Results on ππ-interaction in the reaction πp → ππn at 8 GeV/c

We compare published ππ-phase shifts with results from an analysis of the reaction π⁻p→π^oπ^on. The ‘up’-solution as well as the ‘in-between’ -solution for the I = 0 s-wave ππ-scattering are ruled out. The only set of s-wave phase shifts consistent with our data is the ‘up-down’-solution with a rapid rise of σ₀⁰ near the KK?-threshold.     

ESR Detection of Triplet States in Rare Earth Chelates

Abstract

Energy transfer from ligand molecule to ion in rare earth chelates has been assumed to involve a molecular triplet state. ^1,2 These triplet states manifest themselves optically as long-lived T_{π, π? →S}π,π emission if the lowest resonance level of the ion is of higher energy than the molecular triplet. ³ If the resonance level lies below the triplet, longlived emission is absent or severely reduced in intensity. ^4,5     

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.     

High spin states in 121Te

High spin states of ¹²¹Te, populated in the ¹¹⁴Cd (¹¹B, p3n) reaction, have been studied through γ-ray spectroscopy. The level scheme has been established up to J^π = 51/2^?. Three-quasiparticle states, based on the ^πg _7/2 ² ? vh_11/2 and πg _7/2d_5/2 ? vh_11/2 configurations, have been identified. A favoured 39/2^? state is suggested to be the fully aligned [πg_7/2 ²]6 + ? [vh _11/2 ³]_27/2? yrast non-collective oblate configuration. This assignment is supported by Total Routhian Surface (TRS) calculations which also suggest a similar oblate assignment to the states at J^π = 21/2^? and 23/2^?. A higher 47/2^? state is also found and is suggested to be the fully aligned [πg_7/2 ²]₆+ ? [vh _11/2 ⁵]_35/2? configuration.     

Quasiparticle structures in118Te

The structure of¹¹⁸Te has been investigated following the¹¹⁰Pd(¹³C,5n) reaction using gamma-ray spectroscopic techniques and a substantially extended level scheme is proposed. A negative parity quasirotational band based on πg_7/2h_11/2 configuration has been established upto J^π=19. The level structure, above the fully aligned πg²7/2?vh²11/2 J^π=16⁺ yrast state, is found to evolve into several non-collective states.     

Electron detachment dynamics of the iodide-guanine cluster: does ionization occur from the iodide or from guanine?

Laser photodissociation spectroscopy of the I^‐·guanine complex has been conducted for the first time across the regions above the electron detachment threshold to explore the excited states and whether vertical ionisation occurs from the iodide or the nucleobase. The photofragment spectra reveal a prominent dipole-bound excited state (I) close to the calculated vertical electron detachment energy (～4.0?eV) and a second excited (II) centred around 4.8?eV, which we assign to π-π* nucleobase-localised transitions. The ionic photofragments are identified as I^‐ and I^‐·[G-H], with the later fragment being produced significantly more strongly than the former. Both photofragments are observed across the two excited states, with production of the iodide being attributed to internal conversion to the ground state followed by evaporation. We trace the formation of the I^‐·[G-H] photofragment to initial vertical ionisation of guanine, followed by ejection of a proton. This two-step process is important as it follows known steps in radiation-induced damage to DNA, namely initial formation of a guanine radical cation which then forms a free radical [G-H] moiety through deprotonation. Production of the I^‐·[G-H] photofragment is pronounced through II indicating that its formation is enhanced by coupling of the π-π* transitions to the electron detachment continuum.     

Temperature dependence of the dual phosphorescence from xanthone in n-hexane matrices

The phosphoresence spectrum and lifetime of xanthone embedded in an n-hexane matrix has been investigated as a function of temperature (1·6-100 K). Vibrational analyses of the spectra reveal that emission occurs from three sites, two of which are dominant. Emission from one site (B) occurs from the ³ nπ* state of a planar xanthone molecule and is characterized by strong totally symmetric carbonyl stretching vibrations and a short lifetime (2·4 ms). Emission from the other site (C) is shown to arise from the ³ππ* state of an out-of-plane distorted xanthone molecule. It displays a vibrational structure rich in modes of a ₁, b ₁, and b ₂ (C _2v notation) symmetry and a long lifetime (115 ms). Both direct spin orbit coupling via configurational mixing of the nπ* and ππ* states due to the non-planarity of the molecule in its ³ππ* state and spin-orbit vibronic interaction involving ³ A ₁(ππ*)-¹ A ₂(nπ*) spin-orbit and ¹ A ₂(nπ*)-¹ B ₂(ππ*) vibronic interaction via out-of-plane b ₁ vibrations are shown to be responsible for the C site emission intensity. Vibronic mixing between the ³ππ* and ³ nπ* states is not important. With increasing temperature, the phosphorescence intensity from the B site (³ nπ*) emitters increases at first, reaches a maximum at ～20 K and then decreases. The C site (³ππ*) intensity simply decreases with rising temperature. At a given temperature, the phosphorescence lifetimes are identical and exponential for all emission bands regardless of site origin. These observations indicate an equilibrium between emitters in the two sites throughout the lattice. A phonon-assisted energy transfer mechanism is proposed to account for these observations.     

