HUND'S COUPLING CASES AND TETRAHEDRAL SPLITTINGS IN ROTATIONAL LEVELS OF ELECTRONIC $^{2}F_{2}$ STATES IN $ND_{4}$
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Date
1983
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Ohio State University
Abstract
The Sch\""{u}ler band of the Rydberg radical $ND_{4}$ lying near $14 800 cm^{-1}$ is presumed to arise from the $(5a)^{2}A_{1} - (3p)^{2}F_{2}$ transition, where identification of the lower state rests in part uponthe isotope-independent $6 cm^{-1}$ spin splitting observed between a pair of heads in emission spectra photographed for both $NH_{4}$ (diffuse) and $ND_{4}$ (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 $CH_{4}$ 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 $D_{2d}$ 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.
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Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada; Molecular Spectroscopy Division, National Bureau of Standards