States Of Krypton Research Articles

Equation of state measurements of dense krypton up to the insulator-metal transition regime: Evaluating the exchange-correlation functionals

Motivated by the poor understanding of the applicability of new exchange-correlation (XC) functionals to warm dense matter (WDM), we designed and performed multiple-shock reverberation compression experiments on dense krypton to evaluate explicitly the implications of recently derived XC functionals. The equation of states of krypton up to 155 GPa and 45 000 K, which ranges from an initial dense gaseous state up to the insulator-metal transition regime, were determined accurately. It is found that the experimental data are better reproduced by the strongly constrained and appropriately normed (SCAN) XC functional compared to the conventional Perdew-Burke-Ernzerhof and Van der Waals (vdW) DF1 functionals, elucidating that the introduction of the kinetic energy density and the intermediate-range vdW interaction is decisive. However, the incorporation of long-range interactions into the SCAN ($\mathrm{SCAN}+\mathrm{rVV}10$ XC functional) results in a noticeably stiffer prediction due to an overestimation of the density and internal energy of the system at low densities and temperatures. Our evaluation of the Karasiev-Sjostrom-Dufty-Trickey free-energy functional experimentally validates the XC thermal effect in the WDM regime, verifies the previous predictions, and sheds light on a direction for future theoretical efforts. Finally, a phase diagram of krypton is given, which provides a clear picture for understanding the thermophysical behavior of krypton in a wider temperature-pressure range.

Autoionization dynamics of (2P1/2)ns/d states in krypton probed by noncollinear wave mixing with attosecond extreme ultraviolet and few-cycle near infrared pulses.

The autoionization dynamics of the (2P1/2)ns/d Rydberg states in krypton are investigated using spatially isolated wave-mixing signals generated with a short train of subfemtosecond extreme ultraviolet (XUV) pulses and noncollinear, few-cycle near infrared pulses. Despite ubiquitous quantum beat oscillations from XUV-induced coherences within the excited-state manifold, these wave-mixing spectra allow for the simultaneous evaluation of autoionization lifetimes from a series of Rydberg states above the first ionization potential. Experimentally measured lifetimes of 22 ± 8 fs, 33 ± 6 fs, and 49 ± 6 fs for the wave-mixing signals emitting from the (2P1/2)6d/8s, (2P1/2)7d/9s, and (2P1/2)8d/10s resonances compare favorably with lifetimes for the (2P1/2)6d, 7d, and 8d Rydberg states determined from spectral linewidths. Analysis of the quantum beats reveals that the enhancement of wave-mixing pathways that couple the (2P1/2)nd states to themselves leads to individual reporter state-dependent decays in the wave-mixing signals. The results demonstrate the promise of wave-mixing spectroscopies with subfemtosecond XUV pulses to provide valuable insights into processes governed by electronic dynamics.

Creation and survival of autoionizing states in strong laser fields

Very sharp, low-energy structures observed in photoelectron spectra reveal the population of autoionizing states in krypton and argon in strong laser fields over a large range of different wavelengths. The energies of the electrons, emitted by autoionization in a field-free environment, provide direct information about the spectrum of states involved. Despite their ability to resist ionization by the populating laser pulse, we demonstrate the possibility to promote the excited electrons into the continuum by subsequent absorption of a single photon. Thus, applying a classical pump-probe scheme, we are able to manipulate the autoionization contribution on a picosecond time scale. Different scenarios for the creation of autoionizing states in strong laser fields are discussed.

Excitation Mechanism of Silver Ionic Lines Through Collisions with Metastable Atoms of Plasma Gas in a Glow-Discharge Plasma

