All-trans retinal is the chromophore of microbial rhodopsins initiating energy conversion and cellular signalling by subpicosecond photoinduced switching. Here, we provide detailed UV-Vis transient absorption experiments to disentangle the complex photochemistry of this polyene, which is governed by its terminal aldehyde group. After photoexcitation to the S2((1)Bu(+)) state, the system exhibits polarity-dependent branching, populating separate S1((1)Ag(-)) and intramolecular charge transfer (ICT) species. In all solvents, population of a singlet nπ* state from S1 is observed which represents the precursor of the T1 triplet state. While triplet formation dominates in nonpolar solvents (67% quantum yield), it is dramatically reduced in polar solvents (4%). The channel closes completely upon replacing the aldehyde by a carboxyl group, due to an energetic up-shift of (1)nπ*. In that case, internal conversion via the ICT species becomes the main pathway, with preferential formation of the initially excited isomer.

The temperature dependence of the O 2 and C O 2 S-branch linewidths in a 30/70% O 2 − C O 2 mixture between 295 K and 1900 K has been studied by a picosecond time-resolved pure rotational coherent anti-Stokes Raman scattering (RCARS) approach. The S-branch Raman linewidths are required for diagnostics of thermodynamic properties in oxyfuel combustion processes by RCARS, where this mixture is of special interest, because it is regularly used to replace air when transiting from air-fed to oxyfuel combustion. The obtained linewidths for oxygen and carbon dioxide show a strong deviation from pure self-broadened linewidths and previously used Q-branch linewidths, respectively. A discussion on the expected impact on RCARS thermometry and concentration evaluations as well as a description of specific properties of oxygen and carbon dioxide and their effect on the dephasing behavior of the Raman coherences and, thereby the Raman linewidths, is included, along tabulated linewidths data of both molecules.

No abstract

No abstract