High-Resolution Laser Threshold Photoelectron Spectroscopy of Nitric Oxide and Benzene

Abstract

As is well known, photoelectron spectroscopy (PES) by conventional techniques (i. e. using a geometrical analyser or the time-of-flight method for the photoelectron energy analysis /1, 2/) suffers from the drawback of an inadequately low resolution compared to the line-width available by commercial pulsed dye lasers. The use of conventional PES with its resolution of somewhat better than 10 meV (80 cm⁻¹) is hence restricted to the study of vibronic ion states, and rotational ion structure cannot be studied except for cases of very large rotational level spacing e. g. for H₂ ⁺ and D₂ ⁺ /3, 4/ or levels of very high J⁺ in NO⁺ /5/. In order to make PES a suitable method for the study of ion fine structure and to utilize better the small line-widths of laser sources, a substantial improvement on photoelectron energy resolution is demanded. For this goal, we have developed the technique of threshold photoelectron spectroscopy (TPES), which we have termed photoionization resonance spectroscopy (PIRS). This method is based on the detection of photoelectrons of zero kinetic energy which are found only, if the ionizing photon(s) match exactly the energy difference between an ionic and a molecular state (i. e. if ionic and molecular state are in resonance).