ABSTRACT Emission spectra of silver from glow-discharge plasmas using argon, krypton, and a krypton–argon gas mixture were analyzed to elucidate the excitation phenomenon of silver ionic lines occurring in collisions with the plasma gases. The intensities of the ionic lines that were assigned to the 4d95p–4d95s transition were largely different between argon and krypton; for instance, the intensity of the Ag II 243.78-nm line (9.94 eV) emitted from the krypton plasma was five times larger than that from the argon plasma, while the Ag II 228.00-nm line (11.14 eV) yielded much larger intensity in the argon plasma by a factor of 70. This effect can be explained by an excitation process through collisional energy transfer from the metastable atom of argon or krypton to the silver ion in the ground state (Penning excitation). This type of collision requires both matching in the excitation energy between the colliding partners and conservation in the total spin before and after the collision. The 3p54s metastable state of argon (11.72 eV for the singlet and 11.55 eV for the triplet) and the 4p55s metastable state of krypton (10.56 eV for the singlet and 9.92 eV for the triplet) would take part in the collision and principally determine the population of the 4d95p excited levels of the silver ion.

Electron impact excitation of the (4p5 5s) states in krypton: high-resolution electron scattering experiments and -spline -matrix calculations

In a joint experimental and theoretical effort, we carried out a detailed study of electron impact excitation of the 4p5 5s states of Kr. We present angle-differential cross sections over the entire angular range (0°–180°) for a number of energies in the near-threshold region, as well as energy scans for selected angles. The experimental results are in very satisfactory agreement with predictions from a fully relativistic Dirac B-spline R-matrix model.

High resolution spectroscopy in the XUV with pairs of mutually coherent and time-delayed laser harmonics

We present a Ramsey technique using high-order harmonics for high-resolution atomic spectroscopy in the extreme ultraviolet. Pairs of time-delayed and phase-coherent harmonic pulses generated by the interaction of ultrashort and intense laser pulses with a noble gas are used to study excited states of krypton.

Slow muon experiment by laser resonant ionization method at RIKEN-RAL muon facility

We report first results of the slow muon generation from pulsed surface muon beam using a method of resonant laser ionization of muonium. The muonium is produced from the muon beam by electron capture near the surface of thin tungsten foil heated to 2100 K. The ionization is resonantly enhanced by using a vacuum-ultraviolet (VUV) radiation resonant with 2P state of muonium (λ 1S–2P=122.09 nm). A pulsed beam at 355 nm is used for an efficient ionization from the 2P state. The VUV beam with pulse duration of 4 ns and with bandwidth of over 100 GHz to match the Doppler broadening of muonium (200 GHz) is generated by resonant third-order sum-difference frequency conversion (ω VUV=2ω R−ω T) in krypton gas phase-matched with argon buffer gas. The ω R beam has been tuned to the two-photon resonance of 4p 55p[1/2,0] state in krypton to enhance the conversion process. Yield of the VUV radiation has been investigated for different energies and confocal parameters of the incident beams. The whole apparatus, including a beamline for transport and detection of ionized particles, has been tested by ionizing residual hydrogen atoms at an ultra-high vacuum level of 1.1×10 −9 hPa with efficiency better than 10 −3. The yield of slow muons obtained during the first beamtime was 0.03 μ +/s.

Excitation transfer in the plasma of a barrier discharge in a krypton-xenon mixture

Processes of excitation transfer in the plasma of a barrier discharge in a krypton-xenon mixture are studied. A kinetic diagram of energy transfer is proposed, and a system of coupled kinetic equations describing the dynamics of processes in the plasma of a barrier discharge of mixtures in pure xenon as well as in a krypton-xenon mixture is composed and solved. The effect of excitation transfer on the population distribution over vibrational levels of krypton excimers excited by a barrier discharge in a krypton-xenon mixture is studied. The deviation from the equilibrium distribution over vibrational levels is found. It can be interpreted as an indication of the activation of the mechanism of depopulation of the lowest vibrational levels of excimer states of krypton.

Measurements of photoelectron angular distributions between the 2P3/2,1/2 states of Kr+ and Xe+ using a new magnetic angle-changing technique

Abstract Photoelectron angular distributions have been measured in the energy regions between the 2 P 3/2 and 2 P 1/2 states of Kr + and Xe + containing the ( 2 P 1/2 )nd′ and ( 2 P 1/2 )(n+2)s′ autoionising resonances. A new magnetic angle-changing technique has been used. This features a localised magnetic field created at the interaction region of a photoelectron spectrometer by means of co-axial solenoids. Partial ionisation cross-sections for the 2 P 3/2 ionic states of krypton and xenon are presented. The variations in the β parameters across the autoionising regions have also been deduced.

Threshold photoelectron studies of Kr and Xe

Threshold photoelectron measurements of the ionic `satellite' states ofkrypton and xenon have been undertaken at the Daresbury SynchrotronRadiation Source (SRS) using the field-penetration technique. The photonenergy ranges covered were 27.5-32.3 eV (Kr) and 23.3-34.8 eV (Xe)with a measured energy resolution of 13 meV, which is an order ofmagnitude improvement over the previous measurements. The ionic stateshave been catalogued and where resonance enhancement has been observed,the corresponding doubly excited neutral states have also been identified.

Electron-impact excitation of the Kr 4p55sstates at 15 eV:close-coupling versus distorted-wave treatments

Electron-impact excitation of the 4p55s states inkrypton by 15 eV electrons has been investigated in detail bycomparing results obtained in non-perturbativeclose-coupling-type models and in a first-order perturbativedistorted-wave approach.When the results are compared with recent experimental data, theclose-coupling results are generally in better agreement withexperiment than the DWBA predictions, with the notable exception beingthe ratios of differential cross section data recently publishedby Guo et al (1999 J. Phys. B: At. Mol. Opt. Phys. 32 L155-63).

A study of resonance structures in elastic electron scattering from helium, neon, argon, krypton and xenon over the angular range from 100 to 180

Resonance structures corresponding to the 2sS state in He and the np(n + 1) s(S) states in Ne, Ar, Kr and Xe have been studied in elastic electron scattering over the angular range from 100 to 180. A newly developed magnetic angle-changing technique has been used and this has allowed the first observation of these structures at and near to 180. The widths and energies of the resonance states in krypton and xenon have been determined.

A procedure for measuring photoelectron angular distributions from gas-phase targets using an angle- and energy-dispersive spectrometer

Abstract Angular distributions of the electrons emitted during photoionisation have been obtained using synchrotron radiation and a toroidal photoelectron spectrometer containing a position-sensitive detector. The distributions of the 2P1/2 and 2P3/2 states in krypton in the 24.8–25.3 eV photon energy range have been measured. A high statistical accuracy was maintained throughout that energy range by recording a pre-set number of counts — covering a wide range of emission angles — at each photon energy. The β parameters of the two states have been extracted.

Auger and Coster-Kronig decay of the 3p hole states in krypton

The M2,3-M4,5N Coster-Kronig and the M2,3-NN Auger electron spectra from krypton have been measured using synchrotron radiation and electron beam excitation. By combining information from the different excitation methods, a large number of transitions have been identified. Intensity distributions between the line groups have also been studied both experimentally and theoretically. Coster-Kronig decay widths of the 3p hole states have been determined. The effects due to the initial-state configuration interaction have been revealed by comparing the experimental results with multiconfiguration Dirac-Fock calculations.

Deactivation of two-photon excited Xe(5p56p,6p′,7p) and Kr(4p55p) in xenon and krypton

Lifetimes and bimolecular quenching rate constants have been determined for two-photon laser excited states of Xe*(5p56p,5p56p′,5p57p) and Kr*(4p55p) in krypton and xenon buffer gases. Collisional mixing between Kr*5p[5/2]2 and Kr*5p[5/2]3 in krypton is observed and analyzed using a coupled two-state model to obtain the rate of mixing. The measured rate constants for quenching of Xe*(6p′,7p) by krypton are 15%–20% smaller than those measured previously in xenon while bimolecular rates for the Kr*(5p) states are an order of magnitude larger in xenon than those in a krypton buffer. Measurements of state-to-state rate constants for deactivation and excitation transfer are also reported for these states in krypton and xenon buffer gases.

Electron-photon coincidence study of heavy-noble-gas excitation at small scattering angles.

The electron--polarized-photon coincidence technique has been used to study the finer details of the excitation of the first excited states of the heavy noble gases neon, argon, and krypton by electron impact in the regime of large impact parameters (small scattering angles and intermediate impact energies). Measurements with higher statistical accuracy of the {ital P}{sub 1} coherence parameter in forward scattering for excitation of the ({sup 2}{ital P}{sub 1/2}){ital ns}{prime}(1/2){sub 1}{sup 0}( {sup 1}{ital P}{sub 1}'') state in neon ({ital n}=3) and argon ({ital n}=4) are reported along with {ital P}{sub 1} measurements for both the ({sup 2}{ital P}{sub 1/2})5{ital s}{prime}(1/2){sub 1}{sup 0}( {sup 1}{ital P}{sub 1}'') state and the ({sup 2}{ital P}{sub 3/2})5{ital s}{prime}(3/2){sub 1}{sup 0}( {sup 3}{ital P}{sub 1}'') state in krypton for incident electron energies from 30 to 100 eV. All measurements are consistent with a {ital P}{sub 1} value of +1, which is indicative of the dominance of direct excitation via transfer of orbital angular momentum. No evidence was found that exchange excitation via spin transfer plays a role in forward scattering at these energies, in agreement with theoretical predictions. A series of systematic measurements of the two linear coherence parameters {ital P}{sub 1} and {italmore » P}{sub 2} was carried out for excitation of the {sup 1}{ital P}{sub 1}'' state in argon and the {sup 3}{ital P}{sub 1}'' state in krypton at 50-eV impact energy and electron-scattering angles up to 25{degree}. A detailed comparison with the predictions of the distorted-wave Born approximation and the first-order many-body theory reveals a generally satisfactory agreement and indicates that the theories are capable of reproducing the general features of the measured parameters as a function of scattering angle.« less

Four-photon excitation of even-parity Rydberg states in krypton and xenon.

Multiphoton ionization via four-photon excitation of high-lying Rydberg states in xenon and krypton has been studied. The p and f series leading to the $^{2}\mathrm{P}_{3/2}$ ionization limits as well as the p' and f' autoionizing levels leading to the $^{2}\mathrm{P}_{1/2}$ limits have been recorded for both gases. Lower members of the p series in xenon are resolved into p${[(5/2)]}_{2}$, p${[(3/2)]}_{2}$, and p${[(1/2)]}_{0}$ sublevels. Ionization potentials and quantum defects are obtained by a least-squares fitting of the data to the standard Rydberg formula.

Electron impact excitation of the lowest-lying excited states of krypton

Excitation of the 4p5(2P32/)5s3P1 and 4p5(2P12/)5s 1P1 states of krypton by electron impact has been studied using the electron-photon angular correlation technique. Measurements are reported at an incident electron energy of 60 eV for electron scattering angles theta e up to 30 degrees . The serious disagreement between two previous measurements at theta e=20 degrees is discussed. The difficulty of obtaining a quantitative measure of the importance of spin-orbit coupling through the parameter epsilon using this technique is demonstrated.

Excitation ahead of shock fronts in krypton measured by single line laser absorption

The number densities of the metastable 5s[1 1/2]2 state and the 5s[1 1/2]1 state of krypton ahead of shock fronts have been determined from the measured absorption of single line laser radiation. Shocks with Mach numbers from 12 to 21 were investigated at preshock pressures from 0.7 to 2.7 kPa. An exponential rise of this excitation precursor having time constants of about 8 ws is found. The metastable concentration atM = 20 is about 10 ppm. The experimental results agree within an order of magnitude with published model predictions for argon and xenon shocks.

Perturbation theory for square-well fluids in d=2, 3

In this paper, we study the equation of state behaviour of square-well fluids in the dimensions d=2, 3 via the Zwanzig perturbation theory. As a particular point of emphasis, we focus on a result reported several years ago by Barker and Henderson that the perturbation theory may be used as a surprisingly accurate, predictive tool to locate the critical temperature of argon and xenon in d=3. Here we examine whether this facet of the Zwanzig theory is sensitive to the dimensionality of the configuration space of the system, by calculating the equation of state of krypton, modelled as a squarewell fluid, in d=3 and d=2. In d=3 we find that the critical temperature of krypton is predicted to within 15 per cent, while in d=2 an apparently different, high density transition is signalled by the theory.