Vibrational Spectroscopy of Size-Selected Sodium-Doped Water Clusters

Abstract

The vibrational OH stretch spectra have been measured for Na(H2O)n clusters in the size range from n = 8 to 60. The complete size selection is achieved by coupling the UV radiation of a dye laser below the ionization threshold with the tunable IR radiation of an optical parametric oscillator. The spectra are dominated by intensity peaks around 3400 cm(-1) which we attribute to an increased transition dipole moment of delocalized electrons in this type of doped cluster. Aside from the positions of free (3715 cm(-1)) and double donor (3560 cm(-1)) bonds which are known from pure water clusters, specific transitions are observed at 3640 cm(-1) and in the range of the single donor bonds between 3000 and 3200 cm(-1).

A sodium atom in a large water cluster: Electron delocalization and infrared spectra

“…41 Here, we will present only a short account of the main parts. 24 The infrared radiation used to excite the clusters is obtained from a Nd:YAG ͑yttrium aluminum garnet͒-laser-pumped optical parametric oscillator in the spectral range from 2900 to 3800 cm −1 . In a first step, the water clusters are produced by expanding water vapor of 0.53 bar seeded in helium at 4 bars through a nozzle of conical shape with a diameter of 63 m, an opening angle of 41°, and a lengths of 2 mm.…”

“…24 Size selection was achieved by coupling the UV radiation of a dye laser below the threshold for ionization with the tunable IR radiation from an optical parametric oscillator. 24 Size selection was achieved by coupling the UV radiation of a dye laser below the threshold for ionization with the tunable IR radiation from an optical parametric oscillator.…”

UV Photoionization of Sodium‐Doped Formic Acid Clusters

“…[13,14,42] In these cases, the lowering of the cluster appearance energies in the UV range was primarily attributed to photoelectrons in the Na 3s orbital or an evaporative/ photofragmentation process of larger clusters. This study was performed by combining measurements of appearance energies with DFT calculations.…”

“…[7] Small clusters may be described by a fully microscopic approach, but this may be complex to pursue even for a few molecules/atoms cluster. [12][13][14][15] In particular, the photoionization mechanism of these clusters, and the key role of the 3 s valence electron of sodium, has been much debated, especially regarding the difficulty to correctly interpret the ionization potentials (IPs) that, for water clusters, become constant for n = 4, as already evidenced in early seminal papers. In fact, in the field of aerosol science, the aim is to simplify and rationalize the phenomenon of formation and growth of particles by identifying the cluster aggregations as the first stage of the process.…”

“…[11] Na-(H 2 O) n clusters are the most extensively studied. [12][13][14][15] In particular, the photoionization mechanism of these clusters, and the key role of the 3 s valence electron of sodium, has been much debated, especially regarding the difficulty to correctly interpret the ionization potentials (IPs) that, for water clusters, become constant for n = 4, as already evidenced in early seminal papers. [16] Numerous theoretical studies have been conducted on the sodium valence electron in doped clusters, which can be delocalized on surface states or trapped in a sort of "ion-pair" structure in which it is inside a solvation shell in the vicinity of the Na + solvated cation.…”