W. Denzer

The Photoionization of Ammonia revisited. The Vibrational Autoionization of NH3 and its three Isotopomers in the 10-12 eV photon energy range.

Abstract The photoionization efficiency curves of NH 3 and its three isotopomers have been investigated in the photon energy range of the first ionized state. From the analysis of the corresponding vibrational structure, wavenumbers (ω e ) and anharmonicity constants (ω e χ e ) are deduced. The detailed investigation of the abundant autoionization structure tends to show the adiabatic ionization energy to be 10.072 ± 0.010 eV for NH 3 , NH 2 D and NHD 2 and 10.083 ± 0.010 eV for ND 3 . All autoionization features were classified in vibrational progressions (ν 2 bending mode) belonging to n sa 1 (or n d) and n pe ( n = 5, 6, 7) Rydberg series. Vibrational autoionization occurs through Δν transitions up to −9. A qualitative analysis of the intensity distribution of these series strongly supports that transitions involving odd Δν values are favoured. This observation can be understood by applying group theoretical considerations to the theory of vibrational autoionization.

The threshold-photoelectron spectrum of NH3

Abstract Using synchrotron radiation, we have investigated the threshold-photoelectron spectrum of NH3 between 10 and 30 eV photon energy. In contrast to the He(I)-photoelectron spectrum, the threshold-photoelectron spectrum shows three bands between 10 and 21 eV photon energy. The first band is dominated by the vibrational autoionization of the 5sa1, the 6sa1 and the 6pe Rydberg series. Between the first and second band, a new contribution, starting at 13.26 eV, is assigned to the autoionization of (a) member(s) of Rydberg series converging to the e−1 ionization continuum. Its (their) autoionization populates the upper vibrational levels of the NH+3 ( X 2A1) state. From about 14.5 eV the A 2E band structures are identified. However, differences between the A 2E band shapes in the He(I)- and the threshold-photoelectron spectra suggest that very likely autoionization contributions are involved in the latter spectrum. These phenomena could play a role in the production of the NH+2 and NH+ fragment ions. The last very weak band, at about 25 eV in the photoelectron spectrum, is assigned to the NH+3 ( B 2A1) state.

About the double ionization of ammonia and carbon dioxide. A comparison between photoionization and electron impact

Abstract The double ionization of NH 3 and CO 2 is investigated by photoionization in the 30–60 eV photon energy range and electron impact from 30 to 100 eV. The lowest onset for NH 3 2+ formation, measured for the first time by photoionization, is at 34.5±0.2 eV. By electron impact this threshold is at 34.8±0.2 eV. For CO 2 2+ this onset is measured at 37.5±0.1 eV by photoionization and 38.0±0.1 eV by electron impact. Close to these onsets two double-ionization energies are observed: 38.5±0.1 eV by photoionization and 39.5±0.2 eV by electron impact. These have probably to be ascribed to two different CO 2 2+ states. Higher-lying doubly ionized states of CO 2 are detected in the 60–100 eV electron impact energy range.

Photoionization mass spectrometry of kinetic energy-selected ions. The translational energy distribution of N+ /N2 in the inner-shell ionization energy range

Abstract An ion retarding potential difference (IRPD) method has been used to investigate the ion yield and kinetic energy distributions of N + /N 2 produced by photoionization mass specrometry using synchrotron radiation. Photoion yield curves of energy selected N + ions are deduced. Translational energy distribution of N + at energies of the N(1s)→π*, N(1s)→( nl ) 1 and above the N(1s) −1 threshold are determined. Comparison is made with previous photoin-photoelectron coincidence work using time-of-flight (TOF) measurements.

Core excited states in BF2Cl and BFCl2

Abstract The mixed boron halides BF 2 Cl and BFCl 2 exist in a statistical equilibrium with BF 3 and BCl 3 and cannot be isolated pure. This work has shown that inner-shell excitation processes in these unsymmetrical halides can be studied using specific mass selected fragment ions. The photoion yield spectra have been recorded by means of monochromatized synchroton radiation in the energy range 190–210 eV. Electronic transitions have been assigned on the basis of estimated B(1s) ionization energies (BF 2 Cl:201.8 eV; BFCl 2 :200.8 eV) and a correlation with core excited states in BF 3 and BCl 3 . In agreement with the MO theory, BF 2 Cl and BFCl 2 show four resonances. Two of them, in the case of BF 2 Cl, are shape resonances with term values −2.7 and −4.0 eV, respectively.