Near-infrared diode laser spectroscopy of the HCSi radical

The , , and band spectra of HCSi radical were investigated by means of near-infrared diode laser spectroscopy to determine precise molecular constants for the and states. The detailed analysis of the rotationally resolved band spectra, studied for the first time in the present investigation, leads to the precise determination of molecular constants for the state associated with the Renner-Teller interaction. We obtained −0.15126663(53) and 495.00698(30) cm⁻¹ as the Renner-Teller parameter ε and the bending vibrational frequency ω₂, respectively. Based on the molecular constants for the and states, the rotational levels of the state were analyzed to obtain molecular constants and information on upper state perturbations. Using the available spectroscopic data, valence force fields for both the and states were estimated to aid in understanding the vibrational energy levels of the HCSi radical.     

Measurement of the 4d-photoionization cross section via two-photon and two-step excitation in sodium

We present a comparison of the photoionization cross sections of the 4d excited levels of sodium by using the two-step resonant laser excitation and by two-photon non-resonant excitation from the ground state. Dye lasers, pumped with a Nd: YAG laser, have been used in conjunction with a thermionic diode ion detector to measure cross sections and the atomic densities as a function of laser energy. By applying the saturation technique, the measured values of the cross sections and atomic densities for the 4d level by two-photon excitation are 12.2(2.4) Mb and , respectively. Where as in the case of two-step excitation, the cross section and number density for the 4d level via 3p level and for the 4d levels via 3p level are determined as 9.6(1.9) Mb, and 12.8(2.5) Mb, , respectively.     

First CRDS-measurements of water vapour continuum in the 940 nm absorption band

Measurements of near-infrared water vapour continuum using continuous wave cavity ring down spectroscopy (cw-CRDS) have been performed at around 10611.6 and . The continuum absorption coefficients for N₂-broadening have been determined to be and at , and and at , respectively.These results represent the first near-IR continuum laboratory data determined within the complex spectral environment in the 940 nm water vapour band and are in reasonable agreement with simulations using the semiempirical CKD formulation.     

L to M shell transitions and model comparisons for radiative opacities of sodium fluoride plasma

The radiative opacities of hot dense sodium fluoride (NaF) plasma have been studied in the case of local thermodynamic equilibrium (LTE). The spectrally resolved opacity in the case of and is taken as an example to illustrate the absorption structures of the NaF plasma. The transitions from L to M shells of sodium and fluoride are the main contributions for the plasma absorptions. The isodense opacities of NaF plasma are studied at a density of and temperatures of 20-60 eV. Detailed comparisons among the results of the detailed term accounting (DTA), detailed configuraion accounting (DCA), unresolved transition array (UTA) and average atom (AA) model codes, which have been developed independently in China in the past few years, are performed for both the spectral resolved and mean opacities. Good agreements are found at a temperature of 40 eV and a density of , but discrepancies appear at a temperature of 50 eV and a density of .     

Profile imaging of reconstructed polar and non-polar surfaces of ZnO

The atomic scale surface structures of ZnO non-polar as well as and ±(0 0 0 1) polar surfaces have been directly imaged by high-resolution transmission electron microscopy (HRTEM). The observations were made on clean surfaces created by irradiating a single ZnO nanobelt using 400 keV electron beam in TEM, under which ZnO dots were grown epitaxially and in situ on the surface of the nanobelt. A technique is demonstrated for directly distinguishing the surface polarity of the ±(0 0 0 1) polar surfaces. For the non-polar surface, HRTEM images and simulation results indicate that the Zn ions in the first and second layer suffer from inward and outward relaxation, respectively; the oxygen ions in the first and second layer prefer shifting to vicinal Zn ions to shorten the bonding distance. For the oxygen-terminated polar surface, the oxygen ions at the outmost top layer were directly imaged. a × 2 reconstruction has also been observed at the surface, and its atomic structure has been proposed based on image simulation. Oxygen-terminated polar surface is flat and shows no detectable reconstruction. For the Zn-terminated (0 0 0 1) polar surface, HRTEM may indicate the existence of Zn vacancies and a possibly c-axis, random outward displacement of the top Zn ions. Our data tend to support the mechanism of removal of surface atoms for maintaining the stability of (0 0 0 1) polar surfaces.     

Direct nanosecond Nd→Ce nonradiative energy transfer in cerium trifluoride laser crystals

Using third harmonics of LiF:F₂⁺ tunable color center laser excitation and selective fluorescence detection the temperature and concentration dependencies of fluorescence decay curves of the high-lying manifold of the Nd³⁺ ion were measured in CeF₃ crystals. As a result the temperature dependence of energy transfer kinetics from the manifold of the Nd³⁺ donor ions to the manifold of the acceptor Ce³⁺ ions in the ordered practically 100% filled crystal lattice was determined for 13-. Based on the temperature dependence the mechanisms and the channels of the Nd→Ce nonradiative energy transfer have been recognized. The net growth of the resonance Nd→Ce energy transfer rate in the temperature range from 25 to is found to be almost 3 orders of magnitude from 9.0×10⁴ to .In a crystal a significant contribution of the Nd→Nd resonance energy transfer to the manifold quenching is found for 20- and its channel and mechanism are suggested.Discussion of the possibility of subpicosecond and picosecond nonradiative energy transfer in rare-earth doped laser crystals is provided.