15min:

O. KRECHKIVSKA, M. D. MORSE, Department of Chemistry, University of Utah, Salt Lake City, Utah, 84112.

The optical spectrum of diatomic OsC has been investigated for the first time, with transitions recorded in the range from 17,390 to 22,990 cm^-1. The ground state was found to be X³ ₃, deriving from the 4 ³16 ¹ electronic configuration. Six bands were rotationally resolved and analyzed to obtain ground and excited state rotational constants and bond lengths. Spectra for six OsC isotopomers, ¹⁹²Os¹²C \left(40.3%\right), ¹⁹⁰Os¹²C \left(26%\right), ¹⁸⁹Os¹²C \left(16%\right), ¹⁸⁸Os¹²C \left(13.1%\right), ¹⁸⁷Os¹²C \left(1.9%\right) and ¹⁸⁶Os¹²C \left(1.6%\right), were recorded and rotationally analyzed. Four bands were found to originate from the X³ ₃ ground state, giving B₀^''=0.533492(33) cm^-1 and r₀^''=1.67267(5) \mathringA for the ¹⁹²Os¹²C isotopomer (1 error limits); two of these the 0-0 \left[19.1\right]2 X³ ₃ and 1-0 \left[19.1\right]2 X³ ₃ bands, form a vibrational progression with G^'_1/2=953.019 cm^-1. The remaining two bands were identified as originating from an ^''=0 level that remains populated in the supersonic expansion. We believe that this level corresponds to the low-lying A ^{3 -}₀₊ state, which derives from the 4 ²16 ² electronic configuration. The OsC molecule differs from the isovalent RuC molecule in having an X³ ₃ ground state, rather than the X^{1 +} ground state found in RuC. This difference in electronic structure is due to the relativistic stabilization of the 6s orbital in Os, an effect which favors occupation of the 6s-like 16 orbital. The relativistic stabilization also lowers the energy of the 4 ²16 ², ^{3 -} term, allowing this term to remain populated in the supersonically cooled molecular beam.