62 research outputs found
Relocking of intrinsic angular momenta in collisions of diatoms with ions: Capture of H<sub>2</sub>(j=0,1) by H<sub>2</sub><sup>+</sup>
Rate coefficients for capture of H-2(j = 0,1) by H-2(+) are calculated in perturbed rotor approximation, i.e., at collision energies considerably lower than Bhc (where B denotes the rotational constant of H2). The results are compared with the results from an axially nonadiabatic channel (ANC) approach, the latter providing a very good approximation from the low-temperature Bethe-Wigner to the high temperature Langevin limit. The classical ANC approximation performs satisfactorily at temperatures above 0.1 K. At 0.1 K, the rate coefficient for j = 1 is about 25% higher than that for j = 0 while the latter is close to the Langevin rate coefficient. The Bethe-Wigner limit of the rate coefficient for j = 1 is about twice that for j = 0. The analysis of the relocking of the intrinsic angular momentum of H-2 during the course of the collision illustrates the significance of relocking in capture dynamics in general
Production of long-lived atomic vapor inside high-density buffer gas
Atomic vapor of four different paramagnetic species: gold, silver, lithium,
and rubidium, is produced and studied inside several buffer gases: helium,
nitrogen, neon, and argon. The paramagnetic atoms are injected into the buffer
gas using laser ablation. Wires with diameters 25 m, 50 m, and 100
m are used as ablation targets for gold and silver, bulk targets are used
for lithium and rubidium. The buffer gas cools and confines the ablated atoms,
slowing down their transport to the cell walls. Buffer gas temperatures between
20 K and 295 K, and densities between cm and
cm are explored. Peak paramagnetic atom densities of cm
are routinely achieved. The longest observed paramagnetic vapor density decay
times are 110 ms for silver at 20 K and 4 ms for lithium at 32 K. The
candidates for the principal paramagnetic-atom loss mechanism are impurities in
the buffer gas, dimer formation and atom loss on sputtered clusters.Comment: Some minor editorial changes and corrections, added reference
Giant Helium Dimers Produced by Photoassociation of Ultracold Metastable Atoms
We produce giant helium dimers by photoassociation of metastable helium atoms
in a magnetically trapped, ultracold cloud. The photoassociation laser is
detuned red of the atomic line and produces strong heating
of the sample when resonant with molecular bound states. The temperature of the
cloud serves as an indicator of the molecular spectrum. We report good
agreement between our spectroscopic measurements and our calculations of the
five bound states belonging to a purely long-range potential well.
These previously unobserved states have classical inner turning points of about
150 and outer turning points as large as 1150 .Comment: 4 pages, 4 figure
Correlation diagrams in collisions of three identical particles
We discuss collision of three identical particles and derive scattering
selection rules from initial to final states of the particles. We use either
laboratory-frame, hyperspherical, or Jacobian coordinates depending on which
one is best suited to describe three different configurations of the particles:
(1) three free particles, (2) a quasi-bound trimer, or (3) a dimer and a free
particle. We summarize quantum numbers conserved during the collision as well
as quantum numbers that are appropriate for a given configuration but may
change during the scattering process. The total symmetry of the system depends
on these quantum numbers. Based on the selection rules, we construct
correlation diagrams between different configurations before and after a
collision. In particular, we describe a possible recombination of the system
into one free particle and a dimer, which can be used, for example, to identify
possible decay products of quasi-stationary three-body statesComment: 14 pages,4 figure
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