Coherent laser spectroscopy of ¯pHe+

The facilities of the coherent laser pulse spectroscopy of the ¯pHe⁺ transitions are considered taking the magnetic structure of the energy levels into account. The possibility for the observation of the dynamics of intramolecular motions is also analyzed.     

Magnetic properties of metastable bcc and amorphous Fe1−xMox,alloys produced by vapor quenching

X-ray diffraction, magnetization and Mössbauer measurements have been made on Fe₁−xMo_x alloys produced by vapor quenching. Single bcc phases of α-Fe- and η-Mo-type appear for x < 0.2 and x > 0.7, respectively. On the other hand, an amorphous phase is obtained for 0.3 < x < 0.6, in which region the intermetallic compounds with topologically close-packed structures are stable in the equilibrium phase diagram. The bcc phase is ferromagnetic for x < 0.85, while the amorphous phase is paramagnetic down to 4.2 K. The Mössbauer spectra indicate that the local atomic configuration of the amorphous alloy resembles that of the intermetallic compound with a similar composition.     

Potential energy curves and analytical potential energy functions of the metastable states of B2^＋＋

The multi-reference configuration interaction method and aug-cc-pvqz （AVQZ） have been used to calculate potential energy curves （PECs） of the singlet and triplet states of the riu and rig symmetry of B2＋＋. All of the four states （^l∏u, ^1∏g, ^3∏u and ^3∏g） are found to be metastable states, though the potential well of ^3∏u symmetry is very shallow. Based on the PECs, the analytical potential energy functions （APEFs） of these states have been fitted using the least square fitting method and two models of function. The spectroscopic parameters of each state are also calculated, and are compared with other investigations in the literature. The credibility and veracity of the two functions are evaluated. Some ideas to improve the fitting accuracy are presented. Also the vibrational levels for each state are predicted by solving the SchrSdinger equation of nuclear motion.     

Collisional decomposition of SF6−

The SF₆⁻ ion formed by electron attachment has been impacted upon helium at controlled energies and two thresholds for the formation of SF₅⁻ have been determined. The lower energy threshold at 0.13-eV center of mass (CM) results from excited SF₆⁻. The higher energy threshold at 1.03-eV CM arises from ground state SF₆⁻. The implications of these results are discussed.     

Mössbauer study of the vibrational anisotropy and of the light-induced population of metastable states in single-crystalline guanidinium nitroprusside

M?ssbauer studies were performed on single crystals of guanidinium nitroprusside with different orientations of their principal crystallographic axes (a, b, c) with respect to the incident radiation. The markedly anisotropic Lamb-M?ssbauer factor f _LM , i.e. f _LM ^(a) = 0.118(8), f _LM ^(b) = 0.174(8), f _LM ^(c) = 0.202(8) is in contrast to that of nitroprussides with inorganic anions. The observed anisotropy is ascribed to the anisotropic vibrational mean-square displacement of the nitroprusside anions as a whole which is due to the specific packing of both, anions and cations, as well as the very weak chemical bonding between the ions, typical only for guanidinium nitroprusside. The vibrational anisotropy of iron atoms in barium nitroprusside that has been observed by X-ray structural investigations has a different origin and therefore does not result in an anisotropic Lamb-M?ssbauer factor. We have also investigated metastable states in guanidinium nitroprusside that have been populated by means of incoherent irradiation from light-emitting diodes. With a specific orientation of the guanidinium nitroprusside single crystal a population of the metastable states up to 26% could be achieved. Populations of comparable size on lithium, sodium and potassium nitroprussides have only been reached using coherent laser irradiation. Received 15 December 1998 and Received in final form 3 March 1999     

Laser spectroscopy of the antiprotonic helium atom–molecule {\bar pHe}^+

The metastable antiprotonic helium atom–molecule (in short, atomcule), , which was discovered in 1991 as being the cause of the anomalous longevity of antiprotons with an overall lifetime of about 3 μs, now provides an exotic playground for laser spectroscopy, helped by the existence of numerous long lived states with 1–2 μs lifetimes. This three body system is characterized by a large angular momentum l ∼ 38 of coupled with the electron in the 1s ground orbital, and looks like an exotic hydrogen isotope with many different “nuclear states” as well as an exotic molecule with two centers (He²⁺ and ). So far, a number of laser resonance transitions have been identified. The present talk will cover the following topics: (1) high precision spectroscopy in comparison with three body theories involving the relativistic effect and QED, and (2) hyperfine structure of ;laser-microwave triple resonance. This revised version was published online in August 2006 with corrections to the Cover Date.     

A model for temperature-dependent collisional quenching of NO A2 Σ+

A model for the temperature-dependent electronic quenching of NO A ^{2 +} is presented. The model is appropriate for collision partners having stable negative ions, which are predicted to have large quenching cross-sections. Colliders with relatively large negative electron affinities are predicted to have cross-sections that are near-zero at room temperature and can increase dramatically at very high temperatures. A negligibly small electronic quenching cross-section is predicted for collision partners having negative ions that are unstable on a collisional timescale. Results of the model are compared to experimentally measured cross-sections for a number of species of interest in combustion and aerothermodynamic applications.     

