Search

Single-site N1s and O1s double core ionisation of the NO and N2O molecules has been studied using a magnetic bottle many-electron coincidence time-of-flight spectrometer at photon energies of 1100 eV and 1300 eV. The double core hole energies obtained for NO are 904.8 eV (N1s-2) and 1179.4 eV (O1s-2). The corresponding energies obtained for N2O are 896.9 eV (terminal N1s-2), 906.5 eV (central N1s-2), and 1174.1 eV (O1s-2). The ratio between the double and single ionisation energies are in all cases close or equal to 2.20. Large chemical shifts are observed in some cases which suggest that reorganisation of the electrons upon the double ionization is significant. Δ-self-consistent field and complete active space self-consistent field (CASSCF) calculations were performed for both molecules and they are in good agreement with these results. Auger spectra of N2O, associated with the decay of the terminal and central N1s-2 as well as with the O1s-2 dicationic states, were extracted showing the two electrons emitted as a result of filling the double core holes. The spectra, which are interpreted using CASSCF and complete active space configuration interaction calculations, show atomic-like character. The cross section ratio between double and single core hole creation was estimated as 1.6 × 10-3 for nitrogen at 1100 eV and as 1.3 × 10-3 for oxygen at 1300 eV. [ABSTRACT FROM AUTHOR]

The photoelectron shake-up satellite spectra that accompany the C1s and O1s main lines of carbon monoxide have been studied by a combination of high-resolution x-ray photoelectron spectroscopy and accurate ab initio calculations. The symmetry-adapted cluster-expansion configuration-interaction general-R method satisfactorily reproduces the satellite spectra over a wide energy region, and the quantitative assignments are proposed for the 16 and 12 satellite bands for C1s and O1s spectra, respectively. Satellite peaks above the π-1π* transitions are mainly assigned to the Rydberg excitations accompanying the inner-shell ionization. Many shake-up states, which interact strongly with three-electron processes such as π-2π*2 and n-2π*2, are calculated in the low-energy region, while the continuous Rydberg excitations are obtained with small intensities in the higher-energy region. The vibrational structures of low-lying shake-up states have been examined for both C1s and O1s ionizations. The vibrational structures appear in the low-lying C1s satellite states, and the symmetry-dependent angular distributions for the satellite emission have enabled the Σ and Π symmetries to be resolved. On the other hand, the potential curves of the low-lying O1s shake-up states are predicted to be weakly bound or repulsive. [ABSTRACT FROM AUTHOR]

We have measured the vibrational structures of the N 1s photoelectron mainline and satellites of the gaseous N2 molecule with the resolution better than 75 meV. The gerade and ungerade symmetries of the core-ionized (mainline) states are resolved energetically, and symmetry-dependent angular distributions for the satellite emission allow us to resolve the Σ and Π symmetries of the shake-up (satellite) states. Symmetry-adapted cluster-expansion configuration-interaction calculations of the potential energy curves for the mainline and satellite states along with a Franck-Condon analysis well reproduce the observed vibrational excitation of the bands, illustrating that the theoretical calculations well predict the symmetry-dependent geometry relaxation effects. The energies of both mainline states and satellite states, as well as the splitting between the mainline gerade and ungerade states, are also well reproduced by the calculation: the splitting between the satellite gerade and ungerade states is calculated to be smaller than the experimental detection limit. [ABSTRACT FROM AUTHOR]

A theoretical method for calculating magnetic circular dichroism (MCD) of molecules is presented. We examined the numerical accuracy and the stability of the finite perturbation (FP) method and the sum-over-state (SOS) perturbation method. The relativistic effects are shown to be important for the MCD spectra of molecules containing heavy elements. Calculations using the FP and the SOS methods were carried out for ethylene, para- and ortho-benzoquinone, showing that the FP method is superior to the SOS method, as expected. The relativistic effect was examined using the second-order Douglas-Kroll Hamiltonians for the halogen molecules F2, Cl2, Br2, and I2. The Faraday terms of I2 and Br2 were strongly affected by the relativistic effects, while the effect was negligible for Cl2 and F2. [ABSTRACT FROM AUTHOR]

The SAC-CI method was applied to the electronic excitation spectra of Cl[sub 2]O, ClOOCl, and F[sub 2]O. The ensuing theoretical spectra have well reproduced the experimental spectra for Cl[sub 2]O and Cl[sub 2]O[sub 2] and detailed characterizations of the peaks and structures were given by calculating the oscillator strength, second moment, and dipole moment for each state. For the UV region of Cl[sub 2]O, the observed peaks were assigned to the valence excited states in agreement with the previous theoretical studies. For the VUV region, in the present study we have proposed the first theoretical assignments. Both valence and Rydberg excited states were calculated in this energy region, some of which resulted different from the experimental assignments. For Cl[sub 2]O[sub 2], the broad band of the experimental spectrum was mainly attributed to one intense peak due to the 3B state. The theoretical spectrum above 6 eV was proposed, which so far has not been addressed and clarified before. The excitation spectrum of F[sub 2]O up to about 13.0 eV was calculated and compared with the previous theoretical study. The shape and main features of the calculated spectrum was found to be very similar to that of Cl[sub 2]O, and the valence and Rydberg excited states were clearly discriminated. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]