Ultrafast dynamics of transition metal carbonyls.

Ultrafast Dynamics of Transition Metal Carbonyls. 3. Intracluster Chemistry in [Cr(CO)6]n

“…In addition to a very fast initial rise this transient exhibits a peak after about 250 fs which is probably due to the initial fast dissociation dynamics of Cr(CO) 6 within the clusters. Similar transient peaks have been observed for the decarbonylation dynamics of Cr(CO) 6 in the gas phase 38,40 and in Cr(CO) 6 ·(CH 3 OH) k heteroclusters . In Table the rise times T3 describing the long time part of the transients of the coordinatively most unsaturated mononuclear chromium carbonyl ions are listed for both experiments conducted at pump/probe center wavelengths of 262.5 nm and 280 nm.…”

“…However, since the Cr n + transients (see Figure ) with higher n already decay on the femtosecond time scale, their neutral precursors also contribute. The rise of the mononuclear Cr(CO) m + ( m = 0−3) transients on the picosecond time scale may then derive from evaporation of Cr(CO) 6 clusters of solvated mononuclear photofragments similar to what has been observed for the Cr(CO) 6 ·(CH 3 OH) k heteroclusters in ref . However, additional contributions from the picosecond decay of the neutral photoproducts corresponding to the Cr n + and the Cr n (CO) m + ions will be present.…”

“…In addition, all possible mononuclear metal carbonyl ions Cr(CO) m + with m = 0−6 are present in the mass spectrum. Similar experiments conducted on Cr(CO) 6 ·(CH 3 OH) k heteroclusters only yielded those with m = 0−3 and 6; thus, there may exist different cooling efficiencies between these two types of cluster species. Furthermore, some unexpected ions corresponding to metal oxides and metal carbides are observed in the mass spectrum.…”

“…Similar transient peaks have been observed for the decarbonylation dynamics of Cr(CO) 6 in the gas phase 38,40 and in Cr(CO) 6 ‚(CH 3 OH) k heteroclusters. 41 In Table 2 the rise times T3 describing the long time part of the transients of the coordinatively most unsaturated mononuclear chromium carbonyl ions are listed for both experiments conducted at pump/ probe center wavelengths of 262.5 nm and 280 nm. A rise time for the Cr(CO) 3 + transient is only given for the experiments conducted at 280 nm since these do not exhibit interferences with an isobaric species as will be explained below.…”

“…At present, backed by surface experiments and polynuclear cluster chemistry from the literature cited above, we can thus only speculate on the intracluster chemistry going on in our van der Waals clusters. If the primary reaction after absorption of the pump pulse is essentially unaffected by the cluster environment (for Cr(CO) 6 ‚ (CH 3 OH) k this is most likely the case) 41 the photodissociation product Cr(CO) 5 which is formed within the pump pulse width could readily react with a neighboring Cr(CO) 6 molecule to form solvated Cr 2 (CO) 11 , an 18-electron system. 50 This kind of bimolecular reaction has also been proposed to take place in the gas phase.…”