P. Natalis

On the photoelectron spectra of HBr and DBr

Abstract The photoelectron spectra of HBr and DBr with He I (58.4 nm) are discussed. The photoelectron spectrum of DBr confirms the predissociation of the A 2Σ+ electronic state. A rough estimate of the predissociation rate is calculated.

High resolution photoelectron spectrometry of H2S and H2Se

Abstract The He, Ne, and Ar high resolution photoelectron spectra of H2S and H2Se were investigated. The adiabatic ionization energy corresponding to 2B1, 2A1, and 2B2 states of H2S+ and H2Se+ were measured as well as values of the vibrational frequencies involved in the transitions from the neutral ground state 1A1 to these three ionic states. A sudden loss of vibrational structure in the second band of both compounds is interpreted as being due to a predissociation process leading to S+ or Se+ ion formation. A cross section variation with photon energy for the transition to upper vibrational levels of the 2B1 state, or autoionizing states as intermediate steps, is invoked to account for the extensive vibrational structure of the Ar spectrum of the two compounds.

Ionic states and photon impact-enhanced vibrational excitation in diatomic molecules by photoelectron spectroscopy. Photoelectron spectra of N2, CO and O2

Abstract Photoelectron spectra of N2, CO and O2 have been obtained using 584 A and 736–744 A photons produced in He and in Ne discharges respectively. In addition to various electronic states of N2⨪, CO⨪ and O2− ions, it is shown that vibrational excitation is enhanced by photon impact if 736–744 A rather than 584 A photons are used, especially in the ground state of N2⨪(X2Σ+g), CO⨪ (X2Σ⨪) and O2+ (X2Πg) ions. The present experimental evidence demonstrates that Franck—Condon factors for the probability of vibrational excitation, determined by photoelectron spectroscopy measurements, can be completely erroneous depending upon the mode of excitation.

On the He(I) and Ne(I) photoelectron spectra of OCS

Abstract The He(I) (58.43 nm) and Ne(I) (73.59–74.37 nm) photoelectron spectra of carbonyl sulphide have been reinvestigated at an improved resolution and a high signal-to-noise ratio; deconvolution of the data was carried out to aid interpretation of the spectra. Improved values are deduced for the vibrational wavenumbers and the ionization energies. The spin—orbit components of the A 2 Π II level are well resolved and a value of 135 cm −1 (17 ± 5 meV) is proposed for the splitting. Perturbations in the relative intensities are observed in the Ne(I) spectrum; they suggest that the autoionizing Rydberg state located around 73.7 nm is excited by the 73.59 nm Ne(I) line and contributes to populate, with different probabilities, the ionic levels of lower energy, and particularly the X 2 Π state.

Ionization, preionization and internal energy conversion in CO2, COS and CS2 by photoelectron spectroscopy

Abstract Photoelectron spectra of CO 2 , COS and CS 2 obtained with He, Ne and Ar resonance lines have been investigated. In addition to known direct photo-ionization processes, new ways of producing ions have been observed. Pressure effects and photoionization data suggest that these are the result of internal conversion between superexcited states, followed by autoionization.

On the photoelectron spectrum of CS2

Abstract High-resolution photoelectron spectra of CS 2 have been obtained by photoionization with the He(I) (58.4 nm), Ne(I) (73.58–74.37 nm) and Ar(I) (104.8–106.7 nm) resonance lines. The resolution of about 17 meV was further improved by deconvolution of the experimental data. The formation of the X 2 Π g and B 2 Σ u + states is accompanied by a weak ν 2 excitation. The spin—orbit splitting of the A 2 Π u state is completely resolved, and a value of 186 cm −1 is reported. We confirm the value of 12.689 eV for the ionization threshold of the A 2 Π u 3/2 state, and show that the small peak observed at lower energy is due to a hot band.

Ionisation energy values for the vibronic transitions from HCl X1 Σ+ (v″ = 0) to HCl+ ionic states X2 Π (v′ = 0

Abstract High-resolution Ne (I) (73.6 nm) photoelectron spectroscopic measurements provide values of the ionisation energies to the first 14 vibrational levels

Very high vibrational excitation, up to ν′ = 32, in NO+ X 1Σ+ ions by UV irradiation, evidenced by photoelectron spectroscopy

Abstract The photoelectron spectrum of NO excited by the Ne(I) 73.6 nm component exhibits a very long vibrational progression from ν′ = 0 up to ν′ = 32 for the NO+X1Σ+ ground ionic state, with an intensity distribution showing 5 maxima. This dramatic vibrational excitation is interpreted as being due to autoionization, presumably from a 2Σ− state in a ν = 4 vibrational level.

Vibrational and electronic ionic states of nitric oxide. An accurate method for measuring ionization potentials by photoelectron spectroscopy

Abstract The detailed investigation of the photoionization of nitric oxide by means of three resonance monochromatic light sources and the analysis of the photo-electron spectra leads to the detection of eight (or possibly seven) different electronic ionic states. In many cases, vibrational progressions have been observed and interpreted. The fine structure of the vibrational progression relative to the ground 1Σ+ ionic state is explained as reflecting the rotational-vibrational structure of that level. A potential energy diagram is proposed on the basis of the new results discussed. An accurate method for determining absolute values of ionization potentials by photoelectron spectroscopy without the use of a reference gas is described.

Energy levels of benzene and fluorobenzene ions by photoelectron spectroscopy

Abstract A study of the photoelectrons emitted by photoionization of benzene and fluorobenzene using different wavelength photons has been made. The detection of new ionization processes and the determination of new energy levels in those molecules is discussed. It is shown that two ionic states of benzene are found between the ground ionic state and the state previously considered as the first excited ionic state.