Time-resolved studies on mode-specific non-adiabatic dynamics of non-valence bound states

Abstract

Non-valence bound states have been considered as a doorway state to form the anionic species in the electron attachment process of the interstellar medium or atmosphere. Due to the weakly bound nature of the non-valence bound electron, non-adiabatic dynamics promoted by the excess electron provides quantum mechanical phenomenon such as autodetachment or non-radiative transition to the valence states. These non-adiabatic reactions of non-valence bound states were intensively investigated for several decades in energy domain, however, understanding the chemical dynamics of those reactions in time domain is still in its infancy. Here, non-adiabatic dynamics of non-valence bound states are presented by the means of the time-resolved photoelectron spectroscopy in vibrational mode-specific way. In this dissertation, the mode-specific reaction rates of the non-adiabatic dynamics in non-valence bound states were measured by combining the picosecond time-resolved velocity map photoelectron imaging technique and cryogenically-cooled ion trap. Autodetachment rate on the vibrational Feshbach resonances of the dipole-bound state (phenoxide) and quadrupole-bound state (4-cyanophenoixde) revealed highly mode-specific behaviors, which are originated from the dynamic wobbling of the loosely bound electron by the vibration of the neutral core. The relaxation dynamics on the zero-point level of the dipole-bound states (para-iodophenoxide) into the lower-lying valence anionic state was also observed, which gives several picosecond time scales. In addition, exceptionally slow autodetachment rates were observed in para-bromophenoxide and para-chlorophenoxide, which may originate from the correlation effect between the largely polarizable neutral core and dipole-bound electron. These results shed a light on the role of the doorway state of non-valence bound states, which is central issue on the anion formation in interstellar medium or gas phase reactions. Finally, ponderomotive effect on the dipole-bound state and quadrupole-bound state was firstly observed by exploiting the non-resonant strong picosecond laser pulse. Dramatic discrepancy in spectral shift with respect to the laser intensity between the dipole-bound state and quadrupole-bound state was found, implying the significant difference in polarizability of the dipole- or quadrupole-bound orbital. This study may provide the possibility of the dynamic control of the non-valence bound states by using the strong laser pulse.