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The near ultraviolet photodissociation dynamics of silver atom-rare gas dimers have been studied by velocity map imaging. Ag-RG (RG = Ar, Kr, Xe) species generated by laser ablation are excited in the region of the C ((²Σ+)←X (²Σ+) continuum leading to direct, near-threshold dissociation generating Ag* (²P3/2) + RG¹S0) products. Images recorded at excitation wavelengths throughout the C (²Σ+)←X (²Σ+) continuum, coupled with known atomic energy levels, permit determination of the ground X (²Σ+) state dissociation energies of 85.9 ± 23.4 cm-1 (Ag-Ar), 149.3 ± 22.4 cm-1 (Ag-Kr), and 256.3 ± 16.0 cm-1 (Ag-Xe). Three additional photolysis processes, each yielding Ag atom photoproducts, are observed in the same spectral region. Two of these are markedly enhanced in intensity upon seeding the molecular beam with nitrous oxide, and are assigned to photodissociation of AgO at the two-photon level. These features yield an improved ground state dissociation energy for AgO of 15 965 ± 81 cm-1, which is in good agreement with high level calculations. The third process results in Ag atom fragments whose kinetic energy shows anomalously weak photon energy dependence and is assigned tentatively to dissociative ionization of the silver dimer Ag2. [ABSTRACT FROM AUTHOR]

We present the results of a combined experimental and computational study of the structures of gas-phase M+(N2O)n (M = Li, Al) complexes. Infrared spectra were recorded in the region of the N2O asymmetric (N = N) stretch using photodissociation spectroscopy employing the inert messenger technique. Unlike in our previous studies on M+(N2O)n (M = Cu, Ag, Au and M = Co, Rh, Ir) complexes, N– and O–bound isomers in this case are near isoenergetic and are not distinguished spectroscopically at this resolution. In the case of Li+ complexes, there is, however, evidence for the presence of bound N2 moieties, indicating the presence of inserted, OLi+N2(N2O)n–type structures. The weak N2 band lies to the blue of the signature of molecularly N– and O–bound ligands and is well–reproduced in the simulated spectra of energetically low-lying structures computed from density functional theory. No such inserted isomers are observed in the case of Al+(N2O)n complexes whose infrared spectra can be understood on the basis of molecularly-bound N2O ligands. The differences in M+(N2O)n structures observed for these closed–shell, ns2, metal centres relative to other metal cations are discussed in terms of the likely bonding motifs. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of Au-Xe leading to Xe+ formation via the Ξ1/2-X2Σ+ (v′, 0) band system (41 500-41 800 cm-1) have been investigated by velocity map imaging. Five product channels have been indentified, which can be assigned to photoinduced charge transfer followed by photodissociation in either the neutral or the [Au-Xe]+ species. For the neutral species, charge transfer occurs via a superexcited Rydberg state prior to dissociative ionization, while single-photon excitation of the gold atom in Au+-Xe accesses an (Au+)*-Xe excited state that couples to a dissociative continuum in Au-Xe+. Mechanisms by which charge transfer occurs are proposed, and branching ratios for Xe+ formation via the superexcited Rydberg state are reported. The bond dissociation energy for the first excited state of Au+-Xe is determined to be ∼9720 ± 110 cm-1. [ABSTRACT FROM AUTHOR]

The ultraviolet photodissociation dynamics of the gold-rare gas atom van der Waals complexes (Au–RG, RG=Ar, Kr, and Xe) have been studied by velocity map imaging. Photofragmentation of Au–Ar and Au–Kr at several wavelengths permits extrapolation to zero of the total kinetic energy release (TKER) spectra as monitored in the Au(2P3/2°[5d106p]) fragment channel, facilitating the determination of ground state dissociation energies of D0″(Au–Ar)=149±13 cm-1 and D0″(Au–Kr)=240±19 cm-1, respectively. In the same spectral region, transitions to vibrational levels of an Ω′=1/2 state of the Au–Xe complex result in predissociation to the lower Au(2P1/2°[5d106p])+Xe(1S0[5p6]) fragment channel for which TKER extrapolation yields a value of D0″(Au–Xe)=636±27 cm-1. Asymmetric line shapes for transitions to the v′=14 level of this state indicate coupling to the Au(2P3/2°[5d106p])+Xe(1S0[5p6]) continuum, which allows us to refine this value to D0″(Au–Xe)=607±5 cm-1. The dissociation dynamics of this vibrational level have been studied at the level of individual isotopologues by fitting the observed excitation spectra to Fano profiles. These fits reveal a remarkable variation in the predissociation dynamics for different Au–Xe isotopologues. For Au–Ar and Au–Xe, the determined ground state dissociation energies are in good agreement with recent theoretical calculations; the agreement of the Au–Kr value with theory is less satisfactory. [ABSTRACT FROM AUTHOR]

