Selection Rules For Dipole Transitions Research Articles

Large-scale multiconfiguration Dirac-Hartree-Fock calculations of atomic data, Landé gj -factors and hyperfine constants of the neutral Rn-211 isotope

We computed the atomic data of ns[K]J ( n = 7, 8, 9), np[K]J ( n = 7, 8, 9), nd[K]J ( n = 6, 7, 8, 9), and nf[K]J ( n = 5, 6, 7, 8) and 5g[K]J autoionized Rydberg spectra of the neutral radon-211 isotope. The computations are carried out by using the Multiconfiguration Dirac-Hartree-Fock method (MCDHF) together with the relativistic configuration (RCI) approach. The convergence of the obtained results is monitored by incorporating relativistic electron-electron correlation, the Breit-interaction effect, self-energy, and vacuum-polarization corrections. As a result, we acquired the energy levels, transition rates, oscillator strengths, Landé gJ -factors and magnetic dipole hyperfine constants. The transition parameters between the levels belonging to different series are computed for all allowed electric dipole transition selection rules. The present results are in very good agreement with other experimental and theoretical data available in the literature database. The present data could be useful in predicting spectral lines of radon via astrophysics and stellar spectroscopy.

A comprehensive model for Doppler spectra in thermal atomic vapour

We theoretically and experimentally investigate the Doppler-broadened absorption spectrum of the D2-line (52 S 1/2 → 52 P 3/2) in thermal (room-temperature) Rb vapour over a wide range of probe intensity, probe diameter, and vapour cell temperature to understand the effect of hyperfine pumping and transit-relaxation on the absorption lineshape. We present a relatively simple but comprehensive five-level rate equation model which incorporates optical pumping of the atomic population into the other ‘dark’ ground hyperfine level (leading to absorption saturation), including contributions of the three closely spaced (within one Doppler linewidth) hyperfine levels in the excited state 52 P 3/2 (allowed by the dipole transition selection rules). D2-line transmission spectra predicted by our model show excellent agreement (rms error ) with the experimental data for a wide range of probe intensities (from all the way up to , where I sat0 is the usual two-level saturation intensity for the respective atomic transition), vapour cell temperatures (24.2°C–53.5 °C) and beam diameters (1/e 2 width mm). Our model also takes into account the finite transit time of atoms across the probe beam cross-section, and correctly predicts the dependence of effective saturation intensity on probe diameter (up to lower saturation intensity as compared to I sat0 for few-mm beam sizes). This ab initio five-level model can thus predict accurate Doppler lineshapes for any given experimental parameter set for a linearly polarized probe without any fitting parameters, and can be easily applied to any other atomic system by an appropriate change of the atomic constants in the rate equations.

Large second-harmonic generation and linear electro-optic effect in trigonal selenium and tellurium

Trigonal selenium and tellurium crystalize in helical chain-like structures and thus possess interesting properties such as current-induced spin polarization, gyrotropic effects and nonlinear optical responses. By performing systematic ab initio calculations based on density functional theory in the generalized gradient approximation plus scissors correction, we study their linear and nonlinear optical (NLO) properties. We find that the two materials exhibit significant second-harmonic generation (SHG) and linear electro-optic (LEO) effect. In particular, the SHG coefficients of tellurium are huge in the photon energy range of 0 ~ 3 eV, with the magnitudes of SHG(xxx) being as large as 3640 pm/V, which are about sixteen times larger than that of GaN, a widely used NLO material. On the other hand, trigonal selenium is found to possesses large LEO coefficients r(xxx,0) which are more than six times larger than that of GaN.Therefore, trigonal tellurium and selenium may find valuable applications in NLO and LEO devices such as frequency conversion, electro-optical switch and light signal modulator.The energy positions and shapes of the principal features in the calculated optical dielectric functions of both materials agree rather well with the available experimental ones, and are also analyzed in terms of the calculated band structures especially symmetries of the involved band states and dipole transition selection rules.

Nonlinear Optical Susceptibility of Tetragonal BaTiO<sub>3</sub>

In the framework of the vibronic theory of ferroelectricity for the transparency region of tetragonal BaTiO3 components and of nonlinear optical susceptibility responsible for the second harmonic generation and the optical rectification are calculated. Selection rules for dipole transitions in the Γ point of the first Brilouin zone are extended over the whole zone. Calculations are confined to lowest order in expansion of susceptibilities in power series of low symmetry lattice distortion. Numerical values of susceptibilities have experimentally observed order of magnitude. The spectral behavior of and is calculated as well.

Structure multiformity of inverted Y-type four-level optical quantum coherent systems

According to the dipole transition selection rules and by choosing proper transition channels, it is found that the inverted Y-type four-level scheme can be classified into nine different 2nd-order subschemes when using corresponding laser fields, and they can be further classified into eighty 3rd-order subschemes in detail according to different exciting intensities that are applied in different channels. In this paper, the structure multiformity of inverted Y-type four-level scheme is discussed and the demonstrations on some subschemes are also given. At the same time, the subschemes which have been studied are pointed out, but most of them have not been researched to the best of our knowledge.

