Excited Final States Research Articles

On the double-beta decays of 70Zn, 86Kr, 94Zr, 104Ru, 110Pd and 124Sn

Double-beta decays of 70 Zn, 86 Kr, 94 Zr, 104 Ru, 110 Pd and 124 Sn to the final ground states and the decays of 110 Pd and 124 Sn to the excited states in 110 Cd and 124 Te are studied in the framework of the proton–neutron quasiparticle random-phase approximation (pnQRPA) combined with the multiple-commutator model (MCM) for description of decays to the excited final states. Reasonably large single-particle model spaces and G-matrix-based effective nuclear forces are used to compute the relevant nuclear matrix elements and decay half-lives. The present study is among the very few that have been dedicated to double-beta decays of these nuclei, although the associated double-beta Q values exceed 1.0 MeV for the ground-state decays.

A case study in ultracold reactive scattering: D + H2

We report theoretical results for reaction and vibrational quenching of the ultracold collision D + H(2) (v, j = 0) for a wide range of initial vibrationally excited states v. The v-dependence of the zero-temperature limit of the reaction rate coefficient shows two distinct regimes: a barrier dominated regime for 0 ≤ v ≤ 4, and a barrierless regime for v ≥ 5. We also present detailed distributions over the rovibrational states of the products. We find an approximate conservation of the internal vibrational energy; namely, the branching ratios always favor the highly excited final states, which have vibrational energies similar to that of the entrance channel.

Close Proximity Dibenzo[a,c]phenazine–Fullerene Dyad: Synthesis and Photoinduced Singlet Energy Transfer

AbstractA dibenzo[a,c]phenazine–fullerene (DBPZ‐C60) dyad in which two chromophores are linked in close proximity to each other has been synthesized and studied in detail by optical spectroscopy to explore a new energy donor–acceptor system. The dyad was prepared by Prato reaction between 11‐formyldibenzo[a,c]phenazine and fullerene. 3,5‐Di‐tert‐butylbenzyl group was introduced onto the fulleropyrrolidine unit to achieve adequate solubility of the dyad. A thorough study of the photophysical properties of the dyad and relevant reference compounds, performed by means of steady state and time resolved spectroscopic measurements, has revealed the presence of highly efficient (ca. 98 %) and extremely fast (ken = 5 × 1011 s–1) intramolecular photoinduced singlet–singlet energy‐transfer process from singlet excited state of the DBPZ moiety to fullerene. In both polar and nonpolar environment transduction of singlet excited state energy governs the excited state deactivation, but the efficiency and rate of energy transfer were found to be higher in nonpolar solvents in comparison to polar. The DBPZ singlet excited state decays within 2 and 4.7 ps in toluene andbenzonitrile, respectively, via singlet–singlet energy transfer to produce a fullerene singlet excited state which decays with a life time of 1.5 ns to give a very long‐lived fullerene triplet state as final populated excited state.

Intermediate energy proton knockout to the “island of inversion” isotopeMg31

The ``island of the inversion'' isotope $^{31}\mathrm{Mg}$ was investigated using an intermediate energy proton knockout reaction from $^{32}\mathrm{Al}$ at 90 MeV/nucleon at the National Superconducting Cyclotron Laboratory. A negligible cross section to the ground state supports an intruder-dominant configuration in $^{31}\mathrm{Mg}$. The partial cross sections to excited final states preferentially populate configurations in the $^{31}\mathrm{Mg}$ residues which have no neutron excitations across the $N=20$ shell closure. There is strong evidence that the reaction populates the $3/{2}^{+}$ and $5/{2}^{+}$ states which correspond with the neutron-hole states predicted by the shell model with the model space truncated above the $\mathit{sd}$-shell.

Photoexcitation mechanisms of centrosymmetric and asymmetric fluorene derivatives in two-photon absorption

With the two dimensional (2D) site and the three dimensional (3D) cube representations in two-photon absorption [M.T. Sun, J.N. Chen, H.X. Xu, J. Chem. Phys. 128(1–6) (2008) 064106], the charge transfer and electron–hole coherence for centrosymmetric and asymmetric fluorene derivatives have been investigated theoretically. For centrosymmetric fluorene derivative, the excitation from the ground state to intermediate excited state by the first photon is a Frenkel excitation; while the excitation by the second photon from the intermediate excited state to the final excited state is an intraband excitation, and charge transfers from one substituent to the other substituent. For asymmetric fluorene derivative in TPA, the excitations by the first and second photons are all charge transfer excited states. Theoretical visual evidence has been provided that diphenylamino-end groups do not strongly participate in pure 2PA, which confirmed the experimental assumption. We also visualize the orientation and strength of transition polarizability density (TPD) in TPA with 3D cube representation. The transition probability in TPA also was visualized with 2D site representation.

