Density shift and broadening of dipole transitions in antiprotonic helium

The phase composition of carbon nanotubes (CNTs) with encapsulated iron atoms was examined by ⁵⁷Fe M?ssbauer spectroscopy. It was shown that iron atoms were stabilized in thermodynamically stable iron carbide and oxide phases and phases that are not usual under synthesis conditions (γ-Fe and γ-Fe₂O₃).     

Theoretical analysis of collisional shift and broadening of antiprotonic helium spectral lines

Effect of medium density on shift and broadening of ( ) spectral lines is considered in the framework of binary-collision approximation with an effective ( )–He potential including the long-range attraction and short-range repulsion. Quantum calculations of the scattering phase shifts at reasonable values of the potential parameters allow to explain the main features of the observed density effect on the shape of ( ) spectral lines in low-temperature helium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Convergent calculations for electron impact broadening and shift of neutral helium lines

Using the convergent semiclassical method, we have calculated the electronic widths and shifts of 42 neutral He lines for an electronic density of 10¹⁶/cm³ and T = 5000, 10,000, 20,000, and 40,000 K. To account of ions effects, we have calculated the Stark parameter A and parameter R.     

Stark broadening of neutral helium lines

Using a semiclassical approach for the Stark broadening of atomic lines, we have calculated electron and proton impact line widths and shifts of 56 neutral He lines in the ultraviolet, visible and i.r. region of the spectrum. The comprehensive set of results obtained is used for investigation of Stark-broadening parameter regularities within the spectral series.     

A comparison of self broadening and shift of helium,neon and argon emission lines

Self broadening (van der Waals and resonance) and shift of Ne emission lines and van der Waals broadening and shift of He emission lines have been measured using a high pressure (0.5–3.0 atom), low current discharge. These results are compared with previous measurements in Ar and He to obtain a complete comparison of self broadening and shift of He, Ne and Ar emission lines. Oscillator strengths for the resonance transitions are obtained from the resonance broadening coefficients. The trend of the van der Waals broadening coefficients for the three noble gases is correctly predicted by a theory due to HINDMARSHet al.⁽⁴⁾ in which a Lennard-Jones potential is used in the impact theory formalism. The measured line shifts cannot be accounted for by this theory and reflect the need for more accurate quantum mechanical calculations.     

X-rays from antiprotonic helium in helium gas

X-ray transitions to the 4F, 3D, and 2P atomic levels of p?He have been observed with antiprotons stopped in He gas at 4 and 1.1 atm NT. The population by radiative transitions of the 3D level in gas Y_M(4atm) = (28±14)% and Y_M(1.1 atm) = (43±22)% exceeds by more than one order of magnitude that measured in liquid He. The annihilation width of the 3D level Γ^a_3D = 2.8±1.0 × 10^?3eV is determined from the ratio between the numbers of X-rays feeding and depopulating the 3D level. The strong-interaction shift of the 2P level ε(2P) = ?14±6 eV is obtained by inputting the $\text{p}\text{He}$ experimental X-ray yields into a cascade calculation, the results of which are in good agreement with well-established data from muonic, pionic, and kaonic helium.     

Pressure broadening and shift of argon emission lines

Resonance and van der Waals broadening coefficients, as well as width to shift ratios, have been obtained by scanning argon emission lines produced in a high-pressure (～ 1 atm) glow discharge at a temperature of 1130°K. The resonance broadening coefficients yield absolute oscillator strengths of 0·283 ± 0·024 and 0·076 ± 0·008 for the two resonance lines at 1048 Å and 1067 Å. These oscillator strengths are in good agreement with previous measurements. The importance of higher-order terms in the van der Waals potential expansion is demonstrated by the measured coefficients.     

Stark broadening and shift of fluorine I lines

Stark widths and shifts of some prominent F I spectral lines have been determined experimentally in aZ-pinch plasma in dichlorodifluoromethane on a shot-to-shot basis. The electron density was determined by the laser interferometry while the electron temperature was measured from relative intensities of Cl II lines. Temperatures were in the range 19100–36200 °K; electron densities varied from 0.71 to 1.43×10¹⁷cm^?3. Measured F I linewidths and shifts are compared with theoretical results computed by Griem and it is shown that a) experimental widths are systematically smaller and the degree of discrepancy increases with temperature, b) line shifts are also smaller than theoretical with exception of multiplets 5 and 6 with the shifts of opposite sign than theoretically predicted, c) experimental shift-to-width ratios decrease with the temperature but less than theoretically expected. Attention is drawn in general, to the systematic discrepancy between experimental results for neutral atom lines and the theory. The magnitude of this disagreement is related to the relative position of the energy levels of spectral line to the ionisation limit.     

Stark broadening of neutral helium lines and spectroscopic diagnostics of pulsed helium plasma

Stark broadening parameters (widths and shifts) of two He I isolated spectral lines are measured in a plasma of a low-pressure pulsed arc. Plasma electron densities, determined by spectroscopic method based on previously calibrated He I lines, ranges from 1 x 10¹⁶ cm^-3 to 6 x 10¹⁶ cm^-3. The plasma electron temperature acquired by a Boltzmann plot of several He I lines, lies in the interval 8 000-30 000 K. Results of this work are compared with theoretical predictions and with other experimental data.Received: 30 April 2003, Published online: 29 July 2003PACS: 52.70.-m Plasma diagnostic techniques and instrumentation - 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 32.70.Jz Line shapes, widths, and shiftsR. Santamarta: Present address: DESY/ZEUS Hamburg, Germany.     

