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Angular distributions of C 1s photoelectrons, relative to a dissociation axis for C₂H₂, have been measured with a photoelectron–photoion–photoion coincidence technique. The photoelectron angular distribution (PAD) for three two-body fragmentations (symmetric, non-symmetric and proton-migration fragmentations) is completely different. The PADs for non-symmetric fragmentation provide direct evidence of a localized core-hole and preferential bond breaking following Auger decays. Moreover, the PAD for symmetric fragmentation has been interpreted as the interference between photoemissions from the two carbon atoms.

A conical bubble straight tube apparatus was set up to study sonoluminescence. The spectra of conical bubble sonoluminescence for 1,2-propanediol and glycol were detected. The results show that the luminescence is intense, and the spectra consist of a broad background on which five clear sequences of Swan bands and three sequences of the B²Σ⁺ → X²Σ⁺ transition of CN are superimposed. A band assigned to the A²Δ → X²Π transition of CH was also measured and the vibrational and rotational structures of Swan bands could be resolved. The origin of the C*₂ and C₂H* is discussed. Finally, the achieved molecular vibrational temperature is estimated to be about 5400 ± 350 K.

An explicit model for the third virial coefficient C(T) is presented, based on accurate binary interactions plus three-body forces; its predictions are compared to experimental data for 15 fluids (argon, krypton, xenon, nitrogen, oxygen, fluorine, carbon monoxide, carbon dioxide, perfluoromethane, methane, ethene, ethane, propane, n-butane, and n-pentane). Three-body interactions are represented by the Axilrod–Teller–Muto (ATM) triple-dipole potential, while the binary potential profile is systematically varied using approximate non-conformal (ANC) potentials. Non-conformality affects significantly both two- and three-body contributions to C(T). A formula for C(T) of ANC+ATM systems is obtained in terms of all interaction parameters; the three-body contribution is proportional to the parameter ν of the ATM potential while its temperature dependence is proportional to that of a reference fluid (argon). The ANC+ATM model reproduces C(T) within experimental error for most of the fluids considered, with a small negative deviation in some cases, which may be ascribed to the need of a complement to the ATM term.

We have measured the NEXAFS spectrum and the relative photoionization cross section of the 3d spin–orbit components of the barium atom in the energy range up to 50 eV above the ionization threshold. As in Xe and Cs, also in barium the two spin–orbit components show strongly different energy dependence. A strong enhancement of the 3d_5/2 cross section near the 3d_3/2 ionization threshold, which is attributed to interchannel coupling, is observed. The experimental results are in good agreement with the relativistic time-dependent density functional theory calculations.

We observe the spontaneous evaporation of atoms confined in a bubble-like radio frequency (rf)-dressed trap (Zobay and Garraway 2001 Phys. Rev. Lett.86 1195; 2004 Phys. Rev. A 69 023605). The atoms are confined in a quadrupole magnetic trap and are dressed by a linearly polarized rf field. The evaporation is related to the presence of holes in the trap, at the positions where the rf coupling vanishes, due to its vectorial character. The final temperature results from a competition between residual heating and evaporation efficiency, which is controlled via the height of the holes with respect to the bottom of the trap. The experimental data are modelled by a Monte Carlo simulation predicting a small increase in phase-space density limited by the heating rate. This increase was within the phase-space density determination uncertainty of the experiment.

A B-spline R-matrix (close-coupling) method is applied to study electron-impact excitation of the lowest four excited states of calcium. Results for angle-integrated and angle-differential cross sections, as well as (pseudo-) Stokes parameters of the light emitted in the (4s4p)¹P^o → (4s²)¹S optical decay, are compared with various experimental data and predictions from other close-coupling and distorted-wave calculations. Overall, the agreement between our results and the experimental data is very satisfactory, although a few discrepancies remain.

With the full use of the experimental data obtained by multi-coincidence velocity-map imaging spectrometry, we have determined the dipole amplitudes and their relative phases that describe the C 1s photoionization dynamics in CS₂. It has been found that the σ shape resonance at about 15 eV above the C 1s ionization threshold appears only in the dipole amplitude d_fσ. We have also carried out time-dependent density functional theory calculations so as to better understand the photoemission dynamics and shape resonances in the C 1s photoionization of CS₂ molecules with heavy atoms (sulfur) having 3p valence orbitals, which distinguish the present work from well-studied works such as on CO and CO₂ molecules.

