Recent absolute measurements of many helium excitation functions at low pressure and of the singlet and triplet D functions at several pressures have allowed an extension and upgrading of the multiple-state-transfer process.
Atoms excited to an n1P level are converted to a mixed singlet-triplet F state by an atomic collision. Low-lying singlet and triplet D levels are fed by the many F states thus populated.
Apparent excitation functions were computed by machine for the 33D, 43D, and 41D states and compared with the experimental excitation functions. The computed curves best match the experimental curves when it is assumed that: (a) the transfer cross section for the nth set of 1P-F states is proportional to n1 or n2, and (b) the 1F3 and 3F3 components of the mixed state are active in the transfer—cascade processes, while the 3F2, 4 states are inactive.
The energy is primarily transferred through n1P–nF sets of states with n ≤ 15.
ROBERT M. ST. JOHN and TSU-WEI NEE, "Collisional Transfer of Excitation Energy in Helium," J. Opt. Soc. Am. 55, 426-430 (1965)