Theoretical study on electron impact excitation of highly charged Ne-like ions

The electron impact excitation (EIE) cross sections from the ground state to all of the 2s(2)2p(5)3l and 2s2p(6)3l(l=s, p, d) states along the Ne-like isoelectronic sequence of ions (Z = 50-57) have been calculated by using the multiconfiguration Dirac-Fock package GRASP92 and the fully relativistic distorted-wave program REIE06. In the calculations, the relativistic effects and electron correlation effects are considered systematically. Based on those calculations, the EIE cross sections along the Ne-like isoelectronic sequence of ions for different incident electron energies are discussed, and some important conclusions are drawn. We also study the influence of the correlation effects on the values of the 3C/3D line-intensity ratio [3C: (2p(1/2)3d(3/2))(1) -> 2s(2)2p(6) S-1(0), 3D: (2p(3/2)3d(5/2))(1) -> 2s(2)2p(6) S-1(0)] along the Ne-like sequence. A comparison is made between the present results and previous theoretical calculations and experimental results for the EIE cross sections in Ba-46 (+) ions, and a good agreement is obtained.

Electron impact excitation rate coefficients of N II ion

This paper calculates the electron impact excitation rate coefficients from the ground term 2s(2)2p(2) P-3 to the excited terms of the 2s(2)2p(2), 2s2p(3), 2s(2)2p3s, 2s(2)2p3p, and 2s(2)2p3d configurations of N II. In the calculations, rnulticonfiguration Dirac-Fork wave functions have been applied to describe the target-ion states and relativistic distorted-wave calculation has been performed to generate fine-structure collision strengths. The collision strengths are then averaged over a Maxwellian distribution of electron velocities in order to generate the effective collision strengths. The calculated rate coefficients are compared with available experimental and theoretical data, and some good agreements are found for the outer shell electron excitations. But for the inner shell electron excitations there are still some differences between the present calculations and available experiments.

Differential and Integral Cross Sections for Electron Impact Excitation of Lithium

The differential and integral cross sections for electron impact excitation of lithium from the ground state 1s(2)2s to excited states 1s(2)2p, 1s(2)3l (l = s,p,d) and 1s(2)4l (l = s,p,d,f) at incident energies ranging from 5 eV to 25 eV are calculated by using a full relativistic distorted wave method. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. A part of the cross sections are compared with the available experimental data and with the previous theoretical values. It is found that, for the integral cross sections, the present calculations are in good agreement with the time-independent distorted wave method calculation, for differential cross sections, our results agree with the experimental data very well.

Excitation and dissociation of tungsten hexacarbonyl W(CO)(6): Statistical and nonstatistical dissociation processes

We have studied the excitation and dissociation processes of the molecule W(CO)(6) in collisions with low kinetic energy (3 keV) protons, monocharged fluorine, and chlorine ions using double charge transfer spectroscopy. By analyzing the kinetic energy loss of the projectile anions, we measured the excitation energy distribution of the produced transient dications W(CO)(6)(2+). By coincidence measurements between the anions and the stable or fragments of W(CO)(6)(2+), we determined the energy distribution for each dissociation channel. Based on the experimental data, the emission of the first CO was tentatively attributed to a nonstatistical direct dissociation process and the emission of the second or more CO ligands was attributed to the statistical dissociation processes. The dissociation energies for the successive breaking of the W-CO bond were estimated using a cascade model. The ratio between charge separation and evaporation (by the loss of CO+ and CO, respectively) channels was estimated to be 6% in the case of Cl+ impact. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3523347]

Molecular dynamics and control following excitation with an ultra-short intense laser pulse

Vibronic excitations of the tri-atomic molecule OClO (A(2)A(2)(nu(1), nu(2), nu(3)) <-- (XB1)-B-2 (0, 0, 0)) with weak and strong ultra-short laser fields are studied within full quantum wavepacket dynamics in hyperspherical coordinates. Different dynamics is observed following excitation with laser pulses of different intensities. With a strong laser pulse, many vibrational states are excited and a spatially more localised wavepacket arises. The numerical results show that the population of different vibrational states of the wavepacket on the excited potential energy surface is altered by the intensity of the laser pulse. The numerical results also suggest a related effect on the phase of the wavepacket. These interesting phenomena can be understood by an analysis of the corresponding results for two model diatomic molecules. The possible physical mechanisms of control of chemical processes using strong laser fields are discussed. (C) 2004 Elsevier B.V. All rights reserved.

Photodissociation dynamics of the methyl radical at 212.5 nm: Effect of parent internal excitation

Photodissociation dynamics of the CH3 radical at 212.5 nm has been investigated using the H atom Rydberg tagging time-of-flight method with a pure CH3 radical source generated by the photolysis of CH3I at 266 nm. Time-of-flight spectra of the H atom products from the photolysis of both cold and hot methyl radicals have been measured at different photolysis polarizations. Experimental results indicate that the photodissociation of the methyl radical in its ground vibrational state at 212.5 nm excitation occurs on a very fast time scale in comparison with its rotational period, indicating the CH3 dissociation at 212.5 nm occurs on the excited 3s Rydberg state surface. Experimental evidence also shows that the photodissociation of the methyl radical in the nu(2)=1 state of the umbrella mode at 212.5 nm excitation is characteristically different from that in the ground vibrational state. (C) 2004 American Institute of Physics.