Autoionization decay from Ne⁺ Rydberg states has been investigated by using multi-electron spectroscopy at a photon energy of 200.4 eV, where the autoionizing states have been produced through valence photoemission with simultaneous excitation into Rydberg orbitals. The coincidence measurements enable one to resolve individual autoionization lines corresponding to decays from the Ne⁺ 2p⁻²(¹D)nl, 2p⁻²(¹S)nl, 2s⁻¹2p⁻¹(^1,3P)nl and 2s⁻²(¹S)nl Rydberg states. The present investigation revealed the autoionization decay features of the Rydberg states: branching ratios, which show strong selectivity towards the Ne²⁺ final states and asymmetric line shapes in the electron spectra, which have been analysed in terms of the interaction between the discrete state and each continuum. In addition, it is demonstrated that the autoionization decay feature of the Ne⁺ 2s⁻¹2p⁻¹(¹P)3p ²S state is characterized by a strong interaction with 2s⁻¹2p⁻¹(³P)nl autoionizing states.

We report theoretical studies of a Λ-type five-level atomic system. The density matrix equations are set up and solved numerically to obtain the probe absorption line shape of Rb D₂ transitions for cold (Doppler-free) and room temperature (Doppler-broadened) atoms. Simulated spectra for Doppler-broadened systems lead to four velocity-selective dips along with an electromagnetic induced transparency (EIT) peak as observed earlier from the co-propagating pump–probe spectroscopy of Rb D₂ transitions. Effects of pump power and spontaneous decay rate from the upper levels on the simulated spectra are also studied. For cold atoms a very pronounced EIT peak is observed when the pump frequency is on resonance with one allowed transition. We find that lower pump power leads to a much sharper EIT signal in this case. A simulated dispersion curve shows a rapid variation of the refractive index that may lead to a sharp reduction of the group velocity of photons.

The motivation for this work is the problem of providing accurate values of the atomic transition matrix elements for the Stark components of Rydberg–Rydberg transitions in atomic hydrogen and hydrogenic ions, for use in spectral line broadening calculations applicable to cool, low-density plasmas, such as those found in H II regions. Since conventional methods of calculating these transition matrix elements cannot be used for the high principal quantum numbers now easily attained in radio astronomical spectra, we attempt to show that the recurrence relation (ladder operator) method recently employed by Watson (2006 J. Phys. B: At. Mol. Opt. Phys.39 1889–97) and Hey (2006 J. Phys. B: At. Mol. Opt. Phys.39 2641–64) can be taken over into the parabolic coordinate system used to describe the Stark states of the atomic (ionic) radiators. The present method is therefore suggested as potentially useful for extending the work of Griem (1967 Astrophys. J.148 547–58, 2005 Astrophys. J.620 L133–4), Watson (2006), Stambulchik et al (2007 Phys. Rev. E 75 016401(9 pp) on Stark broadening in transitions between states of high principal quantum number, to physical conditions where the binary, impact approximation is no longer strictly applicable to both electron and ion perturbers. Another possible field of application is the study of Stark mixing transitions in 'ultracold' Rydberg atoms perturbed by long-range interactions with slow atoms and ions. Preparatory to the derivation of recurrence relations for states of different principal quantum number, a number of properties and recurrence relations are also found for states of identical principal quantum number, including the analogue in parabolic coordinates to the relations of Pasternack (1937 Proc. Natl Acad. Sci. USA23 91–4, 250) in spherical polar coordinates.

We have measured the energies of all three fine structure components in the ³P_J ground state of the negative ion of phosphorus using laser photodetachment threshold spectroscopy. The experiment yielded an electron affinity of 746.68(6) meV. The ΔJ = 2–0, 2–1 and 1–0 fine structure splittings were determined to be 32.73(7) meV, 22.48(7) meV and 10.25(3) meV, respectively. In the experiment, a mass selected beam of P⁻ ions was merged with the output from a pulsed infrared optical parametric oscillator. The residual atoms produced in the photodetachment process were detected and used as a monitor of the photon-energy dependence of the relative cross section. The Wigner law was fitted to each of the three observed onsets of production of neutrals in order to extract the threshold energies.

We produce Bose–Einstein condensates of ⁶Li₂ molecules in a low power (22 W) crossed optical dipole trap. Fermionic ⁶Li atoms are collected in a magneto-optical trap from a Zeeman slowed atomic beam and then loaded into the optical dipole trap where they are evaporatively cooled to quantum degeneracy. Our simplified system offers a high degree of flexibility in trapping geometry for studying ultracold Fermi and Bose gases.

We present calculations of the elastic scattering of spin-polarized electrons from caesium in a relativistic treatment based on the Dirac equations. These equations contain a polarization potential obtained from a non-perturbative treatment of the distortion of the atom by the incident charged particle. We present results for impact energies up to 25 eV for the differential cross sections and spin asymmetry parameter A₂ and compare these with recent measurements and other theoretical results.