Subpicosecond Dynamics of Rydberg Excitons Produced from Ultraviolet Excitation of Neutral Cuprite (CuO) Clusters, < 13.

The ultrafast dynamics of subnanometer neutral cuprite clusters (CuO), < 13, are examined with pump probe spectroscopy. Upon absorption of an ultraviolet (400 nm) photon, all clusters exhibit a subpicosecond lifetime that we attribute to carrier recombination. Density functional theory (DFT) shows a change in the structural motif between small planar clusters and three-dimensional structures at = 4.

Sub-picosecond photodynamics of small neutral copper oxide clusters.

The ultrafast dynamics of neutral copper oxide clusters (CuO, < 5) are reported using femtosecond pump probe spectroscopy in the gas phase. The transient spectra recorded for each cluster demonstrate they relax on a 100s of fs timescale followed by a long-lived (>50 ps) response. Density functional theory calculations are performed to determine the lowest energy structures and spin states.

Size onset of metallic behavior in neutral aluminum clusters.

The excited state lifetimes of neutral (Al) clusters up to ∼1 nm in diameter in size, where ≤ 43, are systematically measured with femtosecond time-resolved mass spectrometry. The onset of metallic behavior is identified as a distinct change in the relaxation behavior initiated with single ultraviolet (400 nm) photon excitation. The experimentally measured excited state lifetimes gradually decrease with size for small molecular scale clusters ( < 10) before becoming indistinguishable for larger clusters ( > 9), where the measurements are comparable to electron-lattice relaxation time of bulk Al (∼300 fs).

Ultrafast Proton Transfer and Contact Ion-Pair Formation in Formic Acid Clusters.

The ultrafast proton transfer dynamics of homogeneous formic acid clusters (FA), < 10, are investigated with femtosecond time-resolved mass spectrometry. We monitor the proton transfer pathway following Rydberg state electronic relaxation and find that successful ion pair formation increases logarithmically with cluster size. Ab initio calculations demonstrate similar excitation/relaxation behavior for each cluster, revealing a contact ion pair forms between two molecules composing the cluster before finally a formate anion (HCOO) is dissociated by the probe pulse.

Nonadiabatic Photodissociation and Dehydrogenation Dynamics of -Butyl Bromide Following p-Rydberg Excitation.

Femtosecond time-resolved mass spectrometry, correlation mapping, and density functional theory calculations are employed to reveal the mechanism of C═C and C≡C formation (and related H production) following excitation to the p-Rydberg states of -butyl bromide. Ultrafast pump-probe mass spectrometry shows that nonadiabatic relaxation operates as a multistep process reaching an intermediate state within ∼500 fs followed by relaxation to a final state within 10 ps of photoexcitation. Absorption of three ultraviolet photons accesses the dense p-Rydberg state manifold, which is further excited by the probe beam for C─C bond dissociation and dehydrogenation reactions.