Orientation and alignment of reagent molecules by two-photon excitation

The expressions used for describing the angular distribution of oriented and aligned reagent molecules are derived. The algebraic forms of orientation and alignment parameters of molecules in the excited states are obtained for two-photon excitation. The reagent molecules after absorbing two-photon may produce the higher order orientation and alignment than doing one-photon. (C) 2002 Elsevier Science B.V. All rights reserved.

Controllable Red, Green, Blue (RGB) and Bright White Upconversion Luminescence of Lu2O3:Yb3+/Er3+/Tm3+ Nanocrystals through Single Laser Excitation at 980 nm

Lu2O3:Yb3+/Er3+/Tm3+ nanocrystals have been successfully synthesized by a solvothermal process followed by a subsequent heat treatment at 800 degrees C. Powder X-ray diffraction, transmission electron microscopy, upconversion photoluminescence spectra, and kinetic decay were used to characterize the samples. Under single-wavelength diode laser excitation of 980 nm, the bright blue emissions of Lu2O3:Yb3+, Tm3+ nanocrystals near 477 and 490 nm were observed due to the (1)G(4)-> H-3(6) transition of Tm3+. The bright green UC emissions of Lu2O3:Er3+ nanocrystals appeared near 540 and 565 nm were observed and assigned to the H-2(11/2)-> I-4(15/2) and S-4(3/2)-> I-4(15/2) transitions, respectively, of Er3+. The ratio of the intensity of green luminescence to that of red luminescence decreases with an increase of concentration of Yb3+ in Lu2O3:Er3+ nanocrystals.

Luminescent properties of Mn2+ in hexagonal aluminates under ultraviolet and vacuum ultraviolet excitation

Mn2+-doped xBaO center dot 6Al(2)O(3) and BaMgAl10O17 phosphors were prepared by solid-state reaction. The investigation of vacuum ultraviolet (VUV) excitation spectra of these phosphors exhibits that 0.82BaO center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ have a stronger absorption than BaO center dot 6Al(2)O(3):Mn2+ at about 147 nm. The emission spectra under VUV excitation demonstrated that 0.82BaOBa center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ have a higher luminescent intensity than BaO center dot 6Al(2)O(3):Mn2+. The lifetime analysis indicates that they have similar decay times, indicating that 0.82BaOBa center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ can be used as luminescent materials for plasma display panels. We observed that the critical concentration of the Mn2+ ions by host excitation is different from that of Mn2+ direct excitation, revealing a different mechanism of energy transfer. The critical distance was calculated. A model was suggested to explain the process of the energy transfer from the host to the Mn2+ ions.

Redshift phenomenon of the excitation light of long life emission phosphor

We observed that the SrMg2(PO4)(2):Eu phosphor could emit long life phosphorescence with the excitation light whose wavelength was shorter than 420 nm, however, when La, Ce, or Gd was codoped, the wavelength of the excitation light to cause the phosphorescence had a redshift of 40 nm. A possible mechanism and related discussion for this redshift phenomenon of the excitation light was given. It was suggested that the threshold between the trap and valence band was decreased with the addition of the codopants.

VUV excitation properties of LnAl(3)B(4)O(12): Re (Ln = Y, Gd; Re=Eu, Tb)

Vacuum ultraviolet excitation spectra of LnAl(3)B(4)O(12):Re (Ln = Y, Gd; Re = Eu, To), along with X-ray photoelectron spectra, were measured. The spectra are tentatively interpreted in terms of the optical properties of the rare earth ions and the band structure. It was found that there is an energy transfer from the hosts to the rare earth ions. It was also found that the top of the valence band in the Gd compound is mainly formed by the 2p levels of O2- and the 4f levels of Gd3+, and in the Y compound mainly by the 2p levels of O2-. (C) 2000 Elsevier Science Ltd. All rights reserved.

Infrared spectra and VUV excitation properties of BaLnB(9)O(16): Re (Ln = La, Gd; Re = Eu, Tb)

The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius. (C) 2001 Elsevier Science B.V. All rights reserved.

COMPARATIVE-STUDY OF KALMAN FILTERING, SYNCHRONOUS EXCITATION AND NUMERICAL DERIVATIVE TECHNIQUES IN FLUOROMETRY

The performance of Kalman filtering, synchronous excitation and numerical derivative techniques for the resolution of overlapping emission spectra in spectrofluorimetry was studied. The extent of spectrum overlap was quantitatively described by the separation degree D(s), defined as the ratio of the peak separation to the full width at half-maximum of the emission spectrum of the interferent. For the system of Rhodamine B and Rhodamine 6G with a large D(s) of about 0.4, both Kalman filtering and synchronous techniques are able to resolve the overlapping spectra well and to give satisfactory results while the derivative spectra are still overlapped with each other. Moreover, the sensitivities are greatly decreased in derivative techniques. For more closely spaced spectra emitted by the complexes of Al and Zn with 7-iodo-8-hydroxyquinoline-5-sulphonic acid (Ferron)-hexadecyltrimethylammonium bromide, the synchronous excitation technique cannot completely separate the overlapping peaks, although it increases the separation degree from 0.25 in the conventional spectra to 0.37 in the synchronous spectra. On the other hand, Kalman filtering is capable of resolving this system. When the Al/Zn intensity ratio at the central wavelength of Al was > 1, however, the accuracy and precision of the estimates for Zn concentration produced by the Kalman filter became worse. In this event, the combination of synchronous excitation and Kalman filtering can much improve the analytical results.