Optical spectroscopy of high-Ln=10 Rydberg states of nitrogen

A Doppler-tuned ${\mathrm{CO}}_2$ laser was used to excite n=10 to n=27 Rydberg-Rydberg transitions in a fast beam of atomic nitrogen. The fine structure of n=10, L=3–8 Rydberg levels is partially resolved in the spectrum, giving experimental information about nitrogen Rydberg levels with L≳4. The observed fine structure is well described by an effective potential whose empirical coefficients are adjusted to fit the data, giving estimates of the quadrupole moment and dipole polarizabilities of ${\mathrm{N}}^{+}$. For the highest-L n=27 levels studied, the spectrum shows evidence of a transition to a new coupling regime where the ${\mathrm{N}}^{+}$ hyperfine structure is larger than the Rydberg fine structure. © 1996 The American Physical Society.