New results for double-beta decay of 100Mo to excited final states of 100Ru using the TUNL-ITEP apparatus

The coincidence detection efficiency of the TUNL-ITEP apparatus designed for measuring half-life times of two-neutrino double-beta ( 2 ν β β ) decay transitions to excited final states in daughter nuclei has been measured with a factor of 2.4 improved accuracy. In addition, the previous measuring time of 455 days for the study of the 100Mo 2 ν β β decay to the first excited 0 1 + state in 100Ru has been increased by 450 days, and a new result (combined with the previous measurement obtained with the same apparatus) for this transition is presented: T 1 / 2 = [ 5.5 − 0.8 + 1.2 ( stat ) ± 0.3 ( syst ) ] × 10 20 yr . Measured 2 ν β β decay half-life times to excited states can be used to test the reliability of nuclear matrix element calculations needed for determining the effective neutrino mass from zero-neutrino double-beta decay data. We also present new limits for transitions to higher excited states in 100Ru which, if improved, may be of interest for more exotic conjectures, like a bosonic component to neutrino statistics.

Excited state positronium collisions with helium

Calculations of the discrete positronium (Ps) transition Ps(2s)→Ps(2p) in collisions with ground state helium are reported. Results are presented at total and single differential levels. Calculations are made within the first born approximation (FBA). The Hartley–Walters approximation is used to sum over all possible final excited atom states. In addition, impulse approximation (IA) calculations are reported for Ps(2s) and Ps(2p) fragmentation collisions with ground state helium, where the atom does not change state. Again, the FBA with the HWA is used to account for collisions in which the atom is excited or ionized.

Polarization phenomena in inelastic meson photoproduction on a nucleus whose excited final state undergoes fast gamma decay

The differential cross sections for two-step reactions where inelastic meson photoproduction on light nuclei is followed by a fast gamma decay of the excited final-state nucleus are calculated in the plane-wave impulse approximation on the basis of the shell model for intermediate coupling. The polarization of the recoil nucleus in the photoproduction process is expressed in terms of the angular distribution of secondary photons and their circular asymmetry.

Superabsorbing Fullerenes: Spectral and Kinetic Characterization of Photoinduced Interactions in Perylenediimide−Fullerene-C60 Dyads

Two n-type molecular materials are covalently combined into a new photovoltaic component for polymer solar cells. Light harvesting by the perylenediimide results in very fast energy transfer to the fullerene unit, as shown with femtosecond transient absorption spectroscopy in toluene solution. Two energy transfer rates are observed of 2.5 x 10(12) s-1 (53%) and 2 x 10(11) s-1 (47%), attributed to two conformations. The final excited state that is populated is a perylenediimide-based triplet state that is formed on the nanosecond time scale with a high yield.

Double β decay ofMo100to excited final states

A systematic study of the inclusive ($0\ensuremath{\nu}+2\ensuremath{\nu}$) double beta ($\ensuremath{\beta}\ensuremath{\beta}$) decay of $^{100}\mathrm{Mo}$ to various excited final states of $^{100}\mathrm{Ru}$ was performed. Utilizing two large HPGe detectors operated in coincidence, a search for the subsequent deexcitation $\ensuremath{\gamma}\ensuremath{\gamma}$ cascades was conducted. A 1.05-kg sample of isotopically enriched $(98.4%)$$^{100}\mathrm{Mo}$ was investigated for 455 days, yielding an unambiguous observation of the $\ensuremath{\beta}\ensuremath{\beta}$ decay of $^{100}\mathrm{Mo}$ to the ${0}_{1}^{+}$ state (1130.3 keV) of $^{100}\mathrm{Ru}$. This excited final state decays via the ${0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{\mathrm{gs}}^{+}$ sequence (with ${E}_{\ensuremath{\gamma}1}=590.8$ keV and ${E}_{\ensuremath{\gamma}2}=539.5$ keV), and 22 such coincidence events were detected, with a continuous background estimated to be 2.5 events. This counting rate corresponds to a decay half-life for the $\ensuremath{\beta}\ensuremath{\beta}({0}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ transition of ${T}_{1/2}^{(0\ensuremath{\nu}+2\ensuremath{\nu})}=[6.{0}_{\ensuremath{-}1.1}^{+1.9}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{20}$ years. Lower limits on decay half-lives were achieved for higher excited final states.

