Attosecond timing of electron emission from a molecular shape resonance.

Shape resonances in physics and chemistry arise from the spatial confinement of a particle by a potential barrier. In molecular photoionization, these barriers prevent the electron from escaping instantaneously, so that nuclei may move and modify the potential, thereby affecting the ionization process. By using an attosecond two-color interferometric approach in combination with high spectral resolution, we have captured the changes induced by the nuclear motion on the centrifugal barrier that sustains the well-known shape resonance in valence-ionized N2. We show that despite the nuclear motion altering the bond length by only 2%, which leads to tiny changes in the potential barrier, the corresponding change in the ionization time can be as large as 200 attoseconds. This result poses limits to the concept of instantaneous electronic transitions in molecules, which is at the basis of the Franck-Condon principle of molecular spectroscopy.

Accuracy and precision of the RABBIT technique.

One of the most ubiquitous techniques within attosecond science is the so-called reconstruction of attosecond beating by interference of two-photon transitions (RABBIT). Originally proposed for the characterization of attosecond pulses, it has been successfully applied to the accurate determination of time delays in photoemission. Here, we examine in detail, using numerical simulations, the effect of the spatial and temporal properties of the light fields and of the experimental procedure on the accuracy of the method. This allows us to identify the necessary conditions to achieve the best temporal precision in RABBIT measurements. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

Preventing transmission of bloodborne viruses from infected healthcare workers to patients: Summary of a new Canadian Guideline.

BACKGROUND: Although it is well documented that bloodborne viruses (BBVs), including human immunodeficiency virus (HIV), hepatitis C virus (HCV) and hepatitis B virus (HBV) have been transmitted from patients to healthcare workers (HCWs), there has also been reported transmission from HCWs to patients during the provision of health care. With remarkable progress in infection prevention, diagnosis tools, treatment regimens and major improvements in guideline development methodology, there was a need to develop an evidence-based guideline to replace the 1998 Canadian consensus document for managing HCWs infected with BBVs. PURPOSE: This article summarizes the Canadian Guideline on the Prevention of Transmission of Bloodborne Viruses from Infected Healthcare Workers in Healthcare Settings. METHODS: A Guideline Development Task Group was established and key questions developed to inform the guideline content. Systematic reviews were conducted to evaluate the risk of HCW-to-patient transmission of HIV, HCV and HBV. Environmental scans were used to provide information on Expert Review Panels, disclosure of a HCW's serologic status and lookback investigations. Federal, provincial and territorial partners and key stakeholder organizations were consulted on the Guideline. RESULTS: The risk of HCW-to-patient BBV transmission was found to be negligible, except during exposure-prone procedures, where there is a risk that injury to the HCW may result in exposure of a patient's open tissues to the HCW's blood. Risk of ensuing transmission and the rate of transmission varied by BBV, and were lowest with HIV and highest with HBV. The Guideline provides key content, including recommendations regarding criteria to determine if a procedure is an exposure-prone procedure, management of HCWs infected with a BBV, including considerations for the HCW's fitness for practice, Expert Review Panels, HCW disclosure obligations and right to privacy and lookback investigations. CONCLUSION: This new Guideline provides a pan-Canadian approach for managing HCWs infected with a BBV, with recommendations related to preventing HCW-to-patient transmission of BBVs during the provision of care.

Photoionization in the time and frequency domain.

Ultrafast processes in matter, such as the electron emission after light absorption, can now be studied using ultrashort light pulses of attosecond duration (10-18 seconds) in the extreme ultraviolet spectral range. The lack of spectral resolution due to the use of short light pulses has raised issues in the interpretation of the experimental results and the comparison with theoretical calculations. We determine photoionization time delays in neon atoms over a 40-electron volt energy range with an interferometric technique combining high temporal and spectral resolution. We spectrally disentangle direct ionization from ionization with shake-up, in which a second electron is left in an excited state, and obtain excellent agreement with theoretical calculations, thereby solving a puzzle raised by 7-year-old measurements.