Niels-Henrik Jensen

Resonance Raman spectrum of the transient (SCN)−2 free radical anion

Abstract The resonance Raman spectrum of the transient species (λmax = 475 nm, τ 1 2 = 1.6 μs) formed by pulse radiolysis of aqueous solutions of thiocyanate, SCN2−, is reported. The spectrum is discussed in terms of the previous assignment of this transient to the radical anion, (SCN)−2. The observed vibrational frequencies of the radical anion are consistent with substantial weakening of the SS and the CN bonds are compared with neutral thiocyanogen.

Time-resolved resonance raman spectrum of all-trans-diphenylbutadiene in the lowest excited singlet state

Abstract The resonance Raman spectrwn of all-trans-diphenylbutadiene in its lowest excited S 1 state excited in resonance with the S 1 → S n absorption band at 650 nm in non-polar solvents is reported. Three vibrational bands at 1572, 1481 and 1165 cm −1 are observed. A possible assignment of the the 1481 cm −1 band to the CC double-bond stretching mode may support the lowest S 1 state being of 1 A g *− symmetry.

Resonance Raman spectra of the transient Cl− and Br− radical anions

Abstract The resonance Raman spectra of the short-lived radical anions Cl 2 − and Br − in aqueous solution are reported. The observed wavenumbers of 279 cm −1 for Cl − and 177 cm −1 for Br − are about 10% higher than those published for the corresponding species isolated in solid argon matrices. Under the assumption of a Morse potential. harmonic frequencies and anharmonicity constants are calculated to be 286.4 and 3.83 cm −1 for Cl − and 187.2 and 5.17 cm −1 for Br − . These values lead to extrapolated dissociation energies of 0.66 and 0.21 eV, respectively. These results are compared with those from matrix-isolation studies at low temperatures and work in the gas phase.

RESONANCE RAMAN and ABSORPTION SPECTRA OF ISOMERIC RETINALS IN THEIR LOWEST EXCITED TRIPLET STATES

Abstract— The triplet‐triplet absorption spectra of 9‐cis‐, 13‐cis‐ and all‐fraw‐retinal as well as the time‐resolved resonance Raman spectra of the lowest electronically excited triplet states of 9‐cis‐, 11‐cis, 13‐ciy and all‐trans‐retinal in aromatic solvents at room temperature have been obtained under conditions ensuring the isomeric purity of the starting materials. The triplet states were produced by triplet energy transfer from a sensitizer in pulse‐radiolysis experiments. The overall results suggest that the isomeric retinals form either different relaxed triplet species or different mixtures of relaxed triplet species. The possible implications about the size of the energy barriers separating the various triplet species are discussed. The resonance Raman spectra obtained by using either anthracene (ET= 177.7 kJ mol‐1) or naphthalene (ET= 254.8 kJ mol‐1) as sensitizers were virtually identical for the corresponding triplet states from each of the isomers 11‐cis‐, 13‐as‐ and all‐tams‐retinal, suggesting that the relaxed triplet species or the mixture of relaxed triplet species formed from each isomer is independent of the energy of the sensitizer.

Time-resolved absorption and resonance raman spectra of the lowest excited triplet state of all-trans-1,3,5-heptatriene

Abstract The lowest excited triplet state of all-trans-1,3,5-heptatriene has been studied by time-resolved absorption and resonance Raman spectroscopy. The difference absorption spectrum of the triplet state has a maximum around 315 nm, and the triplet state decays by first-order kinetics with k = (3.4 ± 0.3) × 10 6 s −1 . Time-resolved resonance Raman spectra of the heptatriene triplet excited at 317.5 nm showed bands at 1574, 1298, 1275, 1252, 1209, and 1132 cm −1 .

Time-resolved resonance Raman spectra of the lowest excited triplet state of all-trans-2,4,6-octatriene, alloocimene and neo-alloocimene

Abstract The lowest excited triplet states of all-trans-2,4,6-octatriene, alloocimene and neo-alloocimene have been studied by time-resolved resonance Raman spectroscopy. The spectra showed bands at 1574, 1264, 1252, 1205, and 1136 cm −1 for octatriene, at 1560 cm −1 for alloocimene, and at 1559 cm −1 for the-alloocimene. Possible implications for the relaxed triplet geometries are discussed.

Time-Resolved Resonance Raman Spectroscopy

The primary species in photobiology and photomedicine are excited states of biological molecules and free radicals. To characterize such species two general questions may be asked: 1) What makes these species reactive and what makes them behave differently than their stable parent molecules? 2) How long do they live, in which way and how rapidly do they react with other species and what are their decay and reaction products under given conditions? Obviously these two questions deal with different, but related problems, the first one being the understanding of the identity and characteristic properties of the reactive species, and the second a knowledge of their dynamic behaviour and changes with time.