Collisional excitation of the formyl radical (HCO) by molecular hydrogen

ABSTRACT This paper addresses the need for accurate rate coefficients for transitions between fine- and hyperfine-structure resolved rotational transitions in the formyl (HCO) radical induced by collisions with the two nuclear spin modifications of H2, the dominant molecule in the interstellar medium (ISM). These rate coefficients, as well as radiative transition rate coefficients, are required for accurate determination of the abundance of HCO in the ISM. Time-independent close-coupling quantum scattering calculations have been used to compute rate coefficients for (de-)excitation of HCO in collisions with para- and ortho-H2. These calculations utilized a potential energy surface for the interaction of HCO with H2 recently computed by the explicitly correlated RCCSD(T)-F12a coupled-cluster method. Rate coefficients for temperatures ranging from 5 to 400 K were calculated for all transitions among the fine and hyperfine levels associated with the first 22 rotational levels of HCO, whose energies are less than or equal to 144 K.

Radiative and non-radiative transitions of excited Ti3+ cations in sapphire

We have measured the fluorescence quantum efficiency in Ti3+:sapphire single crystals between 150 K and 550 K. Using literature-given effective fluorescence lifetime temperature dependence, we show that the zero temperature radiative lifetime is (4.44 ± 0.04) μs, compared to the 3.85 μs of the fluorescence lifetime. Fluorescence lifetime thermal shortening resolves into two parallel effects: radiative lifetime shortening, and non-radiative transition rate enhancement. The first is due to thermally enhanced occupation of a ΔE = 1,700 cm−1 higher (top) electronic state of the upper multiplet, exhibiting a transition oscillator strength of f = 0.62, compared to only 0.013 of the bottom electronic state of the same multiplet. The non-radiative rate relates to multi-phonon decay transitions stimulated by the thermal phonon occupation. Thermal enhancement of the configuration potential anharmonicity is also observed. An empiric expression for the figure-of-anharmonicity temperature dependence is given as $$\hat{{\bf{H}}}$$Hˆ (T) = $$\hat{{\bf{H}}}$$Hˆ (0)(1 + β exp(−ℏωco /kBT )), where $$\hat{{\bf{H}}}$$Hˆ (0) = 0.276, β = 5.2, ℏωco = 908 cm−1, and kB is the Boltzmann constant.

Judd-Ofelt Analysis of a Dendrtic Type Europium Complex/Silicone Rubber

A dendritic type europium complex/silicone rubber has been prepared. According to the luminescence spectrum, the Judd-Ofelt theory was adopted to calculate the intensity parameters Ω2and Ω4. The total radiative transition rate (640.1 s-1), radiative lifetime (1.562 ms) and the stimulated emission cross-sections (46.19×10-22cm2) of the5D0exciting state have been evaluated. Analysis reveals that the europium (III) chelating polymer is promising for use in optical devices.

Structure and Photoluminescent Properties of Microstructural YBO3 : Eu3+ Nanocrystals

YBO3 : Eu3+ nanocrystals (NCs) were prepared by a hydrothermal method and characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The results demonstrate that morphology and structure of the NCs varied strongly with hydrothermal temperature. Their luminescent properties were investigated in comparison to the bulk. A large number of NO&minus3 groups were adsorbed at the surface of hydrothermal products, which acted as luminescent killers; Two symmetry sites of Eu3+ ions in NCs, the interior and the surface sites, were identified by the site-selective excitation and time-resolved emission experiments; The intensity ratio of 5D0–7F2 to 5D0–7F1 of Eu3+ at the surface site increased greatly than that at the interior site; as a result, the chromaticity was improved; The total radiative transition rate of 5D0–ΣJ7Fj for Eu3+ at the surface site was 3–5 times larger than that at the interior.