Solvation of Silver Ions in Noble Gases He, Ne, Ar, Kr, and Xe

We use a novel technique to solvate silver cations in small clusters of noble gases. The technique involves the formation of large, superfluid helium nanodroplets that are subsequently electron ionized, mass-selected by deflection in an electric field, and doped with silver atoms and noble gases (Ng) in pickup cells. Excess helium is then stripped from the doped nanodroplets by multiple collisions with helium gas at room temperature, producing cluster ions that contain no more than a few dozen noble gas atoms and just a few (or no) silver atoms. Under gentle stripping conditions, helium atoms remain attached to the cluster ions, demonstrating their low vibrational temperature. Under harsher stripping conditions, some of the heavier noble gas atoms will be evaporated as well, thus enriching stable clusters of Ng_nAg_m⁺ at the expense of less stable ones. This results in local anomalies in the cluster ion abundance, which is measured in a high-resolution time-of-flight mass spectrometer. On the basis of these data, we identify specific "magic" sizes n of particularly stable ions. There is no evidence, however, for enhanced stability of Ng₂Ag⁺, in contrast to the high stability of Ng₂Au⁺ that derives from the covalent nature of the bond for heavy noble gases. "Magic" sizes are also identified for Ag₂⁺ dimer ions complexed with He or Kr. Structural models will be tentatively proposed. A sequence of magic numbers n = 12, 32, and 44, indicative of three concentric solvation shells of icosahedral symmetry, is observed for He_nH₂O⁺.

Xe2 gerade Rydberg states observed in the afterglow of a microplasma by laser spectroscopy of a(3)Σ(+)(u)(1(u), O(-)(u)) absorption in the green (545-555 nm) and near-infrared (675-800 nm)

Bound←bound transitions of the Xe dimer at small internuclear separation (R < 4.0 Å) have been observed in the 545-555 nm and 675-800 nm spectral regions by laser spectroscopy in the afterglow of a pulsed Xe microplasma with a volume of ∼160 nl. Transient suppression of Xe2 A(1)Σ(+)(u)(O(+)(u)) --> X(1)Σ(+)(g)(O(+)(g)) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ω(g) ← a(3)Σ(+)(u)(1(u), O(-)(u)) [Rydberg←Rydberg] transitions of the molecule, has confirmed the existence of structure between 720 and 770 nm (reported by Killeen and Eden [J. Chem. Phys. 84, 6048 (1986)]) but also reveals red-degraded vibrational bands extending to wavelengths beyond 800 nm. Spectral simulations based on calculations of Franck-Condon factors for assumed Ω(g) ← a(3)Σ(+)(u) transitions involving Ω = 0(±),1 gerade Rydberg states suggest that the upper level primarily responsible for the observed spectrum is an Ω = 1 state correlated, in the separated atom limit, with Xe(5p(6) (1)S0) + Xe(5p(5) 6p) and built on a predominantly A(2)Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1(g) ← 1(u), O(±)(u) absorptive transitions are determined to be Te = 13,000 ± 150 cm(-1), ω'(e) = 120 ± 10 cm(-1), ω'(e)x'(e) = 1.1 ± 0.4 cm(-1), De = 3300 ± 300 cm(-1), and ΔR(e) = R'(e) = R''(e) = 0.3 ± 0.1 Å which are in general agreement with the theoretical predictions of the pseudopotential hole-particle formalism, developed by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], for both the (5)1g and (3)O(+)(g) states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular core-switching transition, observed to date for any of the rare gas dimers at small R (<4 Ǻ). Experiments in the green (545-555 nm) also provide improved absorption spectra, relative to data reported in 1986 and 1999, associated with Xe2 Rydberg states derived from the Xe(7p) orbital.

Pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy of metastable He2: Ionization potential and rovibrational structure of He2+

A supersonic beam of metastable He(*) atoms and He(2) (*) a (3)Sigma(u) (+) molecules has been generated using a pulsed discharge at the exit of a pulsed valve prior to the gas expansion into vacuum. Pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the He(2) (+) X(+) (2)Sigma(u) (+) (v(+)=0-2)<--He(2) (*) a (3)Sigma(u) (+) (v(")=0-2) transitions and photoionization spectra of He(2) (*) in the vicinity of the lowest ionization thresholds have been recorded. The energy level structures of (4)He(2) (+) X(+) (2)Sigma(u) (+) (v(+)< or =2,N(+)< or =23) and (3)He(2) (+) X(+) (2)Sigma(u) (+) (v(+)=0,N(+)< or =11) have been determined, and an accurate set of molecular constants for all isotopomers of He(2) (+) has been derived in a global analysis of all spectroscopic data reported to date on the low vibrational levels of He(2) (+). The analysis of the photoionization spectrum by multichannel quantum defect theory has provided a set of parameters describing the threshold photoionization dynamics.