Knowledge Bank

New high resolution spectra of the $B~1/2(2\Sigma +)-X~2\Sigma +$ transitions of LaNH and LaND, near $16000cm-1$, have been obtained under jet-cooled conditions, following the reaction of laser-ablated lanthanum metal with $NH3$ and $ND3$. Rotational analyses have given the ground state structure as $r0(La-N)=1.932072(11)\backslash AA;r0(N-H)=1.01357(31)\backslash AA$. Strong vibronic and spin-orbit coupling is found to occur between the $B~$ state and the $A~2\Pi$ state near $12600cm-1$. This causes various interesting effects: the hyperfine line strengths in the $B~-X~$ transition are unusual, showing that, though it is nominally $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma -2\Sigma$, both parallel and perpendicular transition moments are present; also the bending frequency of the $B~$ state is raised by $150cm-1$ compared to the ground state, while its vibrational structure shows large l-dependent ``spin-vibration'' splittings which can be represented by $Asvl$, where $Asv\simeq -14cm-1$.