James R. Heath

Cavity ring down dye laser spectroscopy of jet-cooled metal clusters: Cu2 and Cu3

Abstract Direct optical absorption measurements of jet-cooled metal clusters formed in a pulsed molecular beam have been made using a sensitive new absorption technique employing pulsed laser sources. Metal clusters and other metal containing species have been observed in this initial study. Absorption measurements of the Cu 3 2 A′ 1  2 E′ system reveal strong intensities for vibronic bands seen only weakly in previous photoionization and LIF studies due to predissociation of the upper level. A previously unobserved weak band has been identified and tentatively assigned as an excitation out of the higher energy Jahn—Teller component of the cluster ground state. These results illustrate the potential of this approach for studying larger metal cluster species.

The structure of the C4 cluster radical

The first infrared spectrum of gas phase, jet-cooled C4 has been measured by high resolution diode laser absorption spectroscopy. Twelve rovibrational transitions are assigned to the nu3(sigmau) antisymmetric stretch of linear 3Sigma - g C4. No evidence is observed for the bent structure of triplet C4 recently observed in a matrix study by Cheung and Graham [J. Chem. Phys. 91, 6664 (1989)]. Indeed, the measured band origin (1548.9368(21) cm^–1) and effective ground state C–C bond length [1.304 31(21)A] are consistent with several ab initio predictions of a rigid, linear, cumulenic structure for this cluster radical.

The C9 cluster: Structure and infrared frequencies

In this Letter we announce the first structural characterization of C9, the largest cluster predicted to have a linear ground state. We have used infrared diode laser absorption spectroscopy of a supersonic carbon cluster jet to measure 51 lines of the nu 6 (sigma u) antisymmetric stretch fundamental transition within the linear 1 sigma g(+) ground electronic state of C9. The measured ground state rotational constant [429.30(50) MHz] indicates an effective C-C bond length of 1.278 68 (75) angstroms, in good agreement with ab initio theory and consistent with cumulenic bonding in this cluster. In addition, the molecule is found to have unusually large ground-state and upper-state distortion constants, and several discrete perturbations are observed in the upper state.

Infrared laser spectroscopy of jet-cooled carbon clusters: structure of triplet C6

We report the first structural characterization of the triplet isomer of C6. Forty-one rovibrational/fine structure transitions in the nu 4(sigma u) antisymmetric stretch fundamental of the C6 cluster have been measured by diode laser absorption spectroscopy of a supersonic carbon cluster beam. The observed spectrum is characteristic of a centrosymmetric linear triplet state with cumulene-type bonding. The measured ground state rotational constant B0 = 0.048 479 (10)cm-1 and the effective bond length r(eff) = 1.2868 (1) angstroms are in good agreement with ab initio predictions for the linear triplet (3 sigma g-) state of C6.

The ν5 band of C7

Abstract Twenty-four rotational lines a associated with the ν 5 (σ u ) antisymmetric stretch vibration of C 7 have been measured by high resolution diode laser absorption spectroscopy of a supersonic carbon cluster beam. A simultaneous fit of spectra connecting the ground state with ν = 1 of ν 4 (J.R. Heath , Science 249 (1990) 895, J.R. Heath and R.J. Saykally, J. Chem. Phys. 94 (1991) 1724 and ν 5 produces the following molecular constants for the ν 5 state (in cm −1 ): ν 5 =1898.3758(8), B′ =0.030556(15), D′ = -0.16(11) × 10 −7 , H′ = −0.44(31) × 10 −11 .

A crystallographic analysis of C60(Buckminsterfullerene)

Crystallographic analysis of C60 grown from a hexane solution revealed a structure which is neither hexagonal nor cubic closest packed [space group P63/m, a= 33.54(1), c= 10.113(8)A]; packing models which are consistent with the Patterson map are described.

Silicon Nanowire Thermoelectrics

Heat dissipation in fundamentally modified in nanoscale materials, leading to new opportunities for high efficiency thermoelectric materials designed for energy conversion. I will review recent work in 3 classes of materials, including Si nanowire thermoelectrics.

The Synthesis of Crystalline Gallium Nitride Using Solid-State Metathhsis Reactions at High Pressures

Solid-state metathesis (exchange) reactions provide a rapid method to produce high quality refractory materials under ambient conditions. An investigation into solid-state metathesis reactions under pressure using Bridgman anvils and a girdle-type apparatus has led to the bulk synthesis of GaN, TaN and CrN, which are inaccessible under ambient pressure/temperature conditions. For example, high quality, crystalline gallium nitride can be rapidly (< 1 sec) synthesized from the reaction of gallium (III) iodide and lithium nitride confined at a pressure of 4. 5 GPa and initiated. Characterization of these compounds includes powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, energy dispersive spectroscopy and scanning electron microscopy. The single-phase gallium nitride made by metathesis reactions under pressure displays significant photoluminescence intensity in the blue/ultraviolet region.