[Show abstract][Hide abstract] ABSTRACT: The scattering of highly excited hydrogen Rydberg atoms, H* (n = 36), with deuterium molecules in their rovibrational ground state, D2(v = 0, j = 0), has been investigated at a relative collision energy of 0.53 eV. Time-of-flight distributions of elastically/inelastically scattered H* Rydberg atoms and reactively scattered D* Rydberg atoms have been measured at different laboratory angles. The extracted rovibrationally resolved state distributions of the HD product molecules from reactive collisions resemble closely those reported for the corresponding ion-molecule reaction, H+ + D2 --> HD + D+. This similarity is rationalised using the free electron model which predicts that the Rydberg electron acts as a spectator while the ionic reaction takes place.
[Show abstract][Hide abstract] ABSTRACT: The strong radiative single photon coupling between two excited states of sodium atoms (3p and 4d) has been studied at high intensities, exceeding 109 W cm-2. These excited states are probed by Raman-like resonant five-photon ionization processes. Using two tunable lasers the authors have observed that the doubly resonant process does not occur. In the model picture of photon-dressed atomic levels, this situation can be described as an avoided crossing, with a large minimum separation of 30 cm-1.
Journal of Physics B Atomic Molecular and Optical Physics 12/1998; 26(2):271. DOI:10.1088/0953-4075/26/2/010 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ionisation spectra of strontium have been measured using tunable laser radiation between 555 and 577 nm. The influence of bound two-photon resonances and autoionising three-photon resonances on the energy spectra and the angular distribution of the photoelectrons is studied for selected wavelengths. Four-photon ionisation via three-photon autoionising resonances is observed.
Journal of Physics B Atomic and Molecular Physics 12/1998; 15(11):1651. DOI:10.1088/0022-3700/15/11/011
[Show abstract][Hide abstract] ABSTRACT: The authors have studied atomic hydrogen in intense, short, visible laser pulses (I<or approximately=1.2*1014 W cm-2, tau approximately=0.5 ps, lambda approximately=608 nm). At high intensities (I>6*1013 W cm-2) they observe a new series of higher order above-threshold ionization peaks in the photoelectron energy spectrum. They discuss some tentative explanations. Two models are described in some detail. One relies on ionization saturation, the second one may be named 'parking of atoms as Rydberg wavepackets'.
Journal of Physics B Atomic Molecular and Optical Physics 12/1998; 26(2):L15. DOI:10.1088/0953-4075/26/2/001 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The three-photon ionisation of strontium atoms via resonance in the last photon absorption with some autoionising states was observed in the excitation range 5560-5640 AA using a tunable dye laser. The spectra as a function of the laser intensity are reported. Very rapid line broadening and ion enhancement together with very asymmetric line profiles are observed.
Journal of Physics B Atomic and Molecular Physics 12/1998; 14(14):2353. DOI:10.1088/0022-3700/14/14/008
[Show abstract][Hide abstract] ABSTRACT: Multiphoton ionisation of strontium atoms to Sr+ and Sr2+ has been investigated with a Nd-YAG laser ( lambda =10642 AA), its second, third and fourth harmonics and a tunable dye laser in a wavelength region around 5321 AA. The power dependence of the Sr+ and Sr2+ production has been obtained. The creation of Sr2+ is discussed with respect to two models: the simultaneous excitation and elimination of two electrons and a stepwise ionisation via Sr+.
Journal of Physics B Atomic and Molecular Physics 12/1998; 15(11):1663. DOI:10.1088/0022-3700/15/11/012
[Show abstract][Hide abstract] ABSTRACT: For the hydrogen atom in crossed, perpendicular, static electric and magnetic fields we show the existence of three elementary Kepler ellipses, two in the plane perpendicular to the magnetic field and one, three-dimensional, largely perpendicular to the electric field. They are determined from the symmetry properties in the low field limit, occurring for all external field combinations. Their parameter dependences and stability properties are analysed in detail. In the case that the orbits are stable the corresponding maximum orientated quantum states are identified. For states with sufficient low principal quantum numbers the total splitting of a given n-shell is described by semiclassical quantization of these three Kepler ellipses.
