???X??+ band systems of jet-cooled ScCo and YCo

Rotationally resolved resonant two-photon ionization (R2PI) spectra of ScCo and YCo are reported. The measured spectra reveal that these molecules possess ground electronic states of 1?+ symmetry, as previously found in the isoelectronic Cr2 and CrMo molecules. The ground state rotational constants for ScCo and YCo are B0"=0.201 31(22) cm?1 and B0"=0.120 96(10) cm?1, corresponding to ground state bond lengths of r0"=1.812 1(10) ? and r0"=1.983 0(8) ?, respectively. A single electronic band system, assigned as a 1II?X 1?+ transition, has been identified in both molecules. In ScCo, the 1II state is characterized by T0=15 428.8, ?e'=246.7, and ?e'xe'=0.73 cm?1. In YCo, the 1II state has T0=13 951.3, ?e'=231.3, and ?e'xe'=2.27 cm?1. For YCo, hot bands originating from levels up to v"=3 are observed, allowing the ground state vibrational constants ?e"=369.8, ?e"xe" =1.47, and ?G"1/2=365.7 cm?1 to be deduced. The bond energy of ScCo has been measured as 2.45 eV from the onset of predissociation in a congested vibronic spectrum. A comparison of the chemical bonding in these molecules to related molecules is presented.