J. G. Eaton

Photoelectron spectra of the alkali metal cluster anions: Na−n=2−5, K−n=2−7, Rb−n=2−3, and Cs−n=2−3

Obtention des spectres de photoelectrons a 2,540 eV sur faisceaux supersoniques. Deduction des energies de detachement vertical et des affinites electroniques adiabatiques, dont on analyse les variations avec n

Negative ion photoelectron spectroscopy of solvated electron cluster anions, (H2O)n− and (NH3)n−

The photodetachment spectra of (H2O)n=2−69/− and (NH3)n=41−1100/− have been recorded, and vertical detachment energies (VDEs) were obtained from the spectra. For both systems, the cluster anion VDEs increase smoothly with increasing sizes and most species plot linearly withn−1/3, extrapolating to a VDE (n=∞) value which is very close to the photoelectric threshold energy for the corresponding condensed phase solvated electron system. The linear extrapolation of this data to the analogous condensed phase property suggests that these cluster anions are gas phase counterparts to solvated electrons, i.e. they are embryonic forms of hydrated and ammoniated electrons which mature with increasing cluster size toward condensed phase solvated electrons.

Electron transfer collisions between small water clusters and laser‐excited Rydberg atoms

The Letters to the Editor section is divided into four categories entitled Communications, Notes, Comments, and Errata. Communications are limited to three and one halfjournal pages, and Notes, Comments, and Errata are limited to one and three-fourths journal pages as described in the Announcement in the I July 1991 issue.

Photoelectron spectra of hydrated electron clusters: Fitting line shapes and grouping isomers

The photoelectron spectra of (H2O)(n = 2-69) - and (D2O)(n = 2-23) - are presented, and their spectral line shapes are analyzed in detail. This analysis revealed the presence of three different groupings of species, each of which are seen over the range, n = 11-16. These three groups are designated as dipole boundlike states, seen from n = 2-16, intermediate states, found from n = 6-16, and bulk embryonts, starting at n = 11 and continuing up through the largest sizes studied. Almost two decades ago [J. V. Coe et al., J. Chem. Phys. 92, 3980 (1990)], before the present comprehensive analysis, we concluded that the latter category of species were embryonic hydrated electrons with internalizing excess electrons (thus the term embryonts). Recent experiments with colder expansion (high stagnation chamber pressures) conditions by Neumark and coworkers [J. R. R. Verlet et al., Science 307, 93 (2005)] have also found three groups of isomers including the long-sought-after surface states of large water cluster anions. This work confirms that the species here designated as embryonts are in the process of internalizing the excess electron states as the cluster size increases (for n > or = 11).

Ammonia cluster anions and their relationship to ammoniated (solvated) electrons: The photoelectron spectra of (NH3)n=41–1100−

We report the negative ion photoelectron spectra of (NH3)n=41–1100−, recorded using 2.540 eV photons. The largest cluster anion in this series has a diameter of approximately 4.3 nm. The vertical detachment energies (VDEs) of these cluster anions increase smoothly from 0.55 eV for n=41 to 1.05 eV for n=1100. The VDEs throughout this size range are linear with n−1/3 and extrapolate to a VDE (n=∞) value, which is very close to the measured photoelectric threshold energy of condensed phase ammoniated electrons. The linear extrapolation of this data to an analogous condensed phase property implies that these cluster anions are gas-phase counterparts to ammoniated electrons, i.e., they are embryonic forms of ammoniated electrons which will mature with increasing cluster size to become condensed phase-solvated electrons. The VDE data further implies that these embryonic ammoniated electrons were generated in solid ammonia environments, consistent with the source conditions under which they were produced.

On the origin of the competition between photofragmentation and photodetachment in hydrated electron clusters, (H2O)n -

Photoexcitation of size‐selected hydrated electron clusters, (H2O)−n , in the near IR results in a competition between photofragmentation and electron photodetachment. To investigate the origin of this competition, the decay probability into ionic fragments for the n=25 cluster was measured as a function of photon energy from 0.91≤hν≤3.49 eV. The photofragmentation probability increases rapidly with decreasing excitation energy in the general vicinity of the vertical detachment energy of this cluster (1.4 eV) determined via photoelectron spectroscopy. This result suggests that fragmentation accompanies photoexcitation of the excess electron with near zero kinetic energy. Thus, photofragmentation appears to proceed through an optically prepared intermediate similar to that reached in electron scattering from neutral clusters, which displays an enhanced dissociative attachment pathway with near zero kinetic energy electrons.

