The near infrared 2P3/2(abJ) ¬ X 2S+(bbS) band systems of TiCo and ZrCo

Resonant two-photon ionization spectroscopy has been used to provide the first rotationally resolved work involving multiply-bonded mixed early-late transition metal dimers. The mixed metal dimers TiCo and ZrCo are shown to possess 2S+ ground states, in agreement with a previous matrix isolation ESR (electron spin resonance) study on TiCo. Two previously observed vibronic bands in ZrCo are rotationally resolved, as is one of several newly discovered vibronic transitions in TiCo. Groundstate rotational constants for 48Ti59Co and 90Zr59Co are measured to be Bʹʹ0 = 0.186 15 (8) cm-1 and Bʹʹ0 = 0.119 78(5) cm-1, giving rʹʹ0 = 1.8508(4) and rʹʹ0 = 1.9883(4) ?, respectively. In both molecules the ground state conforms to the Hundʹs case (bb S) coupling scheme, with Fermi contact interactions between the unpaired s electron and the 59Co (I = 7/2) nucleus of bʹʹF = 0.0468(7) cm-1 for 48Ti59Co and bʹʹF = 0.0549(6) cm-1 for 90Zr59Co. These values indicate that the unpaired electron occupies a s orbital having 32% and 37% Co 4s character in TiCo and ZrCo, respectively. All three of the rotationally resolved bands are 2P3/2 ¬ X2S+ transitions. For 90Zr59Co the 0 ¬ 0 and 1 ¬ 0 bands were resolved at n0 = 10 496.1452(28) and 10 884.3794(25) cm-1, giving Bʹ0 = 0.119 82(6) and Bʹ1 = 0.121 44(5) cm-1. For 48Ti59Co the rotationally resolved band has n0 = 9873.8342(19) cm-1 and Bʹ = 0.191 07(6) cm-1. These results are discussed in the context of prior work on these and related molecules.