Millimeter-wave spectrum of the aluminum monosulfide radical AlS (X 2Σ+)

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Abstract
The millimeter‐wave rotational spectrum of the aluminum monosulfide radical AlS in its ground electronic state X 2Σ+ was observed with a source‐modulated spectrometer combined with a high‐temperature cell. The AlS radical was generated by a reaction between aluminum vapor and carbonyl sulfide. Eight rotational transitions, lowest N=4–3 and highest N=17–16, were measured in the frequency region of 67–284 GHz and 75 observed fine and hyperfine components were analyzed by least‐squares methods. The analysis yielded the rotational and centrifugal distortion constants as well as the spin–rotation coupling constant with its centrifugal term and the hyperfine coupling constants including the nuclear quadrupole coupling term for the aluminum nucleus. The spin density of the unpaired electron was calculated by comparing the derived magnetic hyperfine coupling constants with the corresponding hyperfine coupling constants of the free aluminum atom. Applicability of this spin density calculation is discussed.