High-resolution IR-UV multiple resonance methods are employed to elucidate the photodissociation dynamics of quantum state-selected Ar–HOD and Ar–H2O van der Waals clusters. A single mode pulsed OPO operating in the region of the OH second overtone is used to prepare individual rovibrational states that are selectively photodissociated at specific excimer wavelengths. Subsequent fluorescence excitation of the resulting OH (OD) fragments yields dynamical information on the photofragmentation event and any resulting intracluster collisions. This technique is used to characterize spectroscopically the Π(101), vOH=3←Σ(000), vOH=0 overtone band of the Ar–HOD complex with an origin at 10648.27 cm-1. The effects of Ar complexation on the dissociation dynamics are inferred by comparison of the OD photofragment quantum state distributions resulting from dissociation of single rovibrational states of the complex with those from isolated HOD photodissociation. The important role played by the initial internal state of the complex is demonstrated by comparison of the current Ar–HOD data with previously published results for the Ar–H2O Σ(000)|03-> state. We interpret the dramatic differences in the dynamics of the two systems as manifestations of the nodal structure of the vibrational state in the parent complex and the way in which it governs the collision probability between the Ar atom and the escaping photofragments. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The photodissociation dynamics of Xe2 Rydberg states in the 76,900–80,000 cm−1 region have been studied using a combination of resonance enhanced multi-photon ionization and velocity map imaging. By monitoring photodissociation product channels as a function of excitation energy, several localized and long range perturbations of the excited states have been identified. In addition, several new band systems have been observed and assigned as the Xe2 5d 2[1/2]0°  ← X , 5d 2[1/2]1°  ← X , 5d 2[3/2]2°  ← X , and 5d 2[7/2]3°  ← X transitions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CO 2 complexes efficiently with NbO 2 + and TaO 2 + relevant to sequestration by MOFs. • DFT simulations allow clear structural determination of MO 2 (CO 2) n + complexes. • Possible M–O–CO 2 type features observed in larger complexes. • No evidence of oxalate structures in CO 2 complexation to NbO 2 + or TaO 2 +. Abstract We report the results of an infrared photodissociation spectroscopy study to determine the structures of gas–phase NbO 2 (CO 2) n + and TaO 2 (CO 2) n + (n = 1–7) ion–molecule complexes. The experimental spectra, recorded in the region of the CO 2 asymmetric stretch using the inert messenger technique, are interpreted in terms of energetically low–lying structures calculated from density functional theory. Together, experiment and simulation provide important new information on CO 2 –binding relevant to prototypical metal–oxide frameworks. Key findings include strong binding of the first two CO 2 ligands to the MO 2 + species and clear evidence for a first solvation shell at n = 4. Some features characteristic of a possible CO 3 ("carbonate") moiety are found in spectra for n ≥ 3 but oxalate structures, observed in some similar systems, appear to be too high in energy to be observed experimentally. CO 2 activation, reactivity and sequestration have long been of interest to Prof Helmut Schwarz, in whose honour this special issue is published on the occasion of his 75th birthday. [ABSTRACT FROM AUTHOR]

The structures of gas-phase M+(CO2)n (M = Co, Rh, Ir; n = 2-15) ion-molecule complexes have been investigated using a combination of infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy and density functional theory. The results provide insight into fundamental metal ion-CO2 interactions, highlighting the trends with increasing ligand number and with different group 9 ions. Spectra have been recorded in the region of the CO2 asymmetric stretch around 2350 cm-1 using the inert messenger technique and their interpretation has been aided by comparison with simulated infrared spectra of calculated low-energy isomeric structures. All vibrational bands in the smaller complexes are blue-shifted relative to the asymmetric stretch in free CO2, consistent with direct binding to the metal center dominated by charge-quadrupole interactions. For all three metal ions, a core [M+(CO2)2] structure is identified to which subsequent ligands are less strongly bound. No evidence is observed in this size regime for complete activation or insertion reactions [ABSTRACT FROM AUTHOR]

Abstract: The photodissociation dynamics of Au2 at 157nm have been studied by velocity map imaging. Fragmentation into seven of the nine energetically accessible channels has been observed with a high propensity for the formation of electronically excited fragment atoms. Fragmentation channels are assigned using total energy conservation and confirmed in two-colour experiments in which photolysis is followed by quantum state-selective resonance enhanced multi-photon ionization. The combination of one-and two-colour experiments permits the determination of relative branching ratios at 157nm for product channels correlating to Au 5d96s2(2D3/2) and Au 5d96s2(2D5/2) atomic fragments. [Copyright &y& Elsevier]