We have measured the 1s2s ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$–1s2p ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ and 1s2s ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$–1s2p ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_2$ fine-structure transition wavelengths in the heliumlike ${\mathrm{Ar}}^{16+}$ ion using the beam-foil spectroscopy technique with position-sensitive photon detection. The wavelength results are 559.944(16) Å for the J=1–2 transition and 661.533(18) Å for the J=1–0 transition, which correspond to measurement precisions of about 2×${10}^{\mathrm{-}5}$ a.u. in the transition energies. These values are sensitive to the relativistic contributions in the transition energies to <500 ppm and to the total QED corrections to <0.5%. The measurements confirm the significance of (Zα${)}^4$-dependent relativistic corrections to the n=2 state fine structures suggested by recent calculations. The small remaining discrepancies between these measurements and the accurate theoretical values suggest that the magnitude of uncalculated higher-order QED terms is about 0.15(Zα${)}^4$ a.u. Our experimental results disagree with an earlier recoil-ion measurement for the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$– ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ transition wavelength.

Time-resolved extreme ultraviolet spectra of foil-excited 120-MeV Br ions have been recorded, using a spectrometer equipped with a position-sensitive detector. The spectra near λ=20–30 nm were measured at times after excitation of up to 6 ns. Prominent in the delayed spectra were the long-lived decays of the intercombination transitions in the Mg-like ${\mathrm{Br}}^{23+}$ and Al-like ${\mathrm{Br}}^{22+}$ ions. The present paper reports on lifetime measurements for intercombination transitions in highly charged bromine ions using such a position-sensitive detector.

This research work describes the synthesis and characterization of Si quantum dots of thickness 20Â nm prepared on glass/quartz substrate by Physical Vapour Condensation Technique at the working pressure of 5 and 10Â Torr with fixed substrate temperature 77Â K using liquid nitrogen. The synthesized quantum dots were studied by FESEM, HRTEM, X-ray diffraction, UVâvisible spectroscopy, photoluminescence and FTIR spectroscopy. The X-ray diffraction pattern of synthesized quantum dots shows the amorphous nature. FESEM images of synthesized quantum dots suggest that the size of quantum dots varies from 4â6Â nm which is further confirmed by HRTEM. On the basis of optical absorbance by UVâvisible spectroscopy, a direct band gap has been detected. FTIR spectra suggest that the as-grown Si quantum dots are partially oxidized which is due exposure of samples to air after taking out the samples from the chamber. PL spectra show a broad peak at 444Â nm, which may be attributed to the configuration of amorphous Si quantum dots. A slight shift in the peak position has been observed with increase in working pressure from 5Â Torr to 10Â Torr. The dc conductivity with temperature of Si quantum dots has also been studied from 303 to 454Â K. It is evident that the dc conductivity (Ïdc) enhances linearly with temperature, showing that conduction in Si quantum dots is due to an activated action which further verify the semiconductor deportment of these quantum dots. Keywords: Si quantum dots, Thin films, XRD, Optical properties, Electrical propertie

Following the previous developments to simulate the fully infrared spectra of weak hydrogen bond systems within the linear response theory, an extension of the adiabatic model is presented here. A general formulation including the electrical anharmonicities in the calculation of the damped autocorrelation function of weak H-bonds is adopted to facilitate the support of the additional properties, and thus the IR spectra of the Cl– stretching band in the gaseous (CH₃)₂O⋯HCl complex. We have explored the origins of the broadening of the Cl– stretching band. We found that the main features of the lineshape are attributed to electrical anharmonicity as a consequence of the large mixed second derivatives of the dipole moment with respect to the Cl– bond and of the intermonomer elongations . In addition to providing more accurate theoretical band shapes, inclusion of the electrical anharmonicity in the present model paves the way for a more complete interpretation by generating three new Franck–Condon superposed distributions.

We have measured the total photoattenuation cross section of helium for photons in the energy range of 3–14 keV. At these energies, the photoionization cross section is rapidly decreasing, so that Compton scattering is significant at 4 keV and dominates at the highest energies. Our measurements verify the dominance of Compton scattering in this energy range, and its importance in recent measurements of the ratio of double to single photoionization of helium. The measured cross sections are close to the combined calculated cross sections for Compton scattering and photoionization; we are able to distinguish the contributions of the two effects.

We report observations of simultaneous electron excitation and electron capture in ion-atom collisions of 97-MeV ${\mathrm{Ca}}^{18+}$ and ${\mathrm{Ca}}^{19+}$ in an argon gas target. X-ray spectra at energies near 3.9 keV were collected using a high-resolution x-ray spectrometer. We have resolved transitions from doubly excited 1s2l2l’ and 1s2l3l’ states to singly excited 1${\mathit{s}}^2$2l’ and 1${\mathit{s}}^2$3l’ states in lithiumlike calcium. The observed transitions lie at energies close to the 1s2s-1s2p resonance transitions in heliumlike calcium. We compare the experimental wavelengths and intensities with relativistic Hartree-Fock calculations, and discuss the excitation mechanisms.