Electron-impact excitation of helium: Cross sections, n, and l distributions of high Rydberg states

Journal Article · Fri Jul 01 00:00:00 EDT 1977 · Phys. Rev., A; (United States)

DOI:https://doi.org/10.1103/PhysRevA.16.48· OSTI ID:7097766

Schiavone, J A; Donohue, D E; Herrick, D R; Freund, R S

Helium atoms in highly excited Rydberg states are produced by electron impact and are detected by electric field ionization. The principal quantum numbers n are determined to lie in the range 20 < or approx. = n < or approx. = 80 by ionizing the excited He atoms in a uniform, swept electric field. The absolute excitation cross section for 100-eV incident electrons is found to be (9 +- 5) x 10/sup -17//n/sup 3/ cm/sup 2/. This expression predicts a value for n = 4 that agrees with the optically measured n = 4 cross section. The 108-..mu..sec time of flight requires that the high Rydberg He atoms have lifetimes much longer than those calculated for low-angular-momentum (l < or = 2) states, those expected to be populated by electron impact. The proposed explanation is that the excited He atoms suffer collisions with electrons and/or ground-state He atoms causing longer-lived higher l states to be populated. This explanation is supported by measurements of signal as a function of incident-electron energy, electron current, and He pressure. The cross section for l-changing collisions between electrons and high Rydberg helium atoms is given by sigma/sup e//sub ..delta..//sub 1// approx. = 5 x 10/sup -(15 +- 0.3)/ ln(100En/sup 2/) n/sup 4//E cm/sup 2/.

• Research Organization: Bell Laboratories, Murray Hill, New Jersey 07974
• OSTI ID: 7097766
• Journal Information: Phys. Rev., A; (United States), Vol. 16:1
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ELECTRON-ATOM COLLISIONS
EXCITATION
HELIUM
CROSS SECTIONS
EXCITED STATES
LIFETIME
ORBITAL ANGULAR MOMENTUM
QUANTUM NUMBERS
REACTION KINETICS
ANGULAR MOMENTUM
ATOM COLLISIONS
COLLISIONS
CRYOGENIC FLUIDS
ELECTRON COLLISIONS
ELEMENTS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
FLUIDS
KINETICS
NONMETALS
RARE GASES
640304* - Atomic
Molecular &amp; Chemical Physics- Collision Phenomena