Microwave and UV excitation spectra of 4-fluorobenzyl alcohol at high resolution. S0 and S1 structures and tunneling motions along the low frequency -CH2OH torsional coordinate in both electronic states

Rotationally resolved electronic spectra of several low frequency vibrational bands that appear in the S(1) ← S(0) transition of 4-fluorobenzyl alcohol (4FBA) in the collision-free environment of a molecular beam have been observed and assigned. Each transition is split into two or more components by the tunneling motion of the attached -CH(2)OH group. A similar splitting is observed in the microwave spectrum of 4FBA. Analyses of these data show that 4FBA has a gauche structure in both electronic states, but that the ground state C(1)C(2)-C(7)O dihedral angle of ～60° changes by ～30° when the photon is absorbed. The barriers to the torsional motion of the attached -CH(2)OH group are also quite different in the two electronic states; V(2) ～ 300 cm(-1) high and ～60° wide in the S(0) state, and V(2) ～ 300 cm(-1) high and ～120° wide (or V(2) ～ 1200 cm(-1) high and ～60° wide) in the S(1) state. Possible reasons for these behaviors are discussed.     

Time-resolved predissociation of the vibrationless level of the B state of CH3I

The predissociation dynamics of the vibrationless level of the first Rydberg 6s (B (1)E) state of CH(3)I has been studied by femtosecond-resolved velocity map imaging of both the CH(3) and I photofragments. The kinetic energy distributions of the two fragments have been recorded as a function of the pump-probe delay, and as a function of excitation within the umbrella and stretching vibrational modes of the CH(3) fragment. These observations are made by using (2 + 1) Resonant Enhanced MultiPhoton Ionization (REMPI) via the state of CH(3) to detect specific vibrational levels of CH(3). The vibrational branching fractions of the CH(3) are recovered by using the individual vibrationally state-selected CH(3) distributions to fit the kinetic energy distribution obtained by using nonresonant multiphoton ionization of either the I or the CH(3) fragment. The angular distributions and rise times of the two fragments differ significantly. These observations can be rationalized through a consideration of the alignment of the CH(3) fragment and the effect of this alignment on its detection efficiency. Two additional dissociation channels are detected: one associated with Rydberg states near 9.2 eV that were observed previously in photoelectron studies, and one associated with photodissociation of the parent cation around 15 eV.     

Probing magnetic order in heavily doped La2-xSrxNiO4+\delta with μSR

We report μSR measurements on a series of compounds with composition La_2-xSr_xNiO_4+\delta where the net hole concentration x+2\delta is greater than 0.4. A magnetic transition is found in all the samples studied which occurs at a composition‐dependent temperature T_M. Below T_M, clear precession signals are observed in zero applied magnetic field. The possible muon sites are discussed within the context of dipole‐field calculations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of electron bremsstrahlung in strong Coulomb fields at the ESR storage ring

Electron bremsstrahlung has been investigated for collisions of 223.2 MeV/amu He-like uranium ions with N₂ and Ar gaseous targets. The doubly differential cross-sections for bremsstrahlung are compared to the predictions of relativistic first order Born calculations (Bethe-Heitler formula with Elwert correction factor) and to the calculations based on the exact wavefunctions for electrons moving in the external point-Coulomb potential of the projectile. Whereas the “exact” IPA calculations give an improved agreement with experimental data, as compared to the Bethe-Heitler theory, in particular at the end-point region of the bremsstrahlung spectra, discrepancies still remain at lower photon energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gamma-ray spectroscopy of87Y

The level structure of⁸⁷Y has been studied using in-beam γ-ray spectroscopic methods. Many previously unknown states have been observed. Members of theπ(g _9/2 )ν(g _9/2)^?2 multiplet are identified. The results are discussed in terms of the weak-coupling model.     

THE DISTANCE BETWEEN THE PHYTOCHROME CHROMOPHORE AND THE N-TERMINAL CHAIN DECREASES DURING PHOTOTRANSFORMATION. A NOVEL FLUORESCENCE ENERGY TRANSFER METHOD USING LABELED ANTIBODY FRAGMENTS

A novel antibody-fluorescence method has been developed to elucidate the chromophore topography in phytochrome as it undergoes a photochromic transformation. Förster energy transfer from N-terminal bound, fluorescently labeled Oat-25 Fab antibody fragments to the phytochrome chromophore was measured. The results suggest that the chromophore moves relative to the N-terminus upon the Pr → Pfr phototransformation. This conclusion is consistent with previous models which have proposed a reorientation and an interaction of the Pfr chromophore with the N-terminus. The method described appears to be the first study of a Forster energy transfer measurement using a donor-label attached to a Fab fragment of a photosensor protein.     

Search for lifetime effects of an evaporative source using two-proton correlations

The directional dependence of the measured correlationfunction of two particles emitted from an evaporative source is shown to offer a weak sensitivity to the source lifetime. From the agreement with evaporative calculations, one cannot rule out a sequential emission.     

A new search for the allowed decay π0→4γ

A new search with increased detection efficiency has been made for the decay of the neutral pion into four photons, an allowed decay which is expected to be rare. We have observed no events, placing an upper limit on the branching ratio of 4.4 × 10^?6 at 90% confidence level.     

Synthesis of protected racemic β,γ-unsaturated-α-amino acids via γ-phenylseleno-α,β-unsaturated esters

Oxidative rearrangement of γ-phenylseleno-α,β-unsaturated esters ($\text{1}$) with the N-chlorosuccinimide/N,N-diisopropylethylamine/alkyl carbamate reagent combination affords preparatively useful yields of protected β,γ-unsaturated-α-amino acids ($\text{2}$).     

Hydrodesulfurization activity and transformations of nickel molybdate hydrate

Nickel molybdate hydrate has been found to be an effective precursor catalyst for the hydrodesulfurization of thiophene. Calcination of the hydrate at 300°C and presulfidation with H₂S are favorable treatments for higher activity.

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