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β‐Carotene Revisited by Transient Absorption and Stimulated Raman Spectroscopy
Author(s) -
Quick Martin,
Kasper MarcAndré,
Richter Celin,
Mahrwald Rainer,
Dobryakov Alexander L.,
Kovalenko Sergey A.,
Ernsting Nikolaus P.
Publication year - 2015
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201500586
Subject(s) - raman spectroscopy , chemistry , dihedral angle , ultrafast laser spectroscopy , intermolecular force , picosecond , excited state , absorption (acoustics) , absorption spectroscopy , spectroscopy , femtosecond , vibrational energy relaxation , analytical chemistry (journal) , relaxation (psychology) , absorption band , molecular physics , molecule , atomic physics , materials science , laser , optics , hydrogen bond , organic chemistry , psychology , social psychology , physics , quantum mechanics , composite material
β‐Carotene in n ‐hexane was examined by femtosecond transient absorption and stimulated Raman spectroscopy. Electronic change is separated from vibrational relaxation with the help of band integrals. Overlaid on the decay of S 1 excited‐state absorption, a picosecond process is found that is absent when the C 9 ‐methyl group is replaced by ethyl or isopropyl. It is attributed to reorganization on the S 1 potential energy surface, involving dihedral angles between C 6 and C 9 . In Raman studies, electronic states S 2 or S 1 were selected through resonance conditions. We observe a broad vibrational band at 1770 cm −1 in S 2 already. With 200 fs it decays and transforms into the well‐known S 1 Raman line for an asymmetric C=C stretching mode. Low‐frequency activity (<800 cm −1 ) in S 2 and S 1 is also seen. A dependence of solvent lines on solute dynamics implies intermolecular coupling between β‐carotene and nearby n ‐hexane molecules.