Second-order effects in (e, 2e) ionization–excitation of H2

Ionization–excitation by electron impact of diatomic species in general and hydrogen molecule in particular presents very interesting mechanisms which can be observed in coincidence (e, 2e) experiments. The dissociative character of the final excited state makes these types of experiments easier to perform than those of atomic targets for which the coincidence measurement of the emitted electron and the photon is necessary. Recently Takahashi et al (2003) Phys. Rev. A 68 042710 have shown large disagreements between their experimental results and theoretical ones obtained by the first-order plane-wave impulse approximation at intermediate impact energies. These authors conclude that a second-order treatment, including the two-step mechanisms (TS1 and TS2), would be necessary to explain these differences. In this paper, we present a second-order Born treatment including the two-step mechanisms and study the simple ionization of H2 and the ionization–excitation of H2 to the 2Σg(2sσg) and 2Σu(2pσu) levels of H+2 by electron impact.

Infrared absorption and current–voltage characteristic of GaAs/AlGaAs multiple quantum wells on GaAs (1 1 1)A substrate grown by solid source molecular beam epitaxy

Infrared absorption and current–voltage characteristic of Si-doped GaAs/AlGaAs multiple quantum wells (MQW) grown on GaAs (1 1 1)A substrate by solid source molecular beam epitaxy has been presented in this paper. Strong polarization dependence was found and the normal incidence absorption is dominant in the (1 1 1)A-oriented MQW structure with the peak absorption wavelength around 7 μm. The final excited state is quite higher than the top of the barrier and the polarization property is complicated by the coupling between the valence heavy hole and light hole states in the continuum subband. The symmetric dark current characteristic to the zero voltage under positive and negative bias conditions attributes to the bias symmetric structures for (1 1 1)A-oriented MQW and the negligible outdiffusion of Si during the growth. The activation energies extracted from I– V characteristic curve decrease with increasing bias voltage in an exponential relation. The overall agreement between the activation energy and the calculated result has also been obtained.

Polarization observables and spin-dependent distortion effects in single-nucleon knockout reactions

A formalism is developed and predictions are made for selected polarization observables in one-nucleon knockout reactions within the transfer-to-the-continuum direct reaction model. The effects of nucleon-target spin-orbit distortions are also included and their importance is quantified. The calculated knockout reaction analyzing powers reach an appreciable fraction of their maximum allowed values. They are also found to be quite sensitive to the different approximation schemes used for the transfer probability amplitude within the transfer-to-the-continuum model. In contrast, they are shown to be insensitive to details of the two-body interactions assumed, including the nucleon-target spin-orbit interaction. The angular distributions of \ensuremath{\gamma}-rays, arising from the decay of heavy reaction residues produced in excited final states, are shown to be strongly anisotropic.

(e,2e)ionization-excitation ofH2

Binary $(e,2e)$ measurements are reported for ionization-excitation processes of ${\mathrm{H}}_{2}.$ The experiments were performed at impact energies of 1200, 1600, and 2000 eV using an energy- and momentum-dispersive spectrometer. Momentum profiles for transitions to the $2s{\ensuremath{\sigma}}_{g}$ and $2p{\ensuremath{\sigma}}_{u}$ excited final ion states are presented as normalized intensities relative to the cross section of the primary ionization to the $1s{\ensuremath{\sigma}}_{g}$ ground ion state. The results are compared with theoretical calculations of Lermer et al. [Phys. Rev. A 56, 1393 (1997)] using the first-order plane-wave impulse approximation. Certain features of the discrepancies between experiment and theory can be explained by incorporating contributions from the second-order two-step mechanisms into the $(e,2e)$ cross sections. Furthermore, the present results suggest that $2s{\ensuremath{\sigma}}_{g}$ and $2p{\ensuremath{\sigma}}_{u}$ cross sections approach their high-energy limits in different ways.

High Resolution Inner‐Shell Spectroscopy and ab initio CI Calculations on TiCl4 and Isoelectronic Molecules.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Observation of trielectronic recombination in Be-like Cl ions.

