Pressure shift and broadening of Sr i Rydberg states in noble gases

Pressures shifts and broadenings of 5snd ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}_2$ Rydberg levels of Sr i due to noble gases have been measured by means of Doppler-free two-photon excitation and thermionic detection for a wide range of principal quantum numbers (11<n<150). High accuracy was achieved by means of an active optical-frequency standard. Our results agree well with experimental data obtained by other groups for related systems and confirm existing theories for line shifts and broadenings. Scattering lengths for the various gases extracted from the spectroscopic results for high n show satisfactory agreement with corresponding data from low-energy electron-scattering experiments. With the exception of argon, the same is true for dipole polarizabilities when compared with known values. For neon we find evidence for nonlinear shifts at high principal quantum numbers (n≥100).