Multiphoton Ionization Photoelectron Spectroscopy on Dynamic Behavior of Excited Molecules

Abstract

In the present work, multiphoton ionization (MPI) experiments with one- and two-color lasers were carried out mainly for NO molecule in the gas phase to study dynamic behavior of its highly excited states including super-excited states. Molecules of NO were excited to specific vibrational levels (v'=0 or 4) of Rydberg A and C states. In the ionization experiments, we have initially measured ion-current spectra as a function of laser wavelength, and then obtained photoelectron spectra at several ion-current peaks which correspond to specific vibrational (and rotational) levels of the Rydberg states. In direct (1+1) and (2+1)resonant ionization of NO through the Rydberg A and C states, we have obtained single photoelectron peaks due to Δv=0 ionization transitions. However, when NO is further excited to higher Rydberg states from the C state, we have obtained the photoelectron spectra for the first time which are due to autoionization from specific vibrational levels of super-excited Rydberg states. It is emphasized that the present work presents several typical important examples for studying dynamic behavior of higher excited states of molecules in the gas phase.