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The non-adiabatic relaxation processes and the fragmentation dynamics of Rydberg-excited N,N,N′,N′-tetramethylmethylenediamine (TMMDA) are investigated using femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. Excitation at 208 nm populates TMMDA in a charge-localized 3p state. Rapid internal conversion (IC) to 3s produces two charge-delocalized conformers with independent time constants and distinct population ratios. As the system explores the 3s potential surface, the structural evolution continues on a 1.55 ps timescale, followed by a slower (12.1 ps) relaxation to the ground state. A thorough comparison of the time-dependent mass and photoelectron spectra suggests that ionization out of the 3p state ends up with the parent ion, the vibrational energy of which is insufficient for the bond cleavage. On the contrary, by virtue of the additional energy acquired by IC from 3p, the internal energy deposited in 3s is available to break the C–N bond, leading to the fragment ion. The fragmentation is found to occur on the ion surface instead of the Rydberg surface. [ABSTRACT FROM AUTHOR]

The excited-state intramolecular proton transfer (ESIPT) process and subsequent electronic relaxation dynamics in methyl salicylate have been investigated using femtosecond time-resolved ion yield spectroscopy combined with time-resolved photoelectron imaging. Excitation with a tunable pump pulse populates the keto tautomer in the first excited electronic state S1(ππ*). As a hydrogen atom transfers from the phenolic group to the carbonyl group within 100 fs, the molecular geometry changes gradually, leading to a variation in the electronic photoionization channel. By virtue of the accidental resonance with some intermediate Rydberg states, the time-dependent photoelectron spectra provide a direct mapping of the ESIPT reaction from the initially populated keto tautomer to the proton-transferred enol tautomer. Subsequently, the population around the enol configuration undergoes intramolecular vibrational redistribution on a subpicosecond time scale, followed by internal conversion to the ground state with a wavelength-dependent lifetime in the picosecond range. Furthermore, the excitation energies of several Rydberg states in methyl salicylate are determined experimentally. [ABSTRACT FROM AUTHOR]

Coherent wavepacket motion in photoexcited pyrimidine has been initiated and visualized in real time using femtosecond time-resolved ion-yield spectroscopy. A coherent superposition of at least four low-frequency Frank-Condon (FC) active modes is created in the first excited electronic state (S1), leading to a vibrational wavepacket. Its composition is manipulated experimentally by tuning the excitation wavelength in the range 309–313 nm to populate the selected vibrational levels. Interference among these vibrational levels is directly characterized by a clear quantum beat superimposed on a single-exponential decay. Fourier transform analysis of the wavelength-dependent transients shows modulation at different frequencies, providing a direct signature of multi-mode vibrational coherence resulting from the coherent excitation process. The sensitivity of the parent-ion transient to the vibrational wavepacket dynamics probably arises because different modes are connected by variable FC factors to the 3s and 3p Rydberg states. [ABSTRACT FROM AUTHOR]

The outward diffusion equation of the instantaneously released ion in pores of a porous layer was derived theoretically, and then applied for the study of oxygen ion diffusion in porous Fe which was generated by fast electrochemical reduction of solid Fe2O3 in molten CaCl2. The solid cathode was constructed by filling mixed Fe/Fe2O3 powders (8:1 in mass ratio) into cylindrical cavities in a Mo foil substrate. This fabricated mini porous electrode was subjected to the double-potential treatment with selected potentials according to the cyclic voltammetry (CVs) of Fe2O3. The lower potential of −0.7V (vs. quartz sealed Ag/AgCl) enabled fast reduction of solid Fe2O3, and instantaneous release of O2− ions into the pores of the generated porous Fe. During the standing time at −0.7V, outward O2− diffusion occurred, and the amount of O2− remaining in the porous electrode was determined by re-oxidation at a potential of 0.16V. The experimental outward diffusion of O2− was in good accord with the theoretical equation, consequently, the diffusion coefficients of O2− in CaCl2 contained in porous Fe were evaluated as 8.2×10−6, 9.1×10−6 and 1.0×10−5 cm2 s−1 at 1108, 1123 and 1138K respectively. These data followed the Arrhenius’ equation with diffusion activation energy of about 67.8kJmol−1. The whole work can provide a simple method for the study of diffusion in a porous electrode, and the designed ultrafast deoxidation of solid Fe2O3 may be also helpful to the present effort in developing iron metallurgy by molten salt electrolysis. [ABSTRACT FROM AUTHOR]