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Electronic relaxation dynamics subsequent to s→p excitation of the excess electron in large anionic water clusters, (H2O)n- and (D2O)n- with 25≤n≤200, were investigated using time-resolved photoelectron imaging. Experimental improvements have enabled considerably larger clusters to be probed than in previous work, and the temporal resolution of the instrument has been improved. New trends are seen in the size-dependent p-state lifetimes for clusters with n≥70, suggesting a significant change in the electron-water interaction for clusters in this size range. Extrapolating the results for these larger clusters to the infinite-size limit yields internal conversion lifetimes τIC of 60 and 160 fs for electrons dissolved in H2O and D2O, respectively. In addition, the time-evolving spectra show evidence for solvent relaxation in the excited electronic state prior to internal conversion and in the ground state subsequent to internal conversion. Relaxation in the excited state appears to occur on a time scale similar to that of internal conversion, while ground state solvent dynamics occur on a ∼1 ps time scale, in reasonable agreement with previous measurements on water cluster anions and electrons solvated in liquid water. [ABSTRACT FROM AUTHOR]

We have used femtosecond time-resolved photoelectron spectroscopy to examine the photodissociation dynamics of doubly charged anions IrBr62- after excitation at hνpump=1.6 eV and with a detachment photon energy of hνprobe=4.8 eV. Excited state dynamics proceed by successive decay of the initially excited state, by way of an intermediate and back to the electronic ground state. This is associated with lifetimes of τ1=2.1±0.3 ps and τ2=21±2 ps, respectively. After nonadiabatic relaxation, the internal energy of the dianion is sufficiently large to induce fragmentation and delayed emission of Br- over the repulsive Coulomb barrier with a 79±21 ps time constant. As both fragments are negatively charged, Coulomb repulsion at early times (and correspondingly small separations) is reflected in the transient photoelectron spectra. Analysis of both shifts and intensities of the time-dependent bromide detachment features allows determination of the shape of the dissociation barrier. A lower limit of the outer height was retrieved from the kinetic energy release of KER≥1.6 eV. Modeling of the dissociation rate with statistical rate theory results in an inner barrier height of ERCB=0.95 eV. [ABSTRACT FROM AUTHOR]

Using femtosecond time-resolved photoelectron imaging, electron-hole pairs are created in size-selected Hgn- anion clusters (n=9–20), and the subsequent decay dynamics are measured. These clusters eject electrons via Auger decay on time scales of 100–600 fs. There is an abrupt increase in the Auger decay time for clusters larger than Hg12-, coinciding with the onset of the transition from van der Waals to covalent bonding in mercury clusters. Our results also show evidence for subpicosecond excited state relaxation attributed to inelastic electron-electron and electron-hole scattering as well as hole-induced contraction of the cluster. [ABSTRACT FROM AUTHOR]

Femtosecond time-resolved pump-probe photoelectron spectroscopy was used to study elementary relaxation processes occurring in isolated phthalocyanine-tetrasulfonate tetra-anions ([MPc(SO3)4]4-, M=Cu,Ni, and “free-base” [H2Pc(SO3)4]4-) following Q band excitation by one-photon absorption at 775 nm. Whereas the Cu and Ni systems decay rapidly by means of internal conversion without electron loss, the free-base phthalocyanine primarily undergoes excited state tunneling electron emission. This reflects less efficient coupling to lower lying states within the corresponding spin manifold. Results are interpreted in terms of (time-dependent) density functional theory calculations of ground and electronically excited states and kinetically modeled to yield the associated rates. [ABSTRACT FROM AUTHOR]

We have measured pump/probe photoelectron spectra of mass-selected, near room temperature C60- in the gas phase. The lifetime of the vibrationally excited B-(2Eg) state at a calculated energy of 1.26 eV was found to be τ=2.2±0.2 ps. The dominant decay process corresponds to intramolecular radiationless transitions into ground state C60-. This is in contrast to C60 for which pumping at the absorption onset (1.95 eV) leads to predominantly intersystem crossing. [ABSTRACT FROM AUTHOR]

A tandem time-of-flight mass spectrometer with an intermediate surface was used to quantify electron transfer during glancing incidence scattering of hyperthermal C60+ (Ecoll=250–500 eV, θin=75°) from (i) self-assembled monolayers of n-alkylthiols on gold (of various chain lengths), (ii) partly fluorinated alkylthiols on gold, as well as (iii) clean gold surfaces. Self-assembled monolayers (SAMs) behave as insulating layers with their thicknesses determining the electron tunneling probability during collision. Correspondingly, a roughly exponential dependence of the neutralization probability on the chain length n was found. A pronounced dependence of the neutral yield on the primary beam kinetic energy indicates that dynamic SAM deformation and associated projectile penetration depth also play a role in determining electron transfer efficiency. Results are consistent with the molecular deformability of SAMs as determined with other experimental methods. [ABSTRACT FROM AUTHOR]

