title: 3s Rydberg and cationic States of pyrazine studied by photoelectron spectroscopy.
abstract: We have studied 3s(n-1 and pi-1) Rydberg states and D0(n-1) and D1(pi-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV-PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck-Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1-D0 and 3s(pi-1)-3s(n-1) conical intersections were estimated. From the line width in the D1 <-- S0 spectrum, we estimated the lifetime of D1 to be 12 fs for pyrazine and 15 fs for fully deuterated pyrazine. A similar lifetime was estimated for the 3s(pi-1) state of pyrazine by REMPI spectroscopy. The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to the D0 continuum.
authors.affiliation: Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan.
authors.forename: Mizuki
authors.initials: M
authors.lastname: Oku
authors.forename: Yu
authors.initials: Y
authors.lastname: Hou
authors.forename: Xi
authors.initials: X
authors.lastname: Xing
authors.forename: Beth
authors.initials: B
authors.lastname: Reed
authors.forename: Hong
authors.initials: H
authors.lastname: Xu
authors.forename: Chao
authors.initials: C
authors.lastname: Chang
authors.forename: Cheuk-Yiu
authors.initials: CY
authors.lastname: Ng
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Nishizawa
authors.forename: Keijiro
authors.initials: K
authors.lastname: Ohshimo
authors.forename: Toshinori
authors.initials: T
authors.lastname: Suzuki