Dynamics of multipionp¯ p annihilation

We construct a dynamical model to study the pion correlations in the 5 annihilation ofp¯ p at rest. For the resonant channels, the simplest Lorentz-invariant couplings have been used. It is found that, in addition to the Bose-Einstein correlations caused by the finite size of the source, the dynamical correlations from the channels with intermediate resonances are important for explaining the experimental two-pion correlation function. The reliability of two standard methods for pion interferometry is tested in our model.On leave from Institute of Nuclear Research, Academia Sinica, P.O. Box 800204, Shanghai 201800, China     

Accurate spectroscopic calculations of the 19 Λ-S states and 36 Ω states of the BC+ cation

This work computed the potential energy curves of 19 Λ-S states, which arose from the first five dissociation limits of BC⁺ cation, B⁺(¹S_g) + C(³P_g), B⁺(¹S_g) + C(¹D_g), B⁺(¹S_g) + C(¹S_g), C⁺(²P_u) + B(²P_u), and B⁺(¹S_g) + C(⁵S_u). The calculations were done for internuclear separations from 0.08 to 1.07 nm. The potential energy curves of 36 Ω states yielded from these Λ-S states were also calculated. Core-valence correlation and scalar relativistic correction, basis set extrapolation as well as Davidson correction were accounted for. Of these Λ-S states, the c¹Σ⁺, D³Π, 2¹Π, 2³Σ⁺, 2¹Δ, 3¹Σ⁺, and 4¹Σ⁺ had double wells; the 3³Π and 3¹Π states had three wells; the C³Σ^? and D³Π states were inverted with the spin-orbit coupling effect included; and the second wells of c¹Σ⁺, D³Π and 3¹Σ⁺ states, the second and the third wells of 3³Π state as well as the third well of 3¹Π state were very weakly bound, which well depths were smaller than 400 cm^?1. The spectroscopic parameters were determined for all the states. The vibrational properties were predicted only for some weakly bound states. The spin-orbit coupling effect on the spectroscopic parameters was evaluated.     

A study of π states of H2 + in the one centre approach

The statistical theory of the elastic constants of nematic liquid crystals is applied to detailed calculations based on well-defined approximations for the direct correlation function of Ornstein and Zernike and for the singlet orientational distribution. The model of hard spherocylinders with superimposed r ^-6 attraction modulated by a Maier-Saupe P ₂(cos ?_{1 2}) term, is used. The dependence on temperature, on the order parameter and on the length to breadth ratio, of the reduced elastic constants K* _i (i=1, 2, 3), is discussed in some detail and comparison with experiment is included.     

An investigation of high fractions of metastable helium atoms

Penning type discharge was adopted to excite helium atoms. It is suitable for generating high density metastables at a range from 0.1 mTorr to 0.5 Torr. The highest metastable density of 3.5 x 1010 cm-3 was observed at a static gas pressure of 0.5 Torr. The highest fraction of metastables (N12s/Nhe) of 10-3 in a low gas pressure was obtained. The variation of the magnetic field strength on the discharge does not result in a significant density change of the metastable helium atoms. When no magnetic field was applied, no discharge took place.     

Ab initio potential surfaces for the à and states of HCN+

Ab initio configuration interaction calculations for the à ²Σ⁺ and states of HCN⁺ are presented. Minima occur at r _CH = 2·03 a ₀, r _CN = 2·25 a ₀ (à ²Σ⁺) and r _CH = 2·75 a₀, r _CN = 2·26 a ₀ (). The potential surface for the state has a local maximum as the hydrogen atom is pulled away from CN. The barrier height is calculated to be 0·27 eV.     

Excitation of 1+ AND 2− states in the neon isotopes

High resolution inelastic proton scattering is used to study the excitation of 1⁺ states in ²⁰Ne and ²²Ne. By comparing these results with those from gamma-ray fluorescence measurements, the strong role of the orbital contribution in the electromagnetic transitions, predicted by the theory, is confirmed. Shell model predictions of the 1⁺ strength are compared to the measured strength in ²⁰Ne and ²²Ne. The (p, p′) excitation of 2⁻ states in ²⁰Ne is compared to (π⁻, γ) and (e, e′) results.     

Recombination processes and quenching of negative afterglow by microwaves — Ne,Ne + He

Quenching of the afterglow of an interrupted negative glow by application of microwaves to the decaying plasma has been observed. The time dependences of Ne atomic spectral line intensities show that two distinct groups of spectral lines, each group having its own time dependence in the afterglow, are emitted. Both the potential curves and energy level positions known for Ne ₂ ⁺ and Ne₂ are discussed with respect to the observed effects. The time dependence of Ne spectral lines cannot be explained by the temperature dependence of recombination coefficients only.The enhanced Mo spectral line emission (material evaporated from the cathode) caused by microwaves during the discharge period or after current cutoff, makes it possible to estimate the electron temperature increase and relaxation during and after the microwave pulse.