Effects of Protonation, Hydrogen Bonding, and Photodamaging on X-ray Spectroscopy of the Amine Terminal Group in Aminothiolate Monolayers

• The amine head group, NH2, in aminothiolate monolayers can often generate unexpectedly rich structures in its N K-edge X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra that are difficult to assign. We have carried out density functional theory (DFT) calculations to study the XPS and NEXAFS of amine head group in four different aminothiolate monolayers, namely aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT) and araliphatic 4-aminophenylbutane-1-thiol (APBT) and 3-(4”-amino-1,1’:4’,1”-terphenyl-4-yl)propane-1-thiol (ATPT), with the focus on structure changes caused by protonation, hydrogen bonding and X-ray damaging. Spectra of all possible saturated and unsaturated species, as well as X-ray damage products, such as imine, nitrile, azo species and cumulative double bonds, have been thoroughly examined. It is found that extra spectral structures observed in the experimental XPS spectra are not resulted from protonation, but from the formation of a primary ammonium. The X-ray excitation can induce cross linking between two neighboring molecules to form different complexes that contribute to the π features in NEXAFS spectra.

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NATURVETENSKAP  -- Kemi -- Teoretisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)

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