Anion solvation at the microscopic level: Photoelectron spectroscopy of the solvated anion clusters, NO−(Y)n, where Y=Ar, Kr, Xe, N2O, H2S, NH3, H2O, and C2H4(OH)2

The negative ion photoelectron spectra of the gas-phase, ion-neutral complexes; NO−(Ar)n=1–14, NO−(Kr)1, NO−(Xe)n=1–4, NO−(N2O)n=3–5, NO−(H2S)1, NO−(NH3)1, and NO−(EG)1 [EG=ethylene glycol] are reported herein, building on our previous photoelectron studies of NO−(N2O)1,2 and NO−(H2O)1,2. Anion solvation energetic and structural implications are explored as a function of cluster size in several of these and as a result of varying the nature of the solvent in others. Analysis of these spectra yields adiabatic electron affinities, total stabilization (solvation) energies, and stepwise stabilization (solvation) energies for each of the species studied. An examination of NO−(Ar)n=1–14 energetics as a function of cluster size reveals that its first solvation shell closes at n=12, with an icosahedral structure there strongly implied. This result is analogous to that previously found in our study of O−(Ar)n. Inspection of stepwise stabilization energy size dependencies, however, suggests drastically different st...

Photodetachment Spectroscopy of Negative Cluster Ions

Negative ion photoelectron spectra have been obtained for a variety of gas-phase cluster anions using visible photons. The negative cluster ions were generated by injecting relatively low energy electrons directly into the high density portion of an expanding supersonic jet. The spectra of NO-(N2O)n=1,2, H-(NH3)n=1,2, NH2(NH3)n=1,2, NO-(Ar)1 NO-(Kr)1 NO-(Xe)1, O2 -(Ar)1 (N2O)2, and (CS2)2 - reveal that they are simple ion-molecule complexes in which the excess negative charges are largely localized on sub-ions within the larger cluster anions. In addition to information on the bonding of cluster ions, the spectra also provide electron affinities and ion-solvent dissociation energies as a function of cluster size. The spectra of (CO2)2 -, (SO2)2 -, and (NO)2 -, on the other hand, indicate that these species are more complicated cases, and that they are not well described as simple ion-molecule complexes. Also, in the case of NH4 -, evidence is found not only for the ion-molecule complex, H-(NH3)1, but also for a higher energy isomer of tetrahedral geometry. Other systems studied include negative cluster ions of water and alkali metal cluster anions. Even though H2O- is unstable, clusters of water are able to bind an electron to form (H2O)n -. The spectra of (H2O)n - =2,6,7,10–17,19 and Ar(H2O)n - =2,6,7 provide the vertical detachment energies for these species. The alkali metals are the simplest of metals. The spectra of Na- 2–5, K- 2–8, Rb- 2–4, and Cs- 2,3 yield electron affinities as a function of cluster size as well as the electronic state splittings for neutral alkali metal clusters.

The negative ion photoelectron (photodetachment) spectra of NO−(H2O)n=1,2

We have recorded the negative ion photoelectron spectra of NO-(H,O),=l,z and NO- (D20), using 2.540 eV photons. Vertical detachment energies, adiabatic electron affmities, and anion-single solvent dissociation (sequential solvation) energies were determined from these spectra. For NO- (H20), and NO- (H,O),, the ion-solvent dissociation energies for the loss of single water molecules were found to be 0.72 and 0.68 eV, respectively. This system is discussed in relation both to other hydrated-anion complexes and to other NO- complexes.

The smoke ion source: a device for the generation of cluster ions via inert gas condensation

We report the development of an ion source for generating intense, continuous beams of both positive and negative cluster ions. This device is the result of the marriage of the inert gas condensation method with techniques for injecting electrons directly into expanding jets. In the preliminary studies described here, we have observed cluster ion size distributions ranging fromn=1−400 for Pbn+ and Pbn−, and fromn=12−5700 for Lin−.