Resonant two-photon ionization spectroscopy of jet-cooled OsC

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). Six bands were rotationally resolved and analyzed to obtain ground and excited state rotational constants and bond lengths. Spectra for six OsC isotopomers, (OsC)-Os-192-C-12 (40.3% natural abundance), Os-190 C-12 (26.0%), (OsC)-Os-189-C-12( 16.0%), (OsC)-Os-188-C-12(13.1%), (OsC)-Os-187-C-12(1.9%), and (OsC)-Os-186-C-12(1.6%), were recorded and rotationally analyzed. The ground state was found to be X-3 Delta(3), deriving from the 4 delta(3)16 sigma(1) electronic configuration. Four bands were found to originate from the X-3 Delta(3) ground state, giving B-0"=0.533 492(33) cm-1 and r(0)" = 1.672 67(5) angstrom for the (OsC)-Os-192-C-12 isotopomer (1 sigma error limits); two of these, the 0-0[19.1]2 <- X-3 Delta(3) and 1-0[19.1]2 <- X-3 Delta(3) bands, form a vibrational progression with Delta G'(1/2) = 953.019 cm(-1). The remaining two bands were identified as originating from an Omega"=0 level that remains populated in the supersonic expansion. This level is assigned as the low-lying A (3)Sigma(-)(0+) state, which derives' from the 4 delta(2) 16 sigma(2) electronic configuration. The OsC molecule differs from the isovalent RuC molecule in having an X-3 Delta(3) ground state, rather than the X2 delta(4), (1)Sigma(+) 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 sigma orbital. The relativistic stabilization of the 16 sigma orbital also lowers the energy of the 4 delta(2)16 sigma(2), (3)Sigma(-) term, allowing this term to remain populated in the supersonically cooled molecular beam. (c) 2008 American Institute of Physics.