Types of Actinometers

In principle any photochemical reaction of known quantum yield can be used as an actinometer, the choice depending on the irradiation wavelength(s). It is convenient to measure the concentration of the actinometer by absorption spectrophotometry, and in many cases the same technique can be used to determine the concentration of the sample itself. 

The quantum yield of the primary hydrogen abstraction process is unity, and is independent of irradiation wavelength, light intensity and temperature. Its wavelength range follows of course the absorption spectrum of anthraquinone so that this actinometer is particularly well suited for the UV region. 

In the presence of 1,10-phenanthroline, Fe2+ forms a complex which has a broad absorption band centred at 510 nm. The quantum yield of the reaction is wavelength dependent, but the useful wavelength range is quite wide. The quantum yields are 1.25 at 254 nm, 1.21 at 365 nm and 1.01 at 436 nm (these being important emission lines of mercury arcs). 

---

The type of actinometer being used. A chemical and even a physical actinometer will require a degree of temperature control in order to be accurate. You should know what this temperature requirement is and maintain it. 

---