Knowledge Bank

The Sch""{u}ler band of the Rydberg radical $ND4$ lying near $14800cm-1$ is presumed to arise from the $(5a)2A1-(3p)2F2$ transition, where identification of the lower state rests in part uponthe isotope-independent $6cm-1$ spin splitting observed between a pair of heads in emission spectra photographed for both $NH4$ (diffuse) and $ND4$ (sharper). Any attempt at a detailed rotational analysis of this spectrum requires a knowledge of rotational levels in a tetrahedral molecule exhibiting both spin-orbit interaction and tetrahedral splittings. Such rotational levels can be determined relatively easily by combining with suitable modifications the usual $CH4$ vibration-rotation Hamiltonian and the usual NO spin-orbit and spin-rotation Hamiltonian. The principal qualitative effects of these interactions on the rotational levels will be described and some examples of stick spectra calculated from a computer program with appropriate matrix elements in a $D2d$ basis set will be shown. Unfortunately, even with this program, the Sch""{u}ler band has to date eluded unambiguous assignment, and the extreme overlapping of lines in the region of the two heads may ultimately preclude more than a qualitative theoretical fit of the observed data.