Ionization of low-Rydberg-state He atoms by polar molecules. II. Large rotational-energy transfers and absolute values of the cross sections
The absolute values of cross sections for the collisional ionization of low-Rydberg-state He atoms in the n /sup 1/P state (n = 14) by the polar molecules NH/sub 3/, SO/sub 2/, and acetone (C/sub 3/H/sub 6/O) are measured in a crossed-beam experiment at thermal kinetic energies, for a well-defined relative velocity. Simultaneous Penning ionization of NH/sub 3/ by metastable He(2/sup 3/S) atoms is carried out in situ for calibration. Experimental collisional-ionization cross sections sigma/sub i//sup expt/(v/sub r/), for v/sub r/ = 2400 m/s, as large as 9 x 10/sup -15/ cm/sup 2/ for NH/sub 3/, 5 x 10/sup -15/ cm/sup 2/ for SO/sub 2/, and 10/sup -14/ cm/sup 2/ for C/sub 3/H/sub 6/O at 300 K, are obtained. These large cross sections cannot be explained by the ''free-electron model'' usually used in Rydberg-atom--molecule collisions: This model predicts no ionization of Rydberg levels as low as n = 14, since the amount of energy available from rotational ..delta..J = -1 ..delta..K = 0 relaxation transitions of the molecule is insufficient. Our hypothesis of large /vert bar/..delta..J/vert bar/ rotational transitions is strengthened by comparison of the results for the three studied molecules.
- Research Organization:
- Service de Physique des Atomes et des Surfaces, Centre d'Etudes Nucleaires de Saclay, 91191 Gif-sur-Yvette Cedex, France
- OSTI ID:
- 6682335
- Journal Information:
- Phys. Rev. A; (United States), Journal Name: Phys. Rev. A; (United States) Vol. 38:9; ISSN PLRAA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ACETONE
AMMONIA
ATOM COLLISIONS
ATOM-MOLECULE COLLISIONS
BEAMS
CALIBRATION
COLLIDING BEAMS
COLLISIONS
CROSS SECTIONS
ELEMENTS
ENERGY LEVELS
ENERGY TRANSFER
EXCITED STATES
FLUIDS
GASES
HELIUM
HYDRIDES
HYDROGEN COMPOUNDS
IONIZATION
KETONES
METASTABLE STATES
MOLECULE COLLISIONS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
ORGANIC COMPOUNDS
PENNING EFFECT
POLAR COMPOUNDS
RARE GASES
ROTATIONAL STATES
RYDBERG STATES