Paper accepted for Angewandte Chemie

A study demonstrating that XPS distinguishes reliably between proton transfer and H-bonding in organic systems has now been accepted for publication in Angewandte Chemie.

Crystallography Aided by Atomic Core Level Binding Energies: Proton Transfer vs. Hydrogen Bonding in Organic Crystal Structures
J.S. Stevens, S.J. Byard, C.S. Seaton, G. Sadiq, R.J. Davey, S.L.M. Schroeder
Angewandte Chemie – International Edition 50 (2011), 9916–9918.

Paper in Journal of Fluorine Chemistry

A joint paper with two teams from the FUNFLUOS consortium has been accepted in the Journal of Fluorine Chemistry:

Aluminium(III) fluoride originating from decomposition of hydrazinium fluoroaluminate(III) under oxidative conditions: syntheses, X-ray photoelectron spectroscopy and some catalytic reactions
T. Skapin, Z. Mazej, A. Makarowicz, A. Jesih, M. Nickkho-Amiry, S. L. M. Schroeder, N. Weiher, B. Žemva, J. M. Winfield
Journal of Fluorine Chemistry 132 (2011), 703-712.

Success! VERSOX Beamline at DIAMOND Funded

It was announced today that the VERSOX soft X-ray spectroscopy beamline project at DIAMOND Light Source Ltd has been funded. Sven was one of the original proposers of this project, and as a member of the VERSOX Working Group he contributed to developing the case for supporting this beamline project. This beamline will provide our research team with a unique instrument for studying local interactions in organic materials, their nucleation – and surface chemistry in general. What makes VERSOX unique is its versatility – extending the use of soft X-ray spectroscopy beyond its traditional confines in ultra-high vacuum surface physics and chemistry. For example, soft X-ray studies of ‘wet’ soft matter, practical catalytic systems, biomaterials, pharmaceuticals, liquids and solutions will become possible for the first time in the UK. Right from the design stage the project will also take account of the needs of applied science and industrial users. As such it matches perfectly onto our research philosophy, which brings together fundamental science with its practical application.

More information is available by following this link.

Sven’s Quick Guide to Measuring a Good Absorption Spectrum

The rule to remember is this:

When you measure absorption spectra (X-ray, UV, Vis, IR…) in transmission mode then you must not have any feature in the spectrum with an absorbance higher than approximately 1.2.

The principles from which this follows are nicely explained here:

For an absorbance of 1 90% of the incident light is absorbed. So 10% of the light transmits the sample and is detected. This ensures that the detector for the transmitted light has a signal with reliable intensity.

If you have an absorbance of 2 then 99% of the light is absorbed by your sample – so the transmission detector only sees 1% of the original intensity, which is usually not quite enough to ensure low noise and a linear response of the detector.

For an absorbance of 3 the detector only gets 0.1% of the original light intensity. This intensity is already approaching the noise level in many laboratory spectrometers. So what you are measuring is probably not significant – you are probably just seeing a flat noise line due to … – electronic noise.

So if the concentration of your substance is so that the absorbance is >1.2 then you must dilute your sample or shorten the thickness of the sample.

Most of the time dilution is the better way to do it:*

Just take a defined volume (in practice usually 1 mL or 10 mL) from your solution with a volumetric pipette and fill it up to 100 mL or perhaps even 1000 mL, in a clean volumetric flask. Use clean glassware for all of this – plastics may introduce contaminants.

Accuracy is important here – especially in pipetting. A 10% error in the pipette volume will mean a 10% error in the absorbance. You should aim for 1% accuracy.

Good luck!

*Those of you interested in molecular interactions at high concentrations can’t dilute of course – you will need to get special cuvettes providing a low sample thickness.