J. E. Reddic

Photodissociation spectroscopy of Ca+–H2O and Ca+–D2O

Electronic spectra are observed for the monosolvated metal cation complexes Ca+–H2O and Ca+–D2O using resonance enhanced photodissociation spectroscopy. The clusters are produced in a laser vaporization/supersonic expansion source and the mass‐analyzed product is observed using a time‐of‐flight mass spectrometer. Both Ca+ and CaOH+ (or CaOD+) dissociation channels are observed on sharp resonances. Transitions from the ground electronic state to two excited electronic states are assigned, with vibrational progressions in the Ca–OH2 stretching mode. Spectroscopic constants are Ca+–H2O: (2) 2B2←X 2A1 (T0=21 464 cm−1, ΔG1/2=357.9 cm−1) and (2) 2B1←X 2A1 (T0=23 273 cm−1, ΔG1/2=335.9 cm−1); and Ca+–D2O: (2) 2B2←X 2A1 (T0=21 447 cm−1, ΔG1/2=350.9 cm−1) and (2) 2B1←X 2A1 (T0=23 261 cm−1, ΔG1/2=324.1 cm−1). These transitions are rotationally resolved, confirming the structure of the complex to be C2v. The Ca+–H2O bond distance is 2.22 A and the H–O–H bond angle is 106.8° in the ground state. Comparisons with theor...

NOVEL MIXED LIGAND SANDWICH COMPLEXES : COMPETITIVE BINDING OF IRON WITH BENZENE, CORONENE, AND C60

Abstract Organometallic complexes of iron with benzene, coronene and C60 are produced in a molecular beam and studied with time-of-flight mass spectrometry and laser photodissociation. The cation complexes are produced in a pulsed nozzle laser vaporization source using an iron rod coated with a sublimed film of coronene and/or C60. Benzene is seeded in the expansion gas. Masses of the form [Ax–Fe–By]+ are observed when A and B are benzene, coronene, or C60, taken any two at a time. Masses are observed for all combinations where x + y = 1 or 2, indicating the formation of monoligand and sandwich complexes. Mixed-ligand sandwiches form with comparable abundance to homoligand sandwiches. Mass-selected photodissociation probes the relative bonding strengths in these new species.

Growth and photodissociation of AgxC60 cation complexes

Abstract Gas-phase complexes of C60 with silver atoms and small silver clusters are produced in a molecular beam and studied with time-of-flight mass spectrometry. The cation complexes are produced in a laser vaporization cluster source using a silver rod coated with a sublimed film of C60. Cluster masses of the form [AgxC60]+ are observed for x = 1–5. Additionally, an intense mass is observed at Ag(C60)2+. Mass-selected photodissociation experiments probe the structure and bonding in these novel cluster species.

Photodissociation spectroscopy of the Ca+–N2 complex

The weakly bound complex Ca+–N2 is prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected photodissociation spectroscopy. The chromophore giving rise to the electronic transition is the 2P←2S atomic transition of Ca+. The appearance of spin–orbit doublets in the vibrationally resolved spectrum, as expected for a 2∏r←2∑+ transition, confirms that the complex is linear. The electronic transition in the complex lies to the red of the atomic resonance line indicating that the complex is more strongly bound in the excited state than in the ground state. The vibrationally resolved spectrum contains progressions in the Ca+–N2 stretching mode and in a combination of this stretch with the N–N stretch. Extrapolation of the Ca+–N2 stretch determines the excited state dissociation energy to be D0′=6500±500 cm−1, and an energetic cycle determines the ground state value to be D0″=1755±500 cm−1 (5.02 kcal/mol). The 2∏r(2,0,0)←2∑+(0,0,0) vibronic transition has been rotationally reso...

Photoionization spectroscopy of ionic metal dimers: LiCu and LiAg

Electronic spectra are reported for the heteronuclear metal dimers LiCu and LiAg, with resonant one-color two-photon ionization (R2PI). The dimers are produced in a pulsed supersonic molecular beam by laser vaporization of either a copper or silver rod coated with a thin film of vacuum deposited lithium metal. A total of twelve excited electronic states for LiCu and seven for LiAg are observed. Analysis of the vibrational progressions yields ground and excited state vibrational frequencies and dissociation energies for both LiCu and LiAg. In addition, selected vibronic bands are rotationally resolved. This data, together with that obtained by Morse and co-workers for LiCu [J. Chem. Phys. (to be published)], gives bond lengths for LiCu and LiAg (r0″=2.26 and 2.41 A, respectively). The bond lengths for LiCu and LiAg are significantly shorter than expected by comparison to the homonuclear diatomics Li2 and Cu2 or Ag2. Dissociation energies in the heteronuclear dimers are also much greater than the mean of th...

Photodissociation of exohedral transition metal–C60 complexes

Abstract Laser ablation/vaporization of solid metal samples coated with thin films of C60 is employed in a pulsed-nozzle cluster source to produce various transition metal–C60 complexes. Mass spectra contain species of the form Mx(C60)y, where x = 1–5 and y = 1,2. Mass-selected photodissociation studies investigate the structural and bonding properties of these complexes. Photodissociation shows primarily the elimination of metal in all complexes, demonstrating that the complexes are exohedral. Atomic and molecular desorption of metal are observed in different situations, suggesting that these complexes have metal dispersed to some degree as “films” on the fullerene surface. Some clusters fragment by loss of metal carbides (e.g. C59Fe+, V3C4+), indicating insertion of metal into the fullerene cage wall. Keywords: Clusters; Metallo-fullerenes; Photodissociation

Composite samples and the generation of novel metal carbide clusters

Abstract New methods are described for the preparation of composite metal-carbon samples used for pulsed laser vaporization molecular beam cluster experiments. Samples containing a thin metal film on the surface of a carbon rod are prepared by thermal metal vapor deposition of electrochemical metal deposition. These composite samples are used to produce metal carbide clusters in the gas phase which could not be produced by other techniques. The size distributions of Bi/C, Sb/C, Ni/C, Co/C and Cu/C cluster cations are measured with time-of-flight mass spectrometry.

Photodissociation spectroscopy of the Mg+–C2H2 π-complex

Abstract The Mg + –acetylene complex is produced by pulsed-nozzle laser vaporization and studied with mass-selected resonance-enhanced photodissociation spectroscopy. A progression of broad vibrational bands is observed near 347 nm. The broad linewidths, which preclude rotational resolution, are attributed to rapid predissociation in the excited state. The progression is assigned to the metal–acetylene stretch in the 2 B 1 ← X 2 A 1 band system, which produces vibrational constants of ω e ′=330.5 cm −1 and D 0 ′=13100 cm −1 . The ground-state dissociation energy is estimated as D 0 ″=6100 cm −1 (17.4 kcal mol −1 ). These properties are in good agreement with the predictions of theory.

Ca+-Ar2 complexes : linear or bent?

Abstract Ca+–Ar2 complexes are investigated with mass-selected photodissociation spectroscopy and with high-level ab initio calculations. Theory finds two minima with comparable energies for the ground state, a linear Ar–Ca+–Ar structure and a C 2 v Ca + – Ar 2 structure with a significant argon dimer interaction. The latter is computed to be slightly lower in energy. Electronic spectroscopy finds a sharp spectrum near the forbidden Ca + ( 2 D – 2 S ) atomic interval. Two vibronic progressions are assigned that have significantly different linewidths. Analysis of the spectrum establishes that the complex is most likely linear.