Two-photon spectroscopy of antiprotonic helium

The precision of laser spectroscopy of antiprotonic helium (a helium atom with one of its electrons replaced by an antiproton) has improved by almost 4 orders of magnitude over its 20 years of history. Experimental transition frequencies can be compared to 3-body QED calculations to derive the antiproton-electron mass ratio. In the latest measurements of the Asacusa experiment at CERN, two-photon transitions of antiprotonic helium were excited using two counter-propagating laser beams. This method reduces the Doppler-broadening caused by the thermal motion of the atoms, and allowed us to measure the transition frequencies with a fractional precision of 2.5–5 parts in 10⁹. From these frequencies, we derived an antiproton-electron mass ratio of 1836.1526736(23). Our precision approaches that of the experimental value of the proton-electron mass ratio, and agrees with the latter within errors. Assuming CPT symmetry (i.e. \(m_{p}=m_{\overline {p}}\) ), we further derived the electron’s atomic mass as m _e = 0.0005485799091(7)u from the more accurately known atomic mass of the proton.     

Stark broadening of visible neutral helium lines in a plasma

Side-on observations of the visible spectrum emitted by a helium plasma generated in a wall-stabilized arc are reported. Electron densities range from 0.2 to 1.3 × 10²²m^-3 and electron temperatures vary from 10,000 to 20,000 K. Most of the seventeen measured lines are “isolated” at the conditions of the experiment. Here, “isolated” refers to quantum levels which are non-degenerate even in the presence of perturbing fields. Electron densities derived from the Stark-widths of the isolated lines agree to within 15% of the values determined from Hβ and from the quasi-degenerate He(I) lines at 4471 and 4921 Å. Similar agreement is observed for the static-ion Stark broadening parameters. However, at the conditions of this experiment, the static-ion approximation is not valid near the center of some of the isolated lines. The observation of ion-dynamic effects in neutral isolated lines is reported here for the first time. In the isolated lines, the measured ion-dynamic effects are reasonably consistent with calculations based on an adiabatic “unified” theory for the ion perturbers. A simple parametric expression closely approximates the ion-dynamic contribution to the half-width of isolated lines. Hydrogenic (non-isolated) neutral helium lines exhibit a large discrepancy with theoretical profiles near the line center, where ion-dynamic effects are important.     

Precision spectroscopy of antiprotonic helium

We survey recent progress in the theoretical study of vibrational transitions in the antiprotonic helium atom. Along with the latest experiment they allow to achieve a competitive accuracy in determination of the atomic mass of an electron and thus they have been included into the CODATA06 analysis of the fundamental constants. Improved theoretical calculation of the hyperfine structure in $^{4\!}\mbox{He}\bar{p}\/$ atom will be considered as well. We will discuss contributions of order $R_\infty\alpha^4$ to the electron spin-orbit interaction. These corrections are necessary to confirm the latest measurements of the 12.9 MHz intervals of the (n,l)?=?(37,35) state in $^4\mbox{He}^+\bar{p}$ and for precise determination of the antiproton magnetic moment.     

The shift and broadening of the resonance lines of Ca,Sr and Ba in hot,dense argon and helium

The shift and half-width of the resonance singlet lines of Ca, Sr and Ba in emission were measured under various relative densities between 20 and 70 for Ar (at 2500 K) and between 35 and 121 for He (at 2450 K) by means of a ballistic compressor. The shift due to Ar is always red and increased with increasing relative density. The shift due to He is slightly toward red at densities below 50 and then gradually turns to the violet as the relative density is further increased. The foreign gas shift and broadening is nearly the same for the resonance lines of all these different alkaline-earth atoms but is different for different foreign gases, as in the case of alkali metals. Comparison with previous observations of Ca at 910 K shows that the increase of temperature will cause a decrease in red shifts and half-widths.     

Fine and hyperfine structure of antiprotonic helium

We consider the fine and hyperfine splitting of the energy levels of antiprotonic helium pHe⁺ in highly excited rotational states in connection with the interpretation of the recently discovered delayed annihilation of antiprotons in helium, based on the Condo model.     

Auger decay rates of antiprotonic helium

Auger decay rates of the metastable antiprotonic helium ^3,4He e are calculated. The variational method and solution of coupled differential equations are combined to determine the initial metastable state wave function. Besides metastable states, the calculation reveals specific short-lived states of the antiprotonic helium with an essentially different structure of the wave function. An effect of mixture of the wave functions is taken into account to calculate the decay rate for a few metastable states, which are close in energy to the short-lived ones. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simplified calculation of pressure shift and broadening of molecular lines

Gor'kii State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 12, pp. 1349–1356, December, 1990     

Theory of the pressure broadening and shift of spectral lines

The broadening and shift of spectral lines caused by the interaction of the emitting (or absorbing) atoms with surrounding particles in the plasma are commonly observed in laboratory and astronomical spectra. A detailed analysis of the observed line shapes can give information about the density and temperature of the plasma, and in cases where the interaction between emitter and perturber is not known, some information on its form may be deduced.     

Metastable states of antiprotonic helium atoms

We discuss the latest theoretical achievements in calculations of energy transitions in the antiprotonic helium He⁺ p-0304; atoms. New variational calculations of the nonrelativistic energies with precision of ∼10^-10 a.u. and relativistic and QED corrections to the energy levels of mα ⁵ order are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hadronic lamb shift in antiprotonic atoms

We estimate the difference between the anomalous magnetic moments of bound and free antiprotons and discuss its relevance in the magnetic fine structure of antiprotonic atoms.