The interaction of 800-MeV H ions with a thin foil produces protons, the ground state and excited states of neutral H atoms, and unstripped H 2 ions. We investigated the distributions of individual H 0 Stark states within the n53 and 4 levels produced by C and Al 2O3 foil stripping of H 2 ions. Foils of various thicknesses were placed upstream of a magnet with a linearly increasing transverse field along the beam direction producing a motional electric field strong enough to ionize H 0 states withn>3. We consider three questions: ~i! What are the populations of individual H 0 Stark states produced in the interaction of 800-MeV H 2 ions with thin C and Al2O3 foils, ~ii ! how do the relative population distributions change with foil thickness, and ~iii ! how is the population distribution produced in an Al 2O3 foil modified when the foil is placed in a magnetic field? A simple qualitative model is presented to explain the major trends. @S1050-2947 ~98!02212-4#

The interaction of 800-MeV H ions with a thin foil produces protons, the ground state and excited states of neutral H atoms, and unstripped H 2 ions. We investigated the distributions of individual H 0 Stark states within the n53 and 4 levels produced by C and Al 2O3 foil stripping of H 2 ions. Foils of various thicknesses were placed upstream of a magnet with a linearly increasing transverse field along the beam direction producing a motional electric field strong enough to ionize H 0 states withn>3. We consider three questions: ~i! What are the populations of individual H 0 Stark states produced in the interaction of 800-MeV H 2 ions with thin C and Al2O3 foils, ~ii ! how do the relative population distributions change with foil thickness, and ~iii ! how is the population distribution produced in an Al 2O3 foil modified when the foil is placed in a magnetic field? A simple qualitative model is presented to explain the major trends. @S1050-2947 ~98!02212-4#

We have measured the hydrogen-deuterium isotope shift in the energy of the lowest D-1(e) autodetaching resonance in the two-photon absorption spectrum of H-. The D-1(e) resonance in negative deuterium lies 2.0 +/-0.5 meV, with a possible systematic error of 0.4 meV, above the corresponding resonance in negative hydrogen when measured with respect to the ion ground state. From the isotope shift, we obtain a mass polarization of 2.4+/-1.1 meV, with a possible sytematic error of 0.8 meV, for the D-1(e) in H- under the assumption that the Fano shape parameters, q, for the two isotopes are the same. Recent theoretical calculations give the mass polarization for this resonance in H- as -0.1 meV. The generalized absolute cross section of two-photon absorption at the peak of the D-1(e) is found to be (3.2(-1.2)(+1.8))x10(-49) cm(4) s. The measured asymmetry parameters beta(2) and beta(4) of the photodetachment process are 1.9+/-1.2 and 2.21+/-0.45, respectively, consistent with a pure D-wave distribution. Upper bounds on the second recursion of the lowest S-1(e) resonance and three-photon excess photon detachment are 2.8x10(-49) cm(4) s and 3.1x10(-78) cm(6) s(2), respectively.

The interaction of 800-MeV H- ions with a thin foil produces protons, the ground state and excited states of neutral H-0 atoms, and unstripped H- ions. We investigated the distributions of individual H-0 Stark states within the n=3 and 4 levels produced by C and Al2O3 foil stripping of H- ions. Foils of various thicknesses were placed upstream of a magnet with a linearly increasing transverse field along the beam direction producing a motional electric field strong enough to ionize H-0 states with n greater than or equal to 3. We consider three questions: (i) What are the populations of individual H-0 Stark states produced in the interaction of 800-MeV H- ions with thin C and Al2O3 foils, (ii) how do the relative population distributions change with foil thickness, and (iii) how is the population distribution produced in an Al2O3 foil modified when the foil is placed in a magnetic field? A simple qualitative model is presented to explain the major trends. [S1050-2947(98)02212-4].

We report the first observation of nonresonant excess photon absorption (for ionization as well as detachment) in competition with the single photon process. A 35 keV negative hydrogen ion beam is irradiated with focused Nd:YAC laser pulses: the 1.165 eV photon energy exceeds the electron binding energy by 0.41 eV. The time of flight spectrum of detached electrons exhibits the absorption of one and two photons. The detached electrons exit with a P wave angular distribution for the one-photon detachment and primarily a D wave for the two photon excess photon detachment.

Measurements of H- stripping and H-0 excited-state production for a wide range of foil thicknesses and experimental conditions are reported. An 800-MeV H- beam was passed through carbon or aluminum oxide foils of thicknesses ranging from 10 to 550 mu g/cm(2) and the excited states produced were analyzed by field. stripping in a special magnet downstream of the foil. The foil thicknesses were independently determined. The H-0 atoms emerging in excited states with n>2 can be stripped to protons in fields of up to 1.3 T The yield of excited states as a function of foil thickness and the cross sections for the various interactions are presented. The cross-section ratio of double to single ionization of H- in carbon is found to be (1.8+/-0.9)%.

Recently broadly tunable, coherent VUV radiation down to 111 nm has become available. An experiment is underway using a VUV light source capable of a few {mu}J per 10 ns pulse to study the spectrum of H in the region of 113 nm. The photon energy of the VUV can be easily tuned and may determine whether the shape resonance has a Fano profile as predicted. A non-relativistic (35 keV), low-emittance H{sup {minus}} beam from the GTA injector at LANL will be used as the ion source. The electrons ejected from the intersecting beams will be analyzed using an electron time-of-flight (TOF) spectrometer. A narrow VUV linewidth allows the width of the Feshbach and shape resonances to be measured to high resolution ({approximately}1 cm{sup {minus}1}). The branching ratios of neutral hydrogen states H(1s), H(2s), H(2p) for each resonance will be calculated by measuring the TOF of the ejected electrons. Of particular interest is the differential of the H(2s) and H(2p) branching ratios, since the product states are nearly degenerate in energy. Simulation of TOF data allows determination of both energy and the angular distribution of the electrons, thus permitting the authors to distinguish all three product states.

The lifetime of 800-MeV H- ions against electron detachment in a static electric field was measured over a range of eight orders of magnitude in experiments at the High Resolution Atomic Beam Facility of the Los Alamos Meson Physics Facility. The ions traversed a linear gradient magnetic field of 1.3-T peak strength resulting in a 6-MV/cm peak rest-frame electric field capable of stripping a large fraction of H- ions. The unstripped H- ions, neutral H-0 atoms, and protons were detected 5.5 m from the magnet. This spectrum was analyzed to determine the lifetime of the H- ion versus electric-field strength and the results were compared with previous studies. Three parametrizations of the lifetime formula based on an existing theory were used to calculate the stripping probability. The data were fit to the lifetime formula and good agreement with theoretical predictions was found. Finally, a possible experiment for observing excited states of H- is briefly discussed.

The use of laser spectroscopy for the determination of momentum spread and energy of a relativistic H− beam is discussed, and the results are presented of a successful attempt to reduce the momentum spread δpp by a factor of 5 from its initial value of approximately 5 × 10−4.

Studies of the production of H° its various states by the passage of relativistic H− ions through thin foils are under way at the linear accelerator at Los Alamos. Laser excitation and selective field ionization are used to isolate specific states. We present evidence that the excitation of Rydberg states by a foil at energies up to 800 meV proceeds in a stepwise manner.

Studies of the production of H{sup 0} its various states by the passage of relativistic H{sup {minus}} ions through thin foils are under way at the linear accelerator at Los Alamos. Laser excitation and selective field ionization are used to isolate specific states. We present evidence that the excitation of Rydberg states by a foil at energies up to 800 meV proceeds in a stepwise manner.