Anomalous light-induced drift of lithium atoms in a mixture of noble gases

This paper is a theoretical study of the spectral features of the velocity of light-induced drift (LID) of lithium atoms (Li-7 and Li-6) in a binary m ixture of noble gases: Ne + Ar, Ne + Kr, and Ne + Xe. The spectral shape of the LID signal is predicted to depend strongly on the fraction xi of neon in the buffer mixture in the range xi approximate to 0.8-0.9 (xi=N-Ne/N-b, where N-Ne is the neon concentration, and N-b is the total concentration of the buffer particles). When the velocity of anomalous LID is treated as a function of the radiation frequency, it is found to have one, three, five, or seven zeros and to differ substantially from the dispersion-curve-like b ehavior with one zero predicted by the standard LID theory with velocity-in dependent transport collision rates. The reason for these additional zeros of the drift velocity is the alternating-sign dependence on the lithium-ato m velocity of the relative difference of transport rates of collisions betw een buffer particles and excited and unexcited atoms. What is also establis hed is that the anomalous LID of lithium atoms can be observed at almost al l temperatures, depending on the value of xi. At a fixed temperature, anoma lous LID can be observed only in a narrow range of values of the fraction o f neon in the buffer mixture, Delta xi approximate to 0.02. The results mak e possible highly precise testing in the LID experiments of the interatomic potentials used in calculations of the velocity spectrum of anomalous LID. (C) 1999 American Institute of Physics. [S1063-7761(99)00711-8].