Interaction of 4p54dN+1 and 4p64dN−14f configurations and its influence on the photoexcitation and emission spectra in the isoelectronic and isonuclear sequences

The strong interaction of 4p54dN+1 + 4p64dN−14f configurations and its influence on the photoexcitation and emission spectra corresponding to the excitations from the ground level of 4p64dN have been considered. The results are presented for the isoelectronic sequences from the ionization degree q = 5 up to q = 29–37 as well as for the isonuclear sequences of Snq+ and Wq+. It is shown that depending on the number of 4d electrons, the variation of spectra in the isoelectronic sequences corresponds to three different types. At N = 4 and N = 6–9, the strong concentration of lines takes place in the whole isoelectronic sequence, except for small ionization degrees. At N ⩽ 3, the width of photoexcitation and emission spectra also obtains a relatively larger value at small ionization degrees, decreases with ionization degree rising, but tends to increase again at large ionization degrees. In the whole isoelectronic sequence, a very narrow group of a few intense lines is obtained for N = 5. The transitions from the excited levels mainly proceed to the lowest level of the ground configuration; it is the reason for the similarity of photoexcitation and emission spectra. The quenching of many lines and the concentration of line strengths in a few transitions indicate the existence of some wavefunction basis with strict selection rules for dipole transitions.

Violation of the electric-dipole selection rules in indirect multiphoton excitation of image-potential states on Ag(100).

Photoemission from image potential states on Ag(100) is investigated using angle resolved multiphoton photoemission induced by 150 fs laser pulses. For the first time we demonstrate that image potential states populated by indirect transitions can be observed with light polarized parallel to the plane of incidence and light polarized normal to the plane of incidence. The latter is a process normally forbidden by the dipole transition selection rules. These findings are related to the creation of a hot-electron population whose properties largely remains to be understood.

Soft symmetry selection rules in photoemission spectroscopy: The (1×2) phase of hydrogen adsorbed on Ni(110)

Based on the idea that systems may very well exhibit continuous changes in symmetry if one focuses on physical quantities such as transition matrix elements, the concept of soft symmetry selection rules for dipole transitions is developed. The high-coverage, low-temperature (1×2)-3H phase of H/Ni(110) is chosen to illustrate the new concept. Photoemission measurements on this adsorption system only reveal a single hydrogen-derived band in variance to the stoichiometry of the adlayer. A special procedure to quantitatively decompose the eigenstates of (1×2)-3H/Ni(110) according to their behavior under 2a/3 translation along [001] is derived. It is demonstrated that this symmetry transformation, though not a strict symmetry element of the adsorption system, can be drawn upon to rationalize the unexpected experimental observations in the spirit of soft symmetry selection.

Stark energy level determination of the 3H 4 ground state of U 4+ in the low temperature form α-ThBr 4

The low temperature form α-ThBr 4 has a tetragonal structure I4 1 a (C 4h 6) in which the thorium ion is at a site of S 4 symmetry. Assuming that the 3H 4 ground state in this new form remains Γ 4 as in the β-ThBr 4 form, the polarized absorption spectrum at 4.2 K shows that D 2 d is a good approximation. At the same time that the lines are sharp, a peculiarity of the absorption of U 4+ when excited by white radiation is the existence of seven groups of two or four fluorescences with the same energy difference for each group. Four 3H 4 ground state Stark levels and their assignments have been determined from high resolution absorption Zeeman effect studies at different temperatures, assuming electric dipole transition selection rules for D 2 d symmetry: Γ 5 at 105 cm −1, Γ 1 at 468 cm −1, Γ 1 at 618 cm −1 and Γ 5 at 825 cm −1.

Direct interband dipole-transition selection rules for the Oh^3 space-group compounds

The irreducible representations associated with states of dipole symmetry have been calculated for the space group Oh3, the space group with the correct symmetry for A-15 phase compounds. Also assembled are the character tables of the Oh3 group. Thus all the direct interband dipole-transition selection rules for A-15 phase compounds can easily be determined.

Theory of excitonic molecules

The existence of the excitonic molecule as bound state of Wannier excitons was predicted since 1958. In recent years new lines were observed in the luminescence spectra of crystals excited by high-power lasers. These lines were attributed to the dissociation of the molecule into a free exciton and a photon. We establish the classification of the biexcitonic states taking into account the details of the band structure and the symmetry properties of the crystals. Different numerical calculations of the binding energy of the molecule are presented, some including electron-hole exchange corrections. Discrepancies still exist between different authors. According to the group-theoretical classification of the biexciton states, selection rules of luminescence and two-photon absorption are derived. For two-photon absorption, besides the usual selection rules for dipole transitions, dynamical selection rules were evidenced.

Approach to the calculation of the important many-body effects on photoabsorption oscillator strengths

By a combination of selection rules for dipole transitions and notions from variation-perturbation theory, we develop a first-order theory of oscillator strengths (FOTOS) whereby the important correlations for an accurate treatment of electric dipole processes in atoms and molecules can be easily understood, formally derived and calculated. FOTOS is applied here to certain one- and two-electron transitions in Li I, N I and N II. The calculation of the corresponding oscillator strengths present considerable theoretical problems. Our results resolve the existing discrepancy between lifetime experiments and previous many-body calculations.