Knowledge Bank

Although there is no obvious diffuseness or breaking-off in the rotational structure of observed band systems, the energies of the observed rotational levels and a comparison of the $d1\Sigma +-c1II$ bands with possible Franck-Condon factors suggest that the $c1II$ state of NH predissociates by rotation. The limiting curves of dissociation for NH and ND provide evidence for a maximum in the rotationless potential curve, at an internuclear distance of $1.90\backslash AA$. If this is so, then $D0(MHc1II)$ is less than $4300cm-1$. Such an interpretation is consistent with the $X3\Sigma -$ ground state dissociation energy of $3.21eV(25900cm-1)$ found by Seal and Gaydon (1966) and recent calculations of the energy separation of the singlet and triplet states.