A comprehensive set of transition probabilities and radiative lifetimes of Rydberg states of alkali atoms (for Na, K, Cs, n 30; and for Rb, n 6 50) is obtained by using a simple, exactly solvable potential model for atoms. The results agree well with the available experimental values and other theoretical ones. Scaling relations for evaluating transition probabilities and lifetimes of high Rydberg states are also discussed. The well known (n*)-' scaling law of the transition probabilities A,,,,. with n'= n >> 1 is generally valid; however, we also find deviations from this law for some d-, p and f-* d transitions for Rb. A third-power polynomial is found to be better than the currently used exponential scaling law in predicting the lifetimes of even higher excited states.

The analytical wavefunctions and oscillator strengths between highly excited states of alkali atoms over a wide range of principal quantum number n ( 1 0 s n 6 4 0 , and for Na, n S 60) are calculated straightforwardly by using a simple, one-parameter, exactly soluble model for atoms. The valence electron of the atom is assumed to be in a potential of the following form:ff' where a', p', y' are the parameters to be determined and S is the ionicity. Analytical solutions can be obtained by solving the Schrodinger equation containing V ( r ) . The parameters in the potential and the wavefunction, which are dependent on the atomic states, can be expressed in terms of a single parameter, the quantum defect. The wavefunctions of the alkali atoms were obtained, and their general behaviour and the number of nodes agree with Hartree-Fock-Slater theory. This model is well suited for studying the behaviour of atoms that are mainly dependent of the outer region of high Rydberg states. The oscillator strengths calculated by this model for transitions between high Rydberg states of the alkali atoms agree well with those obtained by the Coulomb approximation, and the calculated scalar polarisabilities agree well with the experimental values. A scaling relation is found to be reliable for evaluating the oscillator strengths between high Rydberg states with n = 100. The variation of oscillator strengths with respect to n and Z are also presented.

On the basis of impulse approximate merhod, a kind of analytical wavefunctions based on a potential model was used to calculate the l mixing cross section of thermal collision of Ryd-berg states of atomic Rb with rare gas (He, Ne). The results were compared with the experimental results and other theoretical values. These results show that there exists a kind of scaling law for the l mixing cross section of Rydberg alkali atoms.

Cs vapour in , Ar, Kr, Ne, He and Xe buffer gases was optically pumped with a diode laser in a magnetic field of 1.516 T. The relaxation of the population imbalance in the hyperfine Zeeman sublevels of the ground state was detected with another diode laser. A phenomenological theory is presented which explains the optical transients and the time variation of the populations in the hyperfine Zeeman sublevels. Both experimental and theoretical results showed that there were relaxation transients of populations in some hyperfine Zeeman sublevels of optically pumped Cs with `anomalous' shapes. The experimental results showed that the `anomalous' relaxation depended strongly on the buffer-gas species and the buffer-gas pressure. Theoretically, it was found that the combined electron-spin - nuclear-spin transition, which is mainly induced by collisional modification , caused the `anomalous' shapes of the transients. The collisional transfer cross section for the binary collisional interactions was estimated to be . `Anomalous' relaxations of populations in the hyperfine Zeeman sublevels are discussed. The results of the calculation are in good agreement with the experimental results.

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