The Lamb-dip spectrum of the J + 1 ← J (J = 0, 1, 3-8) transitions of H13CN: The nuclear hyperfine structure due to H, 13C, and 14N

The pure rotational J + 1 ← J transitions, with J = 0, 1, 3-8, of H13CN have been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to H, 13C, and 14N. The present observations allow us to provide for the first time the spin-rotation constant of 13C and the spin-spin interaction constant S12 (between H and 13C) as well as to remarkably improve the quadrupole coupling and spin-rotation constants of 14N. In addition, a good empirical estimation of CI(H), based on ab initio calculations, has also been provided. Furthermore, our frequencies together with previous data permit to determine the most accurate ground state rotational parameters known up to now.