E. D. Emmons

K-shell photoionization of ground-state Li-like carbon ions [C3+]: experiment, theory and comparison with time-reversed photorecombination

Absolute cross sections for the K-shell photoionization of ground-state Li-like carbon [C3+(1s22s 2S)] ions were measured by employing the ion?photon merged-beams technique at the Advanced Light Source. The energy ranges 299.8?300.15?eV, 303.29?303.58?eV and 335.61?337.57?eV of the [1s(2s2p)3P]2P, [1s(2s2p)1P]2P and [(1s2s)3S 3p]2P resonances, respectively, were investigated using resolving powers of up to 6000. The autoionization linewidth of the [1s(2s2p)1P]2P resonance was measured to be 27 ? 5?meV and compares favourably with a theoretical result of 26?meV obtained from the intermediate coupling R-matrix method. The present photoionization cross section results are compared with the outcome from photorecombination measurements by employing the principle of detailed balance.

Ultraviolet resonance Raman spectroscopy of explosives in solution and the solid state.

Resonance Raman cross sections of common explosives have been measured by use of excitation wavelengths in the deep-UV from 229 to 262 nm. These measurements were performed both in solution and in the native solid state for comparison. While measurements of UV Raman cross sections in solution with an internal standard are straightforward and commonly found in the literature, measurements on the solid phase are rare. This is due to the difficulty in preparing a solid sample in which the molecules of the internal standard and absorbing analyte/explosive experience the same laser intensity. This requires producing solid samples that are mixtures of strongly absorbing explosives and an internal standard transparent at the UV wavelengths used. For the solid-state measurements, it is necessary to use nanostructured mixtures of the explosive and the internal standard in order to avoid this bias due to the strong UV absorption of the explosive. In this study we used a facile spray-drying technique where the analyte of interest was codeposited with the nonresonant standard onto an aluminum-coated microscope slide. The generated resonance enhancement profiles and quantitative UV-vis absorption spectra were then used to plot the relative Raman return as a function of excitation wavelength and particle size.

Lifetime of a K-shell vacancy in atomic carbon created by 1s → 2p photoexcitation of C+

Lifetimes for K-shell vacancy states in atomic carbon have been determined by measurement of the natural linewidth of the 1s → 2p photoexcited states of C + ions. The K-shell vacancy states produced by photoionization of atomic carbon are identical to those produced by 1s → 2p photoexcitation of a C + ion: 1s2s 2 2p 22 D, 2 P, and 2 S autoionizing states occur in both cases. These vacancy states stabilize by emission of an electron to produce C 2+ ions. Measurements are reported for the lifetime of the 1s2s 2 2p 22 D, 2 P and 2 S autoionizing states of C + :6 .3± 0.9 fs, 11.2 ± 1.1 fs and 5.9 ± 1.3 fs respectively. Knowledge of such lifetimes is important for comparative studies of the lifetimes of Kshell vacancies in carbon-containing molecules, benchmarking theory, and interpreting satellite x-ray spectra from astrophysical sources such as x-ray binaries. Absolute cross sections were measured for both ground-state and metastable-state ions providing a stringent test of state-of-the-art theoretical calculations. Carbon is ubiquitous in nature and is the building block of life. This atom in its various stages of ionization has relatively few electrons, and is thus amenable to theoretical study. Lifetimes

Photoionization studies of the B+ valence shell: experiment and theory

We have investigated L-shell photoionization (PI) of 1S ground-state and 3Po metastable states of the Be-like ion, B+, in the photon energy range 22.4–31.3 eV, at an experimental energy resolution of 25 meV. Absolute PI cross sections have been measured using a photon–ion merged-beams arrangement at the Advanced Light Source. Detailed calculations using the semi-relativistic Breit–Pauli R-matrix approach suggest a fraction of 29% of metastable ions in the primary beam of the experiment. Excellent agreement is observed between the theoretical predictions and the experimental high-resolution PI cross sections. The present results are compared with earlier experimental and theoretical work. The cross section for PI of B+ ground-state ions can be very well described by an analytic formula derived from quantum defect theory.

