The field of cluster research can trace its origins back to the mid-nineteenth century when early studies of colloids, aerosols, and nucleation phenomena were reported. The field underwent a resurgence of interest several decades ago when well-defined clusters were observed in supersonic expansions that could be investigated using mass spectrometers. The advent of the laser provided a new dimension, enabling detailed spectroscopic observations through the probing of systems of varying size and degree of solvation. Modern interest derives from recognition that interrogating clusters provides a way of studying the energetics and dynamics of intermediate states of matter as cluster systems evolve from the gas toward the condensed state. Herein, we endeavor to highlight some of the significant advances which have been made during the past several decades that have led to a nearly explosive growth of interest in the field of cluster science. Finally, we conclude that the field will continue to expand through i...

Clusters: Structure, Energetics, and Dynamics of Intermediate States of Matter

High resolution photoionization efficiency curves have been obtained for CH3COCH3+ and CD3COCD3+ using supersonic molecular beam sampling. As a result of adiabatic cooling during the nozzle expansion, sufficient concentrations of (CH3COCH3)2, (CD3COCD3)2, (CH3COCH3)3, and (CH3COCH3)4 were formed to permit the study of their photoion yield curves as well. Appearance potential curves have been determined for CH3CO+, CD3CO+, and (CH3COCH3) ⋅CH3CO+ fragments. The measured ionization potentials of acetone and acetone‐d6 monomers are 9.694±0.006 and 9.695±0.006 eV, respectively. Transitions to higher vibrational levels in CH3COCH3+ are seen at 320, 695, and 930−1370 cm−1 above threshold. The effect of perdeutero substitution is to reduce these frequencies to 260 and 660–1100 cm−1. Appearance potentials of CH3CO+ and CD3CO+ fragments are observed at 10.52±0.02 and 10.56±0.02 eV, respectively. The measured ionization energies for (CH3COCH3)n, n=1–4, are found to decrease linearly as a function of 1/n. Observed ionization thresholds for (CH3COCH3)2, (CH3COCH3)3, and (CH3COCH3)4 are 9.26±0.03, 9.10±0.03, and 9.02±0.03 eV, respectively. Within experimental resolution, the ionization potentials of (CH3COCH3)2 and (CD3COCD3)2 are identical. The appearance potential of the process (CH3COCH3)2 → (CH3COCH3) ⋅CH3CO++CH3+e− is found to be 10.08±0.05 eV. By consideration of appropriate thermodynamic cycles, a lower bound for the acetone dimer ion binding energy is calculated to be 0.538 eV (12.4 kcal/mole) and the desolvation energy of (CH3COCH3) ⋅CH3CO+ is estimated to be 0.544 eV (12.5 kcal/mole).

Molecular beam photoionization study of acetone and acetone‐d6

Using reflection time-of-flight mass spectrometer techniques to investigate cluster dynamics and bonding

Extensive new data, which reveal the statistical nature of the dissociation process of ammonia cluster ions following multiphoton ionization, are presented. Measured values of the evaporative unimolecular rates and the kinetic energy releases are used to determine binding energies of ammonia cluster ions. The appearance of magic numbers in the distribution of cluster ion abundances is discussed in terms of the thermochemical stability of the cluster ions and the concomitant effects expected on their metastable dissociation rates. Common behaviour is noted for other cluster systems, such as CH3OH and (CH3)2CO. However, at certain degrees of aggregation, these systems are found to exhibit particular ‘solvent-driven’ dissociation channels.

Photophysics of clusters. Intracluster reactions and dynamics of dissociation processes

Reactions of the solvated proton system H+ - [(CH3)2CO]n formed in photoionization of acetone

SIECK, L. W., AND AUSLOOS, P. Reactions of the Acetone Cation. Implications for the Radiolysis of Acetone. Radiat. Res. 52, 47-58 (1972). The reactions of the acetone and acetyl cation with acetone have been investigated in a photoionization mass spectrometer. Reaction of the acetone cation with ?-<0.3 eV internal energy occurs essentially at every collision (k = 8.4 X 10-10 ml/molecule sec), but decreases slightly with an increase in internal energy. Two reaction channels are observed for the acetone

L. W. Sieck

Papers

Reactions of the acetone cation. implications for the radiolysis of acetone.