718 



Edgar Inselberg and J. I.. Rosenberg 



Several investigators have considered the possibility that lu- 

 minescence may interfere with measurements of fast absorption 

 changes in the far-red region: for example, V/itt's apparati:is (5) 

 provided for an additional phototube, at ri^t angle to the mono- 

 chroratic and actinic beams, to measure fluorescence; Kok (3) al- 

 lowed for a delay of about one millisecond after the flash was 

 extir^guished before making measurements, ?/e had originall;;' as- 

 sumed that liorainescence resiilting from the actinic light would, 

 essentially, be additive to the luminescence from the monochro- 

 matic beam.. Accordingly, we v/ere using as a blank tlie v.'aveform of 

 the flash (fraction transmitted by F2), whicli would include lumi- 

 nescence caused by the actir.dc li^t. Moreover, the oscilloscope 

 trace was zeroed about 20 seconds after the monochromatic li^t 

 was turned on, prior to f].ashing the sample] by then the trace 

 had been adequately stabilized, indicating that the fluorescence 

 intensity due to the monochromatic li^^t could be considered un- 

 changed over the brief excitation period, 



RESULTS k^m DISCUSGICN 



A marked negative change in Porphjrridium at 703 mp., originally 

 interpreted as decreased absorption, is sh.own in Fig. 2. Wavefoi*m 

 A was observed with actinic lis^.t only, while V/aveform 3 was ob- 

 tained by flashing the sample, with the monochromator set at 703 

 mjj., A spectrum of the changes between 650 and 850 my., obtained 



Fig. 2, Oscilloscope display of the 703 my, change in 

 Porphyridium , 10 mv, AC per vertioa]. di^-ision; 200 

 (isec, per horizontal! division, V/avefonn A: flash on- 

 ly, '.Vaveform B: flash plus 703 mp. measuring li^t of 

 2 V, transmitted signal. 



