Density effect on newly identified high-nRydberg series of krypton by a resonantly enhanced multiphoton ionization method

Four even-parity atomic series corresponding to transitions from the 5s'[1/2]₁⁰ level to the (²{P}3/2⁰$)np,nf levels of krypton have been observed, using a resonant multistep two-color photoionization method. The energies of 7p'[3/2${]}₁$, 7p'[1/2${]}₁$, 7p'[3/2${]}₂$, 7p'[1/2${]}₀$, np[1/2${]}₁$, np[3/2${]}₂$, np[1/2${]}₀$, and nf[3/2${]}1,2$ levels are determined and the principal quantum numbers are calculated for n up to 45, 32, 49, and 44, respectively. Strong spectral irregularities in intensity and position are analyzed with the help of Lu-Fano diagrams and multichannel quantum defect theory in the case of the most intense 5s'[1/2]₁⁰{→}np[1/2]₀ series. Density shift rates have the constant value of -7.4(2)×{}10^-19 cm^-1/cm^-3 for the s'{→}p high-n series members, outside regions where irregularities are observed, in agreement with existing doped krypton data. A close agreement with the Fermi model is obtained for these high-n members of regular series. Departure from this agreement is found for members whose excited levels are mixed with 7p' states. A clear relationship between the p{~}p' admixture and shift rate decrease, in regions of irregularities, is demonstrated.