Browsing by Author "Jhang, Wan Ru"

Now showing 1 - 2 of 2

Communication: Mode-dependent excited-state lifetime of phenol under the S-1/S(2 )conical intersection
(2018-07-21)
Lai, Hsin Ying
;
Jhang, Wan Ru
;
Tseng, Chien-Ming
;
應用化學系
;
Department of Applied Chemistry
Phenol can serve as a model for examining the deactivation of the aromatic amino acid tyrosine following UV excitation, which mainly occurs through a repulsive pi sigma* state along the O-H bond. The reaction barrier formed by the conical intersection between the optically bright S-1 (pi pi*) state and the dissociative S-2 (pi sigma*) state does not inhibit O-H bond rupture even though the excitation energy is below the barrier height. To examine the O-H bond-rupture dynamics in association with the initial excited vibrational modes, we used a picosecond laser to investigate the vibrational-mode-dependent excited-state lifetime of phenol under the S-1/S-2 conical intersection. Unexpectedly short lifetimes were observed in the S-1 state for a '' symmetric vibrational modes (including nu(4), nu(16a), tau OH, and nu(5)). These results clarify recent theoretical calculations showing that the relaxation from S-1 to S-2 either occurs via symmetry-allowed non-adiabatic transitions or is topographically linked to a lower energy minimum on the multidimensional potential energy surface. Published by AIP Publishing.
Triplet vs pi sigma* state mediated N-H dissociation of aniline
(2019-10-14)
Jhang, Wan Ru
;
Lai, Hsin Ying
;
Lin, Yen-Cheng
;
Lee, Chin
;
Lee, Shih-Huang
UV-excited aromatic molecules with N-H/O-H moieties often possess an important nonradiative relaxation pathway, from an optically bright pi pi* state to a dark dissociative pi sigma* state. We apply a new time-selected photofragment translational spectroscopy method to disclose a previously unknown triplet-mediated N-H dissociation of aniline prevented by the multiphoton dissociative ionization in conventional methods. We further determined the branching fractions of aniline dissociated in the pi sigma*, triplet, and ground states at 248 nm. Additionally, we selectively captured the population changes in the singlet and triplet states with ionization from different laser wavelengths, 355 or 266 nm, in time-resolved photoion yields. The combination of experimental data enables us to uniquely determine the relative ionization cross sections of the singlet and triplet states at an ionization laser wavelength of 266 nm and allows us to extensively measure the rate constants of intersystem crossing and the branching fractions at various excitation wavelengths. Published under license by AIP Publishing.