Temperature dependence in the NEXAFS spectra of protonated and deuterated <i>N</i>-hexacontane isotopologues

Abstract

This paper examines the temperature dependence of the Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of protonated and deuterated n-hexacontane isotopologues. We observe a distinctive low-energy broadening in the characteristic C–H band with a change from cryogenic to ambient sample temperature. We model this temperature dependence with density functional theory simulations of the NEXAFS spectra, calculated for geometries obtained from ab initio molecular dynamics simulations. Our results show that thermally populated nuclear motion leads to peak broadening as the sample temperature increases but that this nuclear motion broadening has significant overlap with vibronic transitions. An improved understanding of thermal broadening mechanisms is essential for the use of NEXAFS spectroscopy for chemical microanalysis, particularly where cryogenic cooling is used to reduce radiation damage.