Nuclear spin effect on recombination of H3⁺ ions with electrons at 77 K.

Utilizing different ratios of para to ortho H2 in normal and para enriched hydrogen, we varied the population of para-H3⁺ in an H3⁺ dominated plasma at 77 K. Absorption spectroscopy was used to measure the densities of the two lowest rotational states of H3⁺. Monitoring plasma decays at different populations of para-H3⁺ allowed us to determine the rate coefficients for binary recombination of para-H3⁺ and ortho-H3⁺ ions: (p)α(bin)(77 K) = (1.9 ± 0.4) × 10⁻7 cm³ s⁻¹ and (o)α(bin)(77 K) = (0.2 ± 0.2) × 10⁻7 cm³ s⁻¹.

Binary recombination of para- and ortho-H3+ with electrons at low temperatures.

Results of an experimental study of binary recombination of para- and ortho-H(3)(+) ions with electrons are presented. Near-infrared cavity-ring-down absorption spectroscopy was used to probe the lowest rotational states of H(3)(+) ions in the temperature range of 77-200 K in an H(3)(+)-dominated afterglow plasma. By changing the para/ortho abundance ratio, we were able to obtain the binary recombination rate coefficients for pure and para-H(3)(+) and ortho-H(3)(+). The results are in good agreement with previous theoretical predictions.

A cryogenic electrostatic trap for long-time storage of keV ion beams.

We report on the realization and operation of a fast ion beam trap of the linear electrostatic type employing liquid helium cooling to reach extremely low blackbody radiation temperature and residual gas density and, hence, long storage times of more than 5 min which are unprecedented for keV ion beams. Inside a beam pipe that can be cooled to temperatures <15 K, with 1.8 K reached in some locations, an ion beam pulse can be stored at kinetic energies of 2-20 keV between two electrostatic mirrors. Along with an overview of the cryogenic trap design, we present a measurement of the residual gas density inside the trap resulting in only 2 x 10(3) cm(-3), which for a room temperature environment corresponds to a pressure in the 10(-14) mbar range. The device, called the cryogenic trap for fast ion beams, is now being used to investigate molecules and clusters at low temperatures, but has also served as a design prototype for the cryogenic heavy-ion storage ring currently under construction at the Max-Planck Institute for Nuclear Physics.