J.E. Collin

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.

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.

High resolution electron energy loss spectroscopy of NH3 in the 5.5–11 eV energy range

New data have been obtained about the singlet excited states of ammonia in the 5.5–11 eV energy range by electron energy loss spectroscopy. The 50 eV excitation spectrum has been analyzed with high energy resolution (15 meV) at several scattering angles ranging from 4° to 40°. Some known vibrational progressions have been completed by new additional terms with high quantum numbers v’. The differential cross section for the five lowest energy singlet states have been measured at 50 eV impact energy as a function of the scattering angle. These data lead to discuss the classification of the Rydberg series.

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.

High-resolution HeI photoelectron spectrum of acetonitrile

Abstract The photoelectron spectrum of acetonitrile has been revisited under high resolution and high sensitivity using the HeI resonance line. Ionization of the three outermost valence molecular orbitals has been discussed in terms of ionization energies and vibrational frequencies. Additional vibration terms have been reported. Ionization of the 2e molecular orbital is accompanied by a Jahn—Teller effect involving the ν 8 degenerate mode. The second band of the spectrum shows weak features assigned to the excitation of the degenerate modes ν 6 and ν 8 . The second excited ionic state has been suggested to be of E symmetry.