Molecular beam scattering studies of orbiting resonances and the determination of van der Waals potentials for H--Ne, Ar, Kr, and Xe and for H/sub 2/--Ar, Kr, and Xe

Journal Article · Sun Jul 15 04:00:00 EDT 1979 · J. Chem. Phys.; (United States)

OSTI ID:6095861

Toennies, J P; Welz, W; Wolf, G

The velocity dependence of the integral cross sections for the scattering of H atoms and normal-H/sub 2/ molecules from the rare gases has been measured for primary beam velocities from 300 m/sec (E/sub c.m./=0.5 meV) to about 3000 m/sec (E/sub c.m./=100 meV). Three distinct resonance maxima were observed in each of the systems H--Xe, H--Kr, H/sub 2/--Kr, and H/sub 2/--Ar. At least one resonance maximum was found in H/sub 2/--Xe and H--Ar, while H--Ne showed no maxima. The H/sub 2/--Ar cross sections were also measured with a cold beam of pure para-H/sub 2/ consisting entirely of spherically symmetric j=0 molecules. No noticeable difference was found when compared to the n-H/sub 2/ cross sections indicating that the observed resonances depend only on the spherical symmetric potential. Extensive comparisons with spherical symmetric model potentials showed that all the observed resonances are due to temporary capture in the well of the effective potential. This phenomenon is usually referred to as ''orbiting.'' The energetic location of the observed orbiting resonances and glory maxima were found to be very sensitive to the potential shapes and parameters. Only models which included at least two terms in the long range dispersion potential C/sub 6//R/sup 6/ and C/sub 8//C/sup 8/ could describe the data in a satisfactory way. For H--Ar the data are in very good agreement with the experimental potential of Bassi et al. and in reasonable agreement with the ab initio MCSF potential of Wagner et al. For H/sub 2/--Ar, --Kr, --Xe good agreement is found with the potentials recently determined from infrared spectra by Le Roy and co-workers. For all the other systems new best fit potentials have been determined. The best fit values of epsilon and R/sub m/ are for H--Ne: 1.90 meV and 3.15 A; H--Ar: 4.16 meV and 3.62 A; H--Kr: 5.90 meV and 3.57 A; H--Xe: 7.08 meV and 3.82 A; H/sub 2/--Ar: 6.30 meV and 3.57 A; H/sub 2/--Kr: 7.19 meV and 3.72 A, and H/sub 2/--Xe: 8.10 meV and 3.92 A.

• Research Organization: Max-Planck-Institut fuer Stroemungsforschung Boettinger Str. 4--8, 3400 Goettingen, Federal Republic of Germany
• OSTI ID: 6095861
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 71:2; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ARGON
ATOM COLLISIONS
ATOM-ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
BEAMS
COLLISIONS
CROSS SECTIONS
CRYOGENIC FLUIDS
ELEMENTS
FLUIDS
HYDROGEN
KRYPTON
MOLECULAR BEAMS
MOLECULE COLLISIONS
NEON
NONMETALS
RARE GASES
RESONANCE
XENON