K-shell photoionization of Be-like carbon ions : experiment and theory for C2+

Absolute cross-section measurements for K-shell photoionization of Be-like C2+ ions have been performed in the photon energy range 292 325 eV. These measurements have been made using the photon ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory. Absolute measurements compared with theoretical results from the R-matrix method indicate that the primary C2+ ion beam consisted of 62 percent ground-state (1s22s2 1S) and 38 percent metastable state (1s22s2p 3Po) ions. Reasonable agreement is seen between theory and experiment for absolute photoionization cross sections, resonance energies and autoionization line widths of K-shell-vacancy Auger states.

Fourth-order perturbative extension of the single-double excitation coupled-cluster method

Fourth-order many-body corrections to matrix elements for atoms with one valence electron are derived. The obtained diagrams are classified using coupled-cluster-inspired separation into contributions from n-particle excitations from the lowest-order wave function. The complete set of fourth-order diagrams involves only connected single, double, and triple excitations and disconnected quadruple excitations. Approximately half of the fourth-order diagrams are not accounted for by the popular coupled-cluster method truncated at single and double excitations (CCSD). Explicit formulas are tabulated for the entire set of fourth-order diagrams missed by the CCSD method and its linearized version, i.e., contributions from connected triple and disconnected quadruple excitations. A partial summation scheme of the derived fourth-order contributions to all orders of perturbation theory is proposed.

Photoionization of ions of the nitrogen isoelectronic sequence: experiment and theory for F2+ and Ne3+

Absolute photoionization measurements are reported for admixtures of the ground and metastable states of F2+ from 56.3 eV to 75.6 eV, and of Ne3+ from 89.3 eV to 113.8 eV. The 4So ground-state and the 2Do and 2Po metastable-state fractions present in the primary ion beams were estimated from photoion yield measurements near their respective threshold energies. Most of the observed resonance structure has been spectroscopically assigned. The measurements are compared with new R-matrix theoretical calculations and with those in the TOPbase astrophysical database. The systematic behaviour of the quantum-defect parameter is analysed as a function of the nuclear charge for four Rydberg series observed in both species, and compared to published data for O+ and N.

High-Pressure Raman Spectroscopy of Tris(hydroxymethyl)aminomethane

High-pressure Raman spectroscopy has been used to study tris(hydroxymethyl)aminomethane (C(CH(2)OH)(3)NH(2), Tris). Molecules with globular shapes such as Tris have been studied thoroughly as a function of temperature and are of fundamental interest because of the presence of thermal transitions from orientational order to disorder. In contrast, relatively little is known about their high-pressure behavior. Diamond anvil cell techniques were used to generate pressures in Tris samples up to approximately 10 GPa. A phase transition was observed at a pressure of approximately 2 GPa that exhibited relatively slow kinetics and considerable hysteresis, indicative of a first-order transition. The Raman spectrum becomes significantly more complex in the high-pressure phase, indicating increased correlation splitting and significant enhancement in the intensity of some weak, low-pressure phase Raman-active modes.

Investigation of multi-electron processes in 60 keV O6++Ar collisions using a triple coincidence technique

Multiple electron capture processes in 60 keV O6++Ar collision system have been investigated by means of time-of-flight triple-coincidence measurements of Auger electrons, scattered projectile and target ions. This technique is particularly suited for the investigation of electron capture processes involving capture of three or more electrons. From the measured sub-partial Auger spectra, it can be seen that double electron capture dominantly populates the configurations (3,n) with n=3–5. Triple electron capture is found to dominantly populate the configurations (3,3,3) and (3,3,4), while quadruple electron capture populates the (3,3,3,3) configuration.

Doubly excited resonances in the photoionization spectrum of Li

Absolute cross-section measurements for resonant double photoexcitation of Li+ions followed by autoionization have been performed at high resolution in the photon energy range from 148 eV, just below the (2s2p, 2(0,1)+2) resonance to 198 eV (the region of the double ionization threshold). The measurements have been made using the photon-ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA. The absolute cross-section measurements show excellent agreement with theoretical results from the R-matrix plus pseudo-state (RMPS) method.