FEMTOSECOND INFRARED-SPECTROSCOPY ON BACTERIORHODOPSIN USING A BROAD-BAND CARBON-MONOXIDE LASER

A pump-probe mid infrared transient absorption apparatus was built, em ploying a broad band continuous wave carbon monoxide laser and an opti cal gating technique resulting in femtosecond time resolution. It was used to monitor the an-trans to 13-cis isomerization of the retinal ch romophore in Bacteriorhodopsin (BR). The C=C in-phase stretch vibratio n, located at 1529 cm(-1) in the light adapted, unphotoryzed state BR( 570) 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 scal e the high energy shoulder of this breach is superimposed by newly cre ated IR absorption strength, due to the corresponding vibrational mode s of the J- and the K-state.