Recombination involving the core excitation of two electrons, which may be termed trielectronic recombination, has been experimentally identified for the first time. Using Cl13+ ions circulating in the TSR heavy-ion storage ring, we have observed surprisingly strong low-energy trielectronic recombination resonances, comparable to the dielectronic process. At higher electron-ion collision energies, trielectronic recombination is suppressed due to the autoionization of the triply excited intermediate state into excited final states. The formation of the intermediate state depends sensitively on configuration mixing, making trielectronic recombination a challenge to atomic-structure calculations.

Cascade effects in the excitation ofnp5(n+1)pstates of krypton and xenon atoms by polarized electrons

The integrated Stokes parameters of the decay photons from the excited np{sup 5}(n+1)p[5/2]{sub 3}, np{sup 5}(n+1)p{sup '}[3/2]{sub 2}, and np{sup 5}(n+1)p{sup '}[3/2]{sub 1} (n=5 and 6) states of Kr and Xe, respectively, are measured from near threshold to 100 eV using incident polarized electrons. The effects of the cascade photons on the Stokes parameters have been investigated using a pulsed beam of polarized electrons. The cascade effects for the final excited states are more significant for the linear polarization P{sub 1} parameter than for the circular polarization P{sub 3} parameter and they do not always have depolarization effects. The integrated state multipoles, determined from the integrated Stokes parameters corrected for cascade effects, are closer to, but not in agreement with, the values from semirelativistic R matrix and relativistic distorted-wave approximation methods.

High resolution inner-shell spectroscopy and ab initio CI calculations on TiCl4 and isoelectronic moleculesElectronic supplementary information (ESI) available: All excitation energies and oscillator strengths for TiCl4, VOCl3, CrO2Cl2 and MnO3Cl, including Rydberg levels. See http://www.rsc.org/suppdata/cp/b3/b302805b/

Inner-shell excitation spectra of gas phase TiCl4, VOCl3 and CrO2Cl2 have been recorded in the Cl 2p and O 1s edge regions. The assignment of the core excitations is based on ab initio calculations in the relaxed 1h–1p CI scheme. The computational approach has provided excitation energy patterns and photoabsorption oscillator strengths in satisfactory agreement with the experimental spectra, indicating the reliability of the theoretical model. The calculations are extended also to the compound MnO3Cl and to the Cl 1s core excitation spectra of the whole series of molecules. The interpretation of the final excited states in terms of orbital composition is also discussed as well as the spectral variations along the series with the progressive substitution of the chlorine atom with the oxygen atom.

Two-color pulsed laser excitation of dipolar molecules: Absolute laser carrier-phase effects

The excitation of a two-level dipolar $(d\ensuremath{\ne}0)$ molecule with two Gaussian pulsed lasers is examined theoretically for the case where one laser's frequency is tuned close to the energy level separation (pump laser) while the second laser's frequency is extremely small (probe laser). The final excited state populations are shown to depend on the probe laser's absolute carrier phase while remaining independent of the pump laser's absolute carrier phase. They do not depend on the relative phase difference between the two laser fields as in many other pump-probe scenarios. The absolute carrier-phase effect is negligible for nondipolar $(d=0)$ molecules. The probe laser absolute carrier-phase effect arises through the coherent excitation of multiple optical paths from the initial to the final state containing a common number of pump photons ${(N}_{\mathrm{pump}}=1)$ and a varying number of probe photons. Excited state populations, after the interaction of the pulses with the molecule is complete, are examined as a function of the probe laser's absolute carrier phase for varying field strengths, frequencies, and pulse durations in order to verify the source of the probe laser absolute carrier-phase effect and to determine the conditions needed to most readily detect it.

Anisotropic excitons inMgB2from orientation-dependent electron-energy-loss spectroscopy

The momentum transfer in electron-energy-loss spectra (EELS) recorded in an electron microscope can be controlled in a manner akin to polarization-dependent soft-x-ray absorption spectroscopy, however with much greater spatial resolution. Here we report orientation-dependent EELS from fine-grained ${\mathrm{MgB}}_{2}$ for both B K and Mg ${L}_{2,3}$ edges. Calculations based on an excited final state are used to suggest an anisotropic exciton for the peak at 55 eV at the Mg ${L}_{23}$ edge.