Owen C. Thomas

Cobalt–benzene cluster anions: Mass spectrometry and negative ion photoelectron spectroscopy

(Cobalt)n(benzene)m− cluster anions, (n,m) were generated by laser vaporization and studied by both mass spectrometry and anion photoelectron spectroscopy. Our assignment of the photoelectron spectrum of the (1,2) cluster anion suggests that it possesses a sandwich structure with the cobalt atom located between two parallel benzene rings, that the ground state of this anion is a singlet, and that the ground state of its corresponding neutral is a doublet. The photoelectron spectra of cobalt-rich cluster anions of the form (n,1) are interpreted as cobalt metal cluster anions which have been solvent-stabilized by their interaction with, in each case, a single benzene molecule. The photoelectron spectra of the benzene-rich cluster anions, (2,3), (2,2), and (3,3), are tentatively interpreted as suggesting extended sandwich structures for these anion complexes.

Magic numbers in copper-doped aluminum cluster anions

Copper-doped aluminum cluster anions, CuAln− were generated in a laser vaporization source and examined via mass spectrometry (n=2–30) and anion photoelectron spectroscopy (n=2–15). The mass spectrum of the CuAln− series is dominated by CuAl13− with other magic numbers also appearing at n=6, 19, and 23. The electron affinity versus cluster size trend shows a peak at n=6 and a dip at n=13. These results are discussed in terms of the reordering of shell model energy levels and the enhanced stability of neutral CuAl13. Reordering, which is a consequence of the copper atom residing in the central region of these clusters, provides an anion-oriented electronic rationale for the observed magic numbers.

In search of theoretically predicted magic clusters: Lithium-doped aluminum cluster anions

Lithium-doped aluminum cluster anions, LiAln− were generated in a laser vaporization source and examined via mass spectrometry and anion photoelectron spectroscopy (n=3–15). The mass spectrum of the LiAln− series exhibits a local minimum in intensity at n=13. The electron affinity vs cluster size trend also shows a dip at n=13. Agreement is quite good between our measured electron affinity values and those calculated by Rao, Khanna, and Jena, suggesting that their predictions about the structure and bonding of LiAl13 and other clusters in this series are also largely valid.

Zinc oxide and its anion: A negative ion photoelectron spectroscopic study

We have recorded, assigned, and analyzed the photoelectron spectrum of ZnO−. The adiabatic electron affinity (E.A.a) of ZnO and the vibrational frequencies of both ZnO and ZnO− were determined directly from the spectrum, with a Franck–Condon analysis of its vibrational profile providing additional refinements to these parameters along with structural information. As a result, we found that E.A.a(ZnO)=2.088±0.010 eV, ωe(ZnO)=805±40 cm−1, ωe(ZnO−)=625±40 cm−1, and that re(ZnO−)>re(ZnO) by 0.07 A. Since our measured value of E.A.a(ZnO) is 0.63 eV larger than the literature value of E.A.(O), it was also evident, through a thermochemical cycle, that D0(ZnO−)>D0(ZnO) by 0.63 eV. This, together with the literature value of D0(ZnO), gives a value for D0(ZnO−) of 2.24 eV. Since the extra electron in ZnO− is expected to occupy an antibonding orbital, the combination of D0(ZnO−)>D0(ZnO), ωe(ZnO−) re(ZnO) was initially puzzling. An explanation was provided by the calculations of Bauschlicher and...

The effect of cell-cluster size on intracellular nanoparticle-mediated hyperthermia: is it possible to treat microscopic tumors?

AIM To compare the measured surface temperature of variable size ensembles of cells heated by intracellular magnetic fluid hyperthermia with heat diffusion model predictions. MATERIALS & METHODS Starch-coated Bionized NanoFerrite (Micromod Partikeltechnologie GmbH, Rostock, Germany) iron oxide magnetic nanoparticles were loaded into cultured DU145 prostate cancer cells. Cell pellets of variable size were treated with alternating magnetic fields. The surface temperature of the pellets was measured in situ and the associated cytotoxicity was determined by clonogenic survival assay. RESULTS & CONCLUSION For a given intracellular nanoparticle concentration, a critical minimum number of cells was required for cytotoxic hyperthermia. Above this threshold, cytotoxicity increased with increasing cell number. The measured surface temperatures were consistent with those predicted by a heat diffusion model that ignores intercellular thermal barriers. These results suggest a minimum tumor volume threshold of approximately 1 mm(3), below which nanoparticle-mediated heating is unlikely to be effective as the sole cytotoxic agent.

