LEVEL 8.2
Three Level input files were used: 23Na-1H__Rivlin__Level_X-X.inp was used for ground state transitions(X-X), 23Na-1H__Rivlin__Level_A-A.inp was used for excited state transitions(A-A), and 23Na-1H__Rivlin__Level_A-X.inp was used for excited-ground transitions(A-X).
Potential Energy Curves (PEC) from Walji et al. (2015) were then used as input to the program LEVEL version 8.2 (Le Roy 2007) to produce accurate nuclear motion energy levels, wavefunctions and hence transition intensities. Dipoles were computed as expectation value of a multireference configuration interaction (MRCI) calculation using a full valence complete active space model, which distributes the two outer electrons among five orbitals, and the aug-cc-pwCV5Z basis set.