The triplet spectrum of tetramethyl-1,3-cyclobutanedione

The low-temperature single-crystal spectrum of TMCBD has revealed a low-lying triplet state at 25 718 cm^-1 (72·5 kcal/mol). The observed band is ascribed to a ³ A_u (³ A ₂) ← ¹ A_g nπ* transition on the basis of its small singlet-triplet splitting, its polarization behaviour, and its vibrational structure. The ³ A_u state is first-order spin-orbit coupled to either or both of the ¹ B _2u or ¹ B _3u states. No evidence for two or more nπ* transitions was found. Several multi-membered progressions in the carbonyl wagging mode indicate the presence of a distorted excited state, in which the carbonyl carbons attain a pyramidal conformation. Analysis of the site symmetry shows that TMCBD is distorted to a boat-shaped C _2v structure in its triplet nπ* state.     

Measurements of ϱ - ω interference in the reaction πp → ππn at 15 GeV/c

In a study of the reaction π⁻p → π⁺π⁻n at 15 GeV/c we observe pronounced ?-ω interference effects between the transverse helicity states of the vector mesons. The relative phase of the interfering amplitudes is determined to be −1.40 ± 0.45 rad, and the branching ratio ω → 2π is found to be 2.1_−0.9^+2.8%.     

A multi-reference CI study of the low-lying valence and Rydberg states of CF3 radical

Highly correlated calculations at the multi-reference configuration interaction levels including singles and doubles excitations (MR-CISD) and extensivity corrections (MR-CISD?+?Q) have been performed to study some low-lying valence and Rydberg states of the CF₃ radical. Our highest level results (at the MR-CISD?+?Q level) yield the following energy ordering: 3s (7.90?eV)?2A₂ (8.61?eV)?π (8.72?eV)?z (8.73?eV). MR-CISD results indicate transitions of similar intensities from the ground to the following three final states, in the following order: 3p_π?>?3p_z?>?3s. It has also been found that the aforementioned Rydberg states should be responsible for visible emissions and correspond to transitions between bound states. Therefore, it is suggested that the lack of vibrational structure in the visible band of parent systems (e.g. CF₃Cl) may be due to a transition from a bound to an unbound state of the parent molecule.     

Finite energy bounds for πN scattering

Upper bounds on energy averaged πN cross sections are given. Using low energy data and data from πN backward scattering and $\text{N}\text{N}\text{→ ππ}$ annihilation, we get typically σ_tot ? 80 mb and σ_inel ? 30 mb, for energies just above the phase-shift region. Our bounds are based on assumptions similar to those underlying Froissart's bound and are equal to it asymptotically. However, at finite but large energies, they increase much slower than what might have been anticipated on purely numerological grounds. Related problems in pp and Kp scattering are also discussed.     

The N*(1710) as a resonance in the ππN system

We study the ππN system by solving the Faddeev equations, for which the input two-body t-matrices are obtained by solving the Bethe-Salpeter equation in the coupled-channel formalism. The potentials for the ππ, πN sub-systems and their coupled channels are obtained from chiral Lagrangians, which have been earlier used to study resonances in these systems successfully. In this work, we find a resonance in the ππN system with a mass of 1704 ? i375/2MeV and with quantum numbers I = 1/2, J ^π = 1/2⁺. We identify this state with the N ^*(1710). This peak is found where the energies of the ππ sub-system fall in the region of the σ-resonance. We do not find evidence for the Roper resonance in our study indicating a more complex structure for this resonance, nor for any state with total isospin I = 3/2 or 5/2.     

