Vibronic spectroscopy of unsaturated transition metal complexes: CrC?H, CrCh?, and NiCH?

Vibronically resolved resonant two-photon ionization and dispersed fluorescence spectra of the organometallic radicals CrC2H, CrCH3 , and NiCH3 are reported in the visible and near-infrared wavelength regions. For CrC2H, a complicated vibronic spectrum is found in the 11 100?13 300 cm-1 region, with a prominent vibrational progression having ?'e=426.52?0.84 cm-1, ?'ex'e 50.74?0.13 cm-1. Dispersed fluorescence reveals a v"=1 level of the ground state with ?G"1/2=470?20 m-1. These vibrational frequencies undoubtedly pertain to the Cr?C2H stretching mode. It is suggested that the spectrum corresponds to the A? 6?1+ ? X? 6?+ band system, with the CrC2H molecule being linear in both the ground and the excited state. The related CrCH3 molecule displays a vibronic spectrum in the 11 500?14 000 cm-1 region. The upper state of this system displays six sub-bands that are too closely spaced to be vibrational structure, but too widely separated to be K structure. It is suggested that the observed spectrum is a 6E?X? 6A1 band system, analogous to the well-known B 6II?X 6?+ band systems of CrF and CrCl. The ground state Cr?CH3 vibration is characterized by ?'e=52?17 cm-1 and ?'ex'e=7.9?6 cm-1. The spectrum of NiCH3 lies in the 16 100?17 400 cm-1 range and has ?"e=455.3?0.1 cm21 and ?"ex"e=6.60 ?0.03 cm-1. Dispersed fluorescence studies provide ground state vibrational constants of ?"e=565.8?1.6 cm-1 and ?"ex"e+1.7?3.0 cm-1. Again, these values correspond to the Ni?CH3 stretching motion.