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Raman excitation profiles (REPs) for bands of carotenoid and chlorophyll b (Chl b) from whole cells of green algae at low temperatures are presented. In addition to preventing thermal destruction of the samples during long-term irradiation, the use of a double channel surface scanning technique allowed the recording of the Raman spectrum of a non-resonating substance such as acetone suitable as an intensity reference at the same time. The measured REPs are compared with the absorption spectrum of whole cells at low temperatures.

A surface scanning technique was used to obtain resonant Raman spectra from chlorophylls in solution and in whole cells of diatoms at 80 K. When in vivo samples are excited at 457.9 nm, chlorophyll c becomes observable in the recorded Raman spectra, as shown by comparison with in vitro measurements. In the field of photosynthetic research this becomes Interesting, as chlorophyll c can hardly be detected in electronic absorption spectra from whole cells, even at low temperatures, because of its weak Q bands compared with other plant chlorophylls. Chl a spectra were obtained with the use of 441.6-nm excitation. Working with two-channel recording, we eliminated the solvent contribution from the Raman spectra of pigments in vitro. Moreover, the technique facilitates detection of Raman excitation profiles from pigment lines in vivo at low temperatures by use of a nonresonating reference in the second sample chamber.

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