Journal of Physics B Atomic Molecular and Optical Physics 12/1998; 27(13):2821. DOI:10.1088/0953-4075/27/13/012 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Sr2+ yield has been measured in the wavelength region around 561 nm. Maxima of the yield can be correlated with energy levels of Sr II, indicating that the double ionisation is a step-wise process via Sr+.
Journal of Physics B Atomic and Molecular Physics 12/1998; 15(15):L529. DOI:10.1088/0022-3700/15/15/004
[Show abstract][Hide abstract] ABSTRACT: Although the structure in the total three-photon ionisation cross section around an autoionising resonance at 13.134 eV predicted by a recent calculation has not been observed, the angular distribution of photoelectrons changes considerably at the corresponding wavelength.
Journal of Physics B Atomic and Molecular Physics 12/1998; 19(5):L141. DOI:10.1088/0022-3700/19/5/004
[Show abstract][Hide abstract] ABSTRACT: The authors present a comparison of theoretical and experimental data for the first three above-threshold ionization channels of the photoelectron kinetic energy spectrum of atomic hydrogen when the atom is irradiated by a short pulse of linearly polarized light of wavelength 608 nm and peak intensity 6*1013 W cm-2 or 1.2*1014 W cm-2.
Journal of Physics B Atomic Molecular and Optical Physics 12/1998; 25(12):L275. DOI:10.1088/0953-4075/25/12/001 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Precision measurements of photoabsorption lines of atomic hydrogen in magnetic fields up to 6 T are compared with exact quantum mechanical calculations for energies reaching beyond the regime of approximate separability of the Schrodinger equation. The agreement between measurement and calculation is excellent.
Journal of Physics B Atomic and Molecular Physics 12/1998; 19(17):L557. DOI:10.1088/0022-3700/19/17/002
[Show abstract][Hide abstract] ABSTRACT: The reactivity of H + D2(v = 0, j = 0) → HD(v′,j′) + D has been investigated in a high resolution crossed molecular beam experiment at a collision energy of 2.2 eV. Time-of-flight (TOF) spectra of D atoms at different laboratory (LAB) scattering angles and their total angular distribution were measured using the technique of Rydberg atom TOF spectroscopy. The resolution of this technique allows the identification of individual rovibrational states of the corresponding HD product molecule at the different LAB angles. A detailed simulation of the experimental measurements has been performed by using state resolved differential cross sections from quasiclassical trajectory (QCT) calculations on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) and on the double-many-body-expansion (DMBE) potential energy surfaces (PES). A general good agreement between experiment and theory is found, although there are some discrepancies which are discussed.
Chemical Physics Letters 01/1997; 265(1-2-265):129-136. DOI:10.1016/S0009-2614(96)01416-9 · 1.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the first observations of cylindrical symmetry breaking in highly excited diamagnetic hydrogen with a small crossed electric field, and we give a semiclassical interpretation of this effect. As the small perpendicular electric field is added, the recurrence strengths of closed orbits decrease smoothly to a minimum, and revive again. This phenomenon, caused by interference among the electron waves that return to the nucleus, can be computed from the azimuthal dependence of the classical closed orbits. Comment: 4 page REVTeX file including 5 postscript files (using psfig) Accepted for publication in Physical Review Letters. Difference from earlier preprint: we have discovered the cause of the earlier apparent discrepancy between experiment and theory and now achieve excellent agreement
[Show abstract][Hide abstract] ABSTRACT: We report results of a systematic study of the energy-field dependence of the four elementary periodic orbits of the electron motion of the hydrogen atom in crossed magnetic-electric fields from weak to strong perturbation, up into the continuum regime. We find the classical dynamics of the crossed-field atom to be intimately connected to that of the Sun-Earth-Moon three-body problem in Hill's approximation, exhibited by striking similarities of the four elementary orbits of the atomic and celestial systems in their energy-field dependence.
Physical Review A 10/1996; 54(3):1884-1888. DOI:10.1103/PhysRevA.54.1884 · 2.99 Impact Factor