New determinations of quantitative forward rate constants for reactions of titanium monomer cation with C 2 H 6 , C 3 H 8 , H 2 O, NH 3 , and O 2 are accomplished using a high-pressure (multicollision) flow tube reactor. These experiments were prompted by our observation of conflicting reports in the literature. The reaction rates we consider have been determined previously by both single-collision and multicollision methods, with some systems having generated notably contrasting results. An effort is made to reconcile the difference in values by explicitly addressing possible potential sources of error which have been suggested in earlier publications as the most likely reasons for the discrepancies. A "titration" technique is employed which allows controlled collisional quenching of excited state titanium cations with nitrogen gas such that excited state ion effects can be selectively observed and subsequently eliminated. No evidence is found to cast doubt upon the validity of multicollision methods for the determination of thermal energy rate constants.
A fast-flow reactor quadrupole mass spectrometer coupled with a laser vaporization source is used to study the gas-phase reactions of nickel oxide cluster anions (Ni x O y )with nitric oxide (NO). The results show that nitrogen dioxide (NO 2 ) is formed on the nickel oxide clusters and that this formation leads to the loss of one or more species from the clusters in order to dissipate the heat of formation. The species lost from the clusters are nickel (Ni) and nickel oxide (NiO). Also, there is evidence that the association species of nitric oxide with nickel oxide anions rapidly form NO 2 . Additional experiments were conducted in order to determine if this NO 2 formation mechanism is a function of how the nickel oxide cluster anions are formed. It was observed that a significantly different reaction occurs when nickel clusters are allowed to oxidize at room temperature and are then reacted with nitric oxide.
Reactivities of bimetallic clusters can be controlled by varying their composition, making them potentially valuable as catalysts and for use in elucidating the reactivities of such subnanoscale surfaces. A dual rod laser vaporization source coupled to a fast flow reactor is developed for the study of bimetallic clusters and their reactions. In order to establish the versatility of the technique, the results of studies are presented in which Nb/Al clusters are formed in two plasmas induced by the second harmonic (532 nm photons) of a single Nd:YAG laser and then detected by a quadrupole mass spectrometer. The beam from the laser is split and then focused onto each rod, allowing the mixing ratio within the cluster to vary by altering the laser fluence on each rod. With a low fluence on the Nb rod and a high fluence on the Al rod, an Al rich cluster distribution is formed, NbAlm− (m=2–20), and Alm− (m=5–31). By increasing the fluence on the Nb rod and decreasing the fluence on the Al rod, a Nb rich cluster distribution is formed, NbnAlm− (n=3–8 and m=1–3), NbnOAlm − (n=3–8 and m=1–5), and NbnO− (n=3–8). Additional characterization is also performed on V/Al clusters.
A fast flow reactor−quadrupole mass spectrometer system coupled with a laser vaporization source is used
to study the gas-phase reactions of nickel and nickel oxide cluster cations with nitric oxide. Pseudo-first-order bimolecular rate constants are reported for the reactions of NO with nickel and nickel oxide cluster
cations and O2 reactions with nickel cluster cations. The product distributions indicate that several different
reaction mechanisms occur between NO and Ni
x
+ and Ni
x
O
y
+. Competing processes such as oxidation, NO
addition, and replacement of oxygen with nitric oxide are observed to occur. Also, the presence of magic
peaks in the distributions indicates unusually stable product cluster species.
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