A highly sensitive electron energy analyzer which utilizes a “magnetic bottle” combined with a retarding electrostatic field has been developed for Penning ionization electron spectroscopy. A beam of metastable rare-gas atoms is crossed with a continuous supersonic sample beam in the source region of the analyzer. The emitted electrons are collected by an inhomogeneous magnetic field (the magnetic bottle effect) with a high efficiency of nearly 4π solid angle, which is more than 103 times higher than that of a conventional hemispherical analyzer. The kinetic energy of electrons is analyzed by scanning the retarding field in a flight tube of the analyzer in the presence of a weak magnetic field. The velocity of the metastable atoms can also be resolved by a time-of-flight method in the present instrument. Examples of Penning ionization electron energy spectra as a function of collision energy are presented for Ar and N2 with metastable He*(2 3S) atoms. This instrument has opened the possibility for extensive studies of Penning ionization electron spectroscopy for low-density species, such as clusters, ions, electronically excited species, unstable or transient species, and large molecules with low volatility.

Penning ionization of 2-aminoethanol (AE), ethylamine (EA), N-methyl-2-aminoethanol (MAE), and 2-methoxy-N-methylethylamine (MMA) upon collision with He*(23S) metastable atoms has been studied by two-dimensional electron-energy/collision-energy-resolved Penning ionization electron spectroscopy (2D-PIES) in connection with intramolecular hydrogen bonding of OH···N and NH···O types. In AE and MAE, OH···N type hydrogen bonds were found to be preferentially formed, whereas in MAE, observed data gave a confirmation of the NH···O type hydrogen bond. Effects of hydrogen bond formation were observed for ionization bands of nonbonding orbitals related to the hydrogen bond. Associated with hydrogen bond formation, the relative band intensity in PIES become considerably decreased, the slope of the collision energy dependence of partial ionization cross section become much less negative, and the peak energy shift becomes much less negative.

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Penning ionization electron spectra (PIES) of van der Waals clusters have been observed for the first time by means of a newly developed magnetic bottle electron spectrometer, which is 1000 times more efficient than a conventional PIES apparatus. In the PIES of Ar clusters with He*(2 3S), two bands of Ar 3p hole characters with different ionization energies (IE), band A (IE=ca.15 eV) and band B (IE=ca.13.5 eV), were observed. Band A was assigned to vertical transitions in Franck–Condon regions corresponding to the band in the ultraviolet photoelectron spectra (UPS) of clusters reported by Carnovale et al. [J. Chem. Phys. 90, 1452 (1989)]. Band B, which is an extra band missing in the UPS of clusters, can be ascribed to the autoionization into a stable structure of Arn+ via superexcited states of Arn. Band B can be considered as an adiabatic ionization which is forbidden as a direct ionization. The energy difference of ca. 1.5 eV between the vertical IE for band A and the adiabatic IE for band B was found to agree well with the reported binding energy of the trimer ion core.