Abstract
Replacing the chromophore of bacteriorhodopsin with chemically modified retinal analogs which cannot isomerize, allows to measure directly side effects from the laser pulse used for sample excitation in step-scan FT-IR measurements. Comparison with static temperature difference spectra and temperature-jump experiments shows that the observed effects can mainly be attributed to heating of the sample by the laser pulse. The size of resulting spectral changes is compared to difference bands of the photoreaction.