John C. Mester

Comment on ‘‘The weakest bond: Experimental observation of helium dimer’’ [J. Chem. Phys. 98, 3564 (1993)]

Recently, Luo et al. reported indirect evidence for the formation of dimers in a supersonic expansion of helium. They interpreted their data as confirmation of the existence of a bound state of 4He–4He with a binding energy of order 1 mK. We show that their data are actually consistent with the formation of helium trimers and not dimers. The two control experiments that they performed do not provide any evidence for discarding this alternative hypothesis.

Measurements of giant cross sections in low temperature4He-4He scattering

We have studied binary collisions of ground state4He atoms at temperatures from 340 mK to 430 mK using an atomic beam apparatus built in a dilution refrigerator. Very large s-wave scattering cross sections between 120Å2–250 Å2 have been observed. These are due to the proximity of a dimer state near the continuum of the interaction potential. Results show that the latest potential of Aziz et al. needs modification.

Low temperature scattering of helium and hydrogen

Abstract We investigate two body interactions of 4 He and atomic H in the low energy limit. H- 4 He and 4 He- 4 He integral scattering cross sections are determined from the attenuation of beams of 4 He atoms through target gases of H and 4 He at temperatures below 400 mK. We analyze the results within the Quantum Corresponding States framework. Implications for scattering isotopic species of He and H are discussed.

Observation of giant scattering cross sections in4He

Abstract We have measured absolute integral elastic cross sections for ground state4He-4He scattering at collision energies from 1.35K to 0.5K using a novel atomic beam apparatus built into a dilution refrigerator. Scattering is almost pure s-wave. The effective or average integral cross section ranges from 200A˚2 to 1000A˚2 as collision energy is reduced in our experiment.

Surface recombination in spin-polarized hydrogen: Where does the heat go?

Abstract The recombination of two hydrogen atoms to the molecular state is the most energetic chemical reaction per unit mass known. The heat released from such recombination has so far made it impossible to cool a gas of spin-polarized hydrogen (H↓) into the regime of quantum degeneracy. To better understand this problem, we have studied 2nd-order surface recombination in an absorbed gas of H↓ from the standpoint of heat distribution. We have measured an upper bound on the fraction F of the total recombination energy which is deposited locally on the surface at the point of recombination.