414 



PHOTOMECHANICAL CONSIDERATIONS 



Light-induced absorbancy changes were measured with a double- 

 beam spectrophotometer as described elsewhere in this volume (7). 

 Monochromatic actinic light with a half- maximal band width of 13 mju 

 or less was obtained with interference filters. 



Transmission spectra of whole cell suspensions were obtained by 

 the opal glass method in the Cary 14R spectrophotometer. 



RESULTS 



Fluorescence. 



Emission spectra from Cps. ethylicum excited by 436 m/i light are 

 shown in Fig, 1, Essentially all of the excitation light is absorbed by 

 chlorobium chlorophyll and 7 -carotene. At room temperature (294°K) 

 the main fluorescence emission at 814 m/i comes from chlorophyll- 770 

 (9) and indicates the transfer of electronic excitation energy from 



O 1;^ 



-O T3 



1.2 1.3 



F(,i-i)-»- 



I L 



1:00 0.95 0.90 



0.85 



0.80 

 X (/x)<*- 



0.75 



0.70 



Fig. 1. Fluorescence emission spectra (clQ/dl^) from Cps. elliylicuDi at 77°K 

 and 294° K caused by excitation at 436 mju. The cell-suspension was taken from 

 a one-day-old culture. 



