Marco F. Wiedenhoeft

An investigation of dissociative resonant photoionization in HCl and DCl using two-dimensional photoelectron spectroscopy

Photoelectron spectra in the vicinity of the 2p3/2,1/2 → σ* dissociative resonances in HCl and DCl have been recorded using two-dimensional photoelectron spectroscopy. The comprehensive data suggest that the explanation for the negative spectral contribution observed in an atomic line, which arises from autoionization following dissociation, might be more complex than the one proposed by Feifel et al (2000 Phys. Rev. Lett. 85 3133). These authors attributed this feature solely to continuum–continuum interference between resonant atomic and molecular Auger contributions, the latter occurring prior to complete dissociation, but resulting in an electron with the same kinetic energy as one produced in the atomic decay. The new data reveal a similar spectral feature in a region of the spectrum where this type of interference cannot occur. Consequently, an interference mechanism that does not require the energy of the resonant Auger electron be the same whether it is emitted before or after the molecule dissociates is indicated, such as the one discussed by Pahl et al (1998 Phys. Rev. Lett. 80 1865). Alternatively, the two-dimensional resonant enhancements, observed in the region of the negative spectral contribution, could be attributed to Auger decay to multiple final ion states, before the dissociating molecule has fragmented completely.

New low-lying mirroring singly and doubly excited resonances in neon

Many new resonances in neon have been discovered by virtue of their LS-forbidden mirroring partial cross section profiles. In particular, all six of the previously undetected 2s22p4(3P)3s([2,4]P)3p(3[S, P, D] 1) resonances have been observed. These results confirm our earlier prediction (Canton-Rogan et al 2000 Phys. Rev. Lett. 85 3113) that mirroring triplet resonances are observable in partial cross sections where continuum spin–orbit effects exist, and suggest that future experimental studies of other atoms will also reveal new resonances.

High-resolution photoelectron spectroscopy in atoms and molecules

New features are revealed by critically combining high photon resolution from the Advances Light Source and differential photoelectron spectroscopic techniques. Two LS-forbidden doubly-excited resonances have been observed in the 3p3/2,1/2−1 partial cross-sections of Ar which exhibit mirroring profiles, resulting in complete cancellation in the total photoionization cross-section as was predicted by Liu and Starace [Phys. Rev. A 59, R1731 (1999)]. We will also discuss recent preliminary measurements on the vibrational structure and partial rates of resonant Auger decay of the N 1s→2π core excitation in nitric oxide.