellent agreement with the experimental value for the quantity ${\mathcal{J}}_{J\mathcal{'}}$${\ensuremath{\sigma}}_{0}^{(2)}$(J'\ensuremath{\leftarrow}2)${G}^{(2)}$ =(2.66\ifmmode\pm\else\textpm\fi{}0.80)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}35}$ ${\mathrm{cm}}^{4}$, given in the companion paper, if the photon statistical factor, ${G}^{(2)}$, is evaluated in the chaotic field limit (${G}^{(2)}$=2).
72 citations
TL;DR: In this article, the infrared absorption spectra of ices were measured with a diamond-anvil cell up to 141 GPa at 298 K. The high-pressure spectra corrected for diamond absorption provided the substantial absorption profile of the ices over the whole pressure range measured.
Abstract: The infrared absorption spectra of ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{D}}_{2}\mathrm{O}$ ices were measured with a diamond-anvil cell up to 141 GPa at 298 K. The high-pressure spectra corrected for diamond absorption provided the substantial absorption profile of ices over the whole pressure range measured. A sequence of pressure-induced Fermi resonance was observed between the softening stretch mode and the combinations of rotational and bending modes below 55 GPa as reported previously. One rotational mode showed an abrupt increase in the peak frequency at $58\ifmmode\pm\else\textpm\fi{}3\mathrm{GPa}$ in ${\mathrm{H}}_{2}\mathrm{O}$ ice and $68\ifmmode\pm\else\textpm\fi{}3\mathrm{GPa}$ in ${\mathrm{D}}_{2}\mathrm{O}$ ice. This can be attributed to a transition from ice VII to proton-tunneling-disordered ice VII. A further transition into proton-disordered ice X was inferred from the spectral change to occur roughly at 65--75 GPa for ${\mathrm{H}}_{2}\mathrm{O}$ and 80--90 GPa for ${\mathrm{D}}_{2}\mathrm{O}.$
72 citations
TL;DR: In this paper, an experimental study has been carried out of the osmotic pressure of solutions of the isotope He in liquid at low temperatures, between 0.8 and 1.2°C.
Abstract: An experimental study has been carried out of the osmotic pressure of solutions of the isotope ${\mathrm{He}}^{3}$ in liquid ${\mathrm{He}}^{4}$ at low temperatures, between 0.8 and 1.2\ifmmode^\circ\else\textdegree\fi{}K. A superleak, a tube packed with a fine powder, acted as a semipermeable membrane which allowed only the superfluid ${\mathrm{He}}^{4}$ to pass. The conclusion from these experiments was that the measured osmotic pressures were in reasonable agreement with values expected from the thermodynamic relations with other equilibrium properties of the mixtures, notably their vapor pressures. Thermodynamic equilibrium therefore seemed to have been attained under the conditions of the experiments. The second half of this paper concerns a study of the cooling which must take place during the adiabatic dilution of ${\mathrm{He}}^{3}$ by ${\mathrm{He}}^{4}$. If the dilution is carried out at low temperatures where the solutions separate into two phases, the absorption of heat is estimated to be usefully large. After dilution the solution can be distilled, condensed and recirculated so as to make a continuously acting refrigerator. It should be possible to operate at temperatures of 0.1\ifmmode^\circ\else\textdegree\fi{}K or below.
72 citations