Jussi Eloranta

Solution of time-independent Schrödinger equation by the imaginary time propagation method

Numerical solution of eigenvalues and eigenvectors of large matrices originating from discretization of linear and non-linear Schrodinger equations using the imaginary time propagation (ITP) method is described. Convergence properties and accuracy of 2nd and 4th order operator-splitting methods for the ITP method are studied using numerical examples. The natural convergence of the method is further accelerated with a new dynamic time step adjustment method. The results show that the ITP method has better scaling with respect to matrix size as compared to the implicitly restarted Lanczos method. An efficient parallel implementation of the ITP method for shared memory computers is also demonstrated.

A time dependent density functional treatment of superfluid dynamics: Equilibration of the electron bubble in superfluid 4He

Time dependent density functionals are formulated and implemented in numerical simulations of the equilibration dynamics of an excess electron in superfluid helium. Previously developed density functionals that incorporate nonlocal potential and kinetic correlations and reproduce the dispersion curve of liquid 4He, are used. The electron–helium interaction is treated using pseudopotentials, after testing their accuracy in reproducing the static properties of the solvated electron bubble through its known spectroscopy. The dynamics initiated by the sudden compression of the bubble is dissected, and the results are favorably compared to classical hydrodynamics. In the near-field, the fast motion corresponds to interfacial compressional waves, followed by the slow breathing of the cavity. The far-field motion consists of a shock wave, followed by radiating sound waves. The solitonic shock wave propagates at speeds as high as 580 m/s, determined by the amplitude of excitation. The energy carried by the shock ...

Thermal mobility of atomic hydrogen in solid argon and krypton matrices

Decay patterns of atomic hydrogen trapped in argon and krypton matrices are followed by electron paramagnetic resonance (EPR). Hydrogen atoms are generated by uv-photolysis of HBr and HCl precursor molecules. The EPR signals due to interstitially trapped hydrogen atoms in octahedral sites disappear near 16 and 24 K in Ar and Kr, respectively. Substitutionally trapped H atoms are thermally stable up to evaporation temperature of the solids. The fate of thermally released H atoms in Ar is exclusively due to geminate recombination of the parent molecule. The observed kinetics is well fitted with double exponential decay. The kinetic behavior reflects short-range dissociation and recombination dynamics in Ar. In the Kr matrix, a change from first-order to second-order kinetics is observed at higher concentrations as formation of molecular hydrogen becomes important. From bimolecular decay kinetics, a diffusion constant of 4×10−15 cm2 s−1 is deduced for H-atom diffusion in Kr at 26.9 K. The obtained activation...

A direct interrogation of superfluidity on molecular scales

Time-resolved, pump–probe measurements are used to directly interrogate dissipative fluid dynamics in bulk He-II, on molecular scales, as a function of temperature and pressure. The Rydberg transitions of the triplet He2* excimers, which solvate in bubble states in liquid helium, are used as nanoscale transducers to initiate and to directly monitor the motion of the fluid in the form of damped oscillations of a 13 A spherical bubble. The oscillations are damped out after one period, with a temperature-dependent period that directly tracks the normal fraction. As such, the bubble oscillator acts as a nanoviscosimeter. Through simulations of the observed signals, it is established that the coherent response of the bath obeys hydrodynamic equations of motion of a continuum subject to two-fluid flow. Dissipation occurs through two distinct channels: (a) Radiation of sound in the farfield, driven by the acceleration of volume in the compressible fluid; (b) temperature-dependent drag in the near-field. The drag...

Structure and energetics of He2* bubble-states in superfluid 4He

Structure and energetics of solvation of the triplet Rydberg states of the He2* excimer in liquid 4He (LHe) are analyzed using ab initio potentials and density functional methods. The results are used to interpret the known spectroscopy. Having established the reliability of the various semiempirical functionals, interfacial properties of the superfluid on molecular scales are discussed. Due to its spherical electron density, the a(3Σu) state solvates in a spherical bubble of 7 A radius in which the excimer freely rotates. This explains the observed rotationally resolved 3b←3a and 3c←3a absorption spectra. A deep potential minimum occurs at the equatorial node of the c(3Σu) state, where a radially frozen belt of six He atoms can be sustained at R=2.3 A, inside an ellipsoidal cavity with major axis of 8 A and a more diffuse minor axis of 6 A. Despite the absence of a potential energy barrier, or a many-body interfacial tension preventing the wetting of the belt, the bare 3c state is observed in emission. I...

Ab initio and molecular-dynamics studies on rare gas hydrides: Potential-energy curves, isotropic hyperfine properties, and matrix cage trapping of atomic hydrogen

Ground-state potential-energy curves and distance dependent isotropic hyperfine coupling (IHC) constants for ground-state H–RG (=Ne, Ar, Kr, Xe) are obtained at CCSD(T) (coupled-cluster single double triple) and MP4(SDQ) (fourth-order Moller–Plesset single double quadruple) levels, respectively, with an augmented basis set aug-Stuttgart (RG)/aug-cc-pVQZ (H). The obtained Rm and e are for NeH: 3.45 A and −1.36 meV; ArH: 3.65 A and −3.48 meV; KrH: 3.75 A and −4.32 meV; XeH: 3.90 A and −5.22 meV. The computed pair potentials are utilized in classical molecular-dynamics simulations of H–RG lattices. Along the classical trajectory, the many-body perturbation on the H atom hyperfine coupling constant is computed by pair-wise addition of the individual RG–H contributions obtained from the present quantum-chemical calculations. The computed IHC shifts are compared with electron paramagnetic resonance (EPR) spectra obtained in low-temperature matrix isolation experiments. For most cases this theoretical treatment ...