Extended sources,final state interactions and Bose-Einstein correlations

The isospin 2 ππ interaction is repulsive, thes-wave phase shift reaching ～?20° at the mass of the ρ meson. Theπ ^± π ^±correlation function shows a strong Bose-Einstein enhancement but no clear sign of this dynamical repulsion. I present the theory of final state interactions appropriate to particle production from an extended source and demonstrate that the data are entirely consistent with the known features of the ππI=2 interaction. The results are relevant to multiple pion production ine ⁺ e ^? annihilation, hadronic reactions and heavy ion collisions.     

Structure of28Si from the spectroscopy of high-spin states

A search for high-spin states in²⁸Si has been performed byn?y coincidence measurements in the²⁵Mg(α,nγy) reaction atE _α=14 and 15.5 MeV. Spin-parity assignments of the observed levels were obtained fromn?γ angular correlation and lifetime measurements atE _α=14.5 MeV. Theγ-decay of the 9,164 keV level was investigated separately with the²⁷Al(p, γ) reaction at theE _p=2,160 and 2,312 keV resonances. Rotational bands withK ^π=3^? (comprising levels atE _x=6,879, 8,413, 10,188 and 12,204 keV),K ^π =5^? (comprising levels atE _x=9,702, 11,577 and 13,741 keV) andK ^π=0⁺ (comprising levels atE _x=6,691, 7,381, 9,164 and 11,509 keV) were observed. The finding of the latter band supports the idea of coexisting oblate and prolate shapes in²⁸Si. A level at 14,643 keV excitation energy has the properties of theI ^π=8⁺ member of the ground state band. There are additional positive-parity high-spin states which do not fit into rotational bands. All types of positive-parity states are well accounted for by shell model calculations.     

Nitroaniline Isomers Interaction with Bovine Serum Albumin and Toxicological Implications

The interactions of 2-nitroaniline (2-NA), 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA) with bovine serum albumin (BSA) have been investigated by means of fluorescence spectrometry, synchronous fluorescence spectrometry and UV absorption spectrometry under the simulative physiological conditions. Association constants (K _A ) were estimated by the remarkable static quenching effect of 2-NA, 3-NA and 4-NA to the intrinsic fluorescence of BSA, and thermodynamic parameters such as enthalpy change (ΔH) and entropy change (ΔS) were calculated according to van’t Hoff equation. The results show that hydrophobic force plays a main role in the interaction of nitroanilines to BSA, nitroanilines have high affinity to BSA and the affinity order is as follows: 4-NA?>?2-NA?>?3-NA. On the basis of this study, it is found that percents of the binding of nitroanilines to BSA are almost no relative to the concentrations of nitroanilines, and correlation between K _A and logK _ow is disclosed. In the meantime, relationships between the combination of nitroanilines with BSA and toxicological implications were also discussed. In addition, synchronous fluorescence method was used to study the interaction mechanisms between nitroanilines and BSA, and energy transfer distances from BSA to nitroanilines were estimated based on the Förster’s non-radiation energy transfer theory. The results suggest that the binding site for nitroanilines on BSA is close to the sub-domain IIA where Trp 214 is located.     

Precise excitation energy and γ-ray decay of the lowest T = 2 state in 40K

The excitation energy of the lowest T = 2 state in ⁴⁰K has been determined as E_x = 4384.0 ± 0.3 keV from n-γ and γ-γ coincidence experiments. The state was populated with the ⁴Ar(p,n)⁴⁰K reaction at E_p = 8.30 MeV. Gamma-gamma angular correlation measurements yield unambiguous spin assignments J = 0 and 1 for the 1.64 and 2.290 MeV states, respectively. The excitation energy of the T = 2, J^π = 0⁺ state leads to a calculated mass excess of ?9120 ± 150 keV for ⁴⁰Ti.     

Investigation of 228Th in the (α, α'2n) reaction

The ²³⁰Th(α, α'2n)²²⁸Th reaction at E_α = 56 MeV was used to investigate states of moderately high spin in ²²⁸Th. Conversion electron and e^?-γ coincidence measurements were carried out, where the electrons were detected with an iron-free orange spectrometer. The ground state and low-lying K^π = 0^? rotational bands were observed up to I^π = 14⁺ and 13^?, respectively. The data are interpreted in terms of an ω-expansion for the ground-state rotational band, and an octupole vibrational band distorted by the Coriolis coupling to the K^π ? 1^? excitations for the K^π = 0^? band.