32 



H. LINSCHITZ AND E. W. AimAIIAMSON 



placed in the optical train behind the fla.sh tube-cell assembly, and the 

 distance between the sample cell and entrance slit of the monochroma- 

 tor was made large (120 cm.) to favor the colli mated beam. Scattered 

 light was further decreased by passing the measuring beam through 

 accurately aligned apertures in a series of baffles placed in a light-tight 

 box, completely enclosing the optical path. The whole assembly 

 was mounted on an optical bench. Steady-state bleaching due to the 

 undispersed measuring beam was negligible, compared to that caused 

 by the flash. Provision was made for inserting filters in the beam to 



SAMPLE 



BAFFLES 



FILTER 



SHUTTER 



|o-: 



POWER 



SUPPLY 



X 



MONOCHROMATOR 



|i,PHOTOMULTIPLIER 



Fig. 1. Apparatus for flash-illumination studies. 



improve the purity of the spectrum provided by the monochromator 

 (a constant-deviation Gaertner instrument). The source ">S" was a 500- 

 watt concentrated filament projection lamp, operated from a stabilized 

 d.-c. supply. The sample cell, 50 mm. long and 13 mm. I.D., carried a 

 side ampoule permitting solutions to be prepared and degassed on the 

 vacuum line, and sealed off. The xenon-filled flash tube was made of 

 17-mm. Pyrex tubing, wound in a two-turn helix, within which the 

 sample cell was mounted, the whole being surrounded by a cylindrical 

 magnesia-coated reflector. The tube was operated at 4000 volts and 24 

 mfd., and provided a flash of about 100 microseconds duration. A 

 pulse generator and associated circuitry was used to trigger the sweep 

 of the oscillograph, and after an adjustable delay, to fire the flash 

 tube. 



PROCEDURE 



In order to correct for scattered or fluorescent light the following 

 measuring procedure was used. With the shutter open, and sample in 



