Formation of Cr atoms in the 5 μm multiphoton decomposition of Cr(CO)6 Original Research Article

Bare chromium atom formation in the infrared multiphoton decomposition (IR MPD) of gas-phase Cr(CO)6 with second harmonic radiation (∼ 5 μm) of a TEA CO2 laser is reported. Cr atoms in the ground state a7S3 have been detected by time-resolved laser induced fluorescence. Two regimes for the Cr atom formation have been observed. One is pressure-independent and fast, proceeding during the infrared laser pulse, and the other is pressure-dependent and slow, occurring due to collisions of some molecular photofragments with the buffer gas Ar. The bimolecular rate constant of the latter atom formation has been determined to be (1.0 ± 0.1) × 10−11 cm3 s−1 at room temperature. The former has been explained by the collisionless IR MPD of naturally abundant Cr(CO)5(13CO) species and subsequent IR MPD processes of vibrationally excited photofragments Cr(CO)n (n ≤ 5). The latter has been assigned to collision-induced dissociation of CrCo produced by the IR MPD of the parent molecules.