Microsolvation of small anions by aromatic molecules: An exploratory study

This work was motivated by the experimental finding that the O2−/benzene interaction energy is unexpectedly large. To further explore the interactions of small anions with aromatic molecules, anion photoelectron spectroscopy was utilized to measure interaction strengths of the seed anions, O2− and NO−, complexed with several aromatic molecules, including benzene, naphthalene, pyridine, and pyrimidine. As in the case of O2−(benzene), the anion(aromatic)1 binding energies for the other complexes studied were also higher than one might have anticipated. In addition, the interaction energy of O2− complexed with a given aromatic molecule was, in every case studied, higher (by a factor of ∼1.5) than that of NO− complexed with the same aromatic. While the dependence of interaction strengths on solvent dipole moments and/or polarizabilities implied a substantial electrostatic component to the binding in these complexes, differences in the binding of O2− and NO− with these aromatic molecules showed that there is a...

Photoelectron spectroscopy of nickel-benzene cluster anions

(Nickel)(n)(benzene)(m) (-) cluster anions were studied by both mass spectrometry and anion photoelectron spectroscopy. Only Ni(n)(Bz)(m) (-) species for which n > or =m were observed in the mass spectra. No single-nickel Ni(1)(Bz)(m) (-) species were seen. Adiabatic electron affinities, vertical detachment energies, and second transition energies were determined for (n,m)=(2,1), (2,2), (3,1), and (3,2). For the most part, calculations on Ni(n)(Bz)(m) (-) species by B. K. Rao and P. Jena [J. Chem. Phys. 117, 5234 (2002)] were found to be consistent with our results. The synergy between their calculations and our experiment provided enhanced confidence in the theoretically implied magnetic moments of several nickel-benzene complexes. The magnetic moments of small nickel clusters were seen to be extremely sensitive to immediate molecular environmental effects.

Electronic and geometrical structure of Mn13 anions, cations, and neutrals.

We have computed the electronic and geometrical structures of thirteen atom manganese clusters in all three charge states, Mn(13) (-), Mn(13) (+), and Mn(13) by using density functional theory with the generalized gradient approximation. Our results for Mn(13) (-) are compared with our anion photoelectron spectrum of Mn(13) (-), published in this paper. Our results for Mn(13) (+) are compared with the previously published photoionization results of Knickelbein [J. Chem. Phys. 106, 9810 (1997)]. There is a good agreement between theoretical and experimental values of ionization and electron attachment energies.

Mass Spectrometric and Photoelectron Spectroscopic Studies of Zirconium Oxide Molecular and Cluster Anions

We present a preliminary report on our mass spectrometric and photoelectron spectroscopic studies of zirconium oxide molecular and cluster anions using a newly built laser vaporization/time-of-flight/magnetic bottle, negative ion photoelectron spectrometer. This work was motivated in part by evidence which suggests that zirconium dioxide catalyzes the radiolysis of interfacial water. We present our mass spectrometric observations of oxygen-rich zirconium oxide cluster anions and our photoelectron spectra of ZrO− and ZrO2−. From the photoelectron spectrum of ZrO−, the adiabatic electron affinity of ZrO was determined to be 1.3±0.3 eV, and from this value, the dissociation energy of ZrO− (into Zr and O−) was found to be 7.8±0.3 eV. From the photoelectron spectrum of ZrO2, the adiabatic electron affinity of ZrO2 was determined to be 1.8±0.4 eV.

Magic numbers in Aln+(H2O)1 cluster cations

Abstract We report the observation of magic numbers in the mass spectrum of Al n + (H 2 O) 1 . These cluster cations were produced in a laser vaporization source in the presence of trace amounts of water. The most prominent magic number species observed was Al 13 + (H 2 O) 1 . We attribute its pronounced intensity to its enhanced stability resulting from the formation of a coordinate bond between the Al 13 + moiety and the oxygen atom of water. The sharing of an oxygen lone electron pair with Al 13 + lends to it some of the character of the 40-valence electron, closed shell Al 13 − magic cluster.