Temperature Dependence in the NEXAFS Spectra of Organic Molecules
Date
2025-06-02
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0004-2015-5509
Type
Thesis
Degree Level
Masters
Abstract
Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is a versatile technique for chemically characterizing organic materials. Its sensitivity arises from spectral features tied to functional group identities, oxidation states, and electronic structures, analyzed through electronic transitions from core electrons to unoccupied molecular orbitals. Recent studies emphasize the influence of nuclear motion, such as thermally excited vibrations, gauche defects, and conformational changes, on NEXAFS spectral shapes.
This research project investigates nuclear motion effects on NEXAFS spectra in n-alkanes and amino acids through variable temperature experiments. For n-alkanes, the study examines C 1s NEXAFS spectra of protonated (n-C60H122) and deuterated (n-C60D122) n-hexacontane. Temperature-dependent spectra reveal spectral broadening and redshifts in dominant C-H bands at higher temperatures due to elevated nuclear motion. Deuterated isotopologues display narrower features, highlighting isotope effects. These results, corroborated by molecular dynamics and density functional theory (MD-DFT) simulations, demonstrate the importance of temperature and isotopic substitution in modulating nuclear motion effects.
The study extends to the N 1s NEXAFS spectra of glycine and its derivative, glycine hydrochloride. Variable temperature experiments show how nuclear motion, including molecular vibrations and conformational changes, influences spectral broadening, peak shifts, and inconsistencies. These findings validate computational predictions and underscore the critical role of nuclear motion in defining spectral features.
This project highlights the complex interplay of temperature, isotopic effects, and nuclear motion in shaping NEXAFS spectra, advancing its application for chemical and structural characterization of diverse molecular systems.
Description
Keywords
NEXAFS, Nuclear motion effects
Citation
Degree
Master of Science (M.Sc.)
Department
Chemistry
Program
Chemistry