Ultraviolet-induced excited states in deoxyribonucleic acid.

All measurements were made at 77?K on samples dissolved in a 1:1 ethylene glycol-water mixture. Concentrations used for making optical measurements were in the range of 10-3 to 10-4 M, while the ESR measurements were made on samples varying from 10-2 to 10-3 M. An Aminco-Bowman spectrophotometer was used to obtain optical data at low resolution for quantitative purposes. For higher resolution, Bausch and Lomb 0.5-meter grating monochromators were used for both excitation and emission. A Varian Associates X-band spectrometer with 100-kc/s modulation was used for the ESR measurements. A 200-watt, high-pressure mercury lamp was used for excitation in the microwave cavity.