Energies of the 1s2nd Rydberg states for the lithium atom

- Quantum defects of 1s2nd channel for the lithium atom are calculated.
- The QDF of the 1s2nd channel is obtained by the quantum defect theory.
- The original QDF is calibrated from more accurate experimental value.
- The new QDF is used to calculate term energies of the 1s2nd Rydberg states.
- Present calculations help in performing measurements of 1s2nd Rydberg states.

In this work, energy levels and quantum defects of 1s2nd bound states and their adjacent continuum states for the lithium atom are calculated with the R-matrix theory, and then the quantum defect function of the 1s2nd channel is obtained, which vary smoothly with the energy based on the quantum defect theory. The obtained quantum defect function is calibrated from more accurate experimental value of higher Rydberg state and used to calculate quantum defects, ionization potentials and transition energies (relative to the 1s22s ground state) of 1s2nd high Rydberg states of the lithium atom. Present calculations may help in performing measurements of yet unmeasured 1s2nd Rydberg states of this system in future.