Molar absorptivities,\({\epsilon}\), have units of liters/(mole cm) and range in value from 0 to 10 5 . The relationship between \({\epsilon}\) and the capture cross-section for a photon - chemical species interaction and the probability for an energy-absorbing transition was shown by Braude (J. Am Chem Soc, 379 (1950) to be \({\epsilon}\) = 8.7 x 10 19 PA where P is the transition probability and A is the section target area in units of cm 2 . Typical organic molecules have been shown to have cross-sectional areas on the order of 10 -15 cm 2 and transition probabilities range from 0 to 1. Absorption bands with \({\epsilon}\) ranging from 10 4 to 10 5 are considered strong absorbers while absorption bands with \({\epsilon}\) less than or equal to 10 3 are considered weak absorbers and are likely the results of quantum mechanically forbidden transitions with P < 0.01.