We report laser photoelectron spectra of the doubly negatively charged fullerenes C762-, C782-, and C842- at 2.33, 3.49, and 4.66 eV photon energy. From these spectra, second electron affinities and vertical detachment energies, as well as estimates for the repulsive Coulomb barriers are obtained. These results are discussed in the context of electrostatic models. They reveal that fullerenes are similar to conducting spheres, with electronic properties scaling with their size. The experimental spectra are compared with the accessible excited states of the respective singly charged product ions calculated in the framework of time dependent density functional theory. [ABSTRACT FROM AUTHOR]

We report laser photoelectron spectra of the doubly negatively charged fullerenes C762-, C782-, and C842- at 2.33, 3.49, and 4.66 eV photon energy. From these spectra, second electron affinities and vertical detachment energies, as well as estimates for the repulsive Coulomb barriers are obtained. These results are discussed in the context of electrostatic models. They reveal that fullerenes are similar to conducting spheres, with electronic properties scaling with their size. The experimental spectra are compared with the accessible excited states of the respective singly charged product ions calculated in the framework of time dependent density functional theory. [ABSTRACT FROM AUTHOR]

Photodissociation spectra of free doubly charged anions IrX[sub 2-, sub 6] (X=Cl,Br) were measured in the photon energy range from 1.5 to 2.9 eV. Both data sets show the same features as the spectra of the respective aqueous solutions. Compared to solution, the gas phase absorption bands of IrBr[sup 2-, sub 6] are redshifted by 0.01-0.15 eV. For IrCl[sup 2-, sub 6] no such shift could be observed. Photodissociation of IrBr[sup 2-, sub 6] results in the formation of Br[sup -], IrBr[sup -], and IrBr[sup -, sub 5]. Fluence dependent measurements of fragment formation as well as parent ion depletion, allowed inferences regarding the dissociation pathway and the inner barrier height for the dissociation process which was estimated to be 1.6±0.2 eV. From measurements of the kinetic energy released upon fragmentation into monoanions, we estimate the outer barrier height to be 2.2±0.2 eV. [ABSTRACT FROM AUTHOR]

The first photoelectron (PE) spectra of polypeptide polyanions are described. The spectra obtained from PE and mass spectrometry are interpreted as resulting from a competition between delayed and direct emission.

A combination of experimental and theoretical evidence indicates oxytocin undergoes substantial conformational change when coordinating with Zn(super 2+). These changes directly facilitate binding of specific residues in oxytocin with specific residues in its receptor.

The photoelectron spectroscopy in an ion beam was used to examine the electronic properties of isolated DNA oligonucleotides, consisting of either five adenosine (A) or five thymidine (T) units, [dA5-4H](super 4-) and [dT5-4H](super 4-), carrying four excess negative charges. The result implies a significant influence of the base composition on energetics, which is relevant for analytic applications and also for charge transport properties.

Spontaneous electron loss from Ni(Pc (SO3) sub 4) (super 4-) and Cu(Pc(SO3) sub 4 (super 4-) studied in a UHV Penning trap at ambient temperature is described. The electron detachment energy should be lower for the C (sub 2v) isomer than for the other isomers.

Electronic relaxation dynamics subsequent to s --> p excitation of the excess electron in large anionic water clusters, (H(2)O)(n)(-) and (D(2)O)(n)(-) with 25 < or = n < or = 200, were investigated using time-resolved photoelectron imaging. Experimental improvements have enabled considerably larger clusters to be probed than in previous work, and the temporal resolution of the instrument has been improved. New trends are seen in the size-dependent p-state lifetimes for clusters with n > or = 70, suggesting a significant change in the electron-water interaction for clusters in this size range. Extrapolating the results for these larger clusters to the infinite-size limit yields internal conversion lifetimes tau(IC) of 60 and 160 fs for electrons dissolved in H(2)O and D(2)O, respectively. In addition, the time-evolving spectra show evidence for solvent relaxation in the excited electronic state prior to internal conversion and in the ground state subsequent to internal conversion. Relaxation in the excited state appears to occur on a time scale similar to that of internal conversion, while ground state solvent dynamics occur on a approximately 1 ps time scale, in reasonable agreement with previous measurements on water cluster anions and electrons solvated in liquid water.

We report the laser photoelectron spectra of doubly negatively charged C84 (D2 and D(2d)) using 532 nm and 355 nm radiation. From these spectra, values for the second electron affinity and vertical detachment energy, as well as upper and lower limits for the repulsive Coulomb barrier, are obtained. These values are discussed in the context of classical electrostatic models. The experimental spectra are compared with the accessible excited states of the C-84 product ion calculated in the framework of time dependent density functional theory.