193 NM PHOTODYNAMICS OF NO IN RARE GAS MATRICES : FLUORESCENCE, THERMOLUMINESCENCE, AND PHOTODISSOCIATION

193 nm excited time gated emission spectra of a NO monomer isolated in Ar, Kr, and Xe matrices are presented. In the Ar matrix a 4Π→X 2Π, B 2Π→X 2Π, and A 2Σ→X 2Π band systems are completely separable. In solid Kr, both B 2Π→X 2Π and A 2Σ→X 2Π appear promptly from the laser pulse, and in the Xe matrix only Rydberg A 2Σ→X 2Π fluorescence is observed. Prolonged photolysis at 193 nm yields electron paramagnetic resonance signals attributed to isolated 4S nitrogen atoms. This is the first observation of condensed phase photodissociation of NO. Annealing of the extensively irradiated Ar matrix produces strong a 4Π→X 2Π and B 2Π→X 2Π thermoluminescence emissions due to N(4S)+O(3P) recombination. In the Kr matrix thermoluminescence is entirely due to a 4Π→X 2Π transition. No thermoluminescence is observed in Xe. Thermoluminescence is ascribed to short-range trapping of N and O fragments, and well separated atoms do not have significant contribution to recombination.

Universal molecule injector in liquid helium: Pulsed cryogenic doped helium droplet source

Progress toward the construction of a universal molecule injector for doping bulk liquid helium is reported. A pulsed valve that operates at cryogenic temperatures, down to 4 K, is demonstrated within the confinement of a cryostat, operating in the vapor above a steady level of liquid He. The insulated valve can be operated at elevated temperatures with preseeded helium gas in supersonic expansion mode, as demonstrated through laser-induced fluorescence spectra of seeded NO2. At cryogenic operating temperatures, the expansion into vapor helium produces a well-collimated liquid helium droplet beam, which is then used to transfer to the liquid impurities produced by laser ablation from a cryogenic rotating target. The operation can be visualized using copper as the ablation target: the droplet beam is imaged via Rayleigh scattering, while the beam past the plasma is imaged by the fluorescence of the entrained Cu atoms. The beam drags along copper ions and electrons, the recombination of which controls the f...

Theoretical analysis of alkali metal trapping sites in rare gas matrices

The rare gas (Ne, Ar, Kr, Xe)–alkali metal (Li, Na) ground-state pair interaction potentials and distance-dependent isotropic hyperfine coupling constants are evaluated by coupled-cluster approaches at the van der Waals region of the dimers. The computed properties are further utilized in classical molecular dynamics simulations of rare gas lattices doped with alkali atoms. Atomic trajectories and time averaged hyperfine constants are obtained from the simulations and exploited to provide theoretical insights into experimentally observed atomic trapping and dynamics of alkali metal atoms in rare gas matrices. The simulations support our previous electron paramagnetic resonance (EPR) data [Chem. Phys. Lett, 310, 245 (1999)], suggesting that alkali metal atoms, while generated by laser vaporization, do trap in single substitutional sites, whereas thermal atom sources yield trapping in multiple substitutional sites. In order to theoretically reproduce the EPR spectra for the latter case, more than six neighb...

Dynamics of vortex assisted metal condensation in superfluid helium

Laser ablation of copper and silver targets immersed in bulk normal and superfluid (4)He was studied through time-resolved shadowgraph photography. In normal fluid, only a sub-millimeter cavitation bubble is created and immediate formation of metal clusters is observed within a few hundred microseconds. The metal clusters remain spatially tightly focused up to 15 ms, and it is proposed that this observation may find applications in particle image velocimetry. In superfluid helium, the cavitation bubble formation process is distinctly different from the normal fluid. Due to the high thermal conductivity and an apparent lag in the breakdown of superfluidity, about 20% of the laser pulse energy was transferred directly into the liquid and a large gas bubble, up to several millimeters depending on laser pulse energy, is created. The internal temperature of the gas bubble is estimated to exceed 9 K and the following bubble cool down period therefore includes two separate phase transitions: gas-normal liquid and normal liquid-superfluid. The last stage of the cool down process was assigned to the superfluid lambda transition where a sudden formation of large metal clusters is observed. This is attributed to high vorticity created in the volume where the gas bubble previously resided. As shown by theoretical bosonic density functional theory calculations, quantized vortices can trap atoms and dimers efficiently, exhibiting static binding energies up to 22 K. This, combined with hydrodynamic Bernoulli attraction, yields total binding energies as high as 35 K. For larger clusters, the static binding energy increases as a function of the volume occupied in the liquid to minimize the surface tension energy. For heliophobic species an energy barrier develops as a function of the cluster size, whereas heliophilics show barrierless entry into vortices. The present theoretical and experimental observations are used to rationalize the previously reported metal nanowire assembly in both superfluid bulk liquid helium and helium droplets, both of which share the common element of a rapid passage through the lambda point. The origin of vorticity is tentatively assigned to the Zurek-Kibble mechanism. Implications of the large gas bubble formation by laser ablation to previous experiments aimed at implanting atomic and dimeric species in bulk superfluid helium are also discussed, and it is proposed that the developed visualization method should be used as a diagnostic tool in such experiments to avoid measurements in dense gaseous environments.