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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]

Coherent nuclear wavepacket behavior obtained by time-resolved spectroscopy is a good choice to capture the real-time evolution of molecular configuration. Using femtosecond time-resolved photoelectron imaging, we investigate the real-time evolution of the vibrational wavepacket of 2,5-difluoroaniline following the coherent excitation of an out-of-plane vibrational mode in the S1 state at 289.8 nm. Probed by an accidental resonance with the Rydberg states, the periodic oscillations with the frequency of 99 cm−1 are observed from the photoelectron kinetic energy (PKE) distributions, corresponding to the energy difference between the out-of-plane mode X10 of C–F bond and the band origin. Moreover, phase reversal of π rad between 0.66–0.75 and 1.00–1.08 eV is also observed in the PKE region. Combined with the scan of the potential energy surface in the ground cationic D0 state, the observed two ionization channels corresponding to different phases are attributed to the periodic geometry changes between the planar and the non-planar structures when the coherent wavepacket evolves from the initial vertical Franck–Condon region toward the global minimum of the S1 potential energy surface. [ABSTRACT FROM AUTHOR]

Coherent nuclear wavepacket behavior obtained by time-resolved spectroscopy is a good choice to capture the real-time evolution of molecular configuration. Using femtosecond time-resolved photoelectron imaging, we investigate the real-time evolution of the vibrational wavepacket of 2,5-difluoroaniline following the coherent excitation of an out-of-plane vibrational mode in the S 1 state at 289.8 nm. Probed by an accidental resonance with the Rydberg states, the periodic oscillations with the frequency of 99 cm -1 are observed from the photoelectron kinetic energy (PKE) distributions, corresponding to the energy difference between the out-of-plane mode X 1 0 of C-F bond and the band origin. Moreover, phase reversal of π rad between 0.66-0.75 and 1.00-1.08 eV is also observed in the PKE region. Combined with the scan of the potential energy surface in the ground cationic D 0 state, the observed two ionization channels corresponding to different phases are attributed to the periodic geometry changes between the planar and the non-planar structures when the coherent wavepacket evolves from the initial vertical Franck-Condon region toward the global minimum of the S 1 potential energy surface.

The vibrational wavepacket dynamics at the very early stages of the S 1 -T 1 intersystem crossing in photoexcited pyrimidine is visualized in real time by femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy. A coherent superposition of the vibrational states is prepared by the femtosecond pump pulse at 315.3 nm, resulting in a vibrational wavepacket. The composition of the prepared wavepacket is directly identified by a sustained quantum beat superimposed on the parent-ion transient, possessing a frequency in accord with the energy separation between the 6a 1 and 6b 2 states. The dephasing time of the vibrational wavepacket is determined to be 82 ps. More importantly, the variable Franck-Condon factors between the wavepacket components and the dispersed cation vibrational levels are experimentally illustrated to identify the dark state and follow the energy-flow dynamics on the femtosecond time scale. The time-dependent intensities of the photoelectron peaks originated from the 6a 1 vibrational state exhibit a clear quantum beating pattern with similar periodicity but a phase shift of π rad with respect to those from the 6b 2 state, offering an unambiguous picture of the restricted intramolecular vibrational energy redistribution dynamics in the 6a 1 /6b 2 Fermi resonance.

Potential energy surface for the reaction OH+CO-->H+CO2 has been calculated using the complete active space self-consistent-field and multireference configuration interaction methods with the correlation consistent triple-, quadruple-, and quintuple-zeta basis sets. A specific- reaction-parameters density functional theory has been suggested, in which the B3LYP functional is reoptimized to give the highly accurate potential energy surface with less computational efforts.