Spectroscopic Characterization of Highly Excited Neutral Chromium Tricarbonyl.

Spectroscopic characterization of highly excited neutral transition-metal complexes is important for understanding the multifaceted reaction mechanisms between metals and ligands. In this work, the reactions of neutral chromium atoms with carbon monoxide were probed by size-specific infrared spectroscopy. Interestingly, Cr(CO) 3 was found to have an unprecedented 7 A 2 ″ septet excited state rather than the singlet ground state. A combination of experiment and theory shows that the gas-phase formation of this highly excited Cr(CO) 3 is facile both thermodynamically and kinetically. Electronic structure and bonding analyses indicate that the valence electrons of Cr atoms in the septet Cr(CO) 3 are in a relatively stable configuration, which facilitate the highly excited structure and the planar geometric shape ( D 3 h symmetry). The observed septet Cr(CO) 3 affords a paradigm for exploring the structure, properties, and formation mechanism of a large variety of excited neutral compounds.