Showing papers by "John D. Bozek published in 1999"

Carbon 1s photoelectron spectrum of methane: Vibrational excitation and core-hole lifetime

Abstract: The carbon $1s$ photoelectron spectrum has been measured for ${\mathrm{CH}}_{4}$ at photon energies of 302, 320, and 330 eV and for ${\mathrm{CD}}_{4}$ at 330 eV with an instrumental resolution about half the natural linewidth. These spectra have been analyzed to obtain vibrational spacings, vibrational intensities, and the lifetime of the carbon $1s$ core-hole state. The vibrational intensities vary with photon energy, in agreement with earlier results. At 330 eV, the observed Franck-Condon factors for both ${\mathrm{CH}}_{4}$ and ${\mathrm{CD}}_{4}$ can be understood only if anharmonic effects (consistent with the predictions of theory) are included. On the other hand, the vibrational spacings in ${\mathrm{CH}}_{4}$ show no evidence for anharmonicity (in contrast with theoretical predictions). In ${\mathrm{CD}}_{4}$ the observed anharmonicity in the vibrational energy spacings is about half of the predicted value, but the experimental and theoretical values differ only by an amount comparable to the experimental uncertainty. The measured values of the lifetime show a dependence on photon energy; this is attributed to failure of the theory of post-collision interaction to predict correctly the observed electron spectrum near threshold. At 330 eV, the measured Lorentzian lifetime, 93--95 meV, agrees with predictions of simple theory, but not with the prediction of more complete theory. It is also observed that there are systematic discrepancies between the observed line shapes and those predicted by the theory of postcollision interaction.

Photon Energy Dependence of the 1{sigma}{sub u}/1{sigma}{sub g} Intensity Ratio in Carbon 1s Photoelectron Spectroscopy of Ethyne

Abstract: High-resolution measurements of the C 1s photoelectron spectrum of ethyne (acetylene) at photon energies between 297 and 348thinspthinspeV have been analyzed to give the energy dependence of the relative cross sections for ionization of the 1{sigma}{sub g} and 1{sigma}{sub u} orbitals. The 1{sigma}{sup {minus}1}{sub u}/1{sigma}{sup {minus}1}{sub g} intensity ratio is greater than 1 at the lowest photon energies but reaches a minimum of about 0.6 between 315 and 320thinspthinspeV. These results can be understood in terms of the effect of shape resonance on the ionization cross section and provide quantitative information on the position and magnitude of such resonances. {copyright} {ital 1999} {ital The American Physical Society}

Molecular-field splitting and vibrational structure in the phosphorus 2p photoelectron spectrum of PF3

Abstract: The experimental phosphorus 2p spectrum of PF3 shows vibrational structure corresponding to the symmetric phosphorus-fluorine stretching mode, with a fundamental frequency of 121.7 meV. In addition, the spectrum shows that the 2p3/2 peak is a doublet split by 146 meV. This molecular-field splitting arises because the anisotropic molecular environment lifts the threefold degeneracy of the 2p orbitals. The observed vibrational structure is compared with that predicted by theory, either treating the core hole explicitly or using the equivalent-cores approximation to simulate the effects of the core hole. Ab initio calculations of the molecular-field splitting that include core-valence electron correlation predict a value in good agreement with the experimental value.

Inner-valence states of CO+: Comparison of photoelectron and resonant Auger spectra

Abstract: We have recorded very-high-resolution photoelectron spectra of the inner-valence structure of CO+, excited with synchrotron radiation, and have resolved fine structure never previously observed. Recently presented resonant Auger decay spectra (Sundin et al. 1997 Phys. Rev. A56 480, 1997 J. Phys. B: At. Mol. Opt. Phys. 30 4267) have established the energy of two-hole one-particle Rydberg states, and a comparison with these has been made to explain some details of the spectra.

Synchrotron radiation excited photoelectron spectrum of h2+ with rotational resolution

Abstract: The rotational branching ratio in the photoelectron spectrum of has been investigated using synchrotron radiation. At the photon energy , the S branch has a considerably higher relative intensity than when excited with He I (, or with Ne I (, ) radiation.

the C K-shell and the F K-shell excitation regions

Abstract: Fragment ions from CF Cl (a51-3) have been measured in the soft X-ray region using monochromatized synchrotron a 42a radiation and a time-of-flight mass spectrometer. The atomic chlorine ion exhibits the highest yield at most photon energies. Following Cl 2p photoionization, C-Cl bonds are broken frequently, but the process where only the C-F bond is cleaved 1 does not occur, yielding no production of CF Cl . The reverse phenomenon happens at the F 1s photoionization; the a2 14 2a rupture of one C-Cl bond does not take place. These findings, site-specific fragmentation, are ascribed to the characteristics of Auger transitions creating valence holes in different molecular orbitals. © 1999 Elsevier Science B.V. All rights reserved.