A penetrating field electron-ion coincidence spectrometer for use in photoionization studies

Abstract

A versatile electron-ion coincidence spectrometer for photoionization studies is described. The spectrometer incorporates a 127 degrees cylindrical electrostatic energy analyser and a time-of-flight energy analyser. The two analysers are mounted on a turntable that can be rotated with respect to the polarization axis of the photon beam. Both analysers have a penetrating field stage which provides very high detection efficiency over a large solid angle and excellent threshold energy resolution ( approximately 3 meV) for the detection of charged particles. The analysers can also detect energetic particles. The time-of-flight analyser is used specifically for the separation and detection of different charge states of molecular photodissociation products. The use of the spectrometer to observe photoelectron-photo-ion coincidences and photoelectron-photoelectron coincidences in a variety of experiments (TPEPICO, PEPICO, TPEPECO) is illustrated by a study of the photo-double ionization of argon and of the dissociation products from the v=0 level of the c state of oxygen at 24.56 eV. Additionally, a spectrum of coincidences between threshold photoelectrons (TPESCO) is presented in the region of the 3P double ionization potential of argon.

Threshold photoelectron studies of isoxazole over the energy range 9.9–30eV

“…This structure may be due to the production of very low energy electrons by highly excited Rydberg states. Such signals have been seen previously in threshold photoionization studies, for example in argon [18].…”

“…We suggest tentatively the following vibrational modes for the observed series, with their vibrational energies given in parentheses: v 18 17 is lower than that of the neutral ground state by 5 and 10 meV, respectively. The differences in the remaining series are not more than 4…”

“…Threshold photoelectron spectra were recorded by a photoelectron spectrometer employing the penetrating field technique [17], which has been described in detail previously [18]. The penetrating electrostatic field collects photoelectrons having energies lower than about 5 meV with very high efficiency and simultaneously discriminates against higher energy photoelectrons.…”

“…In the most recent calculations [11,12], the IR and Raman spectra of isoxazole and isoxazole-d 3 have been reassigned with the aid of DFT theory [11] and a systematic study of the anharmonic vibrational frequencies has been carried out using both the B3LYP density functional and MP2 ab initio techniques [12]. The totally symmetric 1 (A')-13 (A') modes are the in-plane vibrations while the 14 (A")- 18 (A") are out-of plane vibrations. The energies of the three C-H stretching modes 1 -3 are located near 3300 cm -1 (409 meV) and the energies of the remaining modes lie below 1700 cm -1 (211 meV).…”

High‐resolution Photoelectron Spectroscopy

“…More recently, threshold photoelectron spectrometers in which the threshold electrons are extracted by a weak electric field penetrating into the photoionization region have proven to be well suited to high-resolution threshold photoelectron spectroscopic studies (Hall et al 1992). An example, taken from the work of Onuma et al (1999), is presented in Fig.…”