Miscellanea. Femtosecond infrared spectroscopy on bacteriorhodopsin using a broad band carbon monoxide laser

Abstract

AbstractA pump‐probe mid infrared transient absorption apparatus was built, employing a broad band continuous wave carbon monoxide laser and an optical gating technique resulting in femtosecond time resolution.It was used to monitor the all‐trans to 13‐cis isomerization of the retinal chromophore in Bacteriorhodopsin (BR). The C=C in‐phase stretch vibration, located at 1529cm−1 in the light adapted, unphotolyzed state BR570 served as marker band. Photoexcitation leads to a bleach centered at this wavenumber and to a partial recovery corresponding to the non unity quantum yield of the BR photocycle. On the picosecond time scale the high energy shoulder of this bleach is superimposed by newly created IR absorption strength, due to the corresponding vibrational modes of the J‐ and the K‐state.