Photofragmentation of Vanadium Oxide Cations

Abstract

Laser-induced fragmentation of mass-selected vanadium oxide cluster cations at 532 nm is investigated in a time-of-flight mass spectrometer. The major species observed in the initial mass distribution can be described as having a stoichiometry similar to bulk vanadium oxides, with some species possessing additional O2 units bonded to the cluster. At low laser fluence, the major photofragmentation channel observed is the loss of O2 or consecutive O2 units from clusters that are oxygen rich. When the laser fluence is increased, additional fragmentation channels are observed. The majority of the clusters investigated, from V2O8 + to V6O16 +, ultimately lose the necessary neutral fragments to form the product ions VO2 + and VO+. The results suggest that VO2 and VO have lower ionization potentials than larger vanadium oxide clusters.

Collision-induced dissociation studies on gas-phase titanium oxide cluster cations

“…The results indicate that the titanium oxide cationic clusters lose mainly neutral O 2 , TiO and/or (TiO 2 ) n units. This trend seems to be a general behavior in many dissociation processes as observed also from the experimental studies of other groups [8,21,22]. The charged fragments observed are those that exhibit the lowest ionization potentials.…”

Gas-Phase Chemistry of Vanadium Oxide Cluster Cations. 2. Reactions with CH2F2

“…The oxygen-rich clusters are considered to be the smaller, more stable parent clusters with molecular oxygen adsorbed to the surface of the cluster, which can be represented as 10 Similar results for the loss of O 2 from the oxygenrich cluster ions have been observed for laser heating experiments performed on these species. 11 These findings provide further evidence for the oxygen-rich species containing weakly adsorbed oxygen molecules on the surface of the smaller clusters. Products representing the association of CH 2 F 2 with the loss of O 2 were also observed for the clusters V 2 O 6 + , V 3 O 8 + , and V 4 O 10,11 + under both single and multiple collision conditions.…”

Mass-selected infrared photodissociation spectroscopy of V4O10+

“…3 Understanding the nature of the reactive sites in heterogeneous catalysis can be aided by gas-phase studies of isolated neutral and ionic clusters. However, only scarce experimental information on the spectroscopy and structure of vanadium oxide clusters is available, [4][5][6][7] complicating the interpretation of the gas-phase reactivity studies. [8][9][10][11][12][13][14][15][16][17] Studies of the mass spectral distributions and cluster growth dynamics of vanadium oxide clusters 18,19 and cluster ions 8,12 show that VO 2 , VO 3 , and V 2 O 5 units are the main building blocks for V x O y À/0/+ clusters.…”

“…Oxygen-rich cluster ions can also contain a weakly bound O 2 species, as was shown in recent collision induced dissociation (CID) and 532 nm photofragmentation studies. 7,8 Gas phase reactivity studies indicate that the reactivity of vanadium oxide cluster anions and cations depends on cluster stoichiometry and generally decreases with cluster size. 10,13 However, with the exception of the diatomic VO (see ref.…”

“…Fragmentation of V 4 O 10 + has previously been studied by CID and photofragmentation using 532 nm radiation. 7,8 Single collisions with Xenon atoms lead to O 2 loss already at thermal energies, while other fragmentation channels are only observed at collision energies above 3 eV. Similarly, absorption of a single 532 nm (2.128 eV) photon leads exclusively to O 2 loss, while other fragmentation channels are only observed at higher laser fluences, i.e., under multi-photon absorption conditions.…”