Evaluation of the energetic position of the lowest excited singlet state of beta-carotene by NEXAFS and photoemission spectroscopy
2001 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1506, no 3, 260-267 p.Article in journal (Refereed) Published
In carotenoids the lowest energetic optical transition belonging to the pi -electron system is forbidden by symmetry, therefore the energetic position of the S-1 (2(1)A(g)) level can hardly be assessed by optical spectroscopy. We introduce a novel experimental approach: For molecules with ir-electron systems the transition C1s --> 2p(pi*) from inner-atomic to the lowest unoccupied molecular orbital (LUMO) appears in X-ray absorption near edge spectra (NEXAFS) as an intense, sharp peak a few eV below the carbon K-edge. Whereas the peak position reflects the energy of the First excited singlet state in relation to the ionization potential of the molecule, intensity and width of the transition depend on hybridization and bonding partners of the selected atom. Complementary information can be obtained from ultraviolet photoelectron spectroscopy (UPS): At the low binding energy site of the spectrum a peak related to the highest occupied molecular orbital (HOMO) appears. We have measured NEXAFS and UPS of beta -carotene. Based on these measurements and quantum chemical calculations the HOMO and LUMO energies can be derived.
Place, publisher, year, edition, pages
2001. Vol. 1506, no 3, 260-267 p.
NEXAFS, UPS, beta-carotene, HOMO, LUMO, S-1, k-shell excitation, fluorescence, molecules, photosynthesis, absorption, energies, spectra
IdentifiersURN: urn:nbn:se:kth:diva-21212ISI: 000173001300013OAI: oai:DiVA.org:kth-21212DiVA: diva2:339909
QC 201005252010-08-102010-08-10Bibliographically approved