The theory of impact broadening of the isolated spectral lines of the Rydberg atomic series perturbed by neutral particles is developed within the framework of the impulse approximation. The analysis of the broadening process is based on the consideration of the inelastic nl to n' transitions between highly excited states of the Rydberg atom. The role of the potential and resonance scattering of the quasifree electron by a perturbing particle in the impact broadening of the Rydberg nl levels is investigated. It is shown that the general expressions for the broadening cross sections presented in this paper contain the results of asymptotic Alekseev and Sobel'man theory (1965) as special cases. Both elastic and inelastic scattering contributions of the perturber by the parent core of Rydberg atom to the broadening cross sections are also considered within the framework of the 'shake' model. The results obtained are used for a quantitative explanation of experimental data on the broadening of Rydberg atomic levels perturbed by alkali-metal atoms. The energies and widths of the 3 P resonances on the quasidiscrete levels of the negative K - and Rb - ions are determined.
The impact broadening rates of Rb ns Rydberg levels by He, Ar and Xe atoms measured by Weber and Niemax (1982) and by Ne and Kr atoms observed by Thompson et al. (1987) are quantitatively explained over the whole range of the principal quantum number n. As Rb ns Rydberg levels (quantum defect delta =3.13) are very close to the nearly hydrogenic high l levels, inelastic collisions make as important a contribution to the broadening rates as elastic collisions. The authors derive the cross sections for the elastic and inelastic using a combination of Kaulakys' (1984) and Lebedev and Marchenko's (1985) impact theories. Good agreement between the theoretical and experimental broadening rates is achieved over the whole range of n.
We have made comprehensive measurements of the noble-gas-induced (He, Ne, Ar, Kr, and Xe) broadening cross sections of the Na $3S\ensuremath{-}nS$ ($3S\ensuremath{-}nD$) transitions, from
n=5to38 (
n=4to40). These measurements were made using the trilevel-echo technique and are an extension and refinement of our earlier work. We find that the cross sections increase as the geometric cross section at low values of
n, and then, at a value of
n which depends on the particular noble gas, begin to decrease and eventually reach an asymptotic value at high
n. The broadening cross sections for the nearly degenerate
D states are significantly larger than those for the
S states and clearly show the effect of
l-changing collisions. We also compare our measured
S-state broadening cross sections with the cross sections calculated using the theory of Omont and find good qualitative agreement.
It is shown that with use of some assumptions the cross sections for the broadening of optical lines originating from Rydberg levels can be interpreted with a simple model which takes into account the elastic and the quenching cross sections of the corresponding Rydberg states. The validity of the model is extensively discussed. Good agreement is observed in most cases between the values derived from the model and the available experimental data for the broadening and quenching cross sections of a wide set of Rb and Na Rydberg levels perturbed by noble gases. It is clearly demonstrated that inelastic processes can significantly affect the broadening cross sections even for large values of the principal quantum number
n.
A theoretical model for the collision of atoms in high Rydberg states (nl) with neutral atoms or molecules is proposed, based on the assumption that the electron-perturber interaction is of very short range compared with the mean radius of the Rydberg atom. A semiclassical method is used to derive a compact expression for the collision probability. The calculations need total cross sections for the scattering of a free and low-energy electron by the perturber. The model is applied to the calculation of a free and low-energy electron by the perturber. The model is applied to the calculation of cross sections for the quenching of n 2 D or n 2 F Rydberg states of Na and Rb by rare-gas atoms of N 2 . On the whole the calculated cross sections are in reasonable agreement with experimental data for n>10 approximately. The model and the results of the calculations are discussed and compared with other theoretical works.
It is shown for the first time that the theoretical model for the collisional l mixing in atomic intermediate Rydberg states proposed by de Prunele and Pascale (1979) can also be applied to J mixing in the intermediate Rydberg states with higher quantum defect delta l values and not only to collisions with noble gas atoms and N 2 but also with ground-state alkali atoms. The model is applied to the calculation of J-mixing cross sections of nD Rydberg states of Rb (n=7-10) and Cs (n=9-23) perturbed by noble gas atoms and N 2 . J mixing in Cs(nD)-Cs(6S 1 2/)(n=11-23) collisions is also considered. The agreement with the available results is rather good.