Development of laser photoelectron spectroscopy based on resonantly enhanced multiphoton ionization

Abstract

Abstract This review article is mainly concerned with laser photoelectron spectroscopy based on REMPI (resonantly enhanced multiphoton ionization), consisting of two parts. One is associated with the measurement of photoelectron kinetic-energy distribution and the other is associated with the measurement of zero-kinetic-energy (ZEKE) photoelectrons in very high resolution. These two techniques are complementary to each other. During the last three decades, the author and co-workers have carried out photoelectron spectroscopic studies of molecules in the gas phase, using the HeI 584 A resonance line and a nanosecond tunable UV–visible laser. In this article, firstly the author’s background in the field of molecular photoelectron spectroscopy is described briefly, by mentioning three topics of HeI photoelectron spectroscopy. Secondly, the principle and characteristics of laser photoelectron kinetic-energy spectroscopy and its application to several typical topics, namely, one-photon forbidden states (O 2 ), autoionization from a super-excited state (NO), and small van der Waals molecules (NO–Ar and the NO 2 dimer), and some others. Thirdly, the principle and characteristics of ZEKE photoelectron spectroscopy are described, together with its application to the following several topics: (1) rotational spectra of NO + , (2) vibrational coupling of (naphthalene) + , (3) large-amplitude torsional motion of (tolane) + , (4) rotational isomers of ( cis and trans n -propylbenzene) + and structural isomers of (2-hydroxypyridine) + , (5) proton tunneling of (tropolone) + and (9-hydroxyphenalenone) + , (6) intramolecular vibrational redistribution of trans stilbene, and (7) cation van der Waals molecules of aniline–Ar n ( n =1,2) and azulene–Ar. All the results mentioned as examples are those obtained in the author’s laboratory.