||The optical spectrum of diatomic OsC has been investigated by means of resonant two-photon ionization spectroscopy. Spectra for six OsC isotopomers, 192Os12C (40.3 % natural abundance), 190Os12C (26.0 %), 189Os12C (16.0 %), 188Os12C (13.1%), 187Os12C (1.9 %), and 186Os12C (1.6 %), were recorded and rotationally analyzed. The ground state was found to be X 3Δ3, deriving from the 1δ3 3σ1 electronic configuration. Four bands were found to originate from the X 3Δ3 ground state, giving B0"=0.533 492(33) cm-1 and r0O=1.672 67(5) Å for the 192Os12C isotopomer (1σ error limits). The optical spectrum of diatomic TaC has been investigated, with transitions recorded in the range from 17 850 to 20 000 cm-1. Seven bands were rotationally resolved and analyzed to obtain ground and excited state parameters, including band origins, upper and lower state rotational constants and bond lengths, Fermi contact parameter, bF, for the ground state, and lambda doubling parameters for the excited states. The ground state of TaC was found to be X2Σ+, originating from the 1σ2 2σ2 1π4 3σ1 electronic configuration, giving B0"=0.489683(83) cm-1, r0"=1.74901(15) Å, and bF"=0.13120(36) cm-1 (1σ error limits), for 181Ta12C. Diatomic ZrFe and TiFe have been spectroscopically investigated for the first time. Band origins, excited state vibrational frequencies and anharmonicities, excited state lifetimes, the ground state vibrational interval, ΔG"1/2, rotational constants and Ω values, bond lengths and rotation-vibration constants are reported for the five most abundant isotopomers of ZrFe and seven most abundant isotopomers of TiFe. The ground states of ZrFe and TiFe are assigned as nominally sextuply-bonded 1Σ+ (Ω = 0+) states deriving from the 1σ21π42σ21δ4 electronic configurations.