NEXAFS and XPS of p-Aminobenzoic Acid Polymorphs: The Influence of Local Environment

16th International Conference on X-ray Absorption Fine Structure

Stevens, J.S.^1 ; Gainar, A.^1 ; Jaye, C.^2 ; Fischer, D.A.^2 ; Schroeder, S.L.M.^3,4

School of Chemical Engineering and Analytical Science, University of Manchester, Oxford Road, Manchester

M13 9PL, United Kingdom^1

Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg

MD

20899, United States^2

School of Chemical and Process Engineering, University of Leeds, Leeds

LS2 9JT, United Kingdom^3

DIAMOND Light Source Ltd., Chilton, Didcot

LS2 9JT, United Kingdom^4

关键词: Aminobenzoic acid;    Carboxylic acid dimers;    Carboxylic acid groups;    Intensity variations;    Inter-molecular bonding;    Local environments;    P-aminobenzoic acid;    Polymorphic forms;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/712/1/012133/pdf
DOI  :  10.1088/1742-6596/712/1/012133

来源: IOP

【 摘 要 】

Nitrogen K-edge XPS and NEXAFS of the two polymorphic forms of para- aminobenzoic acid (PABA) are significantly different reflecting variation in hydrogen bonding. Alteration in hydrogen bonding at the amino group leads to a shift to high energy for both the XPS N 1s core level and the 3π∗ NEXAFS resonance with β-PABA. Participation of the amine group in the aromatic system causes the 1π∗ resonance to be sensitive to the nature of the intermolecular bonding at the para-carboxylic acid group, and a shift to low energy for α- PABA is observed due to hydrogen-bonded carboxylic acid dimer formation. FEFF calculations also successfully reproduce both the energy and intensity variations observed for the σ∗ shape resonance associated with the C-N bond, with the majority of the decrease in energy observed for b-PABA arising from the longer C-N bond.