Excess charge driven dissociative hydrogen adsorption on TiO.

The mechanism of dissociative D adsorption on TiO, which serves as a model for an oxygen vacancy on a titania surface, is studied using infrared photodissociation spectroscopy in combination with density functional theory calculations and a recently developed single-component artificial force induced reaction method. TiO readily reacts with D under multiple collision conditions in a gas-filled ion trap held at 16 K forming a global minimum-energy structure (DO-Ti-(O)-Ti(D)-O). The highly exergonic reaction proceeds quasi barrier-free via several intermediate species, involving heterolytic D-bond cleavage followed by D-atom migration.

Dissociative Water Adsorption by AlO in the Gas Phase.

We use cryogenic ion trap vibrational spectroscopy in combination with density functional theory (DFT) to study the adsorption of up to four water molecules on AlO. The infrared photodissociation spectra of [AlO(DO)] are measured in the O-D stretching (3000-2000 cm) as well as the fingerprint spectral region (1300-400 cm) and are assigned based on a comparison with simulated harmonic infrared spectra for global minimum-energy structures obtained with DFT. We find that dissociative water adsorption is favored in all cases.

Gas-Phase Vibrational Spectroscopy of the Aluminum Oxide Anions (Al O ) AlO.

We use cryogenic ion trap vibrational spectroscopy in combination with density functional theory to probe how the structural variability of alumina manifests itself in the structures of the gas-phase clusters (Al O ) AlO with n=1-6. The infrared photodissociation spectra of the D -tagged complexes, measured in the fingerprint spectral range (400-1200 cm ), are rich in spectral features and start approaching the vibrational spectrum of amorphous alumina particles for n>4. Aided by a genetic algorithm, we find a trend towards the formation of irregular structures for larger n, with the exception of n=4, which exhibits a C ground-state structure.

Spectroscopic snapshots of the proton-transfer mechanism in water.

The Grotthuss mechanism explains the anomalously high proton mobility in water as a sequence of proton transfers along a hydrogen-bonded (H-bonded) network. However, the vibrational spectroscopic signatures of this process are masked by the diffuse nature of the key bands in bulk water. Here we report how the much simpler vibrational spectra of cold, composition-selected heavy water clusters, D(DO), can be exploited to capture clear markers that encode the collective reaction coordinate along the proton-transfer event.

Structure and Fluxionality of B Probed by Infrared Photodissociation Spectroscopy.

We use cryogenic ion vibrational spectroscopy to characterize the structure and fluxionality of the magic number boron cluster B . The infrared photodissociation (IRPD) spectrum of the D -tagged all- B isotopologue of B is reported in the spectral range from 435 to 1790 cm and unambiguously assigned to a planar boron double wheel structure based on a comparison to simulated IR spectra of low energy isomers from density-functional-theory (DFT) computations. Born-Oppenheimer DFT molecular dynamics simulations show that B exhibits internal quasi-rotation already at 100 K.

Gas phase vibrational spectroscopy of the protonated water pentamer: the role of isomers and nuclear quantum effects.

We use cryogenic ion trap vibrational spectroscopy to study the structure of the protonated water pentamer, H(HO), and its fully deuterated isotopologue, D(DO), over nearly the complete infrared spectral range (220-4000 cm) in combination with harmonic and anharmonic electronic structure calculations as well as RRKM modelling. Isomer-selective IR-IR double-resonance measurements on the H(HO) isotopologue establish that the spectrum is due to a single constitutional isomer, thus discounting the recent analysis of the band pattern in the context of two isomers based on AIMD simulations 〈W. Kulig and N.

Infrared Photodissociation Spectroscopy of C N , C N and C N.

The gas-phase vibrational spectroscopy of cold C N (n=2-4) anions is investigated in the CC and CN multiple bond stretching region (1700-2250 cm ) by means of infrared photodissociation (IRPD) spectroscopy in a cryogenically cooled ion trap of the corresponding messenger-tagged complexes. The IRPD spectra are assigned to N-terminated linear structures with triplet ground states ( Σ ) based on a comparison with harmonic vibrational frequencies and intensities from density functional theory computations. In contrast to the polyacetylenic C N anions, the linear C-C chains investigated here exhibit cumulenic character, which is most pronounced in C N and decreases with chain length.

Gas phase structures and charge localization in small aluminum oxide anions: Infrared photodissociation spectroscopy and electronic structure calculations.

We use cryogenic ion trap vibrational spectroscopy in combination with quantum chemical calculations to study the structure of mono- and dialuminum oxide anions. The infrared photodissociation spectra of D2-tagged AlO1-4 (-) and Al2O3-6 (-) are measured in the region from 400 to 1200 cm(-1). Structures are assigned based on a comparison to simulated harmonic and anharmonic IR spectra derived from electronic structure calculations.

Gas phase vibrational spectroscopy of cold (TiO2)n(-) (n = 3-8) clusters.

We report infrared photodissociation (IRPD) spectra for the D2-tagged titanium oxide cluster anions (TiO2)n(-) with n = 3-8 in the spectral region from 450 to 1200 cm(-1). The IRPD spectra are interpreted with the aid of harmonic spectra from BP86/6-311+G* density functional theory calculations of energetically low-lying isomers. We conclusively assign the IRPD spectra of the n = 3 and n = 6 clusters to global minimum energy structures with Cs and C2 symmetry, respectively.

Disentangling the Contribution of Multiple Isomers to the Infrared Spectrum of the Protonated Water Heptamer.

We use infrared/infrared double-resonance population labeling (IR(2)MS(2)) spectroscopy in the spectral region of the free and hydrogen-bonded OH stretching fundamentals (2880-3850 cm(-1)) to identify the number and to isolate the vibrational signatures of individual isomers contributing to the gas-phase IR spectra of the cryogenically cooled protonated water clusters H(+)(H2O)n·H2/D2 with n = 7-10. For n = 7, four isomers are identified and assigned. Surprisingly, the IR(2)MS(2) spectra of the protonated water octa-, nona-, and decamer show no evidence for multiple isomers.

Site-specific vibrational spectral signatures of water molecules in the magic H3O+ (H2O)20 and Cs+ (H2O)20 clusters.

Theoretical models of proton hydration with tens of water molecules indicate that the excess proton is embedded on the surface of clathrate-like cage structures with one or two water molecules in the interior. The evidence for these structures has been indirect, however, because the experimental spectra in the critical H-bonding region of the OH stretching vibrations have been too diffuse to provide band patterns that distinguish between candidate structures predicted theoretically. Here we exploit the slow cooling afforded by cryogenic ion trapping, along with isotopic substitution, to quench water clusters attached to the H3O(+) and Cs(+) ions into structures that yield well-resolved vibrational bands over the entire 215- to 3,800-cm(-1) range.

Isomer-selective detection of hydrogen-bond vibrations in the protonated water hexamer.

The properties of hydrogen ions in aqueous solution are governed by the ability of water to incorporate ions in a dynamical hydrogen bond network, characterized by a structural variability that has complicated the development of a consistent molecular level description of H(+)(aq). Isolated protonated water clusters, H(+)(H2O)n, serve as finite model systems for H(+)(aq), which are amenable to highly sensitive and selective gas phase spectroscopic techniques. Here, we isolate and assign the infrared (IR) signatures of the Zundel-type and Eigen-type isomers of H(+)(H2O)6, the smallest protonated water cluster for which both of these characteristic binding motifs